

<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:roleRef roleURI="http://www.oesx.com/role/CommitmentsAndContingencies" xlink:href="oesx-20160930.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/CommitmentsAndContingenciesDetails" xlink:href="oesx-20160930.xsd#CommitmentsAndContingenciesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/DescriptionOfBusiness" xlink:href="oesx-20160930.xsd#DescriptionOfBusiness" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/DocumentAndEntityInformation" xlink:href="oesx-20160930.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/IncomeTaxes" xlink:href="oesx-20160930.xsd#IncomeTaxes" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/IncomeTaxesNarrativeDetails" xlink:href="oesx-20160930.xsd#IncomeTaxesNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/LongTermDebt" xlink:href="oesx-20160930.xsd#LongTermDebt" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/LongTermDebtDetails" xlink:href="oesx-20160930.xsd#LongTermDebtDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/LongTermDebtNarrativeDetails" xlink:href="oesx-20160930.xsd#LongTermDebtNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/LongTermDebtTables" xlink:href="oesx-20160930.xsd#LongTermDebtTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/RelatedPartyTransactions" xlink:href="oesx-20160930.xsd#RelatedPartyTransactions" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/RelatedPartyTransactionsDetails" xlink:href="oesx-20160930.xsd#RelatedPartyTransactionsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/Segments" xlink:href="oesx-20160930.xsd#Segments" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SegmentsRevenuesAndOperatingIncomeLossDetails" xlink:href="oesx-20160930.xsd#SegmentsRevenuesAndOperatingIncomeLossDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SegmentsTables" xlink:href="oesx-20160930.xsd#SegmentsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/ShareholdersEquity" xlink:href="oesx-20160930.xsd#ShareholdersEquity" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/ShareholdersEquitySharesIssuedFromTreasuryDetails" xlink:href="oesx-20160930.xsd#ShareholdersEquitySharesIssuedFromTreasuryDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/ShareholdersEquityTables" xlink:href="oesx-20160930.xsd#ShareholdersEquityTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/StockOptionsAndRestrictedShares" xlink:href="oesx-20160930.xsd#StockOptionsAndRestrictedShares" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/StockOptionsAndRestrictedSharesNarrativeDetails" xlink:href="oesx-20160930.xsd#StockOptionsAndRestrictedSharesNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/StockOptionsAndRestrictedSharesOutstandingNonVestedStockOptionsDetails" xlink:href="oesx-20160930.xsd#StockOptionsAndRestrictedSharesOutstandingNonVestedStockOptionsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/StockOptionsAndRestrictedSharesRestrictedSharesDetails" xlink:href="oesx-20160930.xsd#StockOptionsAndRestrictedSharesRestrictedSharesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/StockOptionsAndRestrictedSharesStockBasedCompensationDetails" xlink:href="oesx-20160930.xsd#StockOptionsAndRestrictedSharesStockBasedCompensationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/StockOptionsAndRestrictedSharesSummaryOfStockOptionAndStockIncentiveAwardPlansDetails" xlink:href="oesx-20160930.xsd#StockOptionsAndRestrictedSharesSummaryOfStockOptionAndStockIncentiveAwardPlansDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/StockOptionsAndRestrictedSharesTables" xlink:href="oesx-20160930.xsd#StockOptionsAndRestrictedSharesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SubsequentEvents" xlink:href="oesx-20160930.xsd#SubsequentEvents" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPolicies" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesAccountsReceivableDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesAccountsReceivableDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesAccruedExpensesAndOtherDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesAccruedExpensesAndOtherDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesConcentrationRiskDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesConcentrationRiskDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesDilutiveSecuritiesDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesDilutiveSecuritiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesEpsDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesEpsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesEquipmentUnderCapitalLeasesDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesEquipmentUnderCapitalLeasesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesFinancingReceivablesDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesFinancingReceivablesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesInventoriesDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesInventoriesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesOtherIntangibleAssetsDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesOtherIntangibleAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesOtherLongTermAssetsDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesOtherLongTermAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPolicies" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPpeUsefulLivesDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesPpeUsefulLivesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPrepaidExpensesAndOtherCurrentAssetsDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesPrepaidExpensesAndOtherCurrentAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPropPlantAndEquipDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesPropPlantAndEquipDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesTables" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesWarrantyAccrualDetails" xlink:href="oesx-20160930.xsd#SummaryOfSignificantAccountingPoliciesWarrantyAccrualDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/UnauditedCondensedConsolidatedBalanceSheets" xlink:href="oesx-20160930.xsd#UnauditedCondensedConsolidatedBalanceSheets" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/UnauditedCondensedConsolidatedBalanceSheetsParenthetical" xlink:href="oesx-20160930.xsd#UnauditedCondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/UnauditedCondensedConsolidatedStatementsOfCashFlows" xlink:href="oesx-20160930.xsd#UnauditedCondensedConsolidatedStatementsOfCashFlows" xlink:type="simple" />
  <link:roleRef roleURI="http://www.oesx.com/role/UnauditedCondensedConsolidatedStatementsOfOperations" xlink:href="oesx-20160930.xsd#UnauditedCondensedConsolidatedStatementsOfOperations" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/CommitmentsAndContingencies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/CommitmentsAndContingenciesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermPurchaseCommitmentLineItems" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermPurchaseCommitmentTable" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentTable_4B4E00D86B268BC3F548FC5D33D3B3B1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentTable_4B4E00D86B268BC3F548FC5D33D3B3B1" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_F143529CCA1D6DCEED0FFC5D33D3691F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_4B4E00D86B268BC3F548FC5D33D3B3B1" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_F143529CCA1D6DCEED0FFC5D33D3691F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_D3194F7E2142CDDC5577FC5D33D33E56_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_F143529CCA1D6DCEED0FFC5D33D3691F" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_D3194F7E2142CDDC5577FC5D33D33E56_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_D3194F7E2142CDDC5577FC5D33D33E56" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_F143529CCA1D6DCEED0FFC5D33D3691F" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_D3194F7E2142CDDC5577FC5D33D33E56" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_E17C4EB0158F86F20F66FC5D33D3BB64" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_D3194F7E2142CDDC5577FC5D33D33E56" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_E17C4EB0158F86F20F66FC5D33D3BB64" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SaleLeasebackTransactionDescriptionAxis" xlink:label="loc_us-gaap_SaleLeasebackTransactionDescriptionAxis_8F22DFE88A87DE11BF6AFC5D33D3AAB4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_4B4E00D86B268BC3F548FC5D33D3B3B1" xlink:to="loc_us-gaap_SaleLeasebackTransactionDescriptionAxis_8F22DFE88A87DE11BF6AFC5D33D3AAB4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SaleLeasebackTransactionNameDomain" xlink:label="loc_us-gaap_SaleLeasebackTransactionNameDomain_650E68ABC0DE674D7513FC5D33D3E580_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SaleLeasebackTransactionDescriptionAxis_8F22DFE88A87DE11BF6AFC5D33D3AAB4" xlink:to="loc_us-gaap_SaleLeasebackTransactionNameDomain_650E68ABC0DE674D7513FC5D33D3E580_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SaleLeasebackTransactionNameDomain" xlink:label="loc_us-gaap_SaleLeasebackTransactionNameDomain_650E68ABC0DE674D7513FC5D33D3E580" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SaleLeasebackTransactionDescriptionAxis_8F22DFE88A87DE11BF6AFC5D33D3AAB4" xlink:to="loc_us-gaap_SaleLeasebackTransactionNameDomain_650E68ABC0DE674D7513FC5D33D3E580" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_AgreementwithTramontinaU.S.CookwareInc.Member" xlink:label="loc_oesx_AgreementwithTramontinaU.S.CookwareInc.Member_8E0BB07AFE9C599440E9FC5D33D30DF1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleLeasebackTransactionNameDomain_650E68ABC0DE674D7513FC5D33D3E580" xlink:to="loc_oesx_AgreementwithTramontinaU.S.CookwareInc.Member_8E0BB07AFE9C599440E9FC5D33D30DF1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingLeasesRentExpenseNet" xlink:label="loc_us-gaap_OperatingLeasesRentExpenseNet_D91D1C9013836BFA29B4FC5D33D3B77B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_us-gaap_OperatingLeasesRentExpenseNet_D91D1C9013836BFA29B4FC5D33D3B77B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LessorLeasingArrangementsOperatingLeasesTermOfContract" xlink:label="loc_us-gaap_LessorLeasingArrangementsOperatingLeasesTermOfContract_A31B7CFF84B0435659D5FC5D33D374D0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_us-gaap_LessorLeasingArrangementsOperatingLeasesTermOfContract_A31B7CFF84B0435659D5FC5D33D374D0" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_LessorLeasingArrangementsOperatingLeasesNumberofExtensionOptions" xlink:label="loc_oesx_LessorLeasingArrangementsOperatingLeasesNumberofExtensionOptions_764189CF753723B33549FC5D33D37570" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_oesx_LessorLeasingArrangementsOperatingLeasesNumberofExtensionOptions_764189CF753723B33549FC5D33D37570" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LessorLeasingArrangementsOperatingLeasesRenewalTerm" xlink:label="loc_us-gaap_LessorLeasingArrangementsOperatingLeasesRenewalTerm_A89BA4E569A184FE368AFC5D33D3C594" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_us-gaap_LessorLeasingArrangementsOperatingLeasesRenewalTerm_A89BA4E569A184FE368AFC5D33D3C594" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_OperatingLeasesMonthlyRentalPaymentsReceivable" xlink:label="loc_oesx_OperatingLeasesMonthlyRentalPaymentsReceivable_4E72E7243FBA8376397CFC5D33D36048" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_oesx_OperatingLeasesMonthlyRentalPaymentsReceivable_4E72E7243FBA8376397CFC5D33D36048" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SaleLeasebackTransactionNetProceedsInvestingActivities" xlink:label="loc_us-gaap_SaleLeasebackTransactionNetProceedsInvestingActivities_8F14F1285C89562091B8FC5D33D3006F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_us-gaap_SaleLeasebackTransactionNetProceedsInvestingActivities_8F14F1285C89562091B8FC5D33D3006F" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_SaleLeasebackTransactionAreaofLeasedProperty" xlink:label="loc_oesx_SaleLeasebackTransactionAreaofLeasedProperty_6D8922FE350350773A5AFC5D33D3DE24" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_oesx_SaleLeasebackTransactionAreaofLeasedProperty_6D8922FE350350773A5AFC5D33D3DE24" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_SaleLeasebackTransactionLeaseTerm" xlink:label="loc_oesx_SaleLeasebackTransactionLeaseTerm_C6ACFEB5ABFFCF2710B1FC5D33D3B144" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_oesx_SaleLeasebackTransactionLeaseTerm_C6ACFEB5ABFFCF2710B1FC5D33D3B144" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_SaleLeasebackTransactionRentExpensePerSquareFoot" xlink:label="loc_oesx_SaleLeasebackTransactionRentExpensePerSquareFoot_414E9B371043164FEF08FC5D33D3B982" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_oesx_SaleLeasebackTransactionRentExpensePerSquareFoot_414E9B371043164FEF08FC5D33D3B982" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SaleLeasebackTransactionMonthlyRentalPayments" xlink:label="loc_us-gaap_SaleLeasebackTransactionMonthlyRentalPayments_7471BD1E7425312FA923FC5D33D4D3E3" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_us-gaap_SaleLeasebackTransactionMonthlyRentalPayments_7471BD1E7425312FA923FC5D33D4D3E3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LossContingencyClaimsDismissedNumber" xlink:label="loc_us-gaap_LossContingencyClaimsDismissedNumber_1135E4CD2EF275EBC16BFC5D33D40A2C" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_us-gaap_LossContingencyClaimsDismissedNumber_1135E4CD2EF275EBC16BFC5D33D40A2C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LitigationSettlementAmount" xlink:label="loc_us-gaap_LitigationSettlementAmount_B76EF1CB0355AAEA209DFC5D33D4EEB2" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_166EB18E79CB520C3708FC5D33D37250" xlink:to="loc_us-gaap_LitigationSettlementAmount_B76EF1CB0355AAEA209DFC5D33D4EEB2" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/DescriptionOfBusiness" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/DocumentAndEntityInformation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/IncomeTaxes" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingLossCarryforwardsLineItems" xlink:label="loc_us-gaap_OperatingLossCarryforwardsLineItems_78E2FB4D8E1A065A8EECE7AF7EC20F13" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingLossCarryforwardsTable" xlink:label="loc_us-gaap_OperatingLossCarryforwardsTable_8C442BC9543B5E80A6FFE7AF7EC008D1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_78E2FB4D8E1A065A8EECE7AF7EC20F13" xlink:to="loc_us-gaap_OperatingLossCarryforwardsTable_8C442BC9543B5E80A6FFE7AF7EC008D1" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_DAC12D3D6C5C579950F0E7AF7EC11DF3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OperatingLossCarryforwardsTable_8C442BC9543B5E80A6FFE7AF7EC008D1" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_DAC12D3D6C5C579950F0E7AF7EC11DF3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_18BD53918DF1B5385E7AE7AF7EC194C4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_DAC12D3D6C5C579950F0E7AF7EC11DF3" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_18BD53918DF1B5385E7AE7AF7EC194C4_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_18BD53918DF1B5385E7AE7AF7EC194C4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_DAC12D3D6C5C579950F0E7AF7EC11DF3" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_18BD53918DF1B5385E7AE7AF7EC194C4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DomesticCountryMember" xlink:label="loc_us-gaap_DomesticCountryMember_E9767D73EEE9860DD7F1E7AF7EC1E83D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_18BD53918DF1B5385E7AE7AF7EC194C4" xlink:to="loc_us-gaap_DomesticCountryMember_E9767D73EEE9860DD7F1E7AF7EC1E83D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StateAndLocalJurisdictionMember" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_58A2E512F4803F69A823E7AF7EC221BD" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_18BD53918DF1B5385E7AE7AF7EC194C4" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_58A2E512F4803F69A823E7AF7EC221BD" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_IncomeTaxTextualAbstract" xlink:label="loc_oesx_IncomeTaxTextualAbstract_12EF97DE3E812446BDB4E7AF7EC25A4E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_78E2FB4D8E1A065A8EECE7AF7EC20F13" xlink:to="loc_oesx_IncomeTaxTextualAbstract_12EF97DE3E812446BDB4E7AF7EC25A4E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_76DDDC8415369DDF6141E7AF7EC25B79" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_IncomeTaxTextualAbstract_12EF97DE3E812446BDB4E7AF7EC25A4E" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_76DDDC8415369DDF6141E7AF7EC25B79" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationOtherReconcilingItemsPercent" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationOtherReconcilingItemsPercent_10B465DB7F216A44729FE7AF7EC225A6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_IncomeTaxTextualAbstract_12EF97DE3E812446BDB4E7AF7EC25A4E" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationOtherReconcilingItemsPercent_10B465DB7F216A44729FE7AF7EC225A6" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_EffectiveIncomeTaxRateReconciliationNetofDiscreteTaxItemsPercent" xlink:label="loc_oesx_EffectiveIncomeTaxRateReconciliationNetofDiscreteTaxItemsPercent_C88637D71F1680FDA4F5E7AF7EC28A25" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_IncomeTaxTextualAbstract_12EF97DE3E812446BDB4E7AF7EC25A4E" xlink:to="loc_oesx_EffectiveIncomeTaxRateReconciliationNetofDiscreteTaxItemsPercent_C88637D71F1680FDA4F5E7AF7EC28A25" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingLossCarryforwards" xlink:label="loc_us-gaap_OperatingLossCarryforwards_1F526E3795D2958E52DCE7AF7EC320CC" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_IncomeTaxTextualAbstract_12EF97DE3E812446BDB4E7AF7EC25A4E" xlink:to="loc_us-gaap_OperatingLossCarryforwards_1F526E3795D2958E52DCE7AF7EC320CC" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_OperatingLossCarryforwardsAssociatedWithExerciseOfNonQualifiedStockOptions" xlink:label="loc_oesx_OperatingLossCarryforwardsAssociatedWithExerciseOfNonQualifiedStockOptions_A172E6C30ABDC0EDF6A6E7AF7EC3A4F8" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_IncomeTaxTextualAbstract_12EF97DE3E812446BDB4E7AF7EC25A4E" xlink:to="loc_oesx_OperatingLossCarryforwardsAssociatedWithExerciseOfNonQualifiedStockOptions_A172E6C30ABDC0EDF6A6E7AF7EC3A4F8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TaxCreditCarryforwardAmount" xlink:label="loc_us-gaap_TaxCreditCarryforwardAmount_CB90B2CFB94671A58DD9E7AF7EC3CDEB" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_IncomeTaxTextualAbstract_12EF97DE3E812446BDB4E7AF7EC25A4E" xlink:to="loc_us-gaap_TaxCreditCarryforwardAmount_CB90B2CFB94671A58DD9E7AF7EC3CDEB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount" xlink:label="loc_us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_82D04D2C7AF7C7B14219E7AF7EC3854B" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_IncomeTaxTextualAbstract_12EF97DE3E812446BDB4E7AF7EC25A4E" xlink:to="loc_us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_82D04D2C7AF7C7B14219E7AF7EC3854B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnrecognizedTaxBenefits" xlink:label="loc_us-gaap_UnrecognizedTaxBenefits_8E29264748FCBC914833E7AF7EC3E0C2" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_IncomeTaxTextualAbstract_12EF97DE3E812446BDB4E7AF7EC25A4E" xlink:to="loc_us-gaap_UnrecognizedTaxBenefits_8E29264748FCBC914833E7AF7EC3E0C2" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/LongTermDebt" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/LongTermDebtDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ExtinguishmentOfDebtLineItems" xlink:label="loc_us-gaap_ExtinguishmentOfDebtLineItems_4B91A819829A5B9585B4A826CFF69A73" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfExtinguishmentOfDebtTable" xlink:label="loc_us-gaap_ScheduleOfExtinguishmentOfDebtTable_1831B77AF22950F5B8C19B4C7462EBE9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ExtinguishmentOfDebtLineItems_4B91A819829A5B9585B4A826CFF69A73" xlink:to="loc_us-gaap_ScheduleOfExtinguishmentOfDebtTable_1831B77AF22950F5B8C19B4C7462EBE9" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ExtinguishmentOfDebtAxis" xlink:label="loc_us-gaap_ExtinguishmentOfDebtAxis_26C4312B816B5D4E8FB47474C4D0CAB2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfExtinguishmentOfDebtTable_1831B77AF22950F5B8C19B4C7462EBE9" xlink:to="loc_us-gaap_ExtinguishmentOfDebtAxis_26C4312B816B5D4E8FB47474C4D0CAB2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ExtinguishmentOfDebtTypeDomain" xlink:label="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_06B45A1F75506D23C1D93CC8412E8C72_08CE33582584512AA1F704B046BCBDF6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ExtinguishmentOfDebtAxis_26C4312B816B5D4E8FB47474C4D0CAB2" xlink:to="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_06B45A1F75506D23C1D93CC8412E8C72_08CE33582584512AA1F704B046BCBDF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ExtinguishmentOfDebtTypeDomain" xlink:label="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_EBB4B291DFB55B0AB3DD3FDE979A2160" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ExtinguishmentOfDebtAxis_26C4312B816B5D4E8FB47474C4D0CAB2" xlink:to="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_EBB4B291DFB55B0AB3DD3FDE979A2160" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RevolvingCreditFacilityMember" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_98275FA7AEB455099586541BD38DBF9C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_EBB4B291DFB55B0AB3DD3FDE979A2160" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_98275FA7AEB455099586541BD38DBF9C" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_HarrisSellersNoteMember" xlink:label="loc_oesx_HarrisSellersNoteMember_D078DAD4A01950B391A002E451CCB5A2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_EBB4B291DFB55B0AB3DD3FDE979A2160" xlink:to="loc_oesx_HarrisSellersNoteMember_D078DAD4A01950B391A002E451CCB5A2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CapitalLeaseObligationsMember" xlink:label="loc_us-gaap_CapitalLeaseObligationsMember_0ADAFCA09BCF537FBB3E5AA176FF2B38" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_EBB4B291DFB55B0AB3DD3FDE979A2160" xlink:to="loc_us-gaap_CapitalLeaseObligationsMember_0ADAFCA09BCF537FBB3E5AA176FF2B38" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_CustomerEquipmentFinanceNotesPayableMember" xlink:label="loc_oesx_CustomerEquipmentFinanceNotesPayableMember_25EFDCAF6B4B547F86B9B17FCC8A9653" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_EBB4B291DFB55B0AB3DD3FDE979A2160" xlink:to="loc_oesx_CustomerEquipmentFinanceNotesPayableMember_25EFDCAF6B4B547F86B9B17FCC8A9653" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_OtherLongTermDebtMember" xlink:label="loc_oesx_OtherLongTermDebtMember_18E64D91B06C5FBE9C08F4BA7B080AFB" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_EBB4B291DFB55B0AB3DD3FDE979A2160" xlink:to="loc_oesx_OtherLongTermDebtMember_18E64D91B06C5FBE9C08F4BA7B080AFB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract" xlink:label="loc_us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract_9A2B469D150C56F39741EF2CC15C28F7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExtinguishmentOfDebtLineItems_4B91A819829A5B9585B4A826CFF69A73" xlink:to="loc_us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract_9A2B469D150C56F39741EF2CC15C28F7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebt" xlink:label="loc_us-gaap_LongTermDebt_23F4AFB313D2550EAC24457E9C2DF658" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract_9A2B469D150C56F39741EF2CC15C28F7" xlink:to="loc_us-gaap_LongTermDebt_23F4AFB313D2550EAC24457E9C2DF658" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="loc_us-gaap_LongTermDebtCurrent_22146F78F18A5FDA9DE8D6AF1FC62626" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract_9A2B469D150C56F39741EF2CC15C28F7" xlink:to="loc_us-gaap_LongTermDebtCurrent_22146F78F18A5FDA9DE8D6AF1FC62626" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_761B4EB8A4A5501AAE0CDC3E01745CEB" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract_9A2B469D150C56F39741EF2CC15C28F7" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_761B4EB8A4A5501AAE0CDC3E01745CEB" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/LongTermDebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_AE275D74D1BA74CA703220CB322CC10F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_AE275D74D1BA74CA703220CB322CC10F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_A25507981F38D12B797120CB322C74D8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_AE275D74D1BA74CA703220CB322CC10F" xlink:to="loc_us-gaap_DebtInstrumentAxis_A25507981F38D12B797120CB322C74D8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_90DB2BEC2D0952BBCFAC20CB322CE7DF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_A25507981F38D12B797120CB322C74D8" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_90DB2BEC2D0952BBCFAC20CB322CE7DF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_90DB2BEC2D0952BBCFAC20CB322CE7DF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_A25507981F38D12B797120CB322C74D8" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_90DB2BEC2D0952BBCFAC20CB322CE7DF" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_CreditAgreementMember" xlink:label="loc_oesx_CreditAgreementMember_7CE5546358612AB6F9CE20CB322C5502" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_90DB2BEC2D0952BBCFAC20CB322CE7DF" xlink:to="loc_oesx_CreditAgreementMember_7CE5546358612AB6F9CE20CB322C5502" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_December2014OTAFinanceProgramMember" xlink:label="loc_oesx_December2014OTAFinanceProgramMember_84D34AA4F44FD15D07BD20CB322C4380" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_90DB2BEC2D0952BBCFAC20CB322CE7DF" xlink:to="loc_oesx_December2014OTAFinanceProgramMember_84D34AA4F44FD15D07BD20CB322C4380" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaap_CreditFacilityAxis_354C6DE1674C13E91A1420CB322CFDC6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_AE275D74D1BA74CA703220CB322CC10F" xlink:to="loc_us-gaap_CreditFacilityAxis_354C6DE1674C13E91A1420CB322CFDC6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_1434312D57024C3D44ED20CB322C649F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_354C6DE1674C13E91A1420CB322CFDC6" xlink:to="loc_us-gaap_CreditFacilityDomain_1434312D57024C3D44ED20CB322C649F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_1434312D57024C3D44ED20CB322C649F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_354C6DE1674C13E91A1420CB322CFDC6" xlink:to="loc_us-gaap_CreditFacilityDomain_1434312D57024C3D44ED20CB322C649F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RevolvingCreditFacilityMember" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_27A046FACCAA35EE764E20CB322DDE15" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_1434312D57024C3D44ED20CB322C649F" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_27A046FACCAA35EE764E20CB322DDE15" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LetterOfCreditMember" xlink:label="loc_us-gaap_LetterOfCreditMember_38197F1E4187091038FC20CB322D88C5" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_1434312D57024C3D44ED20CB322C649F" xlink:to="loc_us-gaap_LetterOfCreditMember_38197F1E4187091038FC20CB322D88C5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="loc_us-gaap_LineOfCreditFacilityAxis_D5186891D3FF8E60CCAE20CB322D1282" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_AE275D74D1BA74CA703220CB322CC10F" xlink:to="loc_us-gaap_LineOfCreditFacilityAxis_D5186891D3FF8E60CCAE20CB322D1282" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_B8E24C79C815B2F418BE20CB322D63F8_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_D5186891D3FF8E60CCAE20CB322D1282" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_B8E24C79C815B2F418BE20CB322D63F8_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_B8E24C79C815B2F418BE20CB322D63F8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_D5186891D3FF8E60CCAE20CB322D1282" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_B8E24C79C815B2F418BE20CB322D63F8" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_WellsFargoBankNationalAssociationMember" xlink:label="loc_oesx_WellsFargoBankNationalAssociationMember_9BDFF6AA1E25F53A153720CB322D52C4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_B8E24C79C815B2F418BE20CB322D63F8" xlink:to="loc_oesx_WellsFargoBankNationalAssociationMember_9BDFF6AA1E25F53A153720CB322D52C4" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_DeLageLandenFinancialServicesInc.Member" xlink:label="loc_oesx_DeLageLandenFinancialServicesInc.Member_C8FC8B0A6247D36283CB20CB322D4C59" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_B8E24C79C815B2F418BE20CB322D63F8" xlink:to="loc_oesx_DeLageLandenFinancialServicesInc.Member_C8FC8B0A6247D36283CB20CB322D4C59" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_2520A03BD4B75A6570E020CB322D1873" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_AE275D74D1BA74CA703220CB322CC10F" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_2520A03BD4B75A6570E020CB322D1873" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_52F5132104A5E0C7C69520CB322D906C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_2520A03BD4B75A6570E020CB322D1873" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_52F5132104A5E0C7C69520CB322D906C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_52F5132104A5E0C7C69520CB322D906C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_2520A03BD4B75A6570E020CB322D1873" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_52F5132104A5E0C7C69520CB322D906C" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_HarrisSellersNoteMember" xlink:label="loc_oesx_HarrisSellersNoteMember_0886A8CBCE961831299A20CB322D6864" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_52F5132104A5E0C7C69520CB322D906C" xlink:to="loc_oesx_HarrisSellersNoteMember_0886A8CBCE961831299A20CB322D6864" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SecuredDebtMember" xlink:label="loc_us-gaap_SecuredDebtMember_4899D70FA838FDE67C9220CB322DEC4A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_52F5132104A5E0C7C69520CB322D906C" xlink:to="loc_us-gaap_SecuredDebtMember_4899D70FA838FDE67C9220CB322DEC4A" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_June2011OtaFinanceProgramMember" xlink:label="loc_oesx_June2011OtaFinanceProgramMember_81FA2DF6E608A4B70EEA20CB322D0FFA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_52F5132104A5E0C7C69520CB322D906C" xlink:to="loc_oesx_June2011OtaFinanceProgramMember_81FA2DF6E608A4B70EEA20CB322D0FFA" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_AgreementWithWisconsinDepartmentOfCommerceMember" xlink:label="loc_oesx_AgreementWithWisconsinDepartmentOfCommerceMember_FEB6137E6457BCEAFF5B20CB322D8E12" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_52F5132104A5E0C7C69520CB322D906C" xlink:to="loc_oesx_AgreementWithWisconsinDepartmentOfCommerceMember_FEB6137E6457BCEAFF5B20CB322D8E12" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateAxis" xlink:label="loc_us-gaap_VariableRateAxis_CFD2F08C4D8ECFF9683C20CB322D8A18" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_AE275D74D1BA74CA703220CB322CC10F" xlink:to="loc_us-gaap_VariableRateAxis_CFD2F08C4D8ECFF9683C20CB322D8A18" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_521A728DB040C09D828A20CB322D8AAD_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_CFD2F08C4D8ECFF9683C20CB322D8A18" xlink:to="loc_us-gaap_VariableRateDomain_521A728DB040C09D828A20CB322D8AAD_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_521A728DB040C09D828A20CB322D8AAD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_CFD2F08C4D8ECFF9683C20CB322D8A18" xlink:to="loc_us-gaap_VariableRateDomain_521A728DB040C09D828A20CB322D8AAD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_11234D2A27CB0615958720CB322D97C4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_521A728DB040C09D828A20CB322D8AAD" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_11234D2A27CB0615958720CB322D97C4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ExtinguishmentOfDebtAxis" xlink:label="loc_us-gaap_ExtinguishmentOfDebtAxis_28CB859265E638D948A420CB322D90AE" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_AE275D74D1BA74CA703220CB322CC10F" xlink:to="loc_us-gaap_ExtinguishmentOfDebtAxis_28CB859265E638D948A420CB322D90AE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ExtinguishmentOfDebtTypeDomain" xlink:label="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_37567C3340F12C87C00220CB322ECBED_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ExtinguishmentOfDebtAxis_28CB859265E638D948A420CB322D90AE" xlink:to="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_37567C3340F12C87C00220CB322ECBED_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ExtinguishmentOfDebtTypeDomain" xlink:label="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_37567C3340F12C87C00220CB322ECBED" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ExtinguishmentOfDebtAxis_28CB859265E638D948A420CB322D90AE" xlink:to="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_37567C3340F12C87C00220CB322ECBED" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CapitalLeaseObligationsMember" xlink:label="loc_us-gaap_CapitalLeaseObligationsMember_61144CD41FF92BD43F9D20CB322E38E1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_37567C3340F12C87C00220CB322ECBED" xlink:to="loc_us-gaap_CapitalLeaseObligationsMember_61144CD41FF92BD43F9D20CB322E38E1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_27DB9A0887550ABB3EF620CB322E0043" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_27DB9A0887550ABB3EF620CB322E0043" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_LineofCreditFacilityPotentialMaximumBorrowingCapacity" xlink:label="loc_oesx_LineofCreditFacilityPotentialMaximumBorrowingCapacity_6DD08A900144606AC89820CDCC61D343" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_oesx_LineofCreditFacilityPotentialMaximumBorrowingCapacity_6DD08A900144606AC89820CDCC61D343" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_3CB3F950CF57C30FE31D20CB322E8DB2" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_3CB3F950CF57C30FE31D20CB322E8DB2" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_LineofCreditFacilityCovenantTermsMinimumIndebtednessRatio" xlink:label="loc_oesx_LineofCreditFacilityCovenantTermsMinimumIndebtednessRatio_77D7E2B9FA561676BBDF20CB322E2203" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_oesx_LineofCreditFacilityCovenantTermsMinimumIndebtednessRatio_77D7E2B9FA561676BBDF20CB322E2203" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_DB09025886F1B514CF6620CB322E8DDD" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_DB09025886F1B514CF6620CB322E8DDD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentPeriodicPaymentInterest" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPaymentInterest_C0C8B9439ACC0BC39C7520CB322EE6FF" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPaymentInterest_C0C8B9439ACC0BC39C7520CB322EE6FF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_8A985CBB78D135F0AC3220CB322E3DE9" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_8A985CBB78D135F0AC3220CB322E3DE9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_23BC519A9E6961B4EEDB20CB322E6501" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_23BC519A9E6961B4EEDB20CB322E6501" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_99C83A63B09EE8C70C1E20CB322E94C2" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_99C83A63B09EE8C70C1E20CB322E94C2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermLineOfCredit" xlink:label="loc_us-gaap_LongTermLineOfCredit_D57212000F1762AC321C20CB322E461F" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_LongTermLineOfCredit_D57212000F1762AC321C20CB322E461F" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_LineofCreditFacilityAdditionalBorrowingCapacity" xlink:label="loc_oesx_LineofCreditFacilityAdditionalBorrowingCapacity_34412737EDE11CB94EC420CB322E93FF" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_oesx_LineofCreditFacilityAdditionalBorrowingCapacity_34412737EDE11CB94EC420CB322E93FF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_02AAF01F40F3F41A9D8420CB322EF737" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_02AAF01F40F3F41A9D8420CB322EF737" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_9594D1431FBB5CB72EC620CB322EBF23" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_9594D1431FBB5CB72EC620CB322EBF23" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_NumberofLeaseAgreements" xlink:label="loc_oesx_NumberofLeaseAgreements_9EF167E2047A48255D5F20CB322E705B" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_oesx_NumberofLeaseAgreements_9EF167E2047A48255D5F20CB322E705B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentCarryingAmount" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_CFE082D78384E213FA5420CB322E71B2" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_CFE082D78384E213FA5420CB322E71B2" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_DebtInstrumentBuyoutOption" xlink:label="loc_oesx_DebtInstrumentBuyoutOption_11ACA08935B5533912B120CB322E2BE6" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_oesx_DebtInstrumentBuyoutOption_11ACA08935B5533912B120CB322E2BE6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SecuredDebt" xlink:label="loc_us-gaap_SecuredDebt_D1C465FDFD1A7A28243320CB322FC1C1" xlink:type="locator" />
    <link:definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_SecuredDebt_D1C465FDFD1A7A28243320CB322FC1C1" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_DebtInstrumentNumberOfContractsForCollateral" xlink:label="loc_oesx_DebtInstrumentNumberOfContractsForCollateral_C0FC0E863E8D35F179AA20CB322F1DC0" xlink:type="locator" />
    <link:definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_oesx_DebtInstrumentNumberOfContractsForCollateral_C0FC0E863E8D35F179AA20CB322F1DC0" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_PeriodOfTimeWithoutInterestAccruingOrPrincipalPaymentsDue" xlink:label="loc_oesx_PeriodOfTimeWithoutInterestAccruingOrPrincipalPaymentsDue_5796F1481F916C53C5A020CB322F7838" xlink:type="locator" />
    <link:definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_oesx_PeriodOfTimeWithoutInterestAccruingOrPrincipalPaymentsDue_5796F1481F916C53C5A020CB322F7838" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentPeriodicPayment" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPayment_ADDB7B76375491BEDAC820CB322FBF66" xlink:type="locator" />
    <link:definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_4D43192988240C45D04320CB322E7C3F" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPayment_ADDB7B76375491BEDAC820CB322FBF66" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/LongTermDebtTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/RelatedPartyTransactions" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/RelatedPartyTransactionsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_5D6F0AB27EB60970C4B606B82276891C" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_A1582F59E588EF60420506B822760366" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_5D6F0AB27EB60970C4B606B82276891C" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_A1582F59E588EF60420506B822760366" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_A632BF8FA083C5900F7406B82276396C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_A1582F59E588EF60420506B822760366" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_A632BF8FA083C5900F7406B82276396C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_6F4B029C1DE55AEAF9A406B82276CA67_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_A632BF8FA083C5900F7406B82276396C" xlink:to="loc_us-gaap_RelatedPartyDomain_6F4B029C1DE55AEAF9A406B82276CA67_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_6F4B029C1DE55AEAF9A406B82276CA67" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_A632BF8FA083C5900F7406B82276396C" xlink:to="loc_us-gaap_RelatedPartyDomain_6F4B029C1DE55AEAF9A406B82276CA67" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_EntitythatCurrentDirectorOwnsMinorityInterestandServesasBoardofDirectorsChairmanMember" xlink:label="loc_oesx_EntitythatCurrentDirectorOwnsMinorityInterestandServesasBoardofDirectorsChairmanMember_1641A65D1A2A795EAAD406B822763646" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_6F4B029C1DE55AEAF9A406B82276CA67" xlink:to="loc_oesx_EntitythatCurrentDirectorOwnsMinorityInterestandServesasBoardofDirectorsChairmanMember_1641A65D1A2A795EAAD406B822763646" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty" xlink:label="loc_us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty_4DA5EF222BEA33D1C9C906B822768E6D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_5D6F0AB27EB60970C4B606B82276891C" xlink:to="loc_us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty_4DA5EF222BEA33D1C9C906B822768E6D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/Segments" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/SegmentsRevenuesAndOperatingIncomeLossDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_E78525D456C9D5036973D840B56422C3" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_C736ED720A145CFEC109D840B563D2FE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_E78525D456C9D5036973D840B56422C3" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_C736ED720A145CFEC109D840B563D2FE" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_A46EB4F772A69DDCB346D840B5634500" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_C736ED720A145CFEC109D840B563D2FE" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_A46EB4F772A69DDCB346D840B5634500" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_14378AF802C73A53DE82D840B5648663_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_A46EB4F772A69DDCB346D840B5634500" xlink:to="loc_us-gaap_SegmentDomain_14378AF802C73A53DE82D840B5648663_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_14378AF802C73A53DE82D840B5648663" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_A46EB4F772A69DDCB346D840B5634500" xlink:to="loc_us-gaap_SegmentDomain_14378AF802C73A53DE82D840B5648663" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_EnergyManagementMember" xlink:label="loc_oesx_EnergyManagementMember_F2AC2992851E83B8319BD840B564717C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_14378AF802C73A53DE82D840B5648663" xlink:to="loc_oesx_EnergyManagementMember_F2AC2992851E83B8319BD840B564717C" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_EngineeredSystemsMember" xlink:label="loc_oesx_EngineeredSystemsMember_CF5A913EBA1819D0E4EDD840B5643AF3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_14378AF802C73A53DE82D840B5648663" xlink:to="loc_oesx_EngineeredSystemsMember_CF5A913EBA1819D0E4EDD840B5643AF3" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_DistributionServicesMember" xlink:label="loc_oesx_DistributionServicesMember_2C27F051C98BCBB9A390D840B564BA78" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_14378AF802C73A53DE82D840B5648663" xlink:to="loc_oesx_DistributionServicesMember_2C27F051C98BCBB9A390D840B564BA78" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CorporateAndOtherMember" xlink:label="loc_us-gaap_CorporateAndOtherMember_E1A228048C1CA87107C5D840B56403B4" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_14378AF802C73A53DE82D840B5648663" xlink:to="loc_us-gaap_CorporateAndOtherMember_E1A228048C1CA87107C5D840B56403B4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentReportingInformationRevenueAbstract" xlink:label="loc_us-gaap_SegmentReportingInformationRevenueAbstract_A5AC2C589AC9D98E8128D840B5645995" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_E78525D456C9D5036973D840B56422C3" xlink:to="loc_us-gaap_SegmentReportingInformationRevenueAbstract_A5AC2C589AC9D98E8128D840B5645995" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_036C95BBDAAE7B0265DED840B564AA03" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationRevenueAbstract_A5AC2C589AC9D98E8128D840B5645995" xlink:to="loc_us-gaap_Revenues_036C95BBDAAE7B0265DED840B564AA03" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaap_OperatingIncomeLoss_A0B2E1357836E80B7A65D840B564E709" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationRevenueAbstract_A5AC2C589AC9D98E8128D840B5645995" xlink:to="loc_us-gaap_OperatingIncomeLoss_A0B2E1357836E80B7A65D840B564E709" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/SegmentsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/ShareholdersEquity" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/ShareholdersEquitySharesIssuedFromTreasuryDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ClassOfStockLineItems" xlink:label="loc_us-gaap_ClassOfStockLineItems_D8812AE6A0865E2A5008FC7E27460E26" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_F9BEEAFB5934EEE62BC7FC7E27367E1D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_D8812AE6A0865E2A5008FC7E27460E26" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_F9BEEAFB5934EEE62BC7FC7E27367E1D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_7743C5D29D8C66F65000FC7E284379CF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_F9BEEAFB5934EEE62BC7FC7E27367E1D" xlink:to="loc_us-gaap_RangeAxis_7743C5D29D8C66F65000FC7E284379CF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_D29B117A419030842C86FC7E284DB199_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_7743C5D29D8C66F65000FC7E284379CF" xlink:to="loc_us-gaap_RangeMember_D29B117A419030842C86FC7E284DB199_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_D29B117A419030842C86FC7E284DB199" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_7743C5D29D8C66F65000FC7E284379CF" xlink:to="loc_us-gaap_RangeMember_D29B117A419030842C86FC7E284DB199" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_2F87D22AEB2DAA70F130FC7E293525BB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_D29B117A419030842C86FC7E284DB199" xlink:to="loc_us-gaap_MinimumMember_2F87D22AEB2DAA70F130FC7E293525BB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_A577A999961396183897FC7E29D6317B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_D29B117A419030842C86FC7E284DB199" xlink:to="loc_us-gaap_MaximumMember_A577A999961396183897FC7E29D6317B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_1E790830E1A71F85AAE3FC5D33CC8A8B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_D8812AE6A0865E2A5008FC7E27460E26" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_1E790830E1A71F85AAE3FC5D33CC8A8B" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_EmployeeStockPurchasePlanClosingMarketPriceOfSharesPurchased" xlink:label="loc_oesx_EmployeeStockPurchasePlanClosingMarketPriceOfSharesPurchased_FB0C3692C5727573EF05FC5D33CC435A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_D8812AE6A0865E2A5008FC7E27460E26" xlink:to="loc_oesx_EmployeeStockPurchasePlanClosingMarketPriceOfSharesPurchased_FB0C3692C5727573EF05FC5D33CC435A" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_EmployeeStockPurchasePlansDebtStructureSharesIssued" xlink:label="loc_oesx_EmployeeStockPurchasePlansDebtStructureSharesIssued_283C050697C2718CA64CFC5D33CCBA01" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_D8812AE6A0865E2A5008FC7E27460E26" xlink:to="loc_oesx_EmployeeStockPurchasePlansDebtStructureSharesIssued_283C050697C2718CA64CFC5D33CCBA01" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_EmployeeStockPurchasePlansDebtStructureDirectLoanAmount" xlink:label="loc_oesx_EmployeeStockPurchasePlansDebtStructureDirectLoanAmount_1BE2FDB6DC201786CB39FC5D33CCDA4D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_D8812AE6A0865E2A5008FC7E27460E26" xlink:to="loc_oesx_EmployeeStockPurchasePlansDebtStructureDirectLoanAmount_1BE2FDB6DC201786CB39FC5D33CCDA4D" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_EmployeeStockPurchasePlansDebtStructureDirectLoanRepaymentAmount" xlink:label="loc_oesx_EmployeeStockPurchasePlansDebtStructureDirectLoanRepaymentAmount_230E89AB46EC668BADD1FC5D33CC1D95" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_D8812AE6A0865E2A5008FC7E27460E26" xlink:to="loc_oesx_EmployeeStockPurchasePlansDebtStructureDirectLoanRepaymentAmount_230E89AB46EC668BADD1FC5D33CC1D95" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ReceivableFromShareholdersOrAffiliatesForIssuanceOfCapitalStock" xlink:label="loc_us-gaap_ReceivableFromShareholdersOrAffiliatesForIssuanceOfCapitalStock_268723395CF696B591D3FC5D33CCEC95" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_D8812AE6A0865E2A5008FC7E27460E26" xlink:to="loc_us-gaap_ReceivableFromShareholdersOrAffiliatesForIssuanceOfCapitalStock_268723395CF696B591D3FC5D33CCEC95" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/ShareholdersEquityTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/StockOptionsAndRestrictedShares" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/StockOptionsAndRestrictedSharesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_BA06449E38E4E98EA7FB272271CEF625" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_BA06449E38E4E98EA7FB272271CEF625" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_FFB5264E5E00C4224296272271CE7ABE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_BA06449E38E4E98EA7FB272271CEF625" xlink:to="loc_us-gaap_PlanNameAxis_FFB5264E5E00C4224296272271CE7ABE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_C55DF3ED26204F041A48272271CE041C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_FFB5264E5E00C4224296272271CE7ABE" xlink:to="loc_us-gaap_PlanNameDomain_C55DF3ED26204F041A48272271CE041C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_C55DF3ED26204F041A48272271CE041C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_FFB5264E5E00C4224296272271CE7ABE" xlink:to="loc_us-gaap_PlanNameDomain_C55DF3ED26204F041A48272271CE041C" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_A2016OmnibusIncentivePlanMember" xlink:label="loc_oesx_A2016OmnibusIncentivePlanMember_3A47EF55227983E28281272271CEB0AE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_C55DF3ED26204F041A48272271CE041C" xlink:to="loc_oesx_A2016OmnibusIncentivePlanMember_3A47EF55227983E28281272271CEB0AE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_1A1256FDF9BC9D8333A4272271CE5747" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_BA06449E38E4E98EA7FB272271CEF625" xlink:to="loc_us-gaap_AwardTypeAxis_1A1256FDF9BC9D8333A4272271CE5747" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_95C01808ED935947EFBD272271CF99E7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_1A1256FDF9BC9D8333A4272271CE5747" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_95C01808ED935947EFBD272271CF99E7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_95C01808ED935947EFBD272271CF99E7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_1A1256FDF9BC9D8333A4272271CE5747" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_95C01808ED935947EFBD272271CF99E7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_458D4CD851745FC12F9E272271CF96B0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_95C01808ED935947EFBD272271CF99E7" xlink:to="loc_us-gaap_RestrictedStockMember_458D4CD851745FC12F9E272271CF96B0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_D76ED9A3A35CB3B4AFFC272271CF1F43" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_BA06449E38E4E98EA7FB272271CEF625" xlink:to="loc_us-gaap_StatementClassOfStockAxis_D76ED9A3A35CB3B4AFFC272271CF1F43" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_D157E4A17FB268896655272271CF298A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_D76ED9A3A35CB3B4AFFC272271CF1F43" xlink:to="loc_us-gaap_ClassOfStockDomain_D157E4A17FB268896655272271CF298A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_D157E4A17FB268896655272271CF298A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_D76ED9A3A35CB3B4AFFC272271CF1F43" xlink:to="loc_us-gaap_ClassOfStockDomain_D157E4A17FB268896655272271CF298A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_E0B40FB4F1E1BAA38B62272271CF7770" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_D157E4A17FB268896655272271CF298A" xlink:to="loc_us-gaap_CommonStockMember_E0B40FB4F1E1BAA38B62272271CF7770" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TitleOfIndividualAxis" xlink:label="loc_us-gaap_TitleOfIndividualAxis_BAE518E62A092CB019FC272271CF4635" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_BA06449E38E4E98EA7FB272271CEF625" xlink:to="loc_us-gaap_TitleOfIndividualAxis_BAE518E62A092CB019FC272271CF4635" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_1098A46035E3AF02B560272271CFB3F8_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TitleOfIndividualAxis_BAE518E62A092CB019FC272271CF4635" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_1098A46035E3AF02B560272271CFB3F8_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_1098A46035E3AF02B560272271CFB3F8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TitleOfIndividualAxis_BAE518E62A092CB019FC272271CF4635" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_1098A46035E3AF02B560272271CFB3F8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ExecutiveOfficerMember" xlink:label="loc_us-gaap_ExecutiveOfficerMember_DF0AB0E0083951AC6496272271CF6720" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_1098A46035E3AF02B560272271CFB3F8" xlink:to="loc_us-gaap_ExecutiveOfficerMember_DF0AB0E0083951AC6496272271CF6720" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DirectorMember" xlink:label="loc_us-gaap_DirectorMember_E6CD93AC550C77C0A7DB272271CF30D7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_1098A46035E3AF02B560272271CFB3F8" xlink:to="loc_us-gaap_DirectorMember_E6CD93AC550C77C0A7DB272271CF30D7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_97138C2BE3667EBFD3FF272271D4F3D5" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_BA06449E38E4E98EA7FB272271CEF625" xlink:to="loc_us-gaap_RangeAxis_97138C2BE3667EBFD3FF272271D4F3D5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_61784D091F2FD16E94EB272271D4F8F5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_97138C2BE3667EBFD3FF272271D4F3D5" xlink:to="loc_us-gaap_RangeMember_61784D091F2FD16E94EB272271D4F8F5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_61784D091F2FD16E94EB272271D4F8F5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_97138C2BE3667EBFD3FF272271D4F3D5" xlink:to="loc_us-gaap_RangeMember_61784D091F2FD16E94EB272271D4F8F5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_C033D8A5CBC26A77CBC3272271D46B21" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_61784D091F2FD16E94EB272271D4F8F5" xlink:to="loc_us-gaap_MinimumMember_C033D8A5CBC26A77CBC3272271D46B21" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_8DC6E5A1B74C852AE9D2272271D45F18" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_61784D091F2FD16E94EB272271D4F8F5" xlink:to="loc_us-gaap_MaximumMember_8DC6E5A1B74C852AE9D2272271D45F18" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_B500EBBE33E264EC2567272271D5AA7A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_B500EBBE33E264EC2567272271D5AA7A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_FD4B474CBDA5B5FEE5AE272271D5EDE8" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_FD4B474CBDA5B5FEE5AE272271D5EDE8" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerSharePrice" xlink:label="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerSharePrice_5F6FB6D9526E274E7BCE272438D518F1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:to="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerSharePrice_5F6FB6D9526E274E7BCE272438D518F1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross_3124412B5F5D797D743A272271D5CA83" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross_3124412B5F5D797D743A272271D5CA83" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_NumberofRecentlyRetiredMembersoftheBoard" xlink:label="loc_oesx_NumberofRecentlyRetiredMembersoftheBoard_A79AFA2414D5784FB2D4272271D5BAB0" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:to="loc_oesx_NumberofRecentlyRetiredMembersoftheBoard_A79AFA2414D5784FB2D4272271D5BAB0" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_FairValueOfClosingCommonStockPrice" xlink:label="loc_oesx_FairValueOfClosingCommonStockPrice_26DF1C59741E5B0A2F4D272271D595BB" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:to="loc_oesx_FairValueOfClosingCommonStockPrice_26DF1C59741E5B0A2F4D272271D595BB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_C12ACD269112AEF9BA91272271D5DD53" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_C12ACD269112AEF9BA91272271D5DD53" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_B278F25A579DCCBFA60B272271D56C90" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_B278F25A579DCCBFA60B272271D56C90" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_23598208FA9B53D92281272271D55C20" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_23598208FA9B53D92281272271D55C20" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_DeferredCompensationArrangementWithIndividualCompensationExpensePeriodOfRecognition" xlink:label="loc_oesx_DeferredCompensationArrangementWithIndividualCompensationExpensePeriodOfRecognition_84A65CD54ACAA2490357272271D5BBDB" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:to="loc_oesx_DeferredCompensationArrangementWithIndividualCompensationExpensePeriodOfRecognition_84A65CD54ACAA2490357272271D5BBDB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense_81A1A7E6B63910E5578C272271D5A7E7" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_45CFD1CCCFC9BD6EE01F272271D48359" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense_81A1A7E6B63910E5578C272271D5A7E7" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/StockOptionsAndRestrictedSharesOutstandingNonVestedStockOptionsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/StockOptionsAndRestrictedSharesRestrictedSharesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7FC777DD8145530BCEFF901A90566351" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4C3B3041A0C98F19E6E1901A905586D7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7FC777DD8145530BCEFF901A90566351" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4C3B3041A0C98F19E6E1901A905586D7" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_A4300780DAC0D57FB313901A9055F100" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4C3B3041A0C98F19E6E1901A905586D7" xlink:to="loc_us-gaap_AwardTypeAxis_A4300780DAC0D57FB313901A9055F100" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1076FDF16276D61632D2901A905594C9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_A4300780DAC0D57FB313901A9055F100" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1076FDF16276D61632D2901A905594C9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1076FDF16276D61632D2901A905594C9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_A4300780DAC0D57FB313901A9055F100" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1076FDF16276D61632D2901A905594C9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_7379496E5DF44D0912DC901A90551C59" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1076FDF16276D61632D2901A905594C9" xlink:to="loc_us-gaap_RestrictedStockMember_7379496E5DF44D0912DC901A90551C59" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_D0F9D67699B421B58078901A9055D4B6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4C3B3041A0C98F19E6E1901A905586D7" xlink:to="loc_us-gaap_RangeAxis_D0F9D67699B421B58078901A9055D4B6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_91F27FF00AF7C6DB5B60901A9055EFB0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_D0F9D67699B421B58078901A9055D4B6" xlink:to="loc_us-gaap_RangeMember_91F27FF00AF7C6DB5B60901A9055EFB0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_91F27FF00AF7C6DB5B60901A9055EFB0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_D0F9D67699B421B58078901A9055D4B6" xlink:to="loc_us-gaap_RangeMember_91F27FF00AF7C6DB5B60901A9055EFB0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_940E1670922C16611BCB901A90551EA4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_91F27FF00AF7C6DB5B60901A9055EFB0" xlink:to="loc_us-gaap_MinimumMember_940E1670922C16611BCB901A90551EA4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_7A4E2AD49AEA73AE54D4901A9055E6CE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_91F27FF00AF7C6DB5B60901A9055EFB0" xlink:to="loc_us-gaap_MaximumMember_7A4E2AD49AEA73AE54D4901A9055E6CE" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_RestrictedSharesIssuedToKeyEmployeesAbstract" xlink:label="loc_oesx_RestrictedSharesIssuedToKeyEmployeesAbstract_5DAEE926F15C9E339CF4901A9056E5F7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7FC777DD8145530BCEFF901A90566351" xlink:to="loc_oesx_RestrictedSharesIssuedToKeyEmployeesAbstract_5DAEE926F15C9E339CF4901A9056E5F7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_E9C8B3EAF13658C423E7901A905699C4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_RestrictedSharesIssuedToKeyEmployeesAbstract_5DAEE926F15C9E339CF4901A9056E5F7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_E9C8B3EAF13658C423E7901A905699C4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_2C1AC6A8BA563B2F1651901A9056FE38" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_RestrictedSharesIssuedToKeyEmployeesAbstract_5DAEE926F15C9E339CF4901A9056E5F7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_2C1AC6A8BA563B2F1651901A9056FE38" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_255B1540C2F9CDE419D8901A9056CC86" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_RestrictedSharesIssuedToKeyEmployeesAbstract_5DAEE926F15C9E339CF4901A9056E5F7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_255B1540C2F9CDE419D8901A9056CC86" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_AABB71BBECECC20C883C901A90566141" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_RestrictedSharesIssuedToKeyEmployeesAbstract_5DAEE926F15C9E339CF4901A9056E5F7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_AABB71BBECECC20C883C901A90566141" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_A31990FD4EE8A2CC40F2901A90577CA8" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_RestrictedSharesIssuedToKeyEmployeesAbstract_5DAEE926F15C9E339CF4901A9056E5F7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_A31990FD4EE8A2CC40F2901A90577CA8" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/StockOptionsAndRestrictedSharesStockBasedCompensationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_9CF60B4AD4065600BCB07417C8F2F436" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_58F93E37C01C5FEBAA4F2E9E9860DD02" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_9CF60B4AD4065600BCB07417C8F2F436" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_58F93E37C01C5FEBAA4F2E9E9860DD02" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_35F615210E1E5524AF879BBF3C5EDC31" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_58F93E37C01C5FEBAA4F2E9E9860DD02" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_35F615210E1E5524AF879BBF3C5EDC31" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_640F9722276A0C9799E83CC3A5B82ABA_08CE33582584512AA1F704B046BCBDF6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_35F615210E1E5524AF879BBF3C5EDC31" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_640F9722276A0C9799E83CC3A5B82ABA_08CE33582584512AA1F704B046BCBDF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_4358BD6BFCE254F2AC40F771B256916C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_35F615210E1E5524AF879BBF3C5EDC31" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_4358BD6BFCE254F2AC40F771B256916C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CostOfSalesMember" xlink:label="loc_us-gaap_CostOfSalesMember_93B7CB5C802B5AEA99CA2B92D7541E83" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_4358BD6BFCE254F2AC40F771B256916C" xlink:to="loc_us-gaap_CostOfSalesMember_93B7CB5C802B5AEA99CA2B92D7541E83" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_1B492E4B60095523A32F56D3044051F7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_4358BD6BFCE254F2AC40F771B256916C" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_1B492E4B60095523A32F56D3044051F7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SellingAndMarketingExpenseMember" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_A19DB725CE905833958205A86D0E89B0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_4358BD6BFCE254F2AC40F771B256916C" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_A19DB725CE905833958205A86D0E89B0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_0868EA4EA08C58029698DC5C215F40D2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_4358BD6BFCE254F2AC40F771B256916C" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_0868EA4EA08C58029698DC5C215F40D2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationAllocationAndClassificationInFinancialStatementsAbstract" xlink:label="loc_us-gaap_ShareBasedCompensationAllocationAndClassificationInFinancialStatementsAbstract_4BDF2D2C122F59EBA2DB7C912A2D34D1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_9CF60B4AD4065600BCB07417C8F2F436" xlink:to="loc_us-gaap_ShareBasedCompensationAllocationAndClassificationInFinancialStatementsAbstract_4BDF2D2C122F59EBA2DB7C912A2D34D1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_75041A8C9FB5596B80FC4542B60FD1E1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationAllocationAndClassificationInFinancialStatementsAbstract_4BDF2D2C122F59EBA2DB7C912A2D34D1" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_75041A8C9FB5596B80FC4542B60FD1E1" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/StockOptionsAndRestrictedSharesSummaryOfStockOptionAndStockIncentiveAwardPlansDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_62EDC921546CDC7BA77521673403B205" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_048AC335765168C01B5B216734036273" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_62EDC921546CDC7BA77521673403B205" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_048AC335765168C01B5B216734036273" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_2940160B1317A8EBBC4B21673403E909" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_048AC335765168C01B5B216734036273" xlink:to="loc_us-gaap_AwardTypeAxis_2940160B1317A8EBBC4B21673403E909" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5A0A945BE1D42FC54DBE21673403BF37_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_2940160B1317A8EBBC4B21673403E909" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5A0A945BE1D42FC54DBE21673403BF37_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5A0A945BE1D42FC54DBE21673403BF37" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_2940160B1317A8EBBC4B21673403E909" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5A0A945BE1D42FC54DBE21673403BF37" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_F17FC1BE9A7FEDB18DAD216734036829" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5A0A945BE1D42FC54DBE21673403BF37" xlink:to="loc_us-gaap_EmployeeStockOptionMember_F17FC1BE9A7FEDB18DAD216734036829" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_120BED80817D6BFDCF7D21673403DE63" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5A0A945BE1D42FC54DBE21673403BF37" xlink:to="loc_us-gaap_RestrictedStockMember_120BED80817D6BFDCF7D21673403DE63" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantRollForward" xlink:label="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantRollForward_8428D770FBDD6A0AD39921673403F2B2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_62EDC921546CDC7BA77521673403B205" xlink:to="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantRollForward_8428D770FBDD6A0AD39921673403F2B2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_6E9D52F9D523BDD558DB216734030B97" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantRollForward_8428D770FBDD6A0AD39921673403F2B2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_6E9D52F9D523BDD558DB216734030B97" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_EDF6BC7532F912E175DD2167340431D8" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantRollForward_8428D770FBDD6A0AD39921673403F2B2" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_EDF6BC7532F912E175DD2167340431D8" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantSharesIssuedToEmployee" xlink:label="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantSharesIssuedToEmployee_D78891E83A1614F96B12216734044F6C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantRollForward_8428D770FBDD6A0AD39921673403F2B2" xlink:to="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantSharesIssuedToEmployee_D78891E83A1614F96B12216734044F6C" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantSharesIssuedToNonEmployee" xlink:label="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantSharesIssuedToNonEmployee_BC17FCC0BE6C127D8B85216734047841" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantRollForward_8428D770FBDD6A0AD39921673403F2B2" xlink:to="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantSharesIssuedToNonEmployee_BC17FCC0BE6C127D8B85216734047841" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeited" xlink:label="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeited_11EB440F5D091E19940E21673404C170" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantRollForward_8428D770FBDD6A0AD39921673403F2B2" xlink:to="loc_oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeited_11EB440F5D091E19940E21673404C170" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_DFF86BB8EA7F42ACD303216734049216" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_62EDC921546CDC7BA77521673403B205" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_DFF86BB8EA7F42ACD303216734049216" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_0B03464C73EE71B1A5BF21673404CC17" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_DFF86BB8EA7F42ACD303216734049216" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_0B03464C73EE71B1A5BF21673404CC17" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_259A6FF3EE5A4686F82E21673404E959" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_DFF86BB8EA7F42ACD303216734049216" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_259A6FF3EE5A4686F82E21673404E959" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_E239A235DCA4F1CA5F4621673404F080" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_DFF86BB8EA7F42ACD303216734049216" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_E239A235DCA4F1CA5F4621673404F080" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_D4285E84C960B43605EF21673404B2F6" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_DFF86BB8EA7F42ACD303216734049216" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_D4285E84C960B43605EF21673404B2F6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_79AE00F7159382F5DB9421673404E01A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_62EDC921546CDC7BA77521673403B205" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_79AE00F7159382F5DB9421673404E01A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_ECBE10785011137845BF21673404AC13" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_62EDC921546CDC7BA77521673403B205" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_ECBE10785011137845BF21673404AC13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_35A16BAD8AD689834445216734042F96" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_ECBE10785011137845BF21673404AC13" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_35A16BAD8AD689834445216734042F96" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_C6C546CDF5DC977D46712167340462D2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_ECBE10785011137845BF21673404AC13" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_C6C546CDF5DC977D46712167340462D2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_E37972A22B1C1C8FCE0721673404171E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_ECBE10785011137845BF21673404AC13" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_E37972A22B1C1C8FCE0721673404171E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_BE31A3C6AC43A9BC8A32216734049EC0" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_ECBE10785011137845BF21673404AC13" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_BE31A3C6AC43A9BC8A32216734049EC0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_29C623B4237B0EC4587A216734046FE4" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_62EDC921546CDC7BA77521673403B205" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_29C623B4237B0EC4587A216734046FE4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_3E30C11586D1C8830604216734049278" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_62EDC921546CDC7BA77521673403B205" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_3E30C11586D1C8830604216734049278" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_46AA63A773ACE6C1FE0E216734041954" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_62EDC921546CDC7BA77521673403B205" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_46AA63A773ACE6C1FE0E216734041954" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_EFFE7E71A0E3CAF79508216734045799" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_62EDC921546CDC7BA77521673403B205" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_EFFE7E71A0E3CAF79508216734045799" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_9A428357C159B80CE734216734045824" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_62EDC921546CDC7BA77521673403B205" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_9A428357C159B80CE734216734045824" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/StockOptionsAndRestrictedSharesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/SubsequentEvents" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesAccountsReceivableDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesAccruedExpensesAndOtherDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesConcentrationRiskDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskLineItems" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_61B3D656A1CF6B4D7227E2AC196743FF" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskTable" xlink:label="loc_us-gaap_ConcentrationRiskTable_9042D65F798F216EB18FE2AC19653619" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_61B3D656A1CF6B4D7227E2AC196743FF" xlink:to="loc_us-gaap_ConcentrationRiskTable_9042D65F798F216EB18FE2AC19653619" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_68A5FA744DD5D5276464E2AC19652BFB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_9042D65F798F216EB18FE2AC19653619" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_68A5FA744DD5D5276464E2AC19652BFB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_F11F6823C5E09D48B48BE2AC196506A0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_68A5FA744DD5D5276464E2AC19652BFB" xlink:to="loc_us-gaap_SegmentDomain_F11F6823C5E09D48B48BE2AC196506A0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_F11F6823C5E09D48B48BE2AC196506A0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_68A5FA744DD5D5276464E2AC19652BFB" xlink:to="loc_us-gaap_SegmentDomain_F11F6823C5E09D48B48BE2AC196506A0" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_EngineeredSystemsMember" xlink:label="loc_oesx_EngineeredSystemsMember_D77C3E0F4821786D7004E2AC1966B75D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_F11F6823C5E09D48B48BE2AC196506A0" xlink:to="loc_oesx_EngineeredSystemsMember_D77C3E0F4821786D7004E2AC1966B75D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_C2FA1EA32CAEAC325345E2AC19662016" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_9042D65F798F216EB18FE2AC19653619" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_C2FA1EA32CAEAC325345E2AC19662016" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_682FDE432F05A26FF4C0E2AC1966D444_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_C2FA1EA32CAEAC325345E2AC19662016" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_682FDE432F05A26FF4C0E2AC1966D444_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_682FDE432F05A26FF4C0E2AC1966D444" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_C2FA1EA32CAEAC325345E2AC19662016" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_682FDE432F05A26FF4C0E2AC1966D444" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CostOfSalesMember" xlink:label="loc_us-gaap_CostOfSalesMember_F2415713967120C37983E2AC196692E5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_682FDE432F05A26FF4C0E2AC1966D444" xlink:to="loc_us-gaap_CostOfSalesMember_F2415713967120C37983E2AC196692E5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SalesRevenueServicesNetMember" xlink:label="loc_us-gaap_SalesRevenueServicesNetMember_30EDACEFC7FA5711FAEEE2AC19666AFA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_682FDE432F05A26FF4C0E2AC1966D444" xlink:to="loc_us-gaap_SalesRevenueServicesNetMember_30EDACEFC7FA5711FAEEE2AC19666AFA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccountsReceivableMember" xlink:label="loc_us-gaap_AccountsReceivableMember_B16F9371AE1E43E2E34AE2AC1966019B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_682FDE432F05A26FF4C0E2AC1966D444" xlink:to="loc_us-gaap_AccountsReceivableMember_B16F9371AE1E43E2E34AE2AC1966019B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_1DE89C3FE285D185E819E2AC1966A83D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_9042D65F798F216EB18FE2AC19653619" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_1DE89C3FE285D185E819E2AC1966A83D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_7EEBEADE7B0D89932FD3E2AC1967BA85_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_1DE89C3FE285D185E819E2AC1966A83D" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_7EEBEADE7B0D89932FD3E2AC1967BA85_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_7EEBEADE7B0D89932FD3E2AC1967BA85" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_1DE89C3FE285D185E819E2AC1966A83D" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_7EEBEADE7B0D89932FD3E2AC1967BA85" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SupplierConcentrationRiskMember" xlink:label="loc_us-gaap_SupplierConcentrationRiskMember_8C7E8BA42373B2A57EDDE2AC1967FEE8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_7EEBEADE7B0D89932FD3E2AC1967BA85" xlink:to="loc_us-gaap_SupplierConcentrationRiskMember_8C7E8BA42373B2A57EDDE2AC1967FEE8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_9AEC3360D301A5054E49E2AC1967F7EF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_7EEBEADE7B0D89932FD3E2AC1967BA85" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_9AEC3360D301A5054E49E2AC1967F7EF" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_NumberofFinancialInstitutions" xlink:label="loc_oesx_NumberofFinancialInstitutions_128ECC0E833EC56B9FFFE2AC196738C1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_61B3D656A1CF6B4D7227E2AC196743FF" xlink:to="loc_oesx_NumberofFinancialInstitutions_128ECC0E833EC56B9FFFE2AC196738C1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskPercentage1" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_84BD53E871AD3F87155DE2AC1967FF32" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_61B3D656A1CF6B4D7227E2AC196743FF" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_84BD53E871AD3F87155DE2AC1967FF32" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_ConcentrationRiskNumberOfEntitiesInvolvedInRiskCalculation" xlink:label="loc_oesx_ConcentrationRiskNumberOfEntitiesInvolvedInRiskCalculation_4B6E52F82FABC1C350ADE2AC1967C2BE" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_61B3D656A1CF6B4D7227E2AC196743FF" xlink:to="loc_oesx_ConcentrationRiskNumberOfEntitiesInvolvedInRiskCalculation_4B6E52F82FABC1C350ADE2AC1967C2BE" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesDilutiveSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_E383ABDAD8D45D5D8D3859B30C862A84" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_04987C3B1BEA51EF94C4F24CD846A46F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_E383ABDAD8D45D5D8D3859B30C862A84" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_04987C3B1BEA51EF94C4F24CD846A46F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_F1C2EDC0D5715A2E9282D5484217C530" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_04987C3B1BEA51EF94C4F24CD846A46F" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_F1C2EDC0D5715A2E9282D5484217C530" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_03F7FDF8C579C47438673D8438DF82BE_08CE33582584512AA1F704B046BCBDF6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_F1C2EDC0D5715A2E9282D5484217C530" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_03F7FDF8C579C47438673D8438DF82BE_08CE33582584512AA1F704B046BCBDF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_57297F28EFB0533EB402F5A7E2237233" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_F1C2EDC0D5715A2E9282D5484217C530" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_57297F28EFB0533EB402F5A7E2237233" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_DBC7DC022D595BAF9E82C677691F364E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_57297F28EFB0533EB402F5A7E2237233" xlink:to="loc_us-gaap_EmployeeStockOptionMember_DBC7DC022D595BAF9E82C677691F364E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_E6479DAC726658529D0C86790973B1BE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_57297F28EFB0533EB402F5A7E2237233" xlink:to="loc_us-gaap_RestrictedStockMember_E6479DAC726658529D0C86790973B1BE" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_AntidilutiveSharesExcludedFromComputationOfEarningsPerShareAbstract" xlink:label="loc_oesx_AntidilutiveSharesExcludedFromComputationOfEarningsPerShareAbstract_41F00D72D1785F208B6AF7ACCF6B6F1F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_E383ABDAD8D45D5D8D3859B30C862A84" xlink:to="loc_oesx_AntidilutiveSharesExcludedFromComputationOfEarningsPerShareAbstract_41F00D72D1785F208B6AF7ACCF6B6F1F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_745F5164537550088D4FA4E7108A589D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_AntidilutiveSharesExcludedFromComputationOfEarningsPerShareAbstract_41F00D72D1785F208B6AF7ACCF6B6F1F" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_745F5164537550088D4FA4E7108A589D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesEpsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesEquipmentUnderCapitalLeasesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_49142DC6FA8950ABAD975BE0152FECFD" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_0FB24100E2105A438E5405DB5F1BE63E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_49142DC6FA8950ABAD975BE0152FECFD" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_0FB24100E2105A438E5405DB5F1BE63E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_52A6AEFAE95650CFB80F75825E854240" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_0FB24100E2105A438E5405DB5F1BE63E" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_52A6AEFAE95650CFB80F75825E854240" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_CC57E61ABFCB256EEC083CC84200E0A2_08CE33582584512AA1F704B046BCBDF6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_52A6AEFAE95650CFB80F75825E854240" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_CC57E61ABFCB256EEC083CC84200E0A2_08CE33582584512AA1F704B046BCBDF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_FA6749DD60ED54E0AE3E9025111ECF9C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_52A6AEFAE95650CFB80F75825E854240" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_FA6749DD60ED54E0AE3E9025111ECF9C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AssetsHeldUnderCapitalLeasesMember" xlink:label="loc_us-gaap_AssetsHeldUnderCapitalLeasesMember_FBF1398703D95759900B8D323803400F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_FA6749DD60ED54E0AE3E9025111ECF9C" xlink:to="loc_us-gaap_AssetsHeldUnderCapitalLeasesMember_FBF1398703D95759900B8D323803400F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_9FEAC95788E35442AFE8635CBF5FB1B2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_49142DC6FA8950ABAD975BE0152FECFD" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_9FEAC95788E35442AFE8635CBF5FB1B2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_2D49806E6401516EA3EBCA6CCF623382" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_49142DC6FA8950ABAD975BE0152FECFD" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_2D49806E6401516EA3EBCA6CCF623382" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_8E517263FFFA54C0A3067BD345C5DFCA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_49142DC6FA8950ABAD975BE0152FECFD" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_8E517263FFFA54C0A3067BD345C5DFCA" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesFinancingReceivablesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_8D6AE12CA0C8519587063782B4A72028" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_2FF4B8FA6E4E5E808EA78CC3C537DBB9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_8D6AE12CA0C8519587063782B4A72028" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_2FF4B8FA6E4E5E808EA78CC3C537DBB9" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_FinancingReceivableTypeAxis" xlink:label="loc_oesx_FinancingReceivableTypeAxis_02D1F7C6C6B453119495EAA9EBE607A8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_2FF4B8FA6E4E5E808EA78CC3C537DBB9" xlink:to="loc_oesx_FinancingReceivableTypeAxis_02D1F7C6C6B453119495EAA9EBE607A8" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_FinancingReceivableTypeDomain" xlink:label="loc_oesx_FinancingReceivableTypeDomain_127EB8C0D2B8649E921D3CC8423686B9_08CE33582584512AA1F704B046BCBDF6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_oesx_FinancingReceivableTypeAxis_02D1F7C6C6B453119495EAA9EBE607A8" xlink:to="loc_oesx_FinancingReceivableTypeDomain_127EB8C0D2B8649E921D3CC8423686B9_08CE33582584512AA1F704B046BCBDF6" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_FinancingReceivableTypeDomain" xlink:label="loc_oesx_FinancingReceivableTypeDomain_5271083C49325BA289A191B665EE3B13" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_oesx_FinancingReceivableTypeAxis_02D1F7C6C6B453119495EAA9EBE607A8" xlink:to="loc_oesx_FinancingReceivableTypeDomain_5271083C49325BA289A191B665EE3B13" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_NotPastDueMember" xlink:label="loc_oesx_NotPastDueMember_E5167384B76E501281092F97CB3A273C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_FinancingReceivableTypeDomain_5271083C49325BA289A191B665EE3B13" xlink:to="loc_oesx_NotPastDueMember_E5167384B76E501281092F97CB3A273C" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_OneToNinetyDaysMember" xlink:label="loc_oesx_OneToNinetyDaysMember_BC79615C50105EAF94C57B1FCC5BD1C8" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_FinancingReceivableTypeDomain_5271083C49325BA289A191B665EE3B13" xlink:to="loc_oesx_OneToNinetyDaysMember_BC79615C50105EAF94C57B1FCC5BD1C8" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_GreaterThanNinetyDaysMember" xlink:label="loc_oesx_GreaterThanNinetyDaysMember_DC44A2425ECB5EDB8224B874DB65D07C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_FinancingReceivableTypeDomain_5271083C49325BA289A191B665EE3B13" xlink:to="loc_oesx_GreaterThanNinetyDaysMember_DC44A2425ECB5EDB8224B874DB65D07C" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_PastDueLeaseNetMember" xlink:label="loc_oesx_PastDueLeaseNetMember_D978DBD00BA55CFAAD34B704052A8B43" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_FinancingReceivableTypeDomain_5271083C49325BA289A191B665EE3B13" xlink:to="loc_oesx_PastDueLeaseNetMember_D978DBD00BA55CFAAD34B704052A8B43" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_SalesTypeNetMember" xlink:label="loc_oesx_SalesTypeNetMember_224D1360404952C3A5B159394DDFEE18" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_oesx_FinancingReceivableTypeDomain_5271083C49325BA289A191B665EE3B13" xlink:to="loc_oesx_SalesTypeNetMember_224D1360404952C3A5B159394DDFEE18" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableClassifiedAbstract" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableClassifiedAbstract_1B8574668FFC595FBBEE8DC3932BF559" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_8D6AE12CA0C8519587063782B4A72028" xlink:to="loc_us-gaap_AccountsNotesAndLoansReceivableClassifiedAbstract_1B8574668FFC595FBBEE8DC3932BF559" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableNetCurrent_F2C1E99E1AEB54BBA78838F8FC1D1954" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableClassifiedAbstract_1B8574668FFC595FBBEE8DC3932BF559" xlink:to="loc_us-gaap_AccountsNotesAndLoansReceivableNetCurrent_F2C1E99E1AEB54BBA78838F8FC1D1954" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermAccountsNotesAndLoansReceivableNetNoncurrent" xlink:label="loc_us-gaap_LongTermAccountsNotesAndLoansReceivableNetNoncurrent_1D49437B4E23515DB3C381FD33B0CF25" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableClassifiedAbstract_1B8574668FFC595FBBEE8DC3932BF559" xlink:to="loc_us-gaap_LongTermAccountsNotesAndLoansReceivableNetNoncurrent_1D49437B4E23515DB3C381FD33B0CF25" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccountsReceivableGrossCurrent" xlink:label="loc_us-gaap_AccountsReceivableGrossCurrent_55513A25CF3458E3AE367B372FB0C410" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableClassifiedAbstract_1B8574668FFC595FBBEE8DC3932BF559" xlink:to="loc_us-gaap_AccountsReceivableGrossCurrent_55513A25CF3458E3AE367B372FB0C410" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_00D19267431A518BBC29B01890F77302" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableClassifiedAbstract_1B8574668FFC595FBBEE8DC3932BF559" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_00D19267431A518BBC29B01890F77302" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_F6CB5363179157349887512F90FE19DA" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableClassifiedAbstract_1B8574668FFC595FBBEE8DC3932BF559" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_F6CB5363179157349887512F90FE19DA" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesInventoriesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_8A5710CA2B2E6DBD5AAA202AA3CDAE94" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_8A5710CA2B2E6DBD5AAA202AA3CDAE94" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SaleLeasebackTransactionDescriptionAxis" xlink:label="loc_us-gaap_SaleLeasebackTransactionDescriptionAxis_D7828A1DD59297E9A7BE202AA3CD416F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_8A5710CA2B2E6DBD5AAA202AA3CDAE94" xlink:to="loc_us-gaap_SaleLeasebackTransactionDescriptionAxis_D7828A1DD59297E9A7BE202AA3CD416F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SaleLeasebackTransactionNameDomain" xlink:label="loc_us-gaap_SaleLeasebackTransactionNameDomain_7AFF9D0B850159B614D2202AA3D203CF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SaleLeasebackTransactionDescriptionAxis_D7828A1DD59297E9A7BE202AA3CD416F" xlink:to="loc_us-gaap_SaleLeasebackTransactionNameDomain_7AFF9D0B850159B614D2202AA3D203CF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SaleLeasebackTransactionNameDomain" xlink:label="loc_us-gaap_SaleLeasebackTransactionNameDomain_7AFF9D0B850159B614D2202AA3D203CF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SaleLeasebackTransactionDescriptionAxis_D7828A1DD59297E9A7BE202AA3CD416F" xlink:to="loc_us-gaap_SaleLeasebackTransactionNameDomain_7AFF9D0B850159B614D2202AA3D203CF" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_AgreementwithTramontinaU.S.CookwareInc.Member" xlink:label="loc_oesx_AgreementwithTramontinaU.S.CookwareInc.Member_3523580D314B6212C8FA202AA3D2E2C6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleLeasebackTransactionNameDomain_7AFF9D0B850159B614D2202AA3D203CF" xlink:to="loc_oesx_AgreementwithTramontinaU.S.CookwareInc.Member_3523580D314B6212C8FA202AA3D2E2C6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_0EE8699C3A04AAA24ABE202AA3D2B050" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_8A5710CA2B2E6DBD5AAA202AA3CDAE94" xlink:to="loc_us-gaap_RangeAxis_0EE8699C3A04AAA24ABE202AA3D2B050" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_E0B949DD0F80CCF97E09202AA3D245BE_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_0EE8699C3A04AAA24ABE202AA3D2B050" xlink:to="loc_us-gaap_RangeMember_E0B949DD0F80CCF97E09202AA3D245BE_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_E0B949DD0F80CCF97E09202AA3D245BE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_0EE8699C3A04AAA24ABE202AA3D2B050" xlink:to="loc_us-gaap_RangeMember_E0B949DD0F80CCF97E09202AA3D245BE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_33432AF6CEECEB41BE15202AA3D25E91" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_E0B949DD0F80CCF97E09202AA3D245BE" xlink:to="loc_us-gaap_MinimumMember_33432AF6CEECEB41BE15202AA3D25E91" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_0298D942B7BDB728A13D202AA3D21789" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_E0B949DD0F80CCF97E09202AA3D245BE" xlink:to="loc_us-gaap_MaximumMember_0298D942B7BDB728A13D202AA3D21789" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductOrServiceAxis" xlink:label="loc_us-gaap_ProductOrServiceAxis_17187740C6DDF782473E202AA3D2A0AD" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_8A5710CA2B2E6DBD5AAA202AA3CDAE94" xlink:to="loc_us-gaap_ProductOrServiceAxis_17187740C6DDF782473E202AA3D2A0AD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_64B805E9E96AE1689A3D202AA3D34A57_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ProductOrServiceAxis_17187740C6DDF782473E202AA3D2A0AD" xlink:to="loc_us-gaap_ProductsAndServicesDomain_64B805E9E96AE1689A3D202AA3D34A57_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_64B805E9E96AE1689A3D202AA3D34A57" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ProductOrServiceAxis_17187740C6DDF782473E202AA3D2A0AD" xlink:to="loc_us-gaap_ProductsAndServicesDomain_64B805E9E96AE1689A3D202AA3D34A57" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_HighIntensityFluorescentLightingProductsMember" xlink:label="loc_oesx_HighIntensityFluorescentLightingProductsMember_7F5DB0ED5245E80B6105202AA3D33485" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_64B805E9E96AE1689A3D202AA3D34A57" xlink:to="loc_oesx_HighIntensityFluorescentLightingProductsMember_7F5DB0ED5245E80B6105202AA3D33485" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_AccountsReceivablesDueMinimumPeriod" xlink:label="loc_oesx_AccountsReceivablesDueMinimumPeriod_7E1C0E07BA88423B888F202AA3D3548C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:to="loc_oesx_AccountsReceivablesDueMinimumPeriod_7E1C0E07BA88423B888F202AA3D3548C" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_AccountsReceivablesDueMaximumPeriod" xlink:label="loc_oesx_AccountsReceivablesDueMaximumPeriod_EC22A7147658FC528D74202AA3D313CC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:to="loc_oesx_AccountsReceivablesDueMaximumPeriod_EC22A7147658FC528D74202AA3D313CC" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_InventoryReserveLengthofTimeofInventoryUsageConsidered" xlink:label="loc_oesx_InventoryReserveLengthofTimeofInventoryUsageConsidered_629BAA8998E574CEA2DC202AA3D3C698" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:to="loc_oesx_InventoryReserveLengthofTimeofInventoryUsageConsidered_629BAA8998E574CEA2DC202AA3D3C698" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SaleLeasebackTransactionNetProceedsInvestingActivities" xlink:label="loc_us-gaap_SaleLeasebackTransactionNetProceedsInvestingActivities_F7CE92703AACB232B17A202AA3D3988F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:to="loc_us-gaap_SaleLeasebackTransactionNetProceedsInvestingActivities_F7CE92703AACB232B17A202AA3D3988F" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_SaleLeasebackTransactionAreaofLeasedProperty" xlink:label="loc_oesx_SaleLeasebackTransactionAreaofLeasedProperty_A11363606E316610DCF9202AA3D3D704" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:to="loc_oesx_SaleLeasebackTransactionAreaofLeasedProperty_A11363606E316610DCF9202AA3D3D704" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_SaleLeasebackTransactionLeaseTerm" xlink:label="loc_oesx_SaleLeasebackTransactionLeaseTerm_247FAD11C0457B7CD561202AA3D397FC" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:to="loc_oesx_SaleLeasebackTransactionLeaseTerm_247FAD11C0457B7CD561202AA3D397FC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Depreciation" xlink:label="loc_us-gaap_Depreciation_68A3F1E26CF7F249B378202AA3D3B538" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:to="loc_us-gaap_Depreciation_68A3F1E26CF7F249B378202AA3D3B538" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_F1194D6D99DD4FB5D2E2202AA3D30DAC" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_F1194D6D99DD4FB5D2E2202AA3D30DAC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_755129754DDD38378E8B202AA3D39E23" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_755129754DDD38378E8B202AA3D39E23" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_LimitedWarrantyTerm" xlink:label="loc_oesx_LimitedWarrantyTerm_8F0EBDAC3229E7CCB257202AA3D37A17" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:to="loc_oesx_LimitedWarrantyTerm_8F0EBDAC3229E7CCB257202AA3D37A17" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_PowerPurchaseAgreementProductRevenueRecognizableTerm" xlink:label="loc_oesx_PowerPurchaseAgreementProductRevenueRecognizableTerm_EB620800E51F067B0FFE202AA3D35243" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CF11948996741201D397202AA3D3B660" xlink:to="loc_oesx_PowerPurchaseAgreementProductRevenueRecognizableTerm_EB620800E51F067B0FFE202AA3D35243" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesOtherIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_961B9AEBF7555B02961011FB40F884F9" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_C07C8D8AFC7A5505B7358B9ECE78A9C0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_961B9AEBF7555B02961011FB40F884F9" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_C07C8D8AFC7A5505B7358B9ECE78A9C0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_590495DF89AD57B288A9CEAF8E7707B8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_C07C8D8AFC7A5505B7358B9ECE78A9C0" xlink:to="loc_us-gaap_RangeAxis_590495DF89AD57B288A9CEAF8E7707B8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_2D4412F7CBB6B2558C713D8438FA35BD_08CE33582584512AA1F704B046BCBDF6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_590495DF89AD57B288A9CEAF8E7707B8" xlink:to="loc_us-gaap_RangeMember_2D4412F7CBB6B2558C713D8438FA35BD_08CE33582584512AA1F704B046BCBDF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_31E9AEA39DBD590A91339B68973F0F30" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_590495DF89AD57B288A9CEAF8E7707B8" xlink:to="loc_us-gaap_RangeMember_31E9AEA39DBD590A91339B68973F0F30" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_BCC34CBF6575518CBC91DA7FAAE0E260" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_31E9AEA39DBD590A91339B68973F0F30" xlink:to="loc_us-gaap_MinimumMember_BCC34CBF6575518CBC91DA7FAAE0E260" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_6189913524C357DEAFACE1D88616223C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_31E9AEA39DBD590A91339B68973F0F30" xlink:to="loc_us-gaap_MaximumMember_6189913524C357DEAFACE1D88616223C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_A1CA548B5C3D5D7192A05EA37CDC3C16" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_C07C8D8AFC7A5505B7358B9ECE78A9C0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_A1CA548B5C3D5D7192A05EA37CDC3C16" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_B768B1522E200F670B5D3D8438FA5155_08CE33582584512AA1F704B046BCBDF6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_A1CA548B5C3D5D7192A05EA37CDC3C16" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_B768B1522E200F670B5D3D8438FA5155_08CE33582584512AA1F704B046BCBDF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_84FD60FA5D605068A04F47FB9CC6C360" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_A1CA548B5C3D5D7192A05EA37CDC3C16" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_84FD60FA5D605068A04F47FB9CC6C360" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PatentsMember" xlink:label="loc_us-gaap_PatentsMember_F36C77B580E052BCB99C12C357AAFB58" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_84FD60FA5D605068A04F47FB9CC6C360" xlink:to="loc_us-gaap_PatentsMember_F36C77B580E052BCB99C12C357AAFB58" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LicensingAgreementsMember" xlink:label="loc_us-gaap_LicensingAgreementsMember_97B17B1B53FB55F19B0035C988794F7B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_84FD60FA5D605068A04F47FB9CC6C360" xlink:to="loc_us-gaap_LicensingAgreementsMember_97B17B1B53FB55F19B0035C988794F7B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TrademarksAndTradeNamesMember" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_452255C0CF235151B119EE40EFA7AE6B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_84FD60FA5D605068A04F47FB9CC6C360" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_452255C0CF235151B119EE40EFA7AE6B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CustomerRelationshipsMember" xlink:label="loc_us-gaap_CustomerRelationshipsMember_8BAB6E10E59A5BB7987E6585BA5B6D9C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_84FD60FA5D605068A04F47FB9CC6C360" xlink:to="loc_us-gaap_CustomerRelationshipsMember_8BAB6E10E59A5BB7987E6585BA5B6D9C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_D81B547658F35742A87D52BE7199580B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_84FD60FA5D605068A04F47FB9CC6C360" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_D81B547658F35742A87D52BE7199580B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NoncompeteAgreementsMember" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_98E075E0B98759E3B4EB40E8862F42C8" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_84FD60FA5D605068A04F47FB9CC6C360" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_98E075E0B98759E3B4EB40E8862F42C8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_9DCC9701B57557A986F43D5F0C0436FC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_961B9AEBF7555B02961011FB40F884F9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_9DCC9701B57557A986F43D5F0C0436FC" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_FiniteLivedandIndefiniteLivedIntangibleAssetsGross" xlink:label="loc_oesx_FiniteLivedandIndefiniteLivedIntangibleAssetsGross_1B7A67BB6BFC57B8B185C06CF6E3BB1F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_961B9AEBF7555B02961011FB40F884F9" xlink:to="loc_oesx_FiniteLivedandIndefiniteLivedIntangibleAssetsGross_1B7A67BB6BFC57B8B185C06CF6E3BB1F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_0B8ED118EAE35DB78C4AD6106231DD34" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_961B9AEBF7555B02961011FB40F884F9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_0B8ED118EAE35DB78C4AD6106231DD34" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_E6CDE12ECB2D5F7EB140C61C7D695F23" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_961B9AEBF7555B02961011FB40F884F9" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_E6CDE12ECB2D5F7EB140C61C7D695F23" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_932807BA580159EF9B00E18C7BCB9B71" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_961B9AEBF7555B02961011FB40F884F9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_932807BA580159EF9B00E18C7BCB9B71" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_B5AAECD1AC415251B1924E8B06A91F7C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_932807BA580159EF9B00E18C7BCB9B71" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_B5AAECD1AC415251B1924E8B06A91F7C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_8419BC2B340953AD8C34F76BD9C7D179" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_932807BA580159EF9B00E18C7BCB9B71" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_8419BC2B340953AD8C34F76BD9C7D179" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_02DB62CE17285B999E574F5945E6D9B4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_932807BA580159EF9B00E18C7BCB9B71" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_02DB62CE17285B999E574F5945E6D9B4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_5BD0F741F3C552BE996B49DC70ADB266" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_932807BA580159EF9B00E18C7BCB9B71" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_5BD0F741F3C552BE996B49DC70ADB266" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_21455DE2D4A0580ABA5C23CB44A2C709" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_932807BA580159EF9B00E18C7BCB9B71" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_21455DE2D4A0580ABA5C23CB44A2C709" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_C8BB1BA1F8525B60B279C3A2742AA1C0" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_932807BA580159EF9B00E18C7BCB9B71" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_C8BB1BA1F8525B60B279C3A2742AA1C0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_D465E65E6AF154CEBBC665AB13028DBD" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_932807BA580159EF9B00E18C7BCB9B71" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_D465E65E6AF154CEBBC665AB13028DBD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_8B0EC01F3DD15F9CBA634741BBD0D4F3" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_932807BA580159EF9B00E18C7BCB9B71" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_8B0EC01F3DD15F9CBA634741BBD0D4F3" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesOtherLongTermAssetsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPpeUsefulLivesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_18F21DC6DE6A5A66B8C388FB7336DE25" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1ED8E3953BA95DAFAFEE2420E9DDFAAD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_18F21DC6DE6A5A66B8C388FB7336DE25" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1ED8E3953BA95DAFAFEE2420E9DDFAAD" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_B643EB05A8C1529CB699299D354924D4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1ED8E3953BA95DAFAFEE2420E9DDFAAD" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_B643EB05A8C1529CB699299D354924D4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_8FFE811411C7BE9E6D444B8153C0E39D_08CE33582584512AA1F704B046BCBDF6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_B643EB05A8C1529CB699299D354924D4" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_8FFE811411C7BE9E6D444B8153C0E39D_08CE33582584512AA1F704B046BCBDF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_180F204FCAB8514FA9FCC98F10EA8A60" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_B643EB05A8C1529CB699299D354924D4" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_180F204FCAB8514FA9FCC98F10EA8A60" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LandImprovementsMember" xlink:label="loc_us-gaap_LandImprovementsMember_77D7515B48315E69867202840CE0D70B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_180F204FCAB8514FA9FCC98F10EA8A60" xlink:to="loc_us-gaap_LandImprovementsMember_77D7515B48315E69867202840CE0D70B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BuildingAndBuildingImprovementsMember" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_A22EA8D1A57A5570A2B4BF9E730E3CC7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_180F204FCAB8514FA9FCC98F10EA8A60" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_A22EA8D1A57A5570A2B4BF9E730E3CC7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_4A48A0CBD882584DAC8AD119FB29E33B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_180F204FCAB8514FA9FCC98F10EA8A60" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_4A48A0CBD882584DAC8AD119FB29E33B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LeaseholdsAndLeaseholdImprovementsMember" xlink:label="loc_us-gaap_LeaseholdsAndLeaseholdImprovementsMember_24A2F86842375BAD94EBE915DB45FC38" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_180F204FCAB8514FA9FCC98F10EA8A60" xlink:to="loc_us-gaap_LeaseholdsAndLeaseholdImprovementsMember_24A2F86842375BAD94EBE915DB45FC38" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquipmentLeasedToOtherPartyMember" xlink:label="loc_us-gaap_EquipmentLeasedToOtherPartyMember_7085F26EC90D5BD695CF2AB26F40E748" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_180F204FCAB8514FA9FCC98F10EA8A60" xlink:to="loc_us-gaap_EquipmentLeasedToOtherPartyMember_7085F26EC90D5BD695CF2AB26F40E748" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquipmentMember" xlink:label="loc_us-gaap_EquipmentMember_52B75A1C95FC5AF29FB095DF53A2F677" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_180F204FCAB8514FA9FCC98F10EA8A60" xlink:to="loc_us-gaap_EquipmentMember_52B75A1C95FC5AF29FB095DF53A2F677" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_CC4BA88B5284526DB7B93BF8F3033CA3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1ED8E3953BA95DAFAFEE2420E9DDFAAD" xlink:to="loc_us-gaap_RangeAxis_CC4BA88B5284526DB7B93BF8F3033CA3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_727C78071377ECAD67F84B8153C0380F_08CE33582584512AA1F704B046BCBDF6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_CC4BA88B5284526DB7B93BF8F3033CA3" xlink:to="loc_us-gaap_RangeMember_727C78071377ECAD67F84B8153C0380F_08CE33582584512AA1F704B046BCBDF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_598DF009FA2C58378AC683DE249D1E7F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_CC4BA88B5284526DB7B93BF8F3033CA3" xlink:to="loc_us-gaap_RangeMember_598DF009FA2C58378AC683DE249D1E7F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_80AEFAA32C435247919FDAC8BB2D1157" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_598DF009FA2C58378AC683DE249D1E7F" xlink:to="loc_us-gaap_MinimumMember_80AEFAA32C435247919FDAC8BB2D1157" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_A74CE66658C9539A8A664DB3EAD87902" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_598DF009FA2C58378AC683DE249D1E7F" xlink:to="loc_us-gaap_MaximumMember_A74CE66658C9539A8A664DB3EAD87902" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNetAbstract" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_941A76827C4C595BAFC7BD87CDCD7349" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_18F21DC6DE6A5A66B8C388FB7336DE25" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_941A76827C4C595BAFC7BD87CDCD7349" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_E7D5BA850BE957D7B2C6D9E2826E11CD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_941A76827C4C595BAFC7BD87CDCD7349" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_E7D5BA850BE957D7B2C6D9E2826E11CD" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_PropertyPlantAndEquipmentEstimatedUsefulLife" xlink:label="loc_oesx_PropertyPlantAndEquipmentEstimatedUsefulLife_2DEA495FF6625B34BA111415EDC2C62C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_941A76827C4C595BAFC7BD87CDCD7349" xlink:to="loc_oesx_PropertyPlantAndEquipmentEstimatedUsefulLife_2DEA495FF6625B34BA111415EDC2C62C" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPrepaidExpensesAndOtherCurrentAssetsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPropPlantAndEquipDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_68EF48ABC47458D4A9584A4C01BAE6D6" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1C388C9E6E8B55A187EFB6552618101C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_68EF48ABC47458D4A9584A4C01BAE6D6" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1C388C9E6E8B55A187EFB6552618101C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_35A04E78A61751788DB003C153B2A52D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1C388C9E6E8B55A187EFB6552618101C" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_35A04E78A61751788DB003C153B2A52D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1FC703C51D205B2BCC7E4B8153D7C181_08CE33582584512AA1F704B046BCBDF6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_35A04E78A61751788DB003C153B2A52D" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1FC703C51D205B2BCC7E4B8153D7C181_08CE33582584512AA1F704B046BCBDF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1F247CA7E28752F5B6E4B88A50C18122" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_35A04E78A61751788DB003C153B2A52D" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1F247CA7E28752F5B6E4B88A50C18122" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LandImprovementsMember" xlink:label="loc_us-gaap_LandImprovementsMember_C680927185965529B6487CEA8EEC59CD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1F247CA7E28752F5B6E4B88A50C18122" xlink:to="loc_us-gaap_LandImprovementsMember_C680927185965529B6487CEA8EEC59CD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BuildingAndBuildingImprovementsMember" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_6FBAF6D7BE135A62AC86BF2F24E865A4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1F247CA7E28752F5B6E4B88A50C18122" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_6FBAF6D7BE135A62AC86BF2F24E865A4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_A0B36F6CAC19513885456E589DCC7AB8" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1F247CA7E28752F5B6E4B88A50C18122" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_A0B36F6CAC19513885456E589DCC7AB8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LeaseholdImprovementsMember" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_A38B8E981A3E50AA94F81B36A46E5495" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1F247CA7E28752F5B6E4B88A50C18122" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_A38B8E981A3E50AA94F81B36A46E5495" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquipmentLeasedToOtherPartyMember" xlink:label="loc_us-gaap_EquipmentLeasedToOtherPartyMember_CD1B66D9244B5735B10D53C1D3F641FA" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1F247CA7E28752F5B6E4B88A50C18122" xlink:to="loc_us-gaap_EquipmentLeasedToOtherPartyMember_CD1B66D9244B5735B10D53C1D3F641FA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentOtherTypesMember" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentOtherTypesMember_9092A6CDCD6652169E865C481416AF59" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1F247CA7E28752F5B6E4B88A50C18122" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentOtherTypesMember_9092A6CDCD6652169E865C481416AF59" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConstructionInProgressMember" xlink:label="loc_us-gaap_ConstructionInProgressMember_DD7C524CF26351EF91E0E1B87D5C9B54" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1F247CA7E28752F5B6E4B88A50C18122" xlink:to="loc_us-gaap_ConstructionInProgressMember_DD7C524CF26351EF91E0E1B87D5C9B54" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNetAbstract" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_6B194412E1955E37AEB05D1D40853222" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_68EF48ABC47458D4A9584A4C01BAE6D6" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_6B194412E1955E37AEB05D1D40853222" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_9DB8EA73493450DE92455BD995033BFB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_6B194412E1955E37AEB05D1D40853222" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_9DB8EA73493450DE92455BD995033BFB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_2068434386D35DD39A1E3B90FDC7EAC1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_6B194412E1955E37AEB05D1D40853222" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_2068434386D35DD39A1E3B90FDC7EAC1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_A31C87B920BD5205A835BB761711DD6F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_6B194412E1955E37AEB05D1D40853222" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_A31C87B920BD5205A835BB761711DD6F" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesWarrantyAccrualDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductWarrantyLiabilityLineItems" xlink:label="loc_us-gaap_ProductWarrantyLiabilityLineItems_EBC1F1337B7050A457B3214A182B0D72" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductWarrantyLiabilityTable" xlink:label="loc_us-gaap_ProductWarrantyLiabilityTable_DF508803BBAA77968A74214A182BBD1D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ProductWarrantyLiabilityLineItems_EBC1F1337B7050A457B3214A182B0D72" xlink:to="loc_us-gaap_ProductWarrantyLiabilityTable_DF508803BBAA77968A74214A182BBD1D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_B454C2AB3B2AD92BCBAF214A182BDB53" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ProductWarrantyLiabilityTable_DF508803BBAA77968A74214A182BBD1D" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_B454C2AB3B2AD92BCBAF214A182BDB53" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_7A2E98F1CD40E4868943214A182BE884_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_B454C2AB3B2AD92BCBAF214A182BDB53" xlink:to="loc_us-gaap_SegmentDomain_7A2E98F1CD40E4868943214A182BE884_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_7A2E98F1CD40E4868943214A182BE884" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_B454C2AB3B2AD92BCBAF214A182BDB53" xlink:to="loc_us-gaap_SegmentDomain_7A2E98F1CD40E4868943214A182BE884" xlink:type="arc" />
    <link:loc xlink:href="oesx-20160930.xsd#oesx_EngineeredSystemsMember" xlink:label="loc_oesx_EngineeredSystemsMember_C834791D8532BD06D3B6214A182B315F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_7A2E98F1CD40E4868943214A182BE884" xlink:to="loc_oesx_EngineeredSystemsMember_C834791D8532BD06D3B6214A182B315F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductWarrantiesDisclosuresAbstract" xlink:label="loc_us-gaap_ProductWarrantiesDisclosuresAbstract_2897C36CECE8C57A87E5214A182B7299" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductWarrantyLiabilityLineItems_EBC1F1337B7050A457B3214A182B0D72" xlink:to="loc_us-gaap_ProductWarrantiesDisclosuresAbstract_2897C36CECE8C57A87E5214A182B7299" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MovementInStandardProductWarrantyAccrualRollForward" xlink:label="loc_us-gaap_MovementInStandardProductWarrantyAccrualRollForward_A9369E2BE1EBED58A84A214A182B0EA3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductWarrantiesDisclosuresAbstract_2897C36CECE8C57A87E5214A182B7299" xlink:to="loc_us-gaap_MovementInStandardProductWarrantyAccrualRollForward_A9369E2BE1EBED58A84A214A182B0EA3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductWarrantyAccrual" xlink:label="loc_us-gaap_ProductWarrantyAccrual_1A0AD7212688BE2DAC06214A182BC7DC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInStandardProductWarrantyAccrualRollForward_A9369E2BE1EBED58A84A214A182B0EA3" xlink:to="loc_us-gaap_ProductWarrantyAccrual_1A0AD7212688BE2DAC06214A182BC7DC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductWarrantyAccrualWarrantiesIssued" xlink:label="loc_us-gaap_ProductWarrantyAccrualWarrantiesIssued_B4B7131402E697042B0C214A182CA0C0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInStandardProductWarrantyAccrualRollForward_A9369E2BE1EBED58A84A214A182B0EA3" xlink:to="loc_us-gaap_ProductWarrantyAccrualWarrantiesIssued_B4B7131402E697042B0C214A182CA0C0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductWarrantyAccrualPreexistingIncreaseDecrease" xlink:label="loc_us-gaap_ProductWarrantyAccrualPreexistingIncreaseDecrease_8C783A09DCD5AC19D368214A182C689E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInStandardProductWarrantyAccrualRollForward_A9369E2BE1EBED58A84A214A182B0EA3" xlink:to="loc_us-gaap_ProductWarrantyAccrualPreexistingIncreaseDecrease_8C783A09DCD5AC19D368214A182C689E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.oesx.com/role/UnauditedCondensedConsolidatedBalanceSheets" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/UnauditedCondensedConsolidatedBalanceSheetsParenthetical" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/UnauditedCondensedConsolidatedStatementsOfCashFlows" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.oesx.com/role/UnauditedCondensedConsolidatedStatementsOfOperations" xlink:type="extended" />
</link:linkbase>





