this post was submitted on 04 Sep 2024
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Yeah, this should really be the future. There's a lot of unnecessary materials used/energy wasted to give us our current "all power costs the same all the time" system.
According to this, about 70% of US household energy use is heating/cooling the space, or water. Much of that can be time shifted. What can't be time shifted can be stored in cheaper ways than battery storage.
1 tonne of rock heated (or cooled) 20° C above ambient is a store of about 4.7 kWh. According to that same site, the average yearly energy use in the US is 10500 kWh. If 70% is heating/cooling, that's about 20 kWh per day, so you'd need about 5 tonnes of rock to hold that enough energy. That seems like a lot, but it's just about 2 cubic meters of rock.
If you use water, it has 5 times the specific heat (but less density), so you only need 1 cubic meter. Probably easier to heat/cool/use, too. Water can also be heated more than 20 degrees above ambient, too.
Really, we should create incentives for homes to be built with high thermal mass. Even without any sort of fancy direct heating or cooling of a thermal mass, it will store significant heat.
Welcome to traditional housing in Italy and probably elsewhere in the Mediterranean region. Thick stone walls even out the temperature swings through the day. Throw open the windows when the temperature is comfortable and close up when it gets too hot or cold depending on the season. This gets you quite far without any air-conditioning or heating.
My old house had an electric boiler that would automatically heat up at night when electricity was cheap. They have fallen out of fashion in the past two decades or so around here, but I can see them making a come back.
Of course that was direct resistive heating. Stick a heat pump in there and you got something.
Wait until you calculate how much energy you need to tip over to the freezing point for water!
Yeah, freezing water is definitely great. It's just a little trickier to deal with since you need to account for the expansion, and the fact that you can't pump it around anymore.
Ha ha true, I was mostly jesting but also because I was blown away when I found out.