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<!-- DFIN New ActiveDisclosure (SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date :2023-02-09T16:26:42.6780+00:00 -->
<!-- Copyright (c) 2023 Donnelly Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="oesx_IssuanceOfCommonStockForAcquisitionShare" name="IssuanceOfCommonStockForAcquisitionShare" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_LimitedProductWarrantyTerm" name="LimitedProductWarrantyTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_LongTermDebtAndCapitalLeaseObligationsLessCurrentMaturities" name="LongTermDebtAndCapitalLeaseObligationsLessCurrentMaturities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="oesx_NumberOfCustomerMoreThanTenPercentAccountReceivable" name="NumberOfCustomerMoreThanTenPercentAccountReceivable" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="oesx_NumberOfCustomerMoreThanTenPercentOfRevenue" name="NumberOfCustomerMoreThanTenPercentOfRevenue" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_NumberOfFinancialInstitutions" name="NumberOfFinancialInstitutions" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_NumberOfSupplierMoreThanTenPercentOfCostOfRevenue" name="NumberOfSupplierMoreThanTenPercentOfCostOfRevenue" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_PaymentsAndProceedsFromAcquireIntangibleAssets" name="PaymentsAndProceedsFromAcquireIntangibleAssets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="oesx_PaymentsForPreviousAcquisitionInShare" name="PaymentsForPreviousAcquisitionInShare" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="oesx_PayrollTaxCreditCurrent" name="PayrollTaxCreditCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="oesx_ProceedsFromExerciseOfWarrantsAndStockOptions" name="ProceedsFromExerciseOfWarrantsAndStockOptions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="oesx_ProceedsFromIssuanceOfDebtOrSaleOfEquitySecurities" name="ProceedsFromIssuanceOfDebtOrSaleOfEquitySecurities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="oesx_ProceedsFromSaleOfUnbilledContractsReceivable" name="ProceedsFromSaleOfUnbilledContractsReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="oesx_ProductWarrantyAccrualPaymentsNetOfVendorReimbursements" name="ProductWarrantyAccrualPaymentsNetOfVendorReimbursements" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="oesx_ProvisionForInventoryReserves" name="ProvisionForInventoryReserves" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="oesx_RecordedInOpeningBalanceSheet" name="RecordedInOpeningBalanceSheet" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="oesx_RepaymentsOfLongTermDebtExcludingRevolvingLinesOfCredit" name="RepaymentsOfLongTermDebtExcludingRevolvingLinesOfCredit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="oesx_RevolvingCreditFacility" name="RevolvingCreditFacility" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="oesx_RightsAgreementExtendedTerm" name="RightsAgreementExtendedTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_RightsAgreementTerminateAndExpireDate" name="RightsAgreementTerminateAndExpireDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_SalesTypeLeasesRevenue" name="SalesTypeLeasesRevenue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="oesx_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedOrExercisedInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedOrExercisedInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOrExercisedNumberOfShares" name="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedOrExercisedNumberOfShares" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_StockIssuedDuringPeriodSharesStockOptionsExercisedForCash" name="StockIssuedDuringPeriodSharesStockOptionsExercisedForCash" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_StockIssuedDuringPeriodValueStockOptionsExercisedForCash" name="StockIssuedDuringPeriodValueStockOptionsExercisedForCash" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="oesx_AtMarketIssuanceSalesAgreementMember" name="AtMarketIssuanceSalesAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_BankOfAmericaNAMember" name="BankOfAmericaNAMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_CostOfProductsMember" name="CostOfProductsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_CreditAgreementMember" name="CreditAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_CustomerOneMember" name="CustomerOneMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_CustomerTwoMember" name="CustomerTwoMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_DebtInstrumentOneMember" name="DebtInstrumentOneMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_DebtInstrumentTwoMember" name="DebtInstrumentTwoMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_DistributionServicesMember" name="DistributionServicesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_ElectricVehicleChargingMember" name="ElectricVehicleChargingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_EquipmentLeasedToCustomersMember" name="EquipmentLeasedToCustomersMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_LightingProductAndInstallationMember" name="LightingProductAndInstallationMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_MaintenanceServicesMember" name="MaintenanceServicesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_OrionElectricalVehiclesMember" name="OrionElectricalVehiclesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_PriorCreditAgreementMember" name="PriorCreditAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_ServicesGroupMember" name="ServicesGroupMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_SolarEnergyMember" name="SolarEnergyMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_StayLiteLightingIncMember" name="StayLiteLightingIncMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_TradeNameAndTrademarks1Member" name="TradeNameAndTrademarks1Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_TwoThousandSixteenOmnibusIncentivePlanMember" name="TwoThousandSixteenOmnibusIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_USMarketsMember" name="USMarketsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_VendorRelationshipMember" name="VendorRelationshipMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_VoltrekLlcMember" name="VoltrekLlcMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_WesternAllianceBankMember" name="WesternAllianceBankMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="oesx_AcquisitionCostPolicyPolicyTextBlock" name="AcquisitionCostPolicyPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_LesseeOperatingFinanceLeasesAndSaleLeasebackTransactionsTextBlock" name="LesseeOperatingFinanceLeasesAndSaleLeasebackTransactionsTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_ScheduleOfIntangibleAssetsTableTextBlock" name="ScheduleOfIntangibleAssetsTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="oesx_SummaryOfAssetsLeasedFromThirdPartiesTableTextBlock" name="SummaryOfAssetsLeasedFromThirdPartiesTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
</xsd:schema>
