Wonder if anyone can set my mind at ease and tell me that this is impossible;
The mission is to store heat (in form of heated water), from solar or other source. You will need a piece of land, 25.000+ sq metres. Depth before you reach groundwater 15+ metres.
The soil should ideally be able to absorb water. The water is "seeped" (not sure this is the correct word) into the ground, leaving the heat in the ground, principle known from "seeping" down grey water. A size of 30.000 cubic metres is necessary in order to overcome losses from no insulation of the storage. Heat is collected again by u-pipes, washed down in the store, by tubes buried in the store or by other means.
Water may be picked up from rain-water basins, processed grey water, sea-water or the like. Is this mad? Cheers, John, Denmark. Europe.