3 ms·

Use sand [1] instead of water and you'll be able to store a lot more energy in a limited area. Water can't be heated above 98°C at atmospheric pressure which pu

Use sand [1] instead of water and you'll be able to store a lot more energy in a limited area. Water can't be heated above 98°C at atmospheric pressure which puts a limit on how much energy can be stored per m³ while sand can be heated above 1000°C without problems. Add enough insulation and you'll be able to store enough heat to warm your house through the long winter. Sand is cheap, non-corrosive and doesn't freeze or boil [2]. The specific heat for sand (830 J/g K) is markedly lower than that for water (4000 J/g K) but the density is ~50% higher. Together with the much higher temperature spectrum this translates to a higher capacity per m³. [1] https://polarnightenergy.fi/technology https://polarnightenergy.fi/technology [2] it can boil - silicon boils at 3265°C - but it is hard to see how such a temperature can be reached

flaviut 4y ago
Residential water heaters, at least in the USA, don't typically go above 60°C. So there's room to grow here, at least for now, without building a more exotic, and therefore expensive, system.
- tpm 4y ago
  And the reason they don't go much higher could be that at higher temps water hardness starts depositing water stone on the heating element and lining.
- goodpoint 4y ago
  There's nothing exotic in a storage heater. They've been extremely common in UK for many decades. A resistor, some bricks and some insulation. If anything they are too rudimentary.
wongarsu 4y ago
> doesn't freeze In the sense that something that is frozen can't freeze. Apparently the melting point of sand is about 1700°C, so 1000°C sand indeed should handle about the same as 20°C sand or -100°C sand. That does sound rater neat for a large scale setup. In a small-scale setup the convection currents, easy handling and lower insulation requirements of a water setup would probably still win out.
- _0w8t 4y ago
  If water tank holds water above 70C, it’s safety requirements make it significantly more expensive. Plus water close to the boiling temperature is rather corrosive. So I cannot rule out that even for small scale sand setup will be cheaper.
skeptically 4y ago

flaviut 4y ago

Residential water heaters, at least in the USA, don't typically go above 60°C. So there's room to grow here, at least for now, without building a more exotic, and therefore expensive, system.

tpm 4y ago
And the reason they don't go much higher could be that at higher temps water hardness starts depositing water stone on the heating element and lining.
goodpoint 4y ago
There's nothing exotic in a storage heater. They've been extremely common in UK for many decades. A resistor, some bricks and some insulation. If anything they are too rudimentary.

wongarsu 4y ago

> doesn't freeze In the sense that something that is frozen can't freeze. Apparently the melting point of sand is about 1700°C, so 1000°C sand indeed should handle about the same as 20°C sand or -100°C sand. That does sound rater neat for a large scale setup. In a small-scale setup the convection currents, easy handling and lower insulation requirements of a water setup would probably still win out.

_0w8t 4y ago
If water tank holds water above 70C, it’s safety requirements make it significantly more expensive. Plus water close to the boiling temperature is rather corrosive. So I cannot rule out that even for small scale sand setup will be cheaper.

skeptically 4y ago