(3)For purposes of this subpart, the term “energy property” means any property— (A)which is— (i)equipment which uses solar energy to generate electricity, to heat or cool (or provide hot water for use in) a structure, or to provide solar process heat, excepting property used to generate energy for the purposes of heating a swimming pool, (ii)equipment which uses solar energy to illuminate the inside of a structure using fiber-optic distributed sunlight but only with respect to periods ending before, (iii)equipment used to produce, distribute, or use energy derived from a geothermal deposit (within the meaning of section 613(e)(2)), but only, in the case of electricity generated by geothermal power, up to (but not including) the electrical transmission stage, (iv)qualified fuel cell property or qualified microturbine property, (v)combined heat and power system property, (vi)qualified small wind energy property, or (vii)equipment which uses the ground or ground water as a thermal energy source to heat a structure or as a thermal energy sink to cool a structure, but only with respect to periods ending before, (C)with respect to which depreciation (or amortization in lieu of depreciation) is allowable, and (D)which meets the performance and quality standards (if any) which— (i)have been prescribed by the Secretary by regulations (after consultation with the Secretary of Energy), and (ii)are in effect at the time of the acquisition of the property.

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Note added at 14 hrs (2018-03-05 07:57:41 GMT)
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Как нетрудно понять, equipment which uses solar energy to generate electricity — это, скорее всего, (фотоэлектрическая) солнечная батарея.

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Note added at 14 hrs (2018-03-05 07:58:31 GMT)
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В общем, речь идет не только об энергосберегающих устройствах, но и об альтернативных источниках энергии.