; and (2) in denominations of $25, and such other amounts as are determined appropriate by the Secretary, and shall mature within such periods as determined by the Secretary. (c) Limitation The aggregate face amount of the Clean Energy Victory Bonds issued annually under this section shall be not greater than $50,000,000,000. (d) Interest Clean Energy Victory Bonds shall bear interest at the rate the Secretary sets for Savings Bonds of Series EE and Series I, plus a rate of return determined by the Secretary which is based on the valuation of— (1) savings achieved through reduced energy spending by the Federal Government resulting from clean energy projects funded from the proceeds of such bonds; and (2) interest collected on loans financed or guaranteed from the proceeds of such bonds. (e) Full faith and credit Payment of interest and principal with respect to any Clean Energy Victory Bond issued under this section shall be made from the general fund of the Treasury of the United States and shall be backed by the full faith and credit of the United States. (f) Promotion (1) In general The Secretary shall take such actions, independently and in conjunction with financial institutions offering Clean Energy Victory Bonds, to promote the purchase of Clean Energy Victory Bonds, including campaigns describing the financial and social benefits of purchasing Clean Energy Victory Bonds. (2) Promotional activities Such promotional activities may include advertisements, pamphlets, or other promotional materials— (A) in periodicals; (B) on billboards and other outdoor venues; (C) on television; (D) on radio; (E) on the internet; (F) within financial institutions that offer Clean Energy Victory Bonds; or (G) any other venues or outlets the Secretary may identify. (g) Definition For purposes of this section— (1) Clean energy project The term clean energy project means a technology that provides— (A) performance-based energy efficiency improvements