Underground “battery” storage

So you know how geothermal heating works, right? Pull hot water up from the ground, extract the heat to run a turbine or whatever, and inject the water back into the ground for another cycle.

Now Hamburg Germany is going to try reversing the process. Heat the water via waste heat from steel mills or aluminum foundries, or even solar or wind, put the hot water a mile under the surface, then pull it up to use when you want. It turns “intermittent” into, uh, mittent, I guess.


World’s largest thermos bottle: the earth.


I could only read the beginning of the first paragraph of the linked article because I am not a subscriber to Bloomberg.

But I do have some questions and observations. If the waste heat is of high enough enthalpy, why not just build a co-generation plant on the steel mill or aluminum foundry? From what I can find out, those metal smelting operations go on 24 hours a day, 7 days a week in a typical mill. It would be more efficient and cheaper to just use the heat directly than going through this underground burial process. If the waste heat is not of sufficient enthalpy, then pumping it underground isn’t going to help anyway.

Using truly intermittent wind or solar to heat up water is another matter, but pumping the water underground seems like too much trouble. Above ground tanks, sufficiently insulated, would work just as well. This has been used or contemplated for certain thermal solar power plants. They can also use other materials, such as molten sodium, as the heat transfer fluid. This might have certain advantages over high temperature and high pressure water.

One example of a co-generation power plant used at a steel mill.

  • Pete