<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-11-05</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001425565</issuerCik>
        <issuerName>Real Goods Solar, Inc.</issuerName>
        <issuerTradingSymbol>RSOL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001448634</rptOwnerCik>
            <rptOwnerName>McCalmont Darlene J.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2959 WINCHESTER BLVD, SUITE 200A</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CAMPBELL</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>95008</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001448093</rptOwnerCik>
            <rptOwnerName>McCalmont D. Thompson</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2959 WINCHESTER BLVD., SUITE 200A</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CAMPBELL</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>95008</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-11-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>17360</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>3.03</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1829863</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trust</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">(1)  All shares were issued to either Darlene J. McCalmont, in her name alone, or to the McCalmont Living Trust dated September 3, 2004.  The shares are owned directly by the McCalmont Living Trust dated September 3, 2004, and indirectly by D. Thompson McCalmont and Darlene J. McCalmont as co-trustees and sole beneficiaries of that trust; however, D. Thompson McCalmont expressly disclaims beneficial ownership of such shares.</footnote>
    </footnotes>

    <remarks>/s/ Darlene J. McCalmont and D. Thompson McCalmont, individually and as Co-Trustees of the McCalmont Living Trust dated September 3, 2004</remarks>

    <ownerSignature>
        <signatureName>/s/ Darlene J. McCalmont</signatureName>
        <signatureDate>2010-11-08</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/  D. Thompson McCalmont</signatureName>
        <signatureDate>2010-11-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
