<SUBMISSION>
<ACCESSION-NUMBER>0001181431-03-011473
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20030623
<FILING-DATE>20030624
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>WEISBERG ROBERT I
<CIK>0001185772
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>000-15472
<FILM-NUMBER>03754761
</FILING-VALUES>
<MAIL-ADDRESS>
<STREET1>1855 NORMAN AVENUE
<CITY>SANTA CLARA
<STATE>CA
<ZIP>95054
</MAIL-ADDRESS>
</REPORTING-OWNER>
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>ENVIRONMENTAL POWER CORP
<CIK>0000805012
<ASSIGNED-SIC>4991
<IRS-NUMBER>042782065
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>500 MARKET ST
<STREET2>STE 1E
<CITY>PORTSMOUTH
<STATE>NH
<ZIP>03801
<PHONE>6034311780
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>500 MARKET ST
<STREET2>STE 1E
<CITY>PORTSMOUTH
<STATE>NH
<ZIP>03801
</MAIL-ADDRESS>
</ISSUER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>rrd11609.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

    <documentType>4</documentType>
<periodOfReport>2003-06-23</periodOfReport>
<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000805012</issuerCik>
        <issuerName>ENVIRONMENTAL POWER CORP</issuerName>
        <issuerTradingSymbol>( powr )</issuerTradingSymbol></issuer>
<reportingOwner>
<reportingOwnerId>
            <rptOwnerCik>0001185772</rptOwnerCik>
            <rptOwnerName>WEISBERG ROBERT I</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector>
<isOfficer>0</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle></officerTitle>
<otherText></otherText></reportingOwnerRelationship></reportingOwner>
<nonDerivativeSecurity>
<securityTitle>
<value>Common Stock</value></securityTitle>
<transactionDate>
<value>1997-09-09</value></transactionDate>
<deemedExecutionDate>
<value>1997-09-09</value></deemedExecutionDate>
<transactionCoding>
<transactionFormType>4</transactionFormType>
<transactionCode>M</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved></transactionCoding>
<transactionTimeliness>
<value></value></transactionTimeliness>
<transactionAmounts>
<transactionShares>
<value>80000</value></transactionShares>
<transactionValue>
<value>0.607</value></transactionValue>
<transactionAcquiredDisposedCode>
<value>A</value></transactionAcquiredDisposedCode></transactionAmounts>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>80000</value></sharesOwnedFollowingTransaction></postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value></directOrIndirectOwnership>
<natureOfOwnership>
<value></value></natureOfOwnership></ownershipNature></nonDerivativeSecurity>
<derivativeSecurity>
<securityTitle>
<value>2002 Director Options (right to buy)</value></securityTitle>
<conversionOrExercisePrice>
<value>.29</value></conversionOrExercisePrice>
<transactionDate>
<value>2003-06-23</value></transactionDate>
<deemedExecutionDate>
<value>2003-06-23</value></deemedExecutionDate>
<transactionCoding>
<transactionFormType>4</transactionFormType>
<transactionCode>M</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved></transactionCoding>
<transactionAmounts>
<transactionShares>
<value>50000</value></transactionShares>
<transactionValue>
<value>340575</value></transactionValue>
<transactionAcquiredDisposedCode>
<value>D</value></transactionAcquiredDisposedCode></transactionAmounts>
<exerciseDate>
<value>2003-06-23</value></exerciseDate>
<expirationDate>
<value>2013-06-23</value></expirationDate>
<underlyingSecurity>
<underlyingSecurityTitle>
<value>Common</value></underlyingSecurityTitle>
<underlyingSecurityShares>
<value>50000</value></underlyingSecurityShares></underlyingSecurity>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>550000</value></sharesOwnedFollowingTransaction></postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value></directOrIndirectOwnership>
<natureOfOwnership>
<value></value></natureOfOwnership></ownershipNature></derivativeSecurity>
<ownerSignature>
<signatureName>Robert I. Weisberg</signatureName>
<signatureDate>2003-06-24</signatureDate></ownerSignature></ownershipDocument>


</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
