((a)) ** .—** Subject to subsection (b), the Secretary of Defense may enter into a contract for a period not to exceed 10 years for the purchase of electricity from sources of renewable energy, as that term is defined in section 203(b)(2) of the Energy Policy Act of 2005 ().
((b)) ** .—** The Secretary may exercise the authority in subsection (a) to enter into a contract for a period in excess of five years only if the Secretary determines, on the basis of a business case analysis prepared by the Department of Defense, that—
((1)) the proposed purchase of electricity under such contract is cost effective for the Department of Defense; and
((2)) it would not be possible to purchase electricity from the source in an economical manner without the use of a contract for a period in excess of five years.
((c)) ** .—** Nothing in this section shall be construed to preclude the Department of Defense from using other multiyear contracting authority of the Department to purchase renewable energy.