We already have a solution to all our energy needs. Funny to see people come up with outlandish suggestions. I am not sure what I am missing. Because logic points to only one direction.

I don't think there is a viable solution for buffering solar or wind (or nuclear) with renewable sources, unless you happen to have access to a lot of hydro power.

Dynamic remote cut-off of heaters, chargers, and other non-critical consumers is one suggestion, but the equipment cost is probably at least 100 Eur per consumer.

Well... Outlandish is to think that replacing a huge amount of infrastructure of a type to another is as simple as your sentence makes it look like.

By no measure is reverse osmosis or flash distillation of water cheap even if the energy is free.

Imagine building a huge water desalination plant and only running it when there is excess power available on the grid.

I can't see anyone wanting to invest in that, except maybe a financially myopic government, and they tend not to last very long.

If the energy is free, you could just do electrolysis with huge carbon electrodes and immediately ignite the gases, bubbling the exhaust through your freshwater reservoir. You can knock together a setup like that in your own backyard from junkyard parts.

How you do it depends on whether you prioritize capital costs or operating costs.