Quarterly report pursuant to Section 13 or 15(d)

Description of business and summary of significant accounting policies - Revenue by Product Line and Services (Details)

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Description of business and summary of significant accounting policies - Revenue by Product Line and Services (Details) - USD ($)
 3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Revenue by Producks and Services [Line Items]        
Products $ 2,850,901 $ 1,860,860 $ 7,525,909 $ 8,744,306
Services 3,765,554 2,815,182 9,853,369 8,419,001
Total revenues 6,616,455 4,676,042 17,379,278 17,163,307
Cogeneration        
Revenue by Producks and Services [Line Items]        
Products 2,639,713 1,493,335 5,328,184 6,592,075
Chiller & Heat Pump        
Revenue by Producks and Services [Line Items]        
Products 211,188 367,525 2,197,725 2,152,231
Service Contracts        
Revenue by Producks and Services [Line Items]        
Services 2,113,295 1,921,897 6,384,261 5,829,304
Installations        
Revenue by Producks and Services [Line Items]        
Services $ 1,652,259 $ 893,285 $ 3,469,108 $ 2,589,697