Annual report pursuant to Section 13 and 15(d)

Stockholders' equity - Stock Option Activity (Details)

Stockholders' equity - Stock Option Activity (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Exercise Price Per Share [Abstract]
Granted, Exercise Price Lower Range Limit (usd per share)	$ 4.50
Granted, Exercise Price Upper Range Limit (usd per share)	$ 5.39
Tecogen
Stock Options Outstanding [Roll Forward]
Beginning (shares)	1,148,000
Granted (shares)	318,325
Exercised (shares)	(101,575)
Canceled and forfeited (shares)	(8,425)
Expired (shares)	0
Ending (shares)	1,356,325	1,148,000
Exercisable (shares)	863,552
Vested and expected to vest (shares)	1,356,325
Weighted Average Exercise Price [Roll Forward]
Beginning (usd per share)	$ 2.13
Granted (usd per share)	$ 4.85
Exercised (usd per share)	$ 1.59
Canceled and forfeited (usd per share)	$ 3.52
Expired (usd per share)	$ 0.00
Ending (usd per share)	$ 2.77	$ 2.13
Exercisable (usd per share)	$ 2.65
Vested and expected to vest (usd per share)	$ 2.77
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Outstanding, Aggregate Intrinsic Value	$ 3,618,935	$ 2,721,100
Exercisable, Aggregate Intrinsic Value	2,287,760
Vested and expected to vest, Aggregate Intrinsic Value	3,618,935
Exercise Price Per Share [Abstract]
Outstanding, Exercise Price Lower Range Limit (usd per share)	$ 1.20	$ 1.2
Outstanding, Exercise Price Upper Range Limit (usd per share)	$ 5.39	$ 4.5
Canceled and Forfeited, Exercise Price Lower Range Limit (usd per share)	$ 0.12
Canceled and Forfeited, Exercise Price Upper Range Limit (usd per share)	$ 4.50
Expired, Exercise Price (usd per share)	$ 0
Ilois
Stock Options Outstanding [Roll Forward]
Beginning (shares)	575,000
Granted (shares)	100,000
Exercised (shares)	0
Canceled and forfeited (shares)	0
Expired (shares)	0
Ending (shares)	675,000	575,000
Exercisable (shares)	193,750
Vested and expected to vest (shares)	675,000
Weighted Average Exercise Price [Roll Forward]
Beginning (usd per share)	$ 0.29
Granted (usd per share)	$ 0.50
Exercised (usd per share)	$ 0.00
Canceled and forfeited (usd per share)	$ 0.00
Expired (usd per share)	$ 0.00
Ending (usd per share)	$ 0.32	$ 0.29
Exercisable (usd per share)	$ 0.50
Vested and expected to vest (usd per share)	$ 0.32
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Outstanding, Weighted Average Remaining Life	6 years 6 months 22 days	6 years 5 months 7 days
Outstanding, Aggregate Intrinsic Value	120,000	120,000
Exercisable, Aggregate Intrinsic Value	0
Vested and expected to vest, Aggregate Intrinsic Value	$ 120,000
Exercise Price Per Share [Abstract]
Outstanding, Exercise Price Lower Range Limit (usd per share)	$ 0.10	$ 0.10
Outstanding, Exercise Price Upper Range Limit (usd per share)	$ 0.50	$ 0.50
Granted, Exercise Price (usd per share)	$ 0.50
Exercised, Exercise Price (usd per share)	$ 0.00
Canceled and Forfeited, Exercise Price (usd per share)	$ 0.00
Expired, Exercise Price (usd per share)	$ 0.00
Stock Options \| Tecogen
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Outstanding, Weighted Average Remaining Life	5 years 1 month 15 days	5 years 9 months 20 days