[chickenbig]

The big question is how much it will cost. For comparison I believe there is a heat battery in Germany using (atmospheric pressure) liquid water (98 C), 50M EUR for perhaps 20x the thermal storage capacity (versus 20 C water).

The use of sand, presumably heated to a much higher temperature than the boiling point of water, seems overkill for district heating (unless peak heat demand requires flow temperatures above 100 C). But it does reduce the volume of sand required, so the size of the storage system.

[jillesvangurp]

The cost is a function of the size and mass. So, more heat capacity and less mass means lower cost per mwh.

These things are extremely simple and fairly efficient. It's resistive heating (wires and spools) of a thermal mass (sand/stone) in some kind of container (a simple silo) with a lot of insulation and some pipes to heat up water. Higher temperatures mean getting the heat out is easier and that the battery will work for longer. Basically until the temperature drops below the required temperature.

[chickenbig]

> So, more heat capacity and less mass means lower cost per mwh.

Can you compare different technologies with these scaling laws? Also what are the limits of these approximations (e.g. taking temperatures to extremes tends to run into maintenance problems).

In this case the sand battery delivers 400 C steam from 600 C sand [0], via some heat exchange fluid (solar salt?) that flows next to the sand. Going through heating/cooling cycles can cause material issues, especially for larger temperature differences.

[0] https://polarnightenergy.com/sand-battery/

[Ekaros]

Required temperature is 65 to 115... If you are already above those you only need simpler and cheaper heat exchanger instead of more complex heatpump.

[Hamuko]

>The use of sand, presumably heated to a much higher temperature than the boiling point of water

600°C according to their website.