Related party balance and transaction (Details) - USD ($)		Jun. 30, 2018	Dec. 31, 2017
Accounts receivable		$ 431,508	$ 632,704
Other receivable		812	533,134
Amount due from a related party- GZ Highpower		432,320	1,165,838
Other payable-investment (1)	[1]	423,236	0
Amount due to a related party- V-power		$ 423,236	$ 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 7)