Revenue

12 Months Ended

Dec. 31, 2021

Revenue

Revenue

19. Revenue

Disaggregation of revenue

The following table provides information about disaggregation of revenue (in thousands):

Major products/services lines
	Year ended December 31,
	2021		2020		2019
Sales of fuel cell systems	$	225,229	$	(55,091)	$	130,757
Sale of hydrogen infrastructure		135,055		(43,391)		19,163
Sale of electrolyzers		16,667		4,187		—
Sales of oil and gas equipment		7,571		—		—
Services performed on fuel cell systems and related infrastructure		26,706		(9,801)		25,217
Power Purchase Agreements		35,153		26,620		25,553
Fuel delivered to customers		46,917		(16,072)		29,099
Sale of cryogenic equipment		8,255		—		—
Other		789		311		186
Net revenue	$	502,342	$	(93,237)	$	229,975

Contract balances

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

	2021		2020
Accounts receivable	$	92,675	$	43,041
Contract assets		38,757		18,189
Contract liabilities		183,090		76,285

Contract assets relate to contracts for which revenue is recognized on a straight-line basis, however billings escalate over the life of a contract. Contract assets also include amounts recognized as revenue in advance of billings to customers, which are dependent upon the satisfaction of another performance obligation. These amounts are included in contract assets on the consolidated balance sheet.

The contract liabilities relate to the advance consideration received from customers for services that will be recognized over time (primarily fuel cell and related infrastructure services). Contract liabilities also include advance consideration received from customers prior to delivery of products. These amounts are included within deferred revenue and other contract liabilities on the consolidated balance sheet.

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

Contract assets	Year ended
	December 31, 2021
Transferred to receivables from contract assets recognized at the beginning of the period	$	(14,638)
Contract assets assumed as part of acquisitions		9,960
Revenue recognized and not billed as of the end of the period		25,246
Net change in contract assets	$	20,568

Contract liabilities	Year ended
	December 31, 2021
Increases due to cash received, net of amounts recognized as revenue during the period	$	182,052
Contract liabilities assumed as part of acquisitions		35,727
Revenue recognized that was included in the contract liability balance as of the beginning of the period		(110,974)
Net change in contract liabilities	$	106,805

Estimated future revenue

The following table includes estimated revenue included in the backlog 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, including provision for common stock warrants (in thousands):

Estimated future revenue
	December 31,
	2021
Sales of fuel cell systems	$	23,142
Sale of hydrogen installations and other infrastructure		36,243
Sale of electrolyzers		49,158
Sales of oil and gas equipment		91,586
Services performed on fuel cell systems and related infrastructure		102,362
Power Purchase Agreements		249,063
Fuel delivered to customers		61,602
Sale of cryogenic equipment		46,513
Other rental income		22,749
Total estimated future revenue	$	682,418

Contract costs

Contract costs consists of capitalized commission fees and other expenses related to obtaining or fulfilling a contract.

Capitalized contract costs at December 31, 2021 and 2020 were $428 thousand and $1.5 million, respectively.