Summary of Significant Accounting Policies | Summary of Significant Accounting Policies Basis of consolidated financial statement presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”) and include the accounts of its wholly owned subsidiaries and variable interest entities (“VIEs”), for which the Company was the primary beneficiary. All intercompany transactions and balances have been eliminated in consolidation. Certain prior year amounts have been reclassified to conform to the Company’s presentation as of and for the year ended December 31, 2023 and such reclassifications had no effect on the Company’s previously reported financial position, results of operations, or cash flows. On March 28, 2023, the Company was notified by the New York Stock Exchange (the “NYSE”) that it was not in compliance with certain listing requirements since the average closing price of its common stock was less than $1.00 over a consecutive 30 day trading period. Subsequently, on October 6, 2023, the Company effected a 1-for-8 reverse stock split with respect to its issued and outstanding shares of common stock (the “Reverse Stock Split”). Excluding the par value and the number of authorized shares of the Company’s common stock, all share, per share amounts, and the values of the common stock outstanding and related effect on additional paid in capital included in this Form 10-K have been retrospectively presented as if the Reverse Stock Split had been effective from the beginning of the earliest period presented. Use of estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make certain estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the balance sheet date, as well as reported amounts of expenses during the reporting period. The Company’s most significant estimates and judgments involve (i) inventory reserves, (ii) deferred income taxes, (iii) warranty reserves, (iv) valuation of stock-based compensation, (v) valuation of warrant liability, (vi) the useful lives of certain assets and liabilities, (vii) the allowance for current expected credit losses and (viii) the valuation of business combinations, including the fair values and useful lives of acquired assets and assumed liabilities, goodwill and the fair value of purchase consideration of asset acquisitions. Management bases its estimates on historical experience and on various other assumptions believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results could differ from those estimates, and such differences could be material to the Company’s financial statements. Variable interest entities The Company consolidates any variable interest entity (“VIE”) of which it is the primary beneficiary. The Company formed or acquired VIEs which are partially funded by tax equity investors in order to facilitate the funding and monetization of certain attributes associated with solar energy systems. The typical condition for a controlling financial interest ownership is holding a majority of the voting interests of an entity; however, a controlling financial interest may also exist in entities, such as VIEs, through arrangements that do not involve controlling voting interests. A variable interest holder is required to consolidate a VIE if that party has the power to direct the activities of the VIE that most significantly impact the VIE's economic performance and the obligation to absorb losses of the VIE that could potentially be significant to the VIE or the right to receive benefits from the VIE that could potentially be significant to the VIE. The Company does not consolidate a VIE in which it has a majority ownership interest when the Company is not considered the primary beneficiary. The Company evaluates its relationships with the VIEs on an ongoing basis to determine if it is the primary beneficiary. As of December 31, 2022, the Company had its initial investment in Level Solar Fund IV LLC (“Level Solar Fund IV”) and similar investments in the Funds as defined below (collectively, the “Prior Funds”), which were each determined to be a VIE upon investment. During 2023, the Company purchased 100% of the membership interests in Level Solar Fund IV (See Note 13. Redeemable Noncontrolling Interests and Noncontrolling Interests) and it ceased being a VIE upon purchase. A s of December 31, 2023, the Company had its investments in Volta Solar Owner II, LLC and ORE F4 HoldCo, LLC (collectively, the “Funds”). The Company considered the provisions within the contractual arrangements that grant it power to manage and make decisions that affect the operation of the VIEs, including determining the solar energy systems contributed to the VIEs, and the operation and maintenance of the solar energy systems. The Company considers the rights granted to the other investors under the contractual arrangements to be more protective in nature rather than substantive participating rights. As such, the Company was determined to be the primary beneficiary and the assets, liabilities and activities of the Funds and Prior Funds were consolidated by the Company. Redeemable noncontrolling interests and noncontrolling interests The distribution rights and priorities for the Funds and Prior Funds (before any ceased being a VIE) as set forth in their respective operating agreements differ from the underlying percentage ownership interests of the members. As a result, the Company allocates income or loss to the noncontrolling interest holders of the Funds and Prior Funds (before any ceased being a VIE) utilizing the hypothetical liquidation of book value (“HLBV”) method, in which income or loss is allocated based on the change in each member's claim on the net assets at the end of each reporting period, adjusted for any distributions or contributions made during such periods. The HLBV method is commonly applied to investments where cash distribution percentages vary at different points in time and are not directly linked to an equity member's ownership percentage. The HLBV method is a balance sheet-focused approach. Under this method, a calculation is prepared at each reporting date to determine the amount that each member would receive if the entity were to liquidate all of its assets and distribute the resulting proceeds to its creditors and members based on the contractually defined liquidation priorities. The difference between the calculated liquidation distribution amounts at the beginning and the end of the reporting period, after adjusting for capital contributions and distributions, is used to derive each member's share of the income or loss for the period. Factors used in the HLBV calculation include GAAP income (loss), taxable income (loss), capital contributions, ITCs, capital distributions and the stipulated targeted investor return specified in the subsidiaries' operating agreements. Changes in these factors could have a significant impact on the amounts that investors would receive upon a hypothetical liquidation. The Company classifies certain noncontrolling interests with redemption features that are not solely within the Company’s control outside of permanent equity in the consolidated balance sheets. Redeemable noncontrolling interests are reported using the greater of the carrying value at each reporting date as determined by the HLBV method or the estimated redemption value at the end of each reporting period. Estimating the redemption value of the redeemable noncontrolling interests requires the use of significant assumptions and estimates, such as projected future cash flows. Subsequent to the purchase of 100% of the membership interests in Level Solar Fund IV in 2023, the Company had no redeemable noncontrolling interest as of December 31, 2023. Cash and cash equivalents The Company considers all highly liquid investments with a maturity of three months or less at the time of purchase to be cash equivalents. Cash and cash equivalents include cash held in banks, money market accounts and U.S. Treasury securities. Cash equivalents are carried at cost, which approximates fair value due to their short-term nature. The Company’s cash and cash equivalents are placed with high-credit quality financial institutions and issuers, and at times exceed federally insured limits. To date, the Company has experienced no credit losses relating to its cash and cash equivalents. Concentration of credit risks and revenue Financial instruments which potentially subject the Company to concentrations of credit risk consist of cash and cash equivalents. At times, such cash may be in excess of the FDIC limit. At December 31, 2023 and 2022, the Company had cash in excess of the $250,000 federally insured limit. The Company believes it is not exposed to any significant credit risk on cash and cash equivalents as most of the balances are kept in treasury bills, which are government backed securities. As of and for the year ended December 31, 2023 and 2022, the Company had no customers that represented at least 10% of the Company’s revenues or its accounts receivable balances. Restricted cash Restricted cash held at December 31, 2023 and 2022 of $31.6 million and $19.8 million, respectively, primarily consists of cash that is subject to restriction due to provisions in the Company's financing agreements and the operating agreements of the Funds and Prior Funds . The carrying amount reported in the consolidated balance sheets for restricted cash approximates its fair value. The following table provides a reconciliation of cash and cash equivalents and restricted cash reflected on the consolidated balance sheets to the total amounts shown within the consolidated statements of cash flows for each year: As of December 31, (Amounts in thousands) 2023 2022 Cash and cash equivalents $ 141,354 $ 220,321 Restricted cash 31,587 19,823 Total cash, cash equivalents and restricted cash $ 172,941 $ 240,144 Accounts receivable, net Accounts receivable primarily represent amounts due from the Company’s customers. Accounts receivable is recorded net of allowance for expected credit losses in accordance with the current expected credit losses standard (“CECL”), defined below, which is determined by the Company’s assessment of the collectability of customer accounts based on the best available data at the time of the assessment. Management reviews the allowance by considering factors such as historical experience, contractual term, aging category and current economic conditions that may affect customers. The following table presents the changes in the allowance for credit losses recorded within accounts receivable, net on the consolidated balance sheets: As of December 31, (Amounts in thousands) 2023 Balance at the beginning of the period $ 12,164 Impact of ASC 326 adoption (1,285) Write-off of uncollectible accounts (11,447) Provision recognized upon valuation of assets acquired 420 Provision for current expected credit losses 1,841 Balance at the end of the period $ 1,693 Derivative instruments and hedging activities The Company utilizes interest rate swaps to manage interest rate risk on existing and planned future debt issuances. The fair value of all derivative instruments are recognized as assets or liabilities at the balance sheet date on the consolidated balance sheets. The fair value of the interest rate swaps are calculated by discounting the future net cash flows to the present value based on the terms and conditions of the agreements and the forward interest rate curves. As these inputs are based on observable data and valuations of similar instruments, the interest rate derivatives are primarily categorized as Level 2 in the fair value hierarchy. Prepaid expenses and other current assets Prepaid expenses and other current assets include prepaid insurance, prepaid rent, and supplies, which are expected to be recognized or realized within the next 12 months. Investment related to SEMTH master lease agreement and interest income The Company accounts for its investment related to the SEMTH, as defined below, master lease agreement in accordance with Accounting Standards Codification (“ASC”) 325-40, Investments—Other—Beneficial Interests in Securitized Financial Assets . The Company recognizes accretable yield as interest income over the life of the related beneficial interest using the effective yield method, which is reflected within interest income in the consolidated statements of operations in the amount of $11.5 million for the year ended December 31, 2023. On a recurring basis, the Company evaluates changes in the cash flows expected to be collected from the cash flows previously projected, and when favorable or adverse changes are deemed other than temporary, the Company prospectively updates its expectation of cash flows to be collected and recalculates the amount of accretable yield for the related beneficial interest. Property and equipment, net Property and equipment, net consists of solar energy systems and other property and equipment. Solar energy systems , net Solar energy systems, net consists of home solar energy systems which are subject to long-term Customer Agreements and asset retirement costs (“ARC”). Solar energy systems are recorded at their fair value upon acquisition, while ARCs are capitalized as part of the carrying amount of the solar energy systems and depreciated over the remaining useful life. Subsequently, any impairment charges that may arise are recognized and the impairment loss reduces the carrying amount of the asset to its recoverable amount. For all acquired systems, the Company calculates depreciation using the straight-line method over the remaining useful life as of the acquisition date based on a 30-year useful life from the date the asset was placed in service. When a solar energy system is sold or otherwise disposed of, a gain (or loss) is recognized for the amount of cash received in excess of the net book value of the solar energy system (or vice versa), at which time the related solar energy system is removed from the consolidated balance sheets. Other property and equipment, net Other property and equipment, net is stated at cost less accumulated depreciation, or if acquired in a business combination, at fair value as of the date of acquisition. Depreciation is calculated using the straight-line method, based upon the following estimated useful lives: Equipment 5 years Furniture and fixtures 3 years Computer and related equipment 2 years Software 2 years Vehicles 5 years Leasehold improvements Lesser of useful life of the asset or remaining life of the lease Leasehold improvements are capitalized, while replacements, maintenance and repairs, which do not improve or extend the life of the respective asset, are expensed as incurred. When property and equipment is retired or otherwise disposed of, the related cost and accumulated depreciation are removed from the accounts, and any gain or loss on the disposition is recorded in the consolidated statements of operations as a component of other income, net. Intangible assets, net The Company’s intangible assets include solar renewable energy credit agreements, performance based incentive agreements, and a trade name. The Company amortizes its intangible assets that have finite lives based on the pattern in which the economic benefit of the asset is expected to be utilized. The useful life of the Company’s intangible assets generally range between three years and 30 years. The useful life of intangible assets are assessed and assigned based on the facts and circumstances specific to the assets. The Company recognizes the amortization of (i) solar renewable energy credit agreements and performance based incentive agreements as a reduction to revenue and (ii) the trade name as amortization expense within selling, general and administrative expenses. Impairment of long-lived asset s The Company reviews long-lived assets, including solar energy systems, other property and equipment, and intangible assets with definite lives for impairment whenever events or changes in circumstances indicate that an asset group’s carrying amount may not be recoverable. The Company groups assets and liabilities at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities and evaluates the asset group against the sum of the undiscounted future cash flows. If the undiscounted cash flows do not indicate the carrying amount of the asset group is recoverable, an impairment charge is measured as the amount by which the carrying amount of the asset group exceeds its fair value. In the fourth quarter of 2022, the Company determined there was an indicator of impairment for intangible assets in its discontinued operations of the Drivetrain and XL Grid businesses and concluded the asset was not recoverable. Comparing the carrying value of the asset to its fair value, the Company determined the entire asset was impaired and recognized an impairment charge of $0.9 million, which is reflected within net loss from discontinued operations in the consolidated statements of operations for the year ended December 31, 2022 (See Note 20. Discontinued Operations). There was no long-lived asset impairment charge during the year ended December 31, 2023. Leases The Company determines if an arrangement is a lease, or contains a lease, at the inception of the arrangement and evaluates whether the lease is an operating lease or a finance lease at the commencement date. The Company’s assessment is based on: (i) whether the contract involves the use of a distinct identified asset, (ii) whether the Company obtained the right to substantially all the economic benefit from the use of the asset throughout the period, and (iii) whether the Company has the right to direct the use of the asset. The Company recognizes lease right-of-use (“ROU”) assets and lease liabilities for operating and finance leases with initial terms greater than 12 months. ROU assets represent the Company’s right to use an asset for the lease term, while lease liabilities represent the Company’s obligation to make the related lease payments. The ROU assets for all leases are recognized based on the present value of fixed lease payments over the lease term at the lease commencement date. The lease liabilities of all leases are calculated as the present value of fixed payments not yet paid at the measurement date, however subsequent to the measurement date, the finance lease liabilities are presented at amortized cost using the effective interest method. The Company generally uses its incremental borrowing rate as the discount rate for leases unless an interest rate is implicitly stated in the leases. The Company’s incremental borrowing rate is determined using a portfolio approach based on the rate of interest that the Company would have to pay to borrow an amount equal to the lease payments on a collateralized basis over a similar term. The lease term for all of the Company’s leases includes the noncancelable period of the lease, in addition to any additional periods covered by either the Company’s option to extend the lease, which the Company is reasonably certain to exercise, or the option to extend the lease controlled by the lessor. All ROU assets are reviewed periodically for impairment. Lease expense for operating leases consists of the lease payments plus any initial direct costs and is recognized on a straight-line basis over the lease term. Lease expense for finance leases consists of the amortization of the asset on a straight-line basis over the shorter of the lease term or its useful life and interest expense determined on an amortized cost basis, with the lease payments allocated between a reduction of the lease liability and interest expense. Variable lease payments that are not based on an index or a rate, such as common area maintenance fees, taxes and insurance, are expensed as incurred. Asset retirement obligations Asset retirement obligations (“ARO”) can arise from contractual or regulatory requirements to perform certain asset retirement activities at the time the solar energy systems are to be disposed. The Company recognizes AROs at the point an obligating event takes place. The liability is initially measured at fair value based on the present value of estimated removal costs and subsequently adjusted for changes in the underlying assumptions and accretion expense. The corresponding ARCs are considered retired when permanently taken out of service, such as, through a sale or disposal. The Company may revise the ARO based on actual experiences, changes in certain customer-specific estimates and other cost estimate changes. If there are changes in estimated future costs, those changes will be recorded as either a reduction or addition in the carrying amount of the remaining unamortized ARC and the ARO will either increase or decrease in depreciation and accretion expense amounts prospectively. Inherent in the calculation of the fair value of AROs are numerous assumptions and judgments, including the ultimate settlement amounts, inflation factors, credit adjusted discount rates, and timing of settlement. As of December 31, 2023 and 2022, ARO was $3.0 million and $0 million, respectively. For the years ended December 31, 2023 and 2022, accretion expenses were $0.3 million and $0 million, respectively. Asset acquisitions The Company accounts for assets acquired based on the consideration transferred by the Company, including direct and incremental transaction costs incurred by the Company as a result of the acquisition. An asset acquisition’s cost or the consideration transferred by the Company is assumed to be equal to the fair value of the net assets acquired. If the consideration transferred is cash, measurement is based on the amount of cash the Company paid to the seller, as well as transaction costs incurred by the Company. Consideration given in the form of nonmonetary assets, liabilities incurred or equity interests issued is measured based on either the cost to the Company or the fair value of the assets or net assets acquired, whichever is more clearly evident. The cost of an asset acquisition is allocated to the net assets acquired based on their estimated relative fair values. The Company engages third-party appraisal firms to assist in the fair value determination, however management is responsible for, and ultimately determines the fair value. Goodwill is not recognized in an asset acquisition. Business combinations The Company accounts for the acquisition of a business using the acquisition method of accounting. Amounts paid to acquire a business are allocated to the assets acquired and liabilities assumed based on their fair values at the date of acquisition. The Company engages third-party appraisal firms to assist in the fair value determination, which management uses to determine the fair value. The Company determines the fair value of purchase price consideration, including contingent consideration, and acquired intangible assets based on valuations received from the appraisal firm that used information and assumptions provided by Management. The Company allocates any excess purchase price over the fair value of the net tangible and intangible assets acquired to goodwill. The results of operations of acquired businesses are included in the Company's financial statements from the date of acquisition forward. Acquisition-related costs are expensed in periods in which the costs are incurred. Impairment of goodwill Goodwill represents the excess of cost over the fair market value of net tangible and identifiable intangible assets of acquired businesses. Goodwill is not amortized, however it is annually tested for impairment, or more frequently if events or circumstances indicate that the carrying amount of goodwill may be impaired. The Company has historically recorded goodwill in connection with its business combinations. The Company performs its annual goodwill impairment assessment on October 1 of each fiscal year, or more frequently if events or circumstances arise which indicate that goodwill may be impaired. An assessment can be performed by first completing a qualitative assessment of the Company’s single reporting unit. The Company can also bypass the qualitative assessment in any period and proceed directly to the quantitative impairment test, and then resume the qualitative assessment in any subsequent period. Qualitative indicators that may trigger the need for annual or interim quantitative impairment testing include, among other things, deterioration in macroeconomic conditions, declining financial performance, deterioration in the operational environment, or an expectation of selling or disposing of a portion of the reporting unit. Additionally, a significant change in business climate, a loss of a significant customer, increased competition, a sustained decrease in share price, or a decrease in estimated fair value below book value may trigger the need for interim impairment testing of goodwill. If the Company believes that, as a result of its qualitative assessment, it is more likely than not that the fair value of the reporting unit is less than its carrying amount, the quantitative impairment test is required. The quantitative test involves comparing the fair value of the reporting unit with its carrying amount, including goodwill. If the carrying amount of the reporting unit exceeds its fair value, an impairment loss is recorded as a reduction to goodwill with a corresponding charge to earnings in the period the goodwill is determined to be impaired. The income tax effect associated with an impairment of tax-deductible goodwill is also considered in the measurement of the goodwill impairment. Any goodwill impairment is limited to the total amount of goodwill. The Company evaluates the fair value of the Company’s reporting unit using the market and income approach. Under the market approach, the Company uses multiples of EBITDA or revenues of the comparable guideline public companies by selecting a population of public companies with similar operations and attributes. Using this guideline public company data, a range of multiples of enterprise value to EBITDA or revenue is calculated. The income approach of computing fair value is based on the present value of the expected future economic benefits generated by the asset or business, such as cash flows or profits which will then be compared to its book value. In the first quarter of 2022, the Company believed there were indicators that the carrying amount of its goodwill may be impaired due to a decline in the Company’s stock price and market capitalization. As a result, the Company performed an assessment of its goodwill for impairment. The Company elected to forego the qualitative test and proceeded to perform a quantitative test. The Company compared the book value of its single reporting unit to the fair value of its public float. The market capitalization was below the fair value of the Company by an amount in excess of its reported value of goodwill. As a result, the Company recorded a charge of $8.6 million to fully impair its goodwill related to XL Fleet Corp., which is reflected within net loss from discontinued operations in the consolidated statements of operations for the year ended December 31, 2022 (See Note 20. Discontinued Operations). There was no goodwill impairment charge during the year ended December 31, 2023. Warranties Customers who purchased the Company's Drivetrain systems were provided limited-assurance-type warranties for equipment and work performed under the contracts. The warranty period typically extends for three years following transfer of control of the equipment. The warranties solely relate to correction of product defects during the warranty period, which is consistent with similar warranties offered by competitors. Customers of XL Grid were provided limited-assurance-type warranties for a term of one year for installation work performed under its contracts. The Company accrued the estimated cost of product warranties for unclaimed charges based on historical experiences and expected results. Should product failure rates and material usage costs differ from these factors, estimated revisions to the estimated warranty liability will be required. The Company periodically assesses the adequacy of its recorded product warranty liabilities and adjusts the balances as required. Warranty expense is recorded as a component of discontinued operations in the consolidated statements of operations. With the Company’s exit from the Drivetrain business and the subsequent sale of World Energy, the Company will not enter into any additional warranty obligations and expects the existing warranty obligation to substantially run-off over the subsequent 15-month period. The following is a roll forward of the Company’s accrued warranty liability: As of December 31, (Amounts in thousands) 2023 2022 Balance at the beginning of the period $ 1,125 $ 2,547 Accrual for warranties issued — 116 Transfer of inventory to servicers (498) — Accrual related to World Energy (25) — Changes in estimates for preexisting warranties — (955) Warranty fulfillment charges — (583) Balance at the end of the period $ 602 $ 1,125 The Company’s warranty liability is included in accrued expenses and other current liabilities on the consolidated balance sheets. Warrant liabilities As of December 31, 2023 and 2022, the Company had outstanding private warrants, which are related to the December 2020 merger and organization of legacy XL Hybrids Inc. (“Legacy XL”) to become XL Fleet Corp. With the merger, the Company assumed private placement warrants to purchase 529,167 shares of common stock, with an exercise price of $92.00 per share (the “Private Warrants”). The Private Warrants do not meet the criteria for equity classification and must be recorded as liabilities. As the Private Warrants met the definition of a derivative, they were measured at fair value at inception and at each reporting date with changes in fair value recognized in the consolidated statements of operations. The Private Warrants were valued using a Black-Scholes model, with significant inputs consisting of risk-free interest rate, remaining term, expected volatility, exercise price, and the Company’s stock price (See Note 11. Fair Value Measurements). Unfavorable solar renewable energy agreements The Company amortizes its unfavorable solar renewable energy agreements that have finite lives based on the pattern in which the economic benefit of the liability is relieved. The useful life of the Company’s liabilities generally range between three years and six years. The useful life of these liabilities are assessed and assigned based on the facts and circumstances specific to the agreement. The Company recognizes the amortization of unfavorable solar renewable energy agreements as revenues in the consolidated statements of operations. Contingencies The Company is unable to anticipate the ultimate outcome of all pending legal proceedings. When it is probable that a loss has occurred and the loss amount can be reasonably estimated, the Company records liabilities for loss contingencies. In certain cases, the Company may be covered by one or more corporate insurance policies, resulting in insurance loss recoveries. When such recoveries are in excess of a loss recognized in the Company’s financial statements, the Company recognizes a gain contingency at the earlier of when the gain has been realized or when it is realizable, however when the Company expects recovery of proceeds up to the amount of the loss recognized, a receivable, which offsets the related loss contingency, is recognized when realization of the claim for recovery is determined to be probable. Fair value measurements The fair value of the Company’s financial assets and liabilities reflects Management’s estimate of amounts that the Company would have received in connection with the sale of the assets or paid in connection with the transfer of the liabilities in an orderly transaction between market participants at the measurement date. For assets and liabilities measured at fair value on a recurring and nonrecurring basis, a three-level hierarchy of measurements based upon observable and unobservable inputs is used to arrive at fair value. Observable inpu |