Stock-Based Compensation

Stock Options

The following table summarizes the activity for all stock options under all of the Company’s equity incentive plans for the six months ended June 30, 2018 (shares and aggregate intrinsic value in thousands):



	Number of Options		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic Value
Outstanding at December 31, 2017	16,268		$	5.70	7.41	$	14,832
Granted	1,436		8.33
Exercised	(1,529	)	5.25
Cancelled / forfeited	(480	)	4.33
Outstanding at June 30, 2018	15,695		$	5.94	7.27	$	114

Options vested and exercisable at June 30, 2018	8,624		$	5.52	6.18	$	66,074

Restricted Stock Units

The following table summarizes the activity for all restricted stock units (“RSUs”) under all of the Company’s equity incentive plans for the six months ended June 30, 2018 (shares in thousands):



	Number of Awards		Weighted Average Grant Date Fair Value
Unvested balance at December 31, 2017	5,330		$	5.82
Granted	1,778		8.12
Issued	(1,206	)	6.57
Cancelled / forfeited	(820	)	6.72
Unvested balance at June 30, 2018	5,082		$	6.49

Employee Stock Purchase Plan

Under the Company's amended 2015 Employee Stock Purchase Plan ("ESPP"), eligible employees are offered shares bi-annually through a 24-month offering period which encompasses four six month purchase periods. Each purchase period begins on the first trading day on or after May 15 and November 15 of each year. Employees may purchase a limited number of shares of the Company’s common stock via regular payroll deductions at a discount of 15% of the lower of the fair market value of the Company’s common stock on the first trading date of each offering period or on the exercise date. Employees may deduct up to 15% of payroll, with a cap of $25,000 of fair market value of shares in any calendar year and 10,000 shares per employee per purchase period.

Stock-Based Compensation Expense

The Company recognized stock-based compensation expense, including ESPP expenses, in the consolidated statements of operations as follows (in thousands):



	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Cost of customer agreements and incentives	$	667	$	1,110	$	1,279	$	1,861
Cost of solar energy systems and product sales	186		156		357		270
Sales and marketing	834		807		4,984		2,724
Research and development	311		186		605		335
General and administration	3,549		3,256		9,017		6,199
Total	$	5,547	$	5,515	$	16,242	$	11,389

In August 2017, the Company entered into an agreement with an affiliate ("Contractor") of Comcast Corporation ("Comcast") whereby Contractor will receive lead or sales fees for new customers it brings to the Company over a 40-month term. The Company also issued Comcast a warrant to purchase up to 11,793,355 shares of the Company's common stock, at an exercise price of $0.01 per warrant share. The warrant initially vests 50.05% when both (i) Contractor has earned a lead or sales fee with respect to 30,000 of installed solar energy systems, and (ii) Contractor or its affiliates have spent at least $10.0 million in marketing and sales in connection with the agreement. Thereafter, the warrant will vest in five additional increments for each additional 6,000 installed solar energy systems. As of June 30, 2018, none of the shares under this warrant have vested.