In carrying out his duties under this chapter, the Secretary shall, within six months of September 8, 1980, establish procedures to allow any public or private entity wishing to install a large wind energy system to apply for and, upon meeting such terms and conditions as the Secretary may prescribe, to receive a direct grant for a portion of the total purchase and installation cost of such wind energy system: Provided, That grants for the portion of such cost in the case of large wind energy systems shall not exceed (A) 50 per centum of such cost during the first six years of the program under this subsection, and (B) 25 per centum of such cost during the seventh or eighth year of the program.