In Germany there are already Smart Electricity suppliers which also provide a Wallbox in order to automatically charge your car whenever certain price threshold is reached. You could for example configure it to charge your car when prices are even negative. That's not so common anymore, but we had a price of -0.08€/kWh on 21.05.2021. 10 days ago, the prices were also pretty low (0.02€).

https://www.awattar.de/tariffs/hourlycap

Nice theory, assumes that prices stay below your threshold long enough for the car to charge. It can happen, as your examples show, but can it happen at scale, i.e. when 1 in 10 people are running "full house equivalent" energy requests every time the price drops below say 0.02 EUR/kWh?

Been pricing electicity derivatives at work last week; with that context I'm now thinking of your scheme as a limit order, and what happens when the market is oversaturated with limit order?

Night-time electricity can be practically free at times, since people are asleep and a lot of businesses aren't operating. You just need to be on a plan where you pay different rates during the day and night.

South Sweden, if we didn't export huge amounts of energy to Germany and shut down 4 nuclear plants (With 20+ years left of life), it would be a permanent < 0.06/KwH.