| Revenue |
18. Revenue Disaggregation of revenue The following table provides information about disaggregation of revenue (in thousands): | | | | | | | | | | Major products/services lines | | | | | | | | | | | | Year ended December 31, | | | 2023 | | 2022 | | 2021 | Sales of fuel cell systems | | $ | 181,168 | | $ | 207,691 | | $ | 225,229 | Sales of hydrogen infrastructure | | | 183,606 | | | 141,528 | | | 135,055 | Sales of electrolyzers | | | 82,611 | | | 28,463 | | | 16,667 | Sales of engineered equipment | | | 32,361 | | | 93,489 | | | 7,571 | Services performed on fuel cell systems and related infrastructure | | | 39,093 | | | 35,280 | | | 26,706 | Power purchase agreements | | | 63,731 | | | 47,183 | | | 35,153 | Fuel delivered to customers and related equipment | | | 66,246 | | | 57,196 | | | 46,917 | Sales of cryogenic equipment and other | | | 231,687 | | | 87,761 | | | 8,255 | Other | | | 10,837 | | | 2,849 | | | 789 | Net revenue | | $ | 891,340 | | $ | 701,440 | | $ | 502,342 |
Contract balances The following table provides information about receivables, contract assets, and contract liabilities from contracts with customers (in thousands): | | | | | | | | | December 31, | | December 31, | | | 2023 | | 2022 | Accounts receivable | | $ | 243,811 | | $ | 129,450 | Contract assets | | | 155,989 | | | 104,287 | Deferred revenue and contract liabilities | | | 288,302 | | | 229,898 |
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 deferred revenue and 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 and electrolyzer systems and solutions). Deferred revenue and 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 | | | | | December 31, 2023 | | December 31, 2022 | Transferred to receivables from contract assets recognized at the beginning of the period | | $ | (94,860) | | $ | (33,394) | Change in contract assets related to warrants | | | 14,260 | | | 26,455 | Impairment | | | (2,375) | | | — | Revenue recognized and not billed as of the end of the period | | | 134,677 | | | 72,469 | Net change in contract assets | | $ | 51,702 | | $ | 65,530 |
| | | | | | | Deferred revenue and contract liabilities | | | | | December 31, 2023 | | December 31, 2022 | Increases due to customer billings, net of amounts recognized as revenue during the period | | $ | 151,965 | | $ | 200,347 | Change in contract liabilities related to warrants | | | 440 | | | — | Contract liabilities assumed as part of acquisitions | | | — | | | 10,011 | Revenue recognized that was included in the contract liability balance as of the beginning of the period | | | (94,001) | | | (163,550) | Net change in deferred revenue and contract liabilities | | $ | 58,404 | | $ | 46,808 |
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, including provision for common stock warrants (in thousands): | | | | | | | | | December 31, | | Expected recognition | | | 2023 | | period (years) | Sales of fuel cell systems | | $ | 64,954 | | | 1 - 2 | Sales of hydrogen installations and other infrastructure | | | 22,860 | | | 1 | Sales of electrolyzers | | | 301,323 | | | 1 - 2 | Sales of engineered equipment | | | 19,876 | | | 1 | Services performed on fuel cell systems and related infrastructure | | | 123,080 | | | 5 - 10 | Power purchase agreements | | | 435,967 | | | 5 - 10 | Fuel delivered to customers and related equipment | | | 95,444 | | | 5 - 10 | Sales of cryogenic equipment and other | | | 87,927 | | | 1 | Total estimated future revenue | | $ | 1,151,431 | | | |
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