existing unit
(8) The term “existing unit” means a unit (including units subject to section 7411 of this title ) that commenced commercial operation before November 15, 1990 . Any unit that commenced commercial operation before November 15, 1990 , which is modified, reconstructed, or repowered after November 15, 1990 , shall continue to be an existing unit for the purposes of this subchapter. For the purposes of this subchapter, existing units shall not include simple combustion turbines, or units which serve a generator with a nameplate capacity of 25MWe or less.