; incremental production A qualified facility shall include either of the following in connection with a facility described in subparagraph (A)(i) that was previously placed in service, but only to the extent of the increased amount of electricity produced at the facility by reason of the following: (i) A new unit placed in service after December 31, 2018. (ii) Any efficiency improvements or additions of capacity placed in service after December 31, 2018. (D) Coordination with other credits The term qualified facility shall not include any facility for which— (i) a renewable electricity production credit determined under section 45 is allowed under section 38 for the taxable year or any prior taxable year, (ii) an energy credit determined under section 48 is allowed under section 38 for the taxable year or any prior taxable year, or (iii) a clean energy investment credit determined under section 48E is allowed under section 38 for the taxable year or any prior taxable year. (f) Final guidance Not later than January 1, 2018, the Secretary, in consultation with the Administrator of the Environmental Protection Agency, shall issue final guidance regarding implementation of this section, including calculation of greenhouse gas emission rates for qualified facilities and determination of clean energy production credits under this section. (g) Special rules (1) Only production in the United States taken into account Consumption or sales shall be taken into account under this section only with respect to electricity the production of which is within— (A) the United States (within the meaning of section 638(1)), or (B) a possession of the United States (within the meaning of section 638(2)). (2) Combined heat and power system property (A) In general For purposes of subsection (a)(1)(B), the kilowatt hours of electricity produced by a taxpayer at a qualified facility shall include any production in the form of useful thermal energy by any combined heat and power system property within such facility. (B) Combined heat and