UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a)

of the Securities Exchange Act of 1934

(Amendment No. )

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Filed by a Party other than the Registrant ¨

Check the appropriate box:

¨ Preliminary Proxy Statement

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¨ Definitive Proxy Statement

þ Definitive Additional Materials

¨ Soliciting Material under §240.14a-12

Ameresco, Inc.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

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