SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
Jun. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated financial statements of the Company have been prepared in accordance with GAAP for interim reporting and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, the condensed balance sheet at December 31, 2020 has been derived from the audited financial statements at that date, but certain notes or other information that are normally required by GAAP have been omitted if they substantially duplicate the disclosures contained in the Company’s annual audited consolidated financial statements. In the opinion of Stem management, all adjustments considered necessary for a fair statement of the results for the interim period presented have been included in the accompanying unaudited financial statements. The consolidated financial statements include the accounts of the Company, its wholly-owned subsidiaries, and consolidated variable interest entities (“VIEs”). All intercompany balances and transactions have been eliminated in consolidation. These unaudited condensed financial statements should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2020. Operating results three and for the six-month period ended June 30, 2021 are not necessarily indicative of the results that may be expected for the full year ending December 31, 2021 or for any other future year.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting period. The Company bases its estimates on historical experience and on various other assumptions believed to be reasonable. Actual results could differ from those estimates and such differences could be material to the financial position and results of operations. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, depreciable life of energy systems; the amortization of financing obligations; deferred commissions and contract fulfillment costs; the valuation of energy storage systems, internally developed software, and asset retirement obligations; and the fair value of equity instruments, equity-based instruments, warrant liabilities and embedded derivatives.
Segment Information	Segment InformationOperating segments are defined as components of an entity for which discrete financial information is available that is regularly reviewed by the Chief Operating Decision Maker (“CODM”) in deciding how to allocate resources to an individual segment and in assessing performance. Our Chief Executive Officer is the CODM. The CODM reviews financial information presented on a consolidated basis for purposes of making operating decisions, allocating resources, and evaluating financial performance. As such, we have determined that the Company operates as one operating segment that is focused exclusively on innovative technology services that transform the way energy is distributed and consumed.
Significant Customers	Significant CustomersA significant customer represents 10% or more of the Company’s total revenue or accounts receivable, net balance at each respective reporting date.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Assets and liabilities recorded at fair value in the consolidated financial statements are categorized based upon the level of judgment associated with the inputs used to measure their fair value. 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. In connection with measuring the fair value of its assets and liabilities, the Company seeks to maximize the use of observable inputs (market data obtained from independent sources) and to minimize the use of unobservable inputs (internal assumptions about how market participants would price assets and liabilities). Hierarchical levels which are directly related to the amount of subjectivity associated with the inputs to the valuation of these assets or liabilities are as follows: Level 1 — Unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access as of the measurement date. Level 2 — Inputs other than quoted prices included within Level 1 that are directly observable for the asset or liability or indirectly observable through corroboration with observable market data. Level 3 — Unobservable inputs for the asset or liability only used when there is little, if any, market activity for the asset or liability at the measurement date. This hierarchy requires the Company to use observable market data, when available, and to minimize the use of unobservable inputs when determining fair value. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to their fair value measurement. The Company’s assessment of the significance of a specific input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability.
Recently Adopted Accounting Standards And Recently Issued Accounting Standards	Recently Adopted Accounting Standards In August 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework — Changes to the Disclosure Requirements for Fair Value Measurement. The amendments applicable to the Company on the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements and the narrative description of measurement uncertainty should be prospectively applied in the initial fiscal year of adoption. All other amendments applicable to the Company should be applied retrospectively to all periods presented upon their effective date. The Company adopted ASU 2018-13 as of January 1, 2020. The Company’s disclosures related to its level 3 financial instruments were not materially impacted for the periods presented. See Note 4, Fair Value Measurements, for more information. In August 2018, the FASB issued ASU 2018-15, Intangibles — Goodwill and Other — Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”). The intent of this pronouncement is to align the requirements for capitalizing implementation costs incurred in a cloud computing arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software as defined in ASC 350-40. Under ASU 2018-15, the capitalized implementation costs related to a cloud computing arrangement will be amortized over the term of the arrangement and all capitalized implementation amounts will be required to be presented in the same line items of the financial statements as the related hosting fees. ASU 2018-15 is effective for public and private companies’ fiscal years beginning after December 15, 2019, and December 15, 2020, respectively, and interim periods within those fiscal years, with early adoption permitted. The Company adopted ASU 2018-15 as of January 1, 2021. The adoption did not have a material impact to the Company’s condensed consolidated financial statements. Recently Issued Accounting Standards In June 2016, the FASB issued ASU 2016-13, Financial instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, and subsequent related ASUs, which amends the guidance on the impairment of financial instruments by requiring measurement and recognition of expected credit losses for financial assets held. This ASU is effective for public and private companies’ fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2019, and December 15, 2022, respectively. The Company expects to adopt ASU 2016-13 under the private company transition guidance beginning January 1, 2023 and is currently assessing the impact, if any, the guidance will have on the Company’s consolidated financial statements. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”). ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. ASU 2019-12 will be effective for public entities for interim and annual periods beginning after December 15, 2020, with early adoption permitted. ASU 2019-12 will be effective for private entities for annual periods beginning after December 15, 2021, and interim periods beginning after December 15, 2020, with early adoption permitted. The Company plans to adopt ASU 2019-12 for the fiscal year beginning January 1, 2022 and is currently assessing the impact, if any, the guidance will have on the Company's consolidated financial statements. In August 2020, the FASB issued ASU 2020-06, Debt — Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging — Contracts in Entity's Own Equity (Subtopic 815-40) — Accounting For Convertible Instruments and Contracts in an Entity's Own Equity. The ASU simplifies accounting for convertible instruments by removing major separation models required under current GAAP. Consequently, more convertible debt instruments will be reported as a single liability instrument with no separate accounting for embedded conversion features. The ASU removes certain settlement conditions that are required for equity contracts to qualify for the derivative scope exception, which will permit more equity contracts to qualify for it. The ASU also simplifies the diluted net income per share calculation in certain areas. The new guidance is effective for annual and interim periods beginning after December 15, 2023, and early adoption is permitted for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years. The Company plans to adopt 2020-06 for the fiscal year beginning January 1, 2024 and is currently evaluating the impact that this new guidance will have on the Company's financial statements.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

6 Months Ended

Jun. 30, 2021

The accompanying unaudited consolidated financial statements of the Company have been prepared in accordance with GAAP for interim reporting and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, the condensed balance sheet at December 31, 2020 has been derived from the audited financial statements at that date, but certain notes or other information that are normally required by GAAP have been omitted if they substantially duplicate the disclosures contained in the Company’s annual audited consolidated financial statements. In the opinion of Stem management, all adjustments considered necessary for a fair statement of the results for the interim period presented have been included in the accompanying unaudited financial statements. The consolidated financial statements include the accounts of the Company, its wholly-owned subsidiaries, and consolidated variable interest entities (“VIEs”). All intercompany balances and transactions have been eliminated in consolidation. These unaudited condensed financial statements should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2020. Operating results three and for the six-month period ended June 30, 2021 are not necessarily indicative of the results that may be expected for the full year ending December 31, 2021 or for any other future year.

Use of Estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting period. The Company bases its estimates on historical experience and on various other assumptions believed to be reasonable. Actual results could differ from those estimates and such differences could be material to the financial position and results of operations.

Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, depreciable life of energy systems; the amortization of financing obligations; deferred commissions and contract fulfillment costs; the valuation of energy storage systems, internally developed software, and asset retirement obligations; and the fair value of equity instruments, equity-based instruments, warrant liabilities and embedded derivatives.

Segment Information

Segment InformationOperating segments are defined as components of an entity for which discrete financial information is available that is regularly reviewed by the Chief Operating Decision Maker (“CODM”) in deciding how to allocate resources to an individual segment and in assessing performance. Our Chief Executive Officer is the CODM. The CODM reviews financial information presented on a consolidated basis for purposes of making operating decisions, allocating resources, and evaluating financial performance. As such, we have determined that the Company operates as one operating segment that is focused exclusively on innovative technology services that transform the way energy is distributed and consumed.

Significant Customers

Significant CustomersA significant customer represents 10% or more of the Company’s total revenue or accounts receivable, net balance at each respective reporting date.

Fair Value of Financial Instruments

Assets and liabilities recorded at fair value in the consolidated financial statements are categorized based upon the level of judgment associated with the inputs used to measure their fair value. 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. In connection with measuring the fair value of its assets and liabilities, the Company seeks to maximize the use of observable inputs (market data obtained from independent sources) and to minimize the use of unobservable inputs (internal assumptions about how market participants would price assets and liabilities).

Hierarchical levels which are directly related to the amount of subjectivity associated with the inputs to the valuation of these assets or liabilities are as follows:

Level 1 — Unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access as of the measurement date.

Level 2 — Inputs other than quoted prices included within Level 1 that are directly observable for the asset or liability or indirectly observable through corroboration with observable market data.

Level 3 — Unobservable inputs for the asset or liability only used when there is little, if any, market activity for the asset or liability at the measurement date.

This hierarchy requires the Company to use observable market data, when available, and to minimize the use of unobservable inputs when determining fair value. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to their fair value measurement. The Company’s assessment of the significance of a specific input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability.

Recently Adopted Accounting Standards And Recently Issued Accounting Standards

Recently Adopted Accounting Standards

In August 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework — Changes to the Disclosure Requirements for Fair Value Measurement. The amendments applicable to the Company on the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements and the narrative description of measurement uncertainty should be prospectively applied in the initial fiscal year of adoption. All other amendments applicable to the Company should be applied retrospectively to all periods presented upon their effective date. The Company adopted ASU 2018-13 as of January 1, 2020. The Company’s disclosures related to its level 3 financial instruments were not materially impacted for the periods presented. See Note 4, Fair Value Measurements, for more information.

In August 2018, the FASB issued ASU 2018-15, Intangibles — Goodwill and Other — Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”). The intent of this pronouncement is to align the requirements for capitalizing implementation costs incurred in a cloud computing arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software as defined in ASC 350-40. Under ASU 2018-15, the capitalized implementation costs related to a cloud computing arrangement will be amortized over the term of the arrangement and all capitalized implementation amounts will be required to be presented in the same line items of the financial statements as the related hosting fees. ASU 2018-15 is effective for public and private companies’ fiscal years beginning after December 15, 2019, and December 15, 2020, respectively, and interim periods within those fiscal years, with early adoption permitted. The Company adopted ASU 2018-15 as of January 1, 2021. The adoption did not have a material impact to the Company’s condensed consolidated financial statements.

Recently Issued Accounting Standards

In June 2016, the FASB issued ASU 2016-13, Financial instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, and subsequent related ASUs, which amends the guidance on the impairment of financial instruments by requiring measurement and recognition of expected credit losses for financial assets held. This ASU is effective for public and private companies’ fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2019, and December 15, 2022, respectively. The Company expects to adopt ASU 2016-13 under the private company transition guidance beginning January 1, 2023 and is currently assessing the impact, if any, the guidance will have on the Company’s consolidated financial statements.

In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”). ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. ASU 2019-12 will be effective for public entities for interim and annual periods beginning after December 15, 2020, with early adoption permitted. ASU 2019-12 will be effective for private entities for annual periods beginning after December 15, 2021, and interim periods beginning after December 15, 2020, with early adoption permitted. The Company plans to adopt ASU 2019-12 for the fiscal year beginning January 1, 2022 and is currently assessing the impact, if any, the guidance will have on the Company's consolidated financial statements.

In August 2020, the FASB issued ASU 2020-06, Debt — Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging — Contracts in Entity's Own Equity (Subtopic 815-40) — Accounting For Convertible Instruments and Contracts in an Entity's Own Equity. The ASU simplifies accounting for convertible instruments by removing major separation models required under current GAAP. Consequently, more convertible debt instruments will be reported as a single liability instrument with no separate accounting for embedded conversion features. The ASU removes certain settlement conditions that are required for equity contracts to qualify for the derivative scope exception, which will permit more equity contracts to qualify for it. The ASU also simplifies the diluted net income per share calculation in certain areas. The new guidance is effective for annual and interim periods beginning after December 15, 2023, and early adoption is permitted for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years. The Company plans to adopt 2020-06 for the fiscal year beginning January 1, 2024 and is currently evaluating the impact that this new guidance will have on the Company's financial statements.