You're exaggerating a bit. Water heater will stay hot for a day or so, but will rapidly cool when you start using it and cold water flows in. House will be uncomfortably cold after a few hours in the wintertime if the heat is not running, and it's not really practical to overheat it when electric rates are low/free because you can only go maybe 10 degrees before it's really too warm for comfort. You'd need a heat tank of some sort which complicates the system and as a practical matter homes don't have that and might not have space for.

Finally aside from all that I heat my water and my home with natural gas.

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.

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.

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.

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).

>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

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.

A lot of these issues "house will be uncomfortable cold" are because the way houses have been built previously (and still are in a lot of places) is horribly inefficient. In my country (it's -5c outside now, so not exactly warm) the building standards dictate new houses must consume no more than 15W/m2/year of heat energy for heating.

To convert that to US units, that means a 3000sqft house somewhere were electricity is $0.15c/kWh would cost $600/year to heat from electric baseboard heaters. If you have a heat pump you could bring that down to $200/year - and that's before you even consider solar.

I live in a 5 year old apartment, and haven't even turned on the heating this season, but it's still a comfortable 20c/68F inside.

It's technically possible to store heat for several months, e.g. in a large water tank, and use that heat over the winter. Only really feasible for very thermally efficient houses, but it can be done: https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storag...

The obvious solution is not to let cold water flow into the water heater unless you have the electricity to heat it - and if needed make it a bit larger so there is more buffering capacity.

No need for internet connected anything. But there is a need for a "smart grid".

We, in France, have a very primitive system based peak / off-peak hours used in many houses, and I expect other countries to have the same kind of system since it is so simple.

Basically, you have an extra wire coming out of the meter. If there is voltage, it is peak hours, if there is no voltage, if is off-peak. To that wire, you connect a relay which sits in the breaker panel. That relay can turn a circuit on or off, often the water heater, so that it only runs off-peak. You can force it on if you know you are going to use more hot water than usual.

Such a simple thing, but updated in real time can already go a long way. In a more advanced system, the meter could tell you the price of electricity via PLC and you could have a relay in your breaker box that turns on a circuit depending on price.

Even smarter devices could receive the signal from the meter directly and do more things, for example, many appliances have a "delayed start" function. A "start when electricity is cheap" function would be a great addition.

The problem is that would require standardization. A standard protocol shared by utilities and electric device manufacturers. As for communication, PLC sounds ideal, it doesn't have to be fast, and it could also be the same signal used by the utility to remotely check the meter for billing (something that is being deployed in France, BTW).