> It's not obvious that your mostly-idle plant is a better business than a much smaller one which runs all the time.

This process is usually not profitable because of the energy cost it requires. This is why I am proposing it as a way to absorb energy surplus. But I am only talking about what would happen if you got electricity at zero cost. At negative costs, even crazier things would happen.

The reality, is that, to my knowledge, the Australian grid does not "sell" electricity for negative prices, it only "buys" it. If it were to pay clients to absorb electricity, I would just dissipate heat in well ventilated radiators, make a ton of steam, and make a show of giant tesla coils. Radiators can be made out of scrap metal, it really is a small investment that can lie dormant at no cost if negative electricity prices only happen 5% of the time.

Could you please show the calculation of what it costs to build and maintain such a scrap metal radiator thing, and how much money you would have made with such a device over the last 12 months?

"dissipate heat in well ventilated radiators": you've just invented a https://en.wikipedia.org/wiki/Cooling_tower , often the largest building at a power plant.