Description of business and summary of significant accounting policies - Revenue by Product Line and Services (Details) - USD ($)  | 
3 Months Ended | |
|---|---|---|
Mar. 31, 2016  | 
Mar. 31, 2015  | 
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| Revenue by Producks and Services [Line Items] | ||
| Products | $ 2,266,148 | $ 3,537,875 | 
| Services | 2,809,367 | 2,565,559 | 
| Total revenues | 5,075,515 | 6,103,434 | 
| Cogeneration | ||
| Revenue by Producks and Services [Line Items] | ||
| Products | 1,417,972 | 2,571,928 | 
| Chiller | ||
| Revenue by Producks and Services [Line Items] | ||
| Products | 848,176 | 965,947 | 
| Service Contracts | ||
| Revenue by Producks and Services [Line Items] | ||
| Services | 2,188,322 | 1,872,366 | 
| Installations | ||
| Revenue by Producks and Services [Line Items] | ||
| Services | $ 621,045 | $ 693,193 | 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Definition Aggregate revenue during the period from the sale of goods in the normal course of business, after deducting returns, allowances and discounts. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Aggregate revenue during the period from services rendered in the normal course of business, after deducting allowances and discounts. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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