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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 | 9 Months Ended | ||
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Sep. 30, 2014
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Sep. 30, 2013
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Sep. 30, 2014
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Sep. 30, 2013
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| Revenue by Producks and Services [Line Items] | ||||
| Products | $ 1,094,529 | $ 779,455 | $ 5,047,231 | $ 3,639,974 |
| Services | 3,081,334 | 2,113,785 | 7,884,246 | 6,103,044 |
| Total revenues | 4,175,863 | 2,893,240 | 12,931,477 | 9,743,018 |
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Cogeneration
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| Revenue by Producks and Services [Line Items] | ||||
| Products | 626,223 | 457,486 | 3,200,073 | 2,441,740 |
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Chiller
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| Revenue by Producks and Services [Line Items] | ||||
| Products | 468,306 | 350,368 | 1,847,158 | 1,198,234 |
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Service Contracts [Member]
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| Revenue by Producks and Services [Line Items] | ||||
| Services | 1,808,154 | 1,734,588 | 5,503,010 | 5,331,210 |
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Installations [Member]
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| Revenue by Producks and Services [Line Items] | ||||
| Services | $ 1,273,180 | $ 379,197 | $ 2,381,236 | $ 771,834 |