I'm living in a house heated by ground heat (100m depth) used with a heat pump.
We have water storages for heating the house and around for hot water.
They allow to store some heat when the sun shines and we get power from the photovoltaic installed on the roof.
But it doesn't last long.
I'd love to store more heat over longer periods to get more self sufficient.
We considered already an underground tank to have more storage, but the loss despite insulation is high.
