Annual report pursuant to Section 13 and 15(d)

Summary of significant accounting policies - Revenue (Details)

v3.19.1
Summary of significant accounting policies - Revenue (Details) - USD ($)
 9 Months Ended 12 Months Ended
Sep. 30, 2018
Dec. 31, 2018
Disaggregation of Revenue [Line Items]    
Revenue   $ 35,883,684
Payment Term on Product Sales 30 days  
Payment Term on Energy Production Contract Invoices   30 days
Unbilled revenue recognized   $ 2,200,000
Revenue billed that was recognized in previous periods   1,600,000
Deferred revenue recognized   3,000,000
Increase in deferred revenue   4,500,000
Cash payments received   1,600,000
Remaining performance obligations   $ 16,600,000
Performance obligation recognized over next 24 months (percent)   96.00%
Performance obligation recognized over next 12 months (percent)   45.00%
Performance obligation recognized in subsequent 12 months (percent)   51.00%
Product [Member]    
Disaggregation of Revenue [Line Items]    
Revenue   $ 12,624,867
Installation Services [Member]    
Disaggregation of Revenue [Line Items]    
Revenue   8,097,473
Maintenance Service [Member]    
Disaggregation of Revenue [Line Items]    
Revenue   8,761,818
Energy Production    
Disaggregation of Revenue [Line Items]    
Revenue   $ 6,399,526
Light Installation [Member]    
Disaggregation of Revenue [Line Items]    
Payment Term on Installation Services   30 days
Turnkey Installation [Member]    
Disaggregation of Revenue [Line Items]    
Payment Term on Installation Services   30 days
Energy Production    
Disaggregation of Revenue [Line Items]    
Revenue   $ 6,399,526
Energy Production | Product [Member]    
Disaggregation of Revenue [Line Items]    
Revenue   0
Energy Production | Installation Services [Member]    
Disaggregation of Revenue [Line Items]    
Revenue   0
Energy Production | Maintenance Service [Member]    
Disaggregation of Revenue [Line Items]    
Revenue   0
Energy Production | Energy Production    
Disaggregation of Revenue [Line Items]    
Revenue   6,399,526
Product and Service    
Disaggregation of Revenue [Line Items]    
Revenue   29,484,158
Product and Service | Product [Member]    
Disaggregation of Revenue [Line Items]    
Revenue   12,624,867
Product and Service | Installation Services [Member]    
Disaggregation of Revenue [Line Items]    
Revenue   8,097,473
Product and Service | Maintenance Service [Member]    
Disaggregation of Revenue [Line Items]    
Revenue   8,761,818
Product and Service | Energy Production    
Disaggregation of Revenue [Line Items]    
Revenue   0
Certain Energy Production Related Assets    
Disaggregation of Revenue [Line Items]    
Increase in deferred revenue   $ 2,000,000