Is there reason to believe even a majority comes from renewable sources? And then, how much of that clean energy could be powering other things which are instead using fossil fuels?
At least in Europe, the lowest prices (even negative sometimes) for electricity are when renewable energies are producing a lot (e.g. when there's a storm in the north sea). If bitcoin mines are plugged on the real time market of electricity they would have an incentive to turn on when there's a lot of renewable energy produced. Assuming mines optimize their mining schedules on that, there's a scenario in which it could even help soak up the low prices and push investments into renewables.
Maybe, but only running miners when electricity is cheap doesn't work for a proof of work currency. 51% attacks would consist of an individual turning on their ASIC on a windless day. You need a large base load for it to be secure.
A lot of mining is done close to hydro dams, this power was in some cases waste power that would be unused. So it is swings and roundabouts, I don't think any new coal power stations are being built to mine bitcoin but bitcoin miners have taken advantage of excess electricity production to site their mines where power is cheapest.
I’d half remembered mining clusters near large hydro projects in China. As to the opportunity cost, getting the electricity from one place to another where it can be used if you have a local glut isn’t easy, aiui
