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Description of business and summary of significant accounting policies - Revenue by Product Line and Services (Details) (USD $)
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3 Months Ended | 6 Months Ended | ||
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Jun. 30, 2014
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Jun. 30, 2013
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Jun. 30, 2014
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Jun. 30, 2013
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| Revenue by Producks and Services [Line Items] | ||||
| Products | $ 2,007,926 | $ 807,854 | $ 3,952,702 | $ 2,860,519 |
| Services | 2,531,931 | 1,995,606 | 4,802,912 | 3,989,259 |
| Total revenues | 4,539,857 | 2,803,460 | 8,755,614 | 6,849,778 |
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Cogeneration
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| Revenue by Producks and Services [Line Items] | ||||
| Products | 1,419,581 | 457,486 | 2,573,850 | 1,735,642 |
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Chiller
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| Revenue by Producks and Services [Line Items] | ||||
| Products | 588,345 | 350,368 | 1,378,852 | 1,124,877 |
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Service Contracts [Member]
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| Revenue by Producks and Services [Line Items] | ||||
| Services | 1,921,875 | 1,848,675 | 3,694,856 | 3,596,621 |
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Installations [Member]
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| Revenue by Producks and Services [Line Items] | ||||
| Services | $ 610,056 | $ 146,931 | $ 1,108,056 | $ 392,638 |