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Could I build a sand battery to store energy for winter?
One of the biggest energy requirements in my house in Bavaria (Germany) is heat. My wife and I needed about 24,000 kWh ( 2450 L of oil) per year . About 1,900 kWh (194L of oil) per year is for warm water.
Let’s say a sand battery becomes interesting if it can cover at least 10%, so 2,400 kWh.
I assume that we can extract heat until it’s about 15°C and we could heat it up to about 100°C. That is a temperature change of 85°C.
Energy = 840J/kg°C × 2.7×10–7 kWh/J × mass × temperature change
2400 kWh = 0.22 kWh/ ton °C × m ×85°C
m = 128 tons
Dry sand has a density of 1602 kg/m3. So 77m³ of dry sand would be required, e.g. 5m x 6m x 2.6m. That hole would need to be insulated and have pipes within it.
That is gigantic.
1m³ of sand is about 20€/m³. It’s astonishingly cheap, but it would still be 1540€ just for the sand. No digging, no insulation, no pipes.
Including the sand storage into the buildings construction
Obviously, it does not work in my case of an old house with a comparatively small garden. But maybe it’s interesting for new homes? I wonder if the foundation of the house could rest on such a sand head storage. I wonder if that would make the house more stable. What effects would it have it the bottom of the cellar was (very) warm? Probably the foundation would need to be insulated against the sand heat storage, but still the ground floor would likely be warm.
If the house has a cellar, the sand heat storage could surround it:
This way the whole cellar, excluding the foundation, would have warm walls. Again, likely it would make sense to have insulation between the heat storage and house. But mold in the cellar would have no chance 😄 Also, water getting into the building…
