If power is so cheap mid-day, why don't european buildings have sufficient air conditioning not to kill the elderly during heat waves? The laws restricting AC all have power conservation as their rationale.
Certainly a lot of the young wealthy people I know in Europe have AC, even outside of the really hot places.
Most European homes don't have the kind of window that you could stick an AC in, the windows hinge rather than sliding up and down. You can get one of those floor units with a hose for probably ~€300 though.
https://56paris.com/en/cooling-paris-from-below-the-city-s-u...
The cooler parts of the US (e.g. the PNW) are also gradually increasing AC adoption as things heat up, but 20 years ago it was pretty much unheard of.