> Even with renewable energy there's an opportunity cost - you can sell it back to the grid. Plus the fixed costs of buying the solar panels and mining equipment in the first place.

In many cases this doesn't matter, as it 's being paid by someone else. Millions of teenagers mining crypto on their GPUs, their parents pay for electricity, what about enthusiasts? They will mine even if price is higher than the value of the bitcoin, there are bitcoin mines that steal electricity from the grid etc.

And as I wrote before, this is self regulating mechanism, difficulty is adjusted every 2016 blocks. Less miners? then less power needed to mine the block, which means less resources/money needed to mine the block. Price of electricity dosen't matter.