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July 22, 2019

Mr. John N. Hatsopoulos
45 First Ave.
Waltham, MA 02451

Re: Advisory Agreement

Dear John:

This letter confirms the decision today by the Tecogen Board of Directors that
until March 29, 2024, Tecogen will continue to provide the employee benefits
contemplated by the Advisory Agreement dated January 2018 between you and
Tecogen for so long as you continue to provide the advisory services
contemplated by the Advisory Agreement.

Please confirm your agreement with the foregoing by signing a copy of this
letter and returning it to me.

We appreciate your continuing support of Tecogen.

Sincerely,

/s/ Benjamin Locke
Benjamin Locke,
CEO                
    
AGREED:

/s/ John N. Hatsopoulos
John N. Hatsopoulos                

Tecogen Inc.
45 First Avenue, Waltham, MA 02451 • ph: 781-466-6400 • fax: 781-466-6466 •
www.tecogen.com