
	Years Ended December 31,
	2020		2019		2018

Current:
Federal	$	—	$	—	$	—
State	21		26		191
Foreign	472		595		1,407
Total current	493		621		1,598
Deferred:
Federal	—		—		—
State	—		—		—
Foreign	(237)		12		(61)
Total deferred	(237)		12		(61)
Total provision for income taxes	$	256	$	633	$	1,537


	Years Ended December 31,
	2020		2019		2018

Tax at federal statutory rate	$	(37,552)	$	(67,795)	$	(60,845)
State taxes, net of federal effect	21		26		191
Impact on noncontrolling interest	4,522		4,001		3,725
Non-U.S. tax effect	78		264		960
Nondeductible expenses	908		144		6,796
Stock-based compensation	5,956		6,484		3,892
Loss on debt extinguishment	214		—		—
U.S. tax on foreign earnings (GILTI)	203		221		127
Change in valuation allowance	25,906		57,288		46,691
Provision for income taxes	$	256	$	633	$	1,537

For the year ended December 31, 2020, we recognized a provision for income taxes of $0.3 million on a pre-tax loss of $178.8 million, for an effective tax rate of (0.1)%. For the year ended December 31, 2019, we recognized a provision for income taxes of $0.6 million on a pre-tax loss of $322.8 million, for an effective tax rate of (0.2)%. For the year ended December 31, 2018, we recognized a provision for income taxes of $1.5 million on a pre-tax loss of $289.7 million, for an effective tax rate of (0.5)%. The effective tax rate for 2020, 2019 and 2018 is lower than the statutory federal tax rate primarily due to a full valuation allowance against U.S. deferred tax assets.


	December 31,
	2020		2019

Tax credits and net operating loss carryforwards	$	510,599	$	494,084
Lease liabilities	128,151		122,145
Depreciation and amortization	7,541		8,523
Deferred revenue	27,134		6,688
Accruals and reserves	15,068		5,874
Stock-based compensation	35,815		61,808

Other items - deferred tax assets	25,931		24,443
Gross deferred tax assets	750,239		723,565
Valuation allowance	(614,958)		(633,591)
Net deferred tax assets	135,281		89,974
Investment in PPA entities	(10,757)		(13,494)
Debt issuance cost	—		(4,055)
Discount upon issuance of debt	(29,513)		—
Managed services - deferred costs	(21,898)		—
Right-of-use assets and leased assets	(70,818)		(65,978)
Other items - deferred tax liability	(1,413)		(5,803)
Gross deferred tax liabilities	(134,399)		(89,330)
Net deferred tax asset	$	882	$	644

Income taxes are recorded using the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income (or loss) in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date.

A valuation allowance is provided for the amount of deferred tax assets that, based on available evidence, is not more-likely-than-not to be realized. Management believes that, based on available evidence, both positive and negative, it is not more likely than not that the net U.S. deferred tax assets will be utilized. As a result, a full valuation allowance has been recorded.

The valuation allowance for deferred tax assets was $615.0 million and $633.6 million as of December 31, 2020 and 2019, respectively. The net change in the total valuation allowance for the years ended December 31, 2020 and 2019 was a decrease of $18.6 million and an increase of $62.3 million, respectively.

At December 31, 2020, we had federal and state net operating loss carryforwards of $1.9 billion and $1.6 billion, respectively, to reduce future taxable income. Of the federal net operating loss carryforwards, $1.7 billion will begin to expire in 2022 and $224.8 million will carryforward indefinitely, while state net operating losses begin to expire in 2028. In addition, we had approximately $23.0 million of federal research credit, $6.6 million of federal investment tax credit, and $14.7 million of state research credit carryforwards. The federal tax credit carryforwards begin to expire in 2022. The state credit carryforwards may be carried forward indefinitely. We have not reflected deferred tax assets for the federal and state research credit carryforwards as the entire amount of the carryforwards represent unrecognized tax benefits.

Internal Revenue Code Section 382 (“Section 382”) limits the use of net operating loss and tax credit carryforwards in certain situations in which changes occur in our capital stock ownership. Any annual limitation may result in the expiration of net operating losses and credits before utilization. If we should have an ownership change, as defined by the tax law, utilization of the net operating loss and credit carryforwards could be significantly reduced. We completed a Section 382 analysis through December 31, 2020. Based on this analysis, Section 382 limitations will not have a material impact on our net operating loss and credit carryforwards related to any ownership changes.

During the year ended December 31, 2020, the amount of uncertain tax positions increased by $3.3 million. We have not recorded any uncertain tax liabilities associated with our tax positions.


	Years Ended December 31,
	2020		2019
Unrecognized tax benefits beginning balance	$	34,480	$	30,311
Gross decrease for tax positions of prior year	—		(93)
Gross increase for tax positions of prior year	307		615
Gross increase for tax positions of current year	2,966		3,647
Unrecognized tax benefits end balance	$	37,753	$	34,480

If fully recognized in the future, there would be no impact to the effective tax rate, and $34.7 million would result in adjustments to the valuation allowance. We do not have any tax positions that are expected to significantly increase or decrease within the next 12 months.

Interest and penalties, to the extent there are any, would be included in income tax expense. There were no interest or penalties accrued during or for the years ended December 31, 2020 and 2019.

We are subject to taxation in the United States and various states and foreign jurisdictions. We currently do not have any income tax examinations in progress nor have we had any income tax examinations since our inception. All of our tax years will remain open for examination by federal and state authorities for three and four years from the date of utilization of any net operating losses and tax credits.

The Tax Cuts and Jobs Act of 2017 ("Tax Act") includes a provision referred to as Global Intangible Low-Taxed Income ("GILTI") which generally imposes a tax on foreign income in excess of a deemed return on tangible assets. Guidance issued by the Financial Accounting Standards Board in January 2018 allows companies to make an accounting policy election to either (i)

account for GILTI as a component of tax expense in the period in which the tax is incurred ("period cost method"), or (ii) account for GILTI in the measurement of deferred taxes ("deferred method"). We elected to account for the tax effects of this provision using the period cost method.

The Coronavirus Aid, Relief, and Economic Security Act (the "CARES Act") was enacted in the United States on March 27, 2020. The CARES Act includes several U.S. income tax provisions related to, among other things, net operating loss carrybacks, alternative minimum tax credits, modifications to the net interest deduction limitations, and technical amendments regarding the income tax depreciation of qualified improvement property placed in service after December 31, 2017. The CARES Act does not have a material impact on our financial results for the year ended December 31, 2020.

Our accumulated undistributed foreign earnings as of December 31, 2020 have been subject to either the deemed one-time mandatory repatriation under the Tax Act or the current year income inclusion under GILTI regime for U.S. tax purposes. If we were to make actual distributions of some or all of these earnings, including earnings accumulated after December 31, 2017, we would generally incur no additional U.S. income tax but could incur U.S. state income tax and foreign withholding taxes. We have not accrued for these potential U.S. state income tax and foreign withholding taxes because we intend to permanently reinvest our foreign earnings in our international operations. However, any additional income tax associated with the distribution of these earnings would be immaterial.