WAIVER AGREEMENT

Exhibit 10.20

WAIVER AGREEMENT

WAIVER AGREEMENT (“ Waiver Agreement ”) dated as of February 25, 2009 among GSC ACQUISITION COMPANY, a Delaware corporation (“ GSCAC ”), GSCAC Holdings I LLC, a Delaware limited liability company (“ Holdco Sub ”), GSCAC Holdings II LLC, a Delaware limited liability company (“ Holdco Sub2 ”), GSCAC Merger Sub LLC, a Delaware limited liability company (“ Merger Sub ” and together with GSCAC, Holdco Sub and Holdco Sub2, the “ GSCAC Parties ”), and COMPLETE ENERGY HOLDINGS, LLC, a Delaware limited liability company (“ CEH ”).

WHEREAS, the parties hereto are parties to an Agreement and Plan of Merger dated as of May 9, 2008 (the “ Merger Agreement ”); any capitalized term not defined in this Waiver Agreement shall have the meaning given such term in the Merger Agreement.

WHEREAS, Section 6.13 of the Merger Agreement limits the ability of the parties thereto and other person from engaging in discussions or taking certain other actions concerning any proposal for a merger, sale or purchase of substantial assets, sale or purchase of shares of capital stock or other securities, recapitalization or other business combination transaction involving a GSCAC Party or any Project Companies on the one hand and any third party on the other hand; and

WHEREAS, GSCAC and CEH each desires to waive certain provisions of Section 6.13 of the Merger Agreement to the extent provided herein.

NOW, THEREFORE, in consideration of the foregoing recitals and other good and valuable consideration, the receipt and sufficiency of which is hereby acknowledged, the parties hereto agree as follows: