Exhibit 10.89



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|[Logo of Environmental Power Corporation] |  | Environmental Power Corporation One Cate Street, 4th Floor Portsmouth, New Hampshire 03801 Tel. (603) 431-1780 Fax (603)
431-2650

December 30, 2005

Mr. Joseph E. Cresci

c/o Environmental Power Corporation

One Cate Street, 4thFloor

Portsmouth, NH
03801

Dear Joe:

The purpose
of this letter is to set forth our understanding regarding certain matters related to your continued employment with, and transition and retirement from your employment with, Environmental Power Corporation (the Corporation), as set
forth in that certain letter dated July 13, 2005 (the Prior Letter). Capitalized terms used in this letter but not otherwise defined herein shall have the respective meanings ascribed to them in the Prior Letter.

1. The Retirement Date, and, therefore, the Transition Period, has been extended to June 30, 2006. During the remainder of the Transition Period, you will provide
such support for the business of Microgy and the Corporation as the Corporations Board of Directors or management may reasonably request, consistent with the relocation of your principal residence to Florida and a part-time schedule.

2. Your salary during the period beginning on January 1, 2006 and continuing through the Retirement Date will be 50% of your current salary, and your
benefits will remain the same as those you currently enjoy.

3. The other terms of the Prior Letter remain unaffected hereby, except that the payment of
your full current salary and benefits for the one-year period following the Retirement Date in accordance with paragraph 2 of the Prior Letter, or any severance which becomes payable in accordance with Section 7 of the Prior Letter, shall be
paid at such times and in such manner as you and the Company determine comply with, and will not result in any tax penalty to you under, Section 409A of the Internal Revenue Code. In the event that you desire a particular payment schedule that
would, in the opinion of the Company, trigger such a tax penalty, you agree that (i) any such penalty will be your sole responsibility, and that the Company will have no liability to you therefor and (ii) in no event will the Company be
required to make such payments any more quickly than it would otherwise be required to pursuant to the applicable provisions of the Prior Letter.

4. It is
understood that nothing in this letter is intended to affect your status as a member of the Board of Directors of the Corporation.



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Mr. Joseph E. Cresci

December 30, 2005

Page 2

If the foregoing accurately sets forth your understanding of the agreement between you and the Corporation with
regard to the subject matter of this letter, please so indicate by executing a copy of this letter where indicated below and returning it to me.

Very truly yours,



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|/s/ Kamlesh R. Tejwani               
|Kamlesh R. Tejwani                   
|President and Chief Executive Officer
|Environmental Power Corporation      

ACCEPTED:



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|/s/ Joseph E. Cresci
|Joseph E. Cresci    

Dated: December 30, 2005