> In Alberta, Canada, the homes of the Drake Landing Solar Community (in operation since 2007), get 97% of their year-round heat from a district heat system that is supplied by solar heat from solar-thermal panels on garage roofs. This feat – a world record – is enabled by interseasonal heat storage in a large mass of native rock that is under a central park. The thermal exchange occurs via a cluster of 144 boreholes, drilled 37 metres (121 ft) into the earth. Each borehole is 155 mm (6.1 in) in diameter and contains a simple heat exchanger made of small diameter plastic pipe, through which water is circulated. No heat pumps are involved.
That development is 52 homes. They are presumably engineered to be highly energy efficient and it's not a perfect comparison to sand, but it's less than I'd have imagined.
I live in Calgary and have seen a few articles about Drake Landing recently.
Small ground sources, or ground sources with neighbors too close who do the same, will actually accumulate noticeable ground cooldown from season to season if they are not replenished. Free air conditioning comfort from the replenishing effort, or free replenishing from the air conditioning, you can spin it however you like. It's very low gradient and certainly won't get you through winter without a another power source, but it absolutely is seasonal heat storage.
So this would be like, in a mild climate, the sun is going to keep your house warm during the day and you are generating some solar. You use the solar to heat up the sand, and then overnight, you recover some of that energy to use for heat. (I think you can get electricity back out of the heated sand as well, but it's like 70% efficient compared to >90% for a lithium battery. So I think the big application is in heating, less for charging your car after you get home from work.)
https://www.euronews.com/green/2024/03/10/sand-batteries-cou...
This is 8MWh (of heat), the 1000 gallon oil tank is about 40MWh.
Something like a two story basement filled with sand at the maximum temperature of a home oven is probably in the ballpark.
That's a massive fire risk because it is combustible fuel. A pile of hot sand in an auxilary, non-flammable structure isn't going to catch fire.
1000 gallons of sand (about 6000 kg) heated 1000 °C above ambient stores about 1000 K * 6000 kg * 1.1 kJ/kg-K (from the paper, on page 9) = 6.6 gigajoules.
So to match a fuel tank for energy storage, it needs to be at least 22x the volume, have extremely good insulation (even more volume), a heat-exchanger, and sand-handling augers. Additionally, the sand needed to be heated in the first place, which means a good electrical connection, but if you have that power in the first place, just use that during the winter? The nice part about fuel is that a man and a truck can move a few thousand gallons of hydrocarbons several hundred miles out to the middle of nowhere and transfer that energy at megawatt speed with a hose.
I am not planning on doing this, but explaining it on a scale that I can relate to would be helpful, because I know, for example, that said house can store a winter's worth of heat in a 1000 gallon oil tank, or small woodshed big enough for 6 cords of wood.