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<link:roleType roleURI="http://oesx.com/role/DocumentAndEntityInformation" id="DocumentAndEntityInformation">
  <link:definition>00 - Document - Document and Entity Information</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
</link:roleType>
<link:roleType roleURI="http://oesx.com/role/BalanceSheets" id="BalanceSheets">
  <link:definition>01 - Statement - Condensed Consolidated Balance Sheets (Unaudited)</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
</link:roleType>
<link:roleType roleURI="http://oesx.com/role/BalanceSheetsParenthetical" id="BalanceSheetsParenthetical">
  <link:definition>011 - Statement - Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical)</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
</link:roleType>
<link:roleType roleURI="http://oesx.com/role/StatementsOfOperations" id="StatementsOfOperations">
  <link:definition>02 - Statement - Condensed Consolidated Statements of Operations (Unaudited)</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
</link:roleType>
<link:roleType roleURI="http://oesx.com/role/StatementsOfCashFlows" id="StatementsOfCashFlows">
  <link:definition>03 - Statement - Condensed Consolidated Statements of Cash Flows (Unaudited)</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
</link:roleType>

<link:roleType roleURI="http://oesx.com/role/DescriptionOfBusiness" id="DescriptionOfBusiness">
  <link:definition>06001 - Disclosure - Description of Business</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
</link:roleType>
<link:roleType roleURI="http://oesx.com/role/SummaryOfSignificantAccountingPolicies" id="SummaryOfSignificantAccountingPolicies">
  <link:definition>06002 - Disclosure - Summary of Significant Accounting Policies</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
</link:roleType>
<link:roleType roleURI="http://oesx.com/role/RelatedPartyTransactions" id="RelatedPartyTransactions">
  <link:definition>06003 - Disclosure - Related Party Transactions</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
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<link:roleType roleURI="http://oesx.com/role/Debt" id="Debt">
  <link:definition>06004 - Disclosure - Debt</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
</link:roleType>
<link:roleType roleURI="http://oesx.com/role/IncomeTaxes" id="IncomeTaxes">
  <link:definition>06005 - Disclosure - Income Taxes</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
</link:roleType>
<link:roleType roleURI="http://oesx.com/role/CommitmentsAndContingencies" id="CommitmentsAndContingencies">
  <link:definition>06006 - Disclosure - Commitments and Contingencies</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
</link:roleType>
<link:roleType roleURI="http://oesx.com/role/ShareholdersEquity" id="ShareholdersEquity">
  <link:definition>06007 - Disclosure - Shareholders' Equity</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
</link:roleType>
<link:roleType roleURI="http://oesx.com/role/StockOptionsAndWarrants" id="StockOptionsAndWarrants">
  <link:definition>06008 - Disclosure - Stock Options and Warrants</link:definition>
  <link:usedOn>link:presentationLink</link:usedOn>
  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
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<link:roleType roleURI="http://oesx.com/role/Segments" id="Segments">
  <link:definition>06009 - Disclosure - Segments</link:definition>
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  <link:usedOn>link:definitionLink</link:usedOn>
  <link:usedOn>link:calculationLink</link:usedOn>
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