Exhibit 1

JOINT FILING AGREEMENT

Each of the undersigned hereby agrees that this statement on Schedule 13D is being filed with the Securities and Exchange Commission on behalf of each of the undersigned pursuant to Rule 13d-1(k) promulgated under the Securities Exchange Act of 1934, as amended.

Dated: November 21, 2011

TOTAL S.A.
By:	/s/    JÉRÔME SCHMITT
Name:	Jérôme Schmitt
Title:	Treasurer
TOTAL GAS & POWER USA, SAS
By:	/s/    ARNAUD CHAPERON
Name:	Arnaud Chaperon
Title:	Chairman