Balance Sheet Components

Accounts Receivable

Accounts receivable primarily represents trade receivables from sales to customers recorded at net realizable value. One customer accounted for 66.8% of accounts receivable at December 31, 2018. Two customers accounted for 21.4% and 10.1% of accounts receivable at December 31, 2017. At December 31, 2018 and 2017, the Company did not maintain any allowances for doubtful accounts as it deemed all of its receivables fully collectible.

Inventories

The components of inventory consisted of the following (in thousands):



	December 31,
	2018		2017

Raw materials	$	53,273	$	49,963
Work-in-progress	22,303		19,998
Finished goods	56,900		20,299
	$	132,476	$	90,260

Prepaid Expense and Other Current Assets

Prepaid expenses and other current assets consisted of the following (in thousands):



	December 31,
	2018		2017

Government incentives receivable	$	1,001	$	1,836
Prepaid expenses and other current assets	32,741		24,840
	$	33,742	$	26,676

Property, Plant and Equipment, Net

Property, plant and equipment, net consisted of the following (in thousands):



	December 31,
	2018			2017

Energy Servers	$	511,485		$	511,153
Computers, software and hardware	16,536			19,384
Machinery and equipment	99,209			97,158
Furniture and fixtures	4,337			4,679
Leasehold improvements	18,629			22,799
Building	40,512			40,512
Construction in progress	29,084			9,898
	719,792			705,583
Less: Accumulated depreciation	(238,378		)	(207,794		)
	$	481,414		$	497,789

The Company’s construction in progress increased $19.2 million, as compared to 2017, primarily due to the Company's move to its new corporate headquarters. Our headquarters is used for administration, research and development and sales and marketing.

The Company’s property, plant and equipment under operating leases by the PPA Entities was $397.5 million and $397.0 million as of December 31, 2018 and 2017, respectively. The accumulated depreciation for these assets was $77.4 million and $51.9 million as of December 31, 2018 and 2017, respectively. Depreciation expense related to property, plant and equipment for the Company was $43.5 million, $46.1 million and $43.1 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Other Long-Term Assets

Other long-term assets consisted of the following (in thousands):



	December 31,
	2018		2017

Prepaid and other long-term assets	$	27,086	$	31,446
Equity-method investments	6,046		5,014
Long-term deposits	1,660		1,000
	$	34,792	$	37,460

Accrued Warranty

Accrued warranty liabilities consisted of the following (in thousands):



	December 31,
	2018		2017

Product warranty	$	10,935	$	7,661
Operations and maintenance services agreements	8,301		9,150
	$	19,236	$	16,811

Changes in the standard product warranty liability were as follows (in thousands):



Balances at December 31, 2015	$	8,707
Accrued warranty, net	4,124
Warranty expenditures during period	(4,727		)
Balances at December 31, 2016	8,104
Accrued warranty, net	7,058
Warranty expenditures during period	(7,501		)
Balances at December 31, 2017	7,661
Accrued warranty, net	11,155
Warranty expenditures during period	(7,881		)
Balances at December 31, 2018	$	10,935

Accrued Other Current Liabilities

Accrued other current liabilities consisted of the following (in thousands):



	December 31,
	2018		2017

Compensation and benefits	$	16,742	$	13,121
Current portion of derivative liabilities	3,232		5,492
Managed services liabilities	5,091		3,678
Accrued installation	6,859		3,348
Sales tax liabilities	1,700		5,524
Interest payable	4,675		5,520
Other	31,236		30,966
	$	69,535	$	67,649

Other Long-Term Liabilities

Accrued other long-term liabilities consisted of the following (in thousands):



	December 31,
	2018		2017

Delaware grant	$	10,469	$	10,469
Managed services liabilities	29,741		31,087
Other	15,727		11,359
	$	55,937	$	52,915

In March 2012, the Company entered into an agreement with the Delaware Economic Development Authority to provide a grant of $16.5 million to the Company as an incentive to establish a new manufacturing facility in Delaware and to provide employment for full time workers at the facility over a certain period of time. The Company has received $12.0 million of the grant which is contingent upon the Company meeting certain milestones related to the construction of the manufacturing facility and the employment of full time workers at the facility through September 30, 2023. As of December 31, 2018, the Company has paid $1.5 million in October 2017 for recapture provisions and has recorded $10.5 million in other long-term liabilities for potential repayments. See Note 13 - Commitments and Contingencies for a full description of the grant.

The Company has entered into managed services agreements that provide for the payment of property taxes and insurance premiums on behalf of customers. These obligations are included in each agreements' contract value and are recorded as short-term or long-term liabilities based on the estimated payment dates. The long-term managed services liabilities accrued were $29.7 million and $31.1 million as of December 31, 2018 and 2017, respectively.

Customer Financing Leases, Receivable

The components of investment in sales-type financing leases consisted of the following (in thousands):



	December 31,
	2018			2017

Total minimum lease payments to be received	$	100,816		$	109,431
Less: Amounts representing estimated executing costs	(25,180		)	(27,815		)
Net present value of minimum lease payments to be received	75,636			81,616
Estimated residual value of leased assets	1,051			1,051
Less: Unearned income	(4,011		)	(4,781		)
Net investment in sales-type financing leases	72,676			77,886
Less: Current portion	(5,594		)	(5,209		)
Non-current portion of investment in sales-type financing leases	$	67,082		$	72,677

The future scheduled customer payments from sales-type financing leases were as follows as of December 31, 2018 (in thousands):



	2019		2020		2021		2022		2023		Thereafter

Future minimum lease payments, less interest	$	5,594	$	6,022	$	6,415	$	6,853	$	7,310	$	39,431