Revenue Recognition

12 Months Ended

Dec. 31, 2021

Revenue from Contract with Customer [Abstract]

Revenue Recognition

Revenue Recognition

Contract Balances

The following table provides information about accounts receivables, contract assets, customer deposits and deferred revenue from contracts with customers (in thousands):

	December 31,
	2021		2020
Accounts receivable	$	87,788	$	96,186
Contract assets	25,201		3,327
Customer deposits	64,809		66,171
Deferred revenue	115,476		135,578

Contract assets relate to contracts for which revenue is recognized upon transfer of control of performance obligations, however billing milestones have not been reached. Customer deposits and deferred revenue are payments received from customers or invoiced amounts prior to transfer of controls of performance obligations. Customer deposits, except for the $34.2 million related to the transaction with SK ecoplant, are refundable fees until certain milestones are met.

Contract Assets

	Years Ended December 31,
	2021		2020
Beginning balance	$	3,327	$	2,768
Transferred to accounts receivable from contract assets recognized at the beginning of the period	(1,198)		—
Revenue recognized and not billed as of the end of the period	23,072		559
Ending balance	$	25,201	$	3,327

Deferred Revenue

Deferred revenue activity, including deferred incentive revenue activity, during the years ended December 31, 2021 and 2020 consisted of the following (in thousands):

	Years Ended December 31,
	2021		2020
Beginning balance	$	135,578	$	175,619
Additions	916,604		652,960
Revenue recognized	(936,706)		(693,001)
Ending balance	$	115,476	$	135,578

Deferred revenue is equivalent to the total transaction price allocated to the performance obligations that are unsatisfied, or partially unsatisfied, as of the end of the period. The significant component of deferred revenue at the end of the period consists of performance obligations relating to the provision of maintenance services under current contracts and future renewal periods. These obligations provide customers with material rights over a period that we estimate will be largely commensurate with the period of their expected use of the associated Energy Server. As a result, we expect to recognize these amounts as revenue over a period of up to 21 years, predominantly on a relative standalone selling price basis that reflects the cost of providing these services. Deferred revenue also includes performance obligations relating to product acceptance and installation. A significant amount of this deferred revenue is reflected as additions and revenue recognized in the same period and we expect to recognize substantially all amounts within a year. During the years ended December 31, 2021 and 2020, we recognized $1.2 million and $14.2 million, respectively, of previously deferred revenue that was not associated with acceptances or service in the year as a result of a modification of a contract with a customer.

We do not disclose the value of the unsatisfied performance obligations for (i) contracts with an original expected length of one year or less and (ii) contracts for which we recognize revenue at the amount to which we have the right to invoice for services performed.

Disaggregated Revenue

We disaggregate revenue from contracts with customers into four revenue categories: product, installation, services and electricity (in thousands):

	Years Ended December 31,
	2021		2020		2019
Revenue from contracts with customers:
Product revenue	$	663,512	$	518,633	$	557,336
Installation revenue	96,059		101,887		60,826
Services revenue	144,184		109,633		95,786
Electricity revenue	3,103		1,071		10,840
Total revenue from contract with customers	906,858		731,224		724,788
Revenue from contracts accounted for as leases:
Electricity revenue	65,318		63,023		60,389
Total revenue	$	972,176	$	794,247	$	785,177