Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2012

Schedule of Accrued Warranty Activity

Accrued warranty activity consisted of the following for the periods presented (in thousands):

	Three Months Ended, September 30						Nine Months Ended, September 30
	2012			2011			2012			2011
Accrued warranty—beginning of period	$	5,723		$	6,289		$	6,315		$	5,417
Warranty costs incurred		(958	)		(851	)		(2,640	)		(2,078	)
Provision for warranty		1,455			973			2,545			3,072
Accrued warranty—end of period	$	6,220		$	6,411		$	6,220		$	6,411

Summary of Accounts Receivable in Excess of 10% of Total Accounts Receivable

The following summarizes the accounts receivable in excess of 10% of our total accounts receivable:

	September 30, 2012			December 31, 2011
Customer A		43	%		52	%
Customer B		27	%		—
Customer C		17	%		38	%

Schedule of Potential Common Shares Outstanding That Were Excluded from Computation of Basic and Diluted

The following table presents the potential common shares outstanding that were excluded from the computation of basic and diluted net loss per share of common stock for the periods presented:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2012		2011		2012		2011
Period-end stock options to purchase common stock		24,797,047		15,496,749		24,797,047		15,496,749
Period-end Department of Energy warrant to purchase common stock (1)		3,090,111		3,090,111		3,090,111		3,090,111
Period-end common stock subject to repurchase		—		486		—		486

(1) See Note 6 for Department of Energy (DOE) warrant