; (ii) by redesignating clause (ii) as clause (iii); and (iii) by inserting after clause (i) the following new clause: (ii) in the case of energy property described in paragraph (3)(A)(viii) the construction of which begins before January 1, 2024, 15 percent (30 percent in the case of any such property which operates at a thermal output efficiency of not less than 80 percent (measured by the higher heating value of the fuel)), and . (B) Conforming amendment Section 48(a)(2)(A)(iii) of such Code, as so redesignated, is amended by inserting or (ii) after clause (i) . (c) Effective date The amendments made by this section shall apply to periods after December 31, 2018, in taxable years ending after such date, under rules similar to the rules of section 48(m) of the Internal Revenue Code of 1986 (as in effect on the day before the date of the enactment of the Revenue Reconciliation Act of 1990).