It's a misconception to think a miner will only locate on energy sites with continuous supply. It can still make perfect sense for a miner to locate on a site with variable demand (which by the way is basically every energy production site in the world that is by design compelled to build to accommodate peak demand). What a miner will do is then negotiate energy costs (which are 80-90% of their variable costs) with the producer who is happy to sell his excess production at any cost above 0 for all excess power untapped. All it takes is enough excess production at a (much lower) price than conventional rates for this to breakeven positively vs full operation alternatives.

As chips commoditize and energy trends towards 100% of all costs, miners will step into these situations exclusively.

As far as your claim that bitcoin is useless that's a personal judgement. My personal judgement is that reintroducing sound fixed supply censorship resistant money to the world is of enormous benefit. But that's beyond the scope here. I don't think it's constructive to make judgements about what people value and chose to expend resources towards. If you have a problem with externalities then have a debate about that. But who are we to judge if someone wants to heat their pool? If they do so through carbon emissions then consider taxing that. The sustainability of the energy production is your issue really, not the energy use.