No idea.

Even if it was a mix of renewable (e.g., wind and solar) and carbon-based (e.g., natural gas), the only way it makes sense to use this for bitcoin mining is when the generation capacity is in excess of demand, and thus available to Riot at a low price.

And then when the grid demand is such that that the market will pay a higher price, Riot can assist in providing additional capacity for the grid (by powering down their equipment).

This is what makes it so that a grid that uses intermittent renewables can work without suffering repeated unplanned outages, "load shedding", and such.