[Signatures on next page.]

March 13, 2009

Tremisis Energy Acquisition Corporation II

2925 Briarpark, Suite 150-A

Houston, TX 77042

Attention: Ronald D. Ormand

Each of the Investors

set forth in Schedule A

c/o SoftForum Co., Ltd.

(135-270) 7th Floor, SoftForum B/D.

545-7 Dogok-Dong,

Gangnam-Gu, Seoul 135-270 S. Korea

Attention: Sang-Chul Kim, Chairman

Dear Sirs:

Pursuant to that certain Registration Rights Agreement (the “RRA”), dated as of December 6, 2007, by and among Tremisis Energy Acquisition Corporation II, a Delaware Corporation (the “Company”), and the respective undersigned parties (each, individually, a “Stockholder”, and collectively, the “Stockholders”), the Company has granted the Stockholders certain registration rights (the “Registration Rights”) with respect to (a) the shares (the “Warrant Shares”) of common stock of the Company underlying warrants (the “Warrants”) purchased by the Stockholders under the terms of certain Warrant Subscription Agreements (the “Agreements”), by and between the Company and each respective Stockholder, and (b) the shares of common stock (the “Insider Shares”, and together with the Warrant Shares, the “Registrable Securities”) purchased by the Stockholders from the Company prior to the Company’s initial public offering.

The Stockholders have executed an agreement (the “Put/Call Agreement”) of even date herewith pursuant to which the parties have granted each other put and call options by which the Stockholders may sell the Warrants and transfer, for no consideration, certain of the Insider Shares to the investors set forth in Schedule A attached hereto (the “Investors”), in the amounts identified in Schedule A upon consummation of a Business Combination (defined in the RRA).  In connection with the potential sale of the Warrants and transfer of certain of the Insider Shares upon consummation of a Business Combination, the Stockholders desire to assign their Registration Rights conditionally with respect to the Warrants and Insider Shares that may be sold and transferred to the Investors in accordance with Section 6.2 of the RRA, and the Company has agreed to consent to such assignment. Accordingly, upon consummation of a Business Combination and subsequent sale of Warrants and transfer of Insider Shares, the Stockholders’ Registration Rights with respect to such securities shall be assigned to the Investors.  The Stockholders shall maintain their Registration Rights with respect to any Insider Shares not transferred to the Investors.  Until the Warrants and Insider Shares are transferred in accordance with the Put/Call Agreement, the Registration Rights will not be assigned by the Stockholders to the Investors.  Upon consummation of a Business Combination and sale of the Warrants and transfer of Insider Shares, the Investors shall become parties to the RRA and the parties thereto hereby consent to amend such RRA at that time such that the Investors shall have all the benefits of the Stockholders with respect to the transferred Warrants and the Registrable Securities under the RRA as if they were original parties thereto.

This letter serves as each Stockholder’s irrevocable assignment of the Registration Rights, and the Company’s consent to such assignment.

[Signatures on next page.]

[Signature Page - Registration Rights Assignment Letter]

The undersigned acknowledges and consents to the foregoing terms.

TREMISIS ENERGY ACQUISITION CORPORATION II

 

[Signature Page - Registration Rights Assignment Letter]