i think this is the answer
SEP 2017 data are as follows. It has increased by 50% now.

<sub>At $0.12 kW/h a Bitcoin costs $1,567.88 to mine.

At $0.04 kW/h a Bitcoin costs $522.62 to mine.

This, of course, does not include hardware and other costs.</sub>


from：https://grisha.org/blog/2017/09/28/electricity-cost-of-1-bitcoin/