[WalterBright]

I've had power outages for a week more than once, and can vouch for it staying warm enough for a comfortable shower for a couple days.

For HVAC, you can heat/cool it at a minimum to the edge of the comfort range, which will make a big difference. You can take it much further by heating/cooling some thermal mass, and drawing on that mass when the electricity is cheaper.

That mass can simply be a pile of stones in a box with some ductwork added. It's hard to find a cheaper "battery" technology than a box of rocks.

Frankly, I think people are way too focused on batteries and are overlooking the rather obvious.

[xyzzyz]

Water has really good thermal mass already. I think that adding huge water tanks in basements would be pretty beneficial: if the water in those tanks is operated in closed cycle, minerals from water wouldn't accumulate, and if we used rust proof materials, they tanks could last for the lifetime of the house. Then, we could use them to store heat in winter and cold in summer, when electricity is cheap.

[epistasis]

District heating already deploys rather large thermal storage in surprisingly compact volumes. The picture here is 2GWh:

https://en.wikipedia.org/wiki/District_heating#Heat_accumula...

When powered by heat pumps, I imagine this could be used for cooling in the summer as well.

[_ph_]

There were concept houses in Germany, where they had a water tank of 6 cubic meters which was heated through the summer via thermal solar collectors and stored enough energy for the house heating in the winter (and even in the winter the collectors would collect heat on sunny days).

[trhway]

>a pile of stones in a box with some ductwork added

man, the beauty in our lives disappears. Imagine that heated by electricity (especially if during cheap period) instead of coal/wood, and how great it is to sleep on or right next to such a stove (my grandmother house had one :):

https://www.lowtechmagazine.com/2008/12/tile-stoves.html

[bregma]

I don't know about you, but I live in a log cabin in the back woods of Canada and have only wood stoves lined with bricks to keep me warm in winter (and we have a real Winter here). The cook stove has a cistern (water tank) for greater thermal mass and the stoves have baffles for high efficiency. The fuel grows all around me do it's carbon neutral (except for the chainsaw gas, but that's a luxury I will not forego).

This is not a used-to-was thing. It's the norm outside of towns in my county.