Revenue (Tables)

6 Months Ended

Jun. 30, 2018

Revenue

Schedule of disaggregation of revenue

In the following table, revenue is disaggregated by major product line and timing of revenue recognition (in thousands):

Major products/services lines	Three months ended				Six months ended
	June 30, 2018		June 30, 2017		June 30, 2018		June 30, 2017
Sales of fuel cell systems	$	14,633	$	5,582	$	21,207	$	7,400
Sale of hydrogen installations and other infrastructure		5,989		2,978		10,873		3,357
Services performed on fuel cell systems and related infrastructure		7,188		5,049		13,786		10,198
Power Purchase Agreements		5,629		4,945		11,118		9,256
Fuel delivered to customers		6,488		3,986		12,023		7,477
Other		—		64		—		151
Total gross revenue	$	39,927	$	22,604	$	69,007	$	37,839

Schedule of receivables, contract assets and contract liabilities from contracts with customers

The following table provides information about receivables, contract assets and contract liabilities from contracts with customers (in thousands):

	June 30, 2018		December 31, 2017
Accounts receivable	$	31,509	$	15,331
Contract assets		6,246		9,316
Contract liabilities		49,088		46,777

Schedule of changes in contract assets and the contract liabilities

Significant changes in the contract assets and the contract liabilities balances during the period are as follows (in thousands):

Contract assets	Six months ended
	June 30, 2018
Transferred to receivables from contract assets recognized at the beginning of the period	$	(5,502)
Revenue recognized and not billed as of the end of the period		2,432
Net change in contract assets	$	(3,070)

Contract liabilities	Six months ended
	June 30, 2018
Revenue recognized that was included in the contract liability balance as the beginning of the period	$	4,608
Increases due to cash received, net of amounts recognized as revenue during the period		(6,919)
Net change in contract liabilities	$	(2,311)

Schedule of Estimated future revenue

The following table includes estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied (or partially unsatisfied) at the end of the reporting period (in thousands):

	June 30, 2018		December 31, 2017
Sales of fuel cell systems	$	13,478	$	26,298
Sale of hydrogen installations and other infrastructure		8,281		15,512
Services performed on fuel cell systems and related infrastructure		77,496		89,079
Power Purchase Agreements		122,659		130,042
Total estimated future revenue	$	221,914	$	260,931