Property, plant and equipment and construction in progress (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 133,052,311	$ 126,438,769
Less accumulated depreciation	71,803,332	67,557,951
Property, Plant and Equipment, Net, Total	61,248,979	58,880,818
Construction in progress	1,335,597	6,015,043
Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,566,537	3,435,361
Building [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	23,176,106	19,829,575
Plant And Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	64,840,636	61,777,836
Distribution Systems [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	36,538,614	36,057,078
Office furniture, fixtures and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,061,315	3,635,184
Vehicles [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	1,582,053	1,431,719
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	272,092	244,221
Lab equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 14,958	$ 27,795