Cost of revenues and general and administrative expenses (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cost of revenues and general and administrative expenses [Line Items]
Cost of Revenue	$ 36,872,165	$ 33,624,821	$ 33,807,982
Electricity [Member]
Cost of revenues and general and administrative expenses [Line Items]
Cost of Revenue	9,832,128	9,037,347	10,675,287
Depreciation [Member]
Cost of revenues and general and administrative expenses [Line Items]
Cost of Revenue	5,666,394	5,355,529	5,270,454
Fuel oil [Member]
Cost of revenues and general and administrative expenses [Line Items]
Cost of Revenue	5,183,186	4,210,542	4,974,421
Employee costs [Member]
Cost of revenues and general and administrative expenses [Line Items]
Cost of Revenue	5,666,972	5,541,983	4,287,783
Cost of plant sales [Member]
Cost of revenues and general and administrative expenses [Line Items]
Cost of Revenue	0	142,151	878,396
Maintenance [Member]
Cost of revenues and general and administrative expenses [Line Items]
Cost of Revenue	2,613,573	3,545,265	3,436,736
Retail license royalties [Member]
Cost of revenues and general and administrative expenses [Line Items]
Cost of Revenue	1,537,879	1,528,914	1,427,073
Insurance [Member]
Cost of revenues and general and administrative expenses [Line Items]
Cost of Revenue	944,975	992,374	1,187,097
Materials [Member]
Cost of revenues and general and administrative expenses [Line Items]
Cost of Revenue	2,910,514	1,280,794	0
Other [Member]
Cost of revenues and general and administrative expenses [Line Items]
Cost of Revenue	$ 2,516,544	$ 1,989,922	$ 1,670,735