Back of the envelope math: Assuming a fridge has two cubic meters of air and twenty liters of water (the heat capacity of all the food and metal inside the frid

Back of the envelope math: Assuming a fridge has two cubic meters of air and twenty liters of water (the heat capacity of all the food and metal inside the fridge) and takes the temperature from 70 F to just above freezing (20 C difference), there's a heat storage of 472 watt-hours, or 1.6% of the average daily electricity consumption. A 100 gallon (380 liter) hot water heater that raises water from 50 F to 120 F (40 C) can store 17.6 kWh, or just under 60% of daily household power use. Of course this was gonna be huge, and its a good opportunity, since in the mornings a house will use 40-80 gallons with the showers. I'm not sure how much of that is actionable, though. The water would have to stay hot all night. The average newly built house in the US is 2600 sqft, which is 20,800 cubic feet with 8' ceilings. With a 45 F temperature change (25 C) the air in that alone is 5 kWh, which honestly surprised me with how big it is. You'll never want your house to be changing temperature that much during the day, of course. You'd get crazy condensation and whatnot. By the straight math this could cover 17% of daily usage- that could go up by several times due to the heat capacity of the objects and materials in the house, but down by 5 times since you wouldn't want your house changing that much in temperature. Water/heat capacity would be a pretty decent way to store a large amount of electrical load, but I think it's gonna struggle to catch on. In northerly climates you could combine the hot water and home heating, but those places will struggle much more to get cheap solar power, which is 2.5-3x more expensive in the winter. Meanwhile southern climates will have solar power at 70% the price of the rest of the country, and it tracks the summer power demand increase well- but it's way harder to store your energy in cold water. Other than that it makes sense: while you're at work, the system cools down a large insulated tank of water, which it then circulates to a heat exchanger right before you come home. You can't use it for hot water though, and it'll be a lot bigger and more expensive than an AC. Basically it would be good for load leveling, but not overnight storage or seasonal storage. There aren't many indications that load leveling is actually a real problem. It'll probably just be solved with a smarter grid.