

<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <roleRef roleURI="http://www.oesx.com/role/Acquisition" xlink:href="oesx-20150331.xsd#Acquisition" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/AcquisitionAcquisitionAgreementDetails" xlink:href="oesx-20150331.xsd#AcquisitionAcquisitionAgreementDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/AcquisitionConsiderationPaidDetails" xlink:href="oesx-20150331.xsd#AcquisitionConsiderationPaidDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/AcquisitionContingentConsiderationDetails" xlink:href="oesx-20150331.xsd#AcquisitionContingentConsiderationDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/AcquisitionIdentifiableIntangibleAssetsAcquiredDetails" xlink:href="oesx-20150331.xsd#AcquisitionIdentifiableIntangibleAssetsAcquiredDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/AcquisitionProFormaResultsOfOperationsDetails" xlink:href="oesx-20150331.xsd#AcquisitionProFormaResultsOfOperationsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/AcquisitionTables" xlink:href="oesx-20150331.xsd#AcquisitionTables" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/CommitmentsAndContingencies" xlink:href="oesx-20150331.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/CommitmentsAndContingenciesDetailsTextual" xlink:href="oesx-20150331.xsd#CommitmentsAndContingenciesDetailsTextual" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/CommitmentsAndContingenciesScheduleOfAnnualCommitmentsUnderNonCancelableOperatingAgreementsDetails" xlink:href="oesx-20150331.xsd#CommitmentsAndContingenciesScheduleOfAnnualCommitmentsUnderNonCancelableOperatingAgreementsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/CommitmentsAndContingenciesTables" xlink:href="oesx-20150331.xsd#CommitmentsAndContingenciesTables" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/ConsolidatedBalanceSheets" xlink:href="oesx-20150331.xsd#ConsolidatedBalanceSheets" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:href="oesx-20150331.xsd#ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/ConsolidatedStatementOfShareholdersEquity" xlink:href="oesx-20150331.xsd#ConsolidatedStatementOfShareholdersEquity" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/ConsolidatedStatementsOfCashFlows" xlink:href="oesx-20150331.xsd#ConsolidatedStatementsOfCashFlows" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/ConsolidatedStatementsOfOperations" xlink:href="oesx-20150331.xsd#ConsolidatedStatementsOfOperations" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/DescriptionOfBusiness" xlink:href="oesx-20150331.xsd#DescriptionOfBusiness" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/DocumentAndEntityInformation" xlink:href="oesx-20150331.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/IncomeTaxes" xlink:href="oesx-20150331.xsd#IncomeTaxes" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/IncomeTaxesDetailsTextual" xlink:href="oesx-20150331.xsd#IncomeTaxesDetailsTextual" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/IncomeTaxesReconciliationOfTaxRatesDetails" xlink:href="oesx-20150331.xsd#IncomeTaxesReconciliationOfTaxRatesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/IncomeTaxesScheduleOfComponentsOfIncomeTaxExpenseOrBenefitDetails" xlink:href="oesx-20150331.xsd#IncomeTaxesScheduleOfComponentsOfIncomeTaxExpenseOrBenefitDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/IncomeTaxesScheduleOfComponentsOfIncomeTaxExpenseOrBenefitDetailsCalc2" xlink:href="oesx-20150331.xsd#IncomeTaxesScheduleOfComponentsOfIncomeTaxExpenseOrBenefitDetailsCalc2" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/IncomeTaxesScheduleOfDeferredTaxAssetsAndLiabilitiesDetails" xlink:href="oesx-20150331.xsd#IncomeTaxesScheduleOfDeferredTaxAssetsAndLiabilitiesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/IncomeTaxesTables" xlink:href="oesx-20150331.xsd#IncomeTaxesTables" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/IncomeTaxesUnrecognizedTaxBenefitActivityDetails" xlink:href="oesx-20150331.xsd#IncomeTaxesUnrecognizedTaxBenefitActivityDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/LongTermDebt" xlink:href="oesx-20150331.xsd#LongTermDebt" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/LongTermDebtAggregateMaturitiesDetails" xlink:href="oesx-20150331.xsd#LongTermDebtAggregateMaturitiesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/LongTermDebtAllOtherDebtDetails" xlink:href="oesx-20150331.xsd#LongTermDebtAllOtherDebtDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/LongTermDebtDetails" xlink:href="oesx-20150331.xsd#LongTermDebtDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/LongTermDebtRevolvingCreditFacilityDetails" xlink:href="oesx-20150331.xsd#LongTermDebtRevolvingCreditFacilityDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/LongTermDebtTables" xlink:href="oesx-20150331.xsd#LongTermDebtTables" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/QuarterlyFinancialDataDetails" xlink:href="oesx-20150331.xsd#QuarterlyFinancialDataDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/QuarterlyFinancialDataUnaudited" xlink:href="oesx-20150331.xsd#QuarterlyFinancialDataUnaudited" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/QuarterlyFinancialDataUnauditedTables" xlink:href="oesx-20150331.xsd#QuarterlyFinancialDataUnauditedTables" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/RelatedPartyTransactions" xlink:href="oesx-20150331.xsd#RelatedPartyTransactions" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/RelatedPartyTransactionsDetails" xlink:href="oesx-20150331.xsd#RelatedPartyTransactionsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SegmentData" xlink:href="oesx-20150331.xsd#SegmentData" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SegmentDataReconciliationOfSegmentAssetsAndLiabilitiesDetails" xlink:href="oesx-20150331.xsd#SegmentDataReconciliationOfSegmentAssetsAndLiabilitiesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SegmentDataReconciliationOfSegmentOperationsDetails" xlink:href="oesx-20150331.xsd#SegmentDataReconciliationOfSegmentOperationsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SegmentDataTables" xlink:href="oesx-20150331.xsd#SegmentDataTables" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/ShareholdersEquity" xlink:href="oesx-20150331.xsd#ShareholdersEquity" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/ShareholdersEquityDetailsTextual" xlink:href="oesx-20150331.xsd#ShareholdersEquityDetailsTextual" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/ShareholdersEquityScheduleOfEsppActivityDetails" xlink:href="oesx-20150331.xsd#ShareholdersEquityScheduleOfEsppActivityDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/ShareholdersEquityTables" xlink:href="oesx-20150331.xsd#ShareholdersEquityTables" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrants" xlink:href="oesx-20150331.xsd#StockOptionsRestrictedSharesAndWarrants" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsDetailsTextual" xlink:href="oesx-20150331.xsd#StockOptionsRestrictedSharesAndWarrantsDetailsTextual" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsOutstandingWarrantsDetails" xlink:href="oesx-20150331.xsd#StockOptionsRestrictedSharesAndWarrantsOutstandingWarrantsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsScheduleOfRestrictedSharesDetails" xlink:href="oesx-20150331.xsd#StockOptionsRestrictedSharesAndWarrantsScheduleOfRestrictedSharesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsScheduleOfSharesAvailableForGrantDetails" xlink:href="oesx-20150331.xsd#StockOptionsRestrictedSharesAndWarrantsScheduleOfSharesAvailableForGrantDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsStockBasedCompensationDetails" xlink:href="oesx-20150331.xsd#StockOptionsRestrictedSharesAndWarrantsStockBasedCompensationDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsSummaryOfExercisePriceRangeDetails" xlink:href="oesx-20150331.xsd#StockOptionsRestrictedSharesAndWarrantsSummaryOfExercisePriceRangeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsSummaryOfOutstandingStockOptionsDetails" xlink:href="oesx-20150331.xsd#StockOptionsRestrictedSharesAndWarrantsSummaryOfOutstandingStockOptionsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsSummaryOfUnrecognizedCompensationCostDetails" xlink:href="oesx-20150331.xsd#StockOptionsRestrictedSharesAndWarrantsSummaryOfUnrecognizedCompensationCostDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsTables" xlink:href="oesx-20150331.xsd#StockOptionsRestrictedSharesAndWarrantsTables" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SubsequentEvents" xlink:href="oesx-20150331.xsd#SubsequentEvents" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPolicies" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPolicies" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesCashAndCashEquivalentsDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesCashAndCashEquivalentsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesConcentrationRiskDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesConcentrationRiskDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesDilutiveSecuritiesDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesDilutiveSecuritiesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesEpsDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesEpsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesFinancingReceivablesDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesFinancingReceivablesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesGoodwillAndOtherIntangibleAssetsDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesGoodwillAndOtherIntangibleAssetsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesIncentiveCompDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesIncentiveCompDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesInventoriesDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesInventoriesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesLtReceivablesDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesLtReceivablesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesLtReceivablesDetailsCalc2" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesLtReceivablesDetailsCalc2" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPolicies" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesPolicies" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPpeUsefulLivesDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesPpeUsefulLivesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPropPlantAndEquipDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesPropPlantAndEquipDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesStockOptionAssumptionsDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesStockOptionAssumptionsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesTables" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesTables" xlink:type="simple" />
  <roleRef roleURI="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesWarrantyAccrualDetails" xlink:href="oesx-20150331.xsd#SummaryOfSignificantAccountingPoliciesWarrantyAccrualDetails" xlink:type="simple" />
  <calculationLink xlink:role="http://www.oesx.com/role/Acquisition" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/AcquisitionAcquisitionAgreementDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/AcquisitionConsiderationPaidDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_1126089a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_8ad60816-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferred1_1126089a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_8ad60816-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_104f78ca-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferred1_1126089a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_104f78ca-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_10a2243a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferred1_1126089a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_10a2243a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="oesx-20150331.xsd#oesx_BusinessCombinationConsiderationTransferredContingentConsiderationAdjustment" xlink:label="loc_oesx_BusinessCombinationConsiderationTransferredContingentConsiderationAdjustment_2277a6de-e822-11e3-b035-22000a1e8102" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferred1_1126089a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_BusinessCombinationConsiderationTransferredContingentConsiderationAdjustment_2277a6de-e822-11e3-b035-22000a1e8102" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_13b6e3b8-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_1303979a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_13b6e3b8-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_1303979a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_5c519906-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_13b6e3b8-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_Goodwill_5c519906-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/AcquisitionContingentConsiderationDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/AcquisitionIdentifiableIntangibleAssetsAcquiredDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/AcquisitionProFormaResultsOfOperationsDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/AcquisitionTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/CommitmentsAndContingencies" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/CommitmentsAndContingenciesDetailsTextual" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/CommitmentsAndContingenciesScheduleOfAnnualCommitmentsUnderNonCancelableOperatingAgreementsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDue" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDue_814b431a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent_80207e60-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDue_814b431a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent_80207e60-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_813e614a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDue_814b431a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_813e614a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_8014ac16-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDue_814b431a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_8014ac16-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter_800588bc-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDue_814b431a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter_800588bc-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/CommitmentsAndContingenciesTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/ConsolidatedBalanceSheets" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_0ce13e30-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaap_AssetsCurrent_0d216a96-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_0ce13e30-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AssetsCurrent_0d216a96-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_18320242-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_0d216a96-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_18320242-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShortTermInvestments" xlink:label="loc_us-gaap_ShortTermInvestments_ac3ee1b2-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_0d216a96-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ShortTermInvestments_ac3ee1b2-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_05404162-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_0d216a96-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_05404162-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InventoryNet" xlink:label="loc_us-gaap_InventoryNet_6952f2e4-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_0d216a96-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_InventoryNet_6952f2e4-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredCostsCurrent" xlink:label="loc_us-gaap_DeferredCostsCurrent_2a1ffdce-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="5" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_0d216a96-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredCostsCurrent_2a1ffdce-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_90f899ac-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="6" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_0d216a96-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_90f899ac-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_940b342e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_0ce13e30-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_940b342e-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InventoryNoncurrent" xlink:label="loc_us-gaap_InventoryNoncurrent_69e8e16e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_0ce13e30-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_InventoryNoncurrent_69e8e16e-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_5c519906-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_0ce13e30-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_Goodwill_5c519906-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_6701f814-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="5" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_0ce13e30-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_6701f814-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsReceivableNetNoncurrent" xlink:label="loc_us-gaap_AccountsReceivableNetNoncurrent_05476ab4-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="6" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_0ce13e30-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AccountsReceivableNetNoncurrent_05476ab4-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_837d6190-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="7" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_0ce13e30-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_837d6190-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_6e1ed1d0-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Liabilities" xlink:label="loc_us-gaap_Liabilities_6e59ec02-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquity_6e1ed1d0-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_Liabilities_6e59ec02-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="loc_us-gaap_LiabilitiesCurrent_6e17fb62-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_6e59ec02-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_LiabilitiesCurrent_6e17fb62-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="loc_us-gaap_AccountsPayableCurrent_05630b34-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_6e17fb62-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AccountsPayableCurrent_05630b34-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_0607a31a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_6e17fb62-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_0607a31a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredRevenueCurrent" xlink:label="loc_us-gaap_DeferredRevenueCurrent_2a991f10-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_6e17fb62-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredRevenueCurrent_2a991f10-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="loc_us-gaap_LongTermDebtCurrent_761ef1a8-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_6e17fb62-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_LongTermDebtCurrent_761ef1a8-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredRevenueNoncurrent" xlink:label="loc_us-gaap_DeferredRevenueNoncurrent_2abf064e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_6e59ec02-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredRevenueNoncurrent_2abf064e-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_85390368-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_6e59ec02-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_85390368-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermLineOfCredit" xlink:label="loc_us-gaap_LongTermLineOfCredit_761d7602-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_6e59ec02-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_LongTermLineOfCredit_761d7602-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLongTermDebtNoncurrent" xlink:label="loc_us-gaap_OtherLongTermDebtNoncurrent_8543454e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="5" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_6e59ec02-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_OtherLongTermDebtNoncurrent_8543454e-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_adc32df4-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquity_6e1ed1d0-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_StockholdersEquity_adc32df4-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="loc_us-gaap_AdditionalPaidInCapital_06e972fe-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_adc32df4-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AdditionalPaidInCapital_06e972fe-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReceivableFromShareholdersOrAffiliatesForIssuanceOfCapitalStock" xlink:label="loc_us-gaap_ReceivableFromShareholdersOrAffiliatesForIssuanceOfCapitalStock_987d2e22-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_adc32df4-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ReceivableFromShareholdersOrAffiliatesForIssuanceOfCapitalStock_987d2e22-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TreasuryStockValue" xlink:label="loc_us-gaap_TreasuryStockValue_b2297f42-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_adc32df4-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_TreasuryStockValue_b2297f42-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_a33a731a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_adc32df4-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_a33a731a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="loc_us-gaap_CommitmentsAndContingencies_1e12e4ba-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquity_6e1ed1d0-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_CommitmentsAndContingencies_1e12e4ba-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/ConsolidatedStatementOfShareholdersEquity" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/ConsolidatedStatementsOfCashFlows" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:label="loc_us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_181e990a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_181e990a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_7cc2c354-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_NetIncomeLoss_7cc2c354-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Depreciation" xlink:label="loc_us-gaap_Depreciation_3283801c-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_Depreciation_3283801c-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="loc_us-gaap_ShareBasedCompensation_ab78f61e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ShareBasedCompensation_ab78f61e-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:label="loc_us-gaap_GainLossOnSaleOfPropertyPlantEquipment_5a9adb72-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_GainLossOnSaleOfPropertyPlantEquipment_5a9adb72-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProvisionForDoubtfulAccounts" xlink:label="loc_us-gaap_ProvisionForDoubtfulAccounts_94b5f6e8-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="5" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ProvisionForDoubtfulAccounts_94b5f6e8-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherNoncashIncomeExpense" xlink:label="loc_us-gaap_OtherNoncashIncomeExpense_83825128-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="6" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_OtherNoncashIncomeExpense_83825128-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_62c142a0-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="7" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_62c142a0-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInInventories" xlink:label="loc_us-gaap_IncreaseDecreaseInInventories_63654850-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="8" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_IncreaseDecreaseInInventories_63654850-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredCharges" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredCharges_631b6410-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="9" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredCharges_631b6410-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_63b112d0-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="10" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_63b112d0-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_63111686-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="11" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_63111686-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredRevenue_63454b68-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="12" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredRevenue_63454b68-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayable" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_62fc0fe8-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="13" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_62fc0fe8-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccretionExpense" xlink:label="loc_us-gaap_AccretionExpense_0599cb42-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="14" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AccretionExpense_0599cb42-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdjustmentForAmortization" xlink:label="loc_us-gaap_AdjustmentForAmortization_072ed9b6-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="15" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AdjustmentForAmortization_072ed9b6-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetImpairmentCharges" xlink:label="loc_us-gaap_AssetImpairmentCharges_0c8b96ce-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="16" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AssetImpairmentCharges_0c8b96ce-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredIncomeTaxesAndTaxCredits" xlink:label="loc_us-gaap_DeferredIncomeTaxesAndTaxCredits_29f61004-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="17" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredIncomeTaxesAndTaxCredits_29f61004-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InventoryWriteDown" xlink:label="loc_us-gaap_InventoryWriteDown_69d86ed8-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="18" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_7cb5e5da-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_InventoryWriteDown_69d86ed8-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7c8e1730-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_181e990a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7c8e1730-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_8b21b464-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7c8e1730-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_8b21b464-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" xlink:label="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_933fdd60-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7c8e1730-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_933fdd60-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquireShortTermInvestments" xlink:label="loc_us-gaap_PaymentsToAcquireShortTermInvestments_8bb6856c-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7c8e1730-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_PaymentsToAcquireShortTermInvestments_8bb6856c-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquireIntangibleAssets" xlink:label="loc_us-gaap_PaymentsToAcquireIntangibleAssets_8b6ec042-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7c8e1730-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_PaymentsToAcquireIntangibleAssets_8b6ec042-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_8acc97f4-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="5" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7c8e1730-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_8acc97f4-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromSaleOfShortTermInvestments" xlink:label="loc_us-gaap_ProceedsFromSaleOfShortTermInvestments_92ff1a82-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="6" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7c8e1730-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ProceedsFromSaleOfShortTermInvestments_92ff1a82-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7ca2b500-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_181e990a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7ca2b500-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RepaymentsOfLongTermDebt" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_a118d45a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7ca2b500-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_a118d45a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromIssuanceOfDebt" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_91901b4c-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7ca2b500-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_91901b4c-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromRelatedPartyDebt" xlink:label="loc_us-gaap_ProceedsFromRelatedPartyDebt_92c1e856-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7ca2b500-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ProceedsFromRelatedPartyDebt_92c1e856-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_8932a1c2-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7ca2b500-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_8932a1c2-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities" xlink:label="loc_us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities_43eda0b2-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="5" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7ca2b500-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities_43eda0b2-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsOfFinancingCosts" xlink:label="loc_us-gaap_PaymentsOfFinancingCosts_8b6b5182-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="6" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7ca2b500-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_PaymentsOfFinancingCosts_8b6b5182-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_92ead8b0-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="7" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7ca2b500-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_92ead8b0-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromLongTermLinesOfCredit" xlink:label="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_92e3dbe6-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="8" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7ca2b500-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_92e3dbe6-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="oesx-20150331.xsd#oesx_ProceedsfromExerciseofWarrantsandStockOptions" xlink:label="loc_oesx_ProceedsfromExerciseofWarrantsandStockOptions_FF96A9C4D47DC13CFFFAD389F96DD9BB" xlink:type="locator" />
    <calculationArc order="9" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7ca2b500-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_ProceedsfromExerciseofWarrantsandStockOptions_FF96A9C4D47DC13CFFFAD389F96DD9BB" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/ConsolidatedStatementsOfOperations" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_7cc2c354-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_6058d0a0-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetIncomeLoss_7cc2c354-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_6058d0a0-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaap_OperatingIncomeLoss_8028df7e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_6058d0a0-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_OperatingIncomeLoss_8028df7e-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GrossProfit" xlink:label="loc_us-gaap_GrossProfit_5c8cb1f8-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingIncomeLoss_8028df7e-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_GrossProfit_5c8cb1f8-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_a489395e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_GrossProfit_5c8cb1f8-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_Revenues_a489395e-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SalesRevenueGoodsNet" xlink:label="loc_us-gaap_SalesRevenueGoodsNet_a73282be-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Revenues_a489395e-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_SalesRevenueGoodsNet_a73282be-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SalesRevenueServicesNet" xlink:label="loc_us-gaap_SalesRevenueServicesNet_a73bc11c-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Revenues_a489395e-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_SalesRevenueServicesNet_a73bc11c-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CostOfRevenue" xlink:label="loc_us-gaap_CostOfRevenue_235acf32-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_GrossProfit_5c8cb1f8-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_CostOfRevenue_235acf32-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CostOfGoodsSold" xlink:label="loc_us-gaap_CostOfGoodsSold_22d5e98e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CostOfRevenue_235acf32-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_CostOfGoodsSold_22d5e98e-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CostOfServices" xlink:label="loc_us-gaap_CostOfServices_236e061a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CostOfRevenue_235acf32-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_CostOfServices_236e061a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingExpenses" xlink:label="loc_us-gaap_OperatingExpenses_800dbf32-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingIncomeLoss_8028df7e-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_OperatingExpenses_800dbf32-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_5b9b5a38-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingExpenses_800dbf32-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_5b9b5a38-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SellingAndMarketingExpense" xlink:label="loc_us-gaap_SellingAndMarketingExpense_aacb810a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingExpenses_800dbf32-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_SellingAndMarketingExpense_aacb810a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_a17a5cf2-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingExpenses_800dbf32-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_a17a5cf2-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_130fe766-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingExpenses_800dbf32-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_130fe766-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NonoperatingIncomeExpense" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_7d82877a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_6058d0a0-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_7d82877a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestExpense" xlink:label="loc_us-gaap_InterestExpense_678fa826-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NonoperatingIncomeExpense_7d82877a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_InterestExpense_678fa826-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InvestmentIncomeInterest" xlink:label="loc_us-gaap_InvestmentIncomeInterest_6a12f3d2-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NonoperatingIncomeExpense_7d82877a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_InvestmentIncomeInterest_6a12f3d2-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_610ca94a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetIncomeLoss_7cc2c354-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_610ca94a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/DescriptionOfBusiness" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/DocumentAndEntityInformation" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/IncomeTaxes" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/IncomeTaxesDetailsTextual" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/IncomeTaxesReconciliationOfTaxRatesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_3fd4c686-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_400c73ec-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_3fd4c686-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_400c73ec-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_3fe5a168-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_3fd4c686-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_3fe5a168-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsResearch" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsResearch_40154c74-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_3fd4c686-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsResearch_40154c74-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsOther" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsOther_4022febe-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_3fd4c686-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsOther_4022febe-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance_3ff86e60-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="5" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_3fd4c686-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance_3ff86e60-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpense" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpense_3ff2e0ee-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="6" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_3fd4c686-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpense_3ff2e0ee-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTaxContingencies" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxContingencies_402eb9d4-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="7" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_3fd4c686-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxContingencies_402eb9d4-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments_3ff59f64-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="8" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_3fd4c686-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments_3ff59f64-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/IncomeTaxesScheduleOfComponentsOfIncomeTaxExpenseOrBenefitDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_610ca94a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CurrentIncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_CurrentIncomeTaxExpenseBenefit_24375614-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_610ca94a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_CurrentIncomeTaxExpenseBenefit_24375614-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_2a198e26-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_610ca94a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_2a198e26-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/IncomeTaxesScheduleOfComponentsOfIncomeTaxExpenseOrBenefitDetailsCalc2" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_EB703452E79D8046FF3CE3D19727A512_610ca94a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FederalIncomeTaxExpenseBenefitContinuingOperations" xlink:label="loc_us-gaap_FederalIncomeTaxExpenseBenefitContinuingOperations_EB703452E79D8046FF3CE3D19727A512_4d95b064-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_EB703452E79D8046FF3CE3D19727A512_610ca94a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_FederalIncomeTaxExpenseBenefitContinuingOperations_EB703452E79D8046FF3CE3D19727A512_4d95b064-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StateAndLocalIncomeTaxExpenseBenefitContinuingOperations" xlink:label="loc_us-gaap_StateAndLocalIncomeTaxExpenseBenefitContinuingOperations_EB703452E79D8046FF3CE3D19727A512_ace68bec-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_EB703452E79D8046FF3CE3D19727A512_610ca94a-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_StateAndLocalIncomeTaxExpenseBenefitContinuingOperations_EB703452E79D8046FF3CE3D19727A512_ace68bec-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/IncomeTaxesScheduleOfDeferredTaxAssetsAndLiabilitiesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsNet" xlink:label="loc_us-gaap_DeferredTaxAssetsNet_2afbcf16-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsNetCurrent" xlink:label="loc_us-gaap_DeferredTaxAssetsNetCurrent_2af7d532-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNet_2afbcf16-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredTaxAssetsNetCurrent_2af7d532-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="oesx-20150331.xsd#oesx_DeferredTaxAssetsInventoryAccrualsAndReserves" xlink:label="loc_oesx_DeferredTaxAssetsInventoryAccrualsAndReserves_018cfbeb-9e0e-cab0-629f-28e753fef112" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNetCurrent_2af7d532-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_DeferredTaxAssetsInventoryAccrualsAndReserves_018cfbeb-9e0e-cab0-629f-28e753fef112" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsOther" xlink:label="loc_us-gaap_DeferredTaxAssetsOther_2ae70d38-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNetCurrent_2af7d532-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredTaxAssetsOther_2ae70d38-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="oesx-20150331.xsd#oesx_DeferredTaxAssetDeferredIncomeCurrent" xlink:label="loc_oesx_DeferredTaxAssetDeferredIncomeCurrent_7484fc10-9ccd-33fb-245c-28e7577ca4de" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNetCurrent_2af7d532-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_DeferredTaxAssetDeferredIncomeCurrent_7484fc10-9ccd-33fb-245c-28e7577ca4de" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsValuationAllowanceCurrent" xlink:label="loc_us-gaap_DeferredTaxAssetsValuationAllowanceCurrent_2b2e4810-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNetCurrent_2af7d532-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredTaxAssetsValuationAllowanceCurrent_2b2e4810-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsNetNoncurrent" xlink:label="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_2b1f2682-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwards" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_2b23d3c6-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_2b1f2682-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_2b23d3c6-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsTaxCreditCarryforwards" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxCreditCarryforwards_2b2a64fc-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_2b1f2682-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredTaxAssetsTaxCreditCarryforwards_2b2a64fc-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="oesx-20150331.xsd#oesx_DeferredTaxAssetDeferredIncomeNoncurrent" xlink:label="loc_oesx_DeferredTaxAssetDeferredIncomeNoncurrent_0cbcf031-b248-b089-ff1f-28e74aa0cba2" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_2b1f2682-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_DeferredTaxAssetDeferredIncomeNoncurrent_0cbcf031-b248-b089-ff1f-28e74aa0cba2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsValuationAllowanceNoncurrent" xlink:label="loc_us-gaap_DeferredTaxAssetsValuationAllowanceNoncurrent_2b365da2-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_2b1f2682-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredTaxAssetsValuationAllowanceNoncurrent_2b365da2-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost_2ad7a794-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="5" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_2b1f2682-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost_2ad7a794-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment_2b4fcb20-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="6" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_2b1f2682-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment_2b4fcb20-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssets" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssets_2b50381c-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="7" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_2b1f2682-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssets_2b50381c-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/IncomeTaxesTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/IncomeTaxesUnrecognizedTaxBenefitActivityDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/LongTermDebt" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/LongTermDebtAggregateMaturitiesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebt" xlink:label="loc_us-gaap_LongTermDebt_754fc3b0-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_7621d26a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_754fc3b0-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_7621d26a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_760cfcdc-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_754fc3b0-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_760cfcdc-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_761ba6b0-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_754fc3b0-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_761ba6b0-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_7616a25a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_754fc3b0-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_7616a25a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive_761b364e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="5" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_754fc3b0-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive_761b364e-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/LongTermDebtAllOtherDebtDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/LongTermDebtDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebt" xlink:label="loc_us-gaap_LongTermDebt_754fc3b0-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="loc_us-gaap_LongTermDebtCurrent_761ef1a8-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_754fc3b0-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_LongTermDebtCurrent_761ef1a8-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_761f7682-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_754fc3b0-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_761f7682-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/LongTermDebtRevolvingCreditFacilityDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/LongTermDebtTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/QuarterlyFinancialDataDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/QuarterlyFinancialDataUnaudited" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/QuarterlyFinancialDataUnauditedTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/RelatedPartyTransactions" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/RelatedPartyTransactionsDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SegmentData" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SegmentDataReconciliationOfSegmentAssetsAndLiabilitiesDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SegmentDataReconciliationOfSegmentOperationsDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SegmentDataTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/ShareholdersEquity" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/ShareholdersEquityDetailsTextual" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/ShareholdersEquityScheduleOfEsppActivityDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/ShareholdersEquityTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrants" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsDetailsTextual" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsOutstandingWarrantsDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsScheduleOfRestrictedSharesDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsScheduleOfSharesAvailableForGrantDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsStockBasedCompensationDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsSummaryOfExercisePriceRangeDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsSummaryOfOutstandingStockOptionsDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsSummaryOfUnrecognizedCompensationCostDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_408d7ffa-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="oesx-20150331.xsd#oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedNextTwelveMonths" xlink:label="loc_oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedNextTwelveMonths_d34720da-f53b-bb8a-04e8-28e746e6ed22" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_408d7ffa-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedNextTwelveMonths_d34720da-f53b-bb8a-04e8-28e746e6ed22" xlink:type="arc" />
    <loc xlink:href="oesx-20150331.xsd#oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInTwoYears" xlink:label="loc_oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInTwoYears_7ebfd1e0-c509-b324-97b2-28e7521b1374" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_408d7ffa-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInTwoYears_7ebfd1e0-c509-b324-97b2-28e7521b1374" xlink:type="arc" />
    <loc xlink:href="oesx-20150331.xsd#oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInThreeYears" xlink:label="loc_oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInThreeYears_96702ff4-b3bb-6069-5045-28e74c9efe34" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_408d7ffa-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInThreeYears_96702ff4-b3bb-6069-5045-28e74c9efe34" xlink:type="arc" />
    <loc xlink:href="oesx-20150331.xsd#oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInFourYears" xlink:label="loc_oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInFourYears_bd5124b8-30bb-4bf7-5f07-28e74cb9ccbf" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_408d7ffa-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInFourYears_bd5124b8-30bb-4bf7-5f07-28e74cb9ccbf" xlink:type="arc" />
    <loc xlink:href="oesx-20150331.xsd#oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInFiveYears" xlink:label="loc_oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInFiveYears_60be2a6f-8dfd-d9ba-5986-28e752098efc" xlink:type="locator" />
    <calculationArc order="5" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_408d7ffa-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueInFiveYears_60be2a6f-8dfd-d9ba-5986-28e752098efc" xlink:type="arc" />
    <loc xlink:href="oesx-20150331.xsd#oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueThereafter" xlink:label="loc_oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueThereafter_cfed4127-5274-6c5c-f509-28e75794705c" xlink:type="locator" />
    <calculationArc order="6" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_408d7ffa-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostNotYetRecognizedDueThereafter_cfed4127-5274-6c5c-f509-28e75794705c" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/StockOptionsRestrictedSharesAndWarrantsTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SubsequentEvents" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPolicies" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesCashAndCashEquivalentsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_0dd8a5a8-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="oesx-20150331.xsd#oesx_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax" xlink:label="loc_oesx_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax_90c14d5a-db9f-11e3-b035-22000a1e8102" xlink:type="locator" />
    <calculationArc order="1" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_0dd8a5a8-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax_90c14d5a-db9f-11e3-b035-22000a1e8102" xlink:type="arc" />
    <loc xlink:href="oesx-20150331.xsd#oesx_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax" xlink:label="loc_oesx_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax_b528c1a0-db9f-11e3-b035-22000a1e8102" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_0dd8a5a8-9656-11e2-88e7-12313d1a0274" xlink:to="loc_oesx_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedLossbeforeTax_b528c1a0-db9f-11e3-b035-22000a1e8102" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_0dd57554-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_0dd8a5a8-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_0dd57554-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashEquivalentsAtCarryingValue_18499eca-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_0dd57554-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_CashEquivalentsAtCarryingValue_18499eca-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShortTermInvestments" xlink:label="loc_us-gaap_ShortTermInvestments_ac3ee1b2-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_0dd57554-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ShortTermInvestments_ac3ee1b2-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesConcentrationRiskDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesDilutiveSecuritiesDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesEpsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_b93d27d4-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_b91dcd62-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_b93d27d4-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_b91dcd62-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_6554f444-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_b93d27d4-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_6554f444-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesFinancingReceivablesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_05404162-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsReceivableGrossCurrent" xlink:label="loc_us-gaap_AccountsReceivableGrossCurrent_05534032-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccountsReceivableNetCurrent_05404162-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AccountsReceivableGrossCurrent_05534032-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableNetCurrent_052d4d78-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccountsReceivableGrossCurrent_05534032-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AccountsNotesAndLoansReceivableNetCurrent_052d4d78-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermAccountsNotesAndLoansReceivableNetNoncurrent" xlink:label="loc_us-gaap_LongTermAccountsNotesAndLoansReceivableNetNoncurrent_75e2a572-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccountsReceivableGrossCurrent_05534032-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_LongTermAccountsNotesAndLoansReceivableNetNoncurrent_75e2a572-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_0ba1ef88-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccountsReceivableNetCurrent_05404162-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_0ba1ef88-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesGoodwillAndOtherIntangibleAssetsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_54e9c33c-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_559d614e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNet_54e9c33c-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_559d614e-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_55a37d54-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNet_54e9c33c-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_55a37d54-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_54d60892-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNet_54e9c33c-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_54d60892-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_55a0e896-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNet_54e9c33c-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_55a0e896-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_54c18c14-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="5" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNet_54e9c33c-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_54c18c14-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_54f15dae-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="6" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNet_54e9c33c-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_54f15dae-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesIncentiveCompDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesInventoriesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InventoryNet" xlink:label="loc_us-gaap_InventoryNet_6952f2e4-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InventoryFinishedGoodsNetOfReserves" xlink:label="loc_us-gaap_InventoryFinishedGoodsNetOfReserves_69867b82-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_InventoryNet_6952f2e4-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_InventoryFinishedGoodsNetOfReserves_69867b82-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InventoryWorkInProcessNetOfReserves" xlink:label="loc_us-gaap_InventoryWorkInProcessNetOfReserves_69eed312-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_InventoryNet_6952f2e4-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_InventoryWorkInProcessNetOfReserves_69eed312-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InventoryRawMaterialsNetOfReserves" xlink:label="loc_us-gaap_InventoryRawMaterialsNetOfReserves_698b130e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_InventoryNet_6952f2e4-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_InventoryRawMaterialsNetOfReserves_698b130e-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesLtReceivablesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsReceivableBilledForLongTermContractsOrPrograms" xlink:label="loc_us-gaap_AccountsReceivableBilledForLongTermContractsOrPrograms_058bf422-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ContractReceivableDueOneToTwoYears" xlink:label="loc_us-gaap_ContractReceivableDueOneToTwoYears_219e8a8a-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccountsReceivableBilledForLongTermContractsOrPrograms_058bf422-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ContractReceivableDueOneToTwoYears_219e8a8a-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ContractReceivableDueOneYearOrLess" xlink:label="loc_us-gaap_ContractReceivableDueOneYearOrLess_21912930-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccountsReceivableBilledForLongTermContractsOrPrograms_058bf422-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ContractReceivableDueOneYearOrLess_21912930-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesLtReceivablesDetailsCalc2" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsReceivableBilledForLongTermContractsOrPrograms" xlink:label="loc_us-gaap_AccountsReceivableBilledForLongTermContractsOrPrograms_DEC56D8B4A8D5657C156B4A986ADF355_058bf422-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ContractReceivableDueInNextRollingTwelveMonths" xlink:label="loc_us-gaap_ContractReceivableDueInNextRollingTwelveMonths_DEC56D8B4A8D5657C156B4A986ADF355_219ca68e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccountsReceivableBilledForLongTermContractsOrPrograms_DEC56D8B4A8D5657C156B4A986ADF355_058bf422-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_ContractReceivableDueInNextRollingTwelveMonths_DEC56D8B4A8D5657C156B4A986ADF355_219ca68e-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestReceivable" xlink:label="loc_us-gaap_InterestReceivable_DEC56D8B4A8D5657C156B4A986ADF355_68275702-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccountsReceivableBilledForLongTermContractsOrPrograms_DEC56D8B4A8D5657C156B4A986ADF355_058bf422-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_InterestReceivable_DEC56D8B4A8D5657C156B4A986ADF355_68275702-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermInvestmentsAndReceivablesNet" xlink:label="loc_us-gaap_LongTermInvestmentsAndReceivablesNet_DEC56D8B4A8D5657C156B4A986ADF355_76118266-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccountsReceivableBilledForLongTermContractsOrPrograms_DEC56D8B4A8D5657C156B4A986ADF355_058bf422-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_LongTermInvestmentsAndReceivablesNet_DEC56D8B4A8D5657C156B4A986ADF355_76118266-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPolicies" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPpeUsefulLivesDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesPropPlantAndEquipDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_940b342e-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_9406abd4-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNet_940b342e-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_9406abd4-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_061c48ec-9656-11e2-88e7-12313d1a0274" xlink:type="locator" />
    <calculationArc order="2" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNet_940b342e-9656-11e2-88e7-12313d1a0274" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_061c48ec-9656-11e2-88e7-12313d1a0274" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesStockOptionAssumptionsDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.oesx.com/role/SummaryOfSignificantAccountingPoliciesWarrantyAccrualDetails" xlink:type="extended" />
</linkbase>





