Revenue

12 Months Ended

Dec. 31, 2020

Revenue

Revenue

19. Revenue, as restated

Disaggregation of revenue

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

Major products/services lines
	Year ended December 31,
			2019		2018
	2020		(as restated)		(as restated)
Sales of fuel cell systems	$	(55,091)	$	130,757	$	75,029
Sale of hydrogen infrastructure		(39,204)		19,163		32,146
Services performed on fuel cell systems and related infrastructure		(9,801)		25,217		22,002
Power Purchase Agreements		26,620		25,553		22,569
Fuel delivered to customers		(16,072)		29,099		22,469
Other		311		186		—
Net revenue	$	(93,237)	$	229,975	$	174,215

Contract balances

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

	2020		2019
Accounts receivable	$	43,041	$	25,768
Contract assets		18,189		13,251
Contract liabilities		76,285		40,743

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 prepaid expenses and other 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 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, 2020
Transferred to receivables from contract assets recognized at the beginning of the period	$	(5,483)
Revenue recognized and not billed as of the end of the period		10,421
Net change in contract assets	$	4,938

Contract liabilities	Year ended
	December 31, 2020
Increases due to cash received, net of amounts recognized as revenue during the period	$	100,492
Contract liabilities assumed as part of acquisitions		2,350
Revenue recognized that was included in the contract liability balance as of the beginning of the period		(67,300)
Net change in contract liabilities	$	35,542

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,
	2020
Sales of fuel cell systems	$	16,209
Sale of hydrogen installations and other infrastructure		28,282
Services performed on fuel cell systems and related infrastructure		75,467
Power Purchase Agreements		178,450
Fuel delivered to customers		65,704
Other rental income		3,294
Total estimated future revenue	$	367,406

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, 2020 and 2019 were $1.5 million and $0.5, respectively.