Revenue (Tables)

9 Months Ended

Sep. 30, 2019

Revenue

Schedule of disaggregation of revenue

Major products/services lines
	Three months ended  September 30,				Nine months ended September 30,
	2019		2018		2019		2018
Sales of fuel cell systems	$	31,264	$	21,594	$	72,031	$	40,948
Sale of hydrogen installations and other infrastructure		6,901		15,074		6,901		25,153
Services performed on fuel cell systems and related infrastructure		5,920		5,156		17,415		16,330
Power Purchase Agreements		5,599		5,555		16,613		16,365
Fuel delivered to customers		6,557		5,786		18,942		16,016
Other		135		—		135		—
Net revenue	$	56,376	$	53,165	$	132,037	$	114,812

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):

	September 30,		December 31,
	2019		2018
Accounts receivable	$	24,392	$	37,347
Contract assets		4,319		3,328
Contract liabilities		43,248		40,476

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	Nine months ended
	September 30, 2019
Transferred to receivables from contract assets recognized at the beginning of the period	$	(180)
Revenue recognized and not billed as of the end of the period		1,171
Net change in contract assets	$	991

Schedule of Estimated future revenue

The following table includes estimated revenue expected to be recognized in the future (sales of fuel cell systems and hydrogen installations are expected to be recognized as revenue within one year; sales of services and PPAs are expected to be recognized as revenue over five to seven years) related to performance obligations that are unsatisfied (or partially unsatisfied) at the end of the reporting period, excluding provision for common stock warrants as it is not readily estimable as it depends on the valuation of the common stock warrants when revenue is recognized (in thousands):

	September 30,
	2019		2018
Sales of fuel cell systems	$	25,954	$	21,029
Sale of hydrogen installations and other infrastructure		11,448		6,705
Services performed on fuel cell systems and related infrastructure		60,196		73,484
Power Purchase Agreements		134,871		114,757
Other rental income		5,373		7,056
Total estimated future revenue	$	237,842	$	223,031