It's almost all hydro power every thing else is too expensive to be competitive.

If the miners weren't tapping all the hydro power they wouldn't have to burn as much coal to power the rest of the country.

Miner is an ideal consumer of the electricity, doesn't have peak hours, can put equipment near the hydro power plant, so it is very likely a lot of this energy has been just wasted before c. 2013-2014.

The entire Bitcoin network consumes about 2GW at the moment, which is something but not much compared to China's total generation capacity which iirc is something like 900GW

Probably less, see http://blog.zorinaq.com/bitcoin-electricity-consumption/#eco...