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: June 23, 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 | ||||||
