Renewables have been cheaper (in monetary and carbon) than running existing coal plants for a while. Even more so if you reuse the sites grid connection. So it still doesn't add up to me.

Clearly the couldn't sell energy before if they were about to shutdown, so there must be something different about the miners compared with their usual market, can't just be cheaper.

In the article they seem to be suggesting they couldn't buy renewable power in 2020 which seems odd, but no follow up detail on it, apparently they're phasing coal out in a year so it may just have been a short term thing.