Related party balances and transactions (Details) - USD ($)		Dec. 31, 2018	Dec. 31, 2017
Accounts receivable		$ 476,093	$ 632,704
Other receivable- GZ Highpower		1,570	533,134
Amount due from a related party- GZ Highpower		477,663	1,165,838
Other payable-investment	[1]	408,867	0
Loan from Mr. Dang Yu Pan	[2]	5,707,984	0
Amount due to related parties		$ 6,116,851	$ 0

[1] The Company signed an investment agreement with an aggregate amount of RMB4.9 million (approximately $0.7 million) in investing for 49% of the equity interest of V-power which was set up on March 1, 2018. On April 28, 2018, the Company injected RMB2.1million (approximately $0.3 million) to V-power, and the unpaid amount was recorded as amount due to a related party. (See Note 13)

[2] The Company entered into a loan agreement with a maximum amount of RMB60 million (approximately $8.8 million) with Mr. Dang Yu Pan on July 20, 2018. For the year ended December 31, 2018, the Company withdrew an aggregate amount of RMB39.45 million (approximately $5.9 million) and repaid an aggregate amount of RMB1.3 million (approximately $0.2 million). The interest rate is 5.65% per annum. The Company accrued interest expense $141,577 for the year ended December 31, 2018.