Solar Energy Systems, net

Solar energy systems, net consists of the following (in thousands):



	June 30, 2018			December 31, 2017
Solar energy system equipment costs	$	3,455,457		$	3,124,407
Inverters	353,422			317,390
Total solar energy systems	3,808,879			3,441,797
Less: accumulated depreciation and amortization	(463,983		)	(399,280		)
Add: construction-in-progress	92,926			119,053
Total solar energy systems, net	$	3,437,822		$	3,161,570

All solar energy systems, construction-in-progress and inverters have been leased to or are subject to signed Customer Agreements with customers. The Company recorded depreciation expense related to solar energy systems of $33.9 million and $27.4 million for the three months ended June 30, 2018 and 2017, respectively, and $66.2 million and $53.2 million for the six months ended June 30, 2018 and 2017, respectively. The depreciation expense was reduced by the amortization of deferred grants of $1.9 million and $1.8 million for the three months ended June 30, 2018 and 2017, respectively, and $3.8 million and $3.8 million for the six months ended June 30, 2018 and 2017, respectively.