It is interesting to hear of someone else attempting to use seasonal heat storage. It should be the main way to heat buildings in winter and would be relatively easy to do on a big scale for groups of houses with a large combined store. The difficulty in a small scale system is that there has to be a lot of insulation in a store to retain heat for half of a year.
I have a fairly large store, about 180 cubic metres, insulated with straw bales. The main cost was the straw at €800, a JCB for a day and the plumbing parts. It would have been about €1500 total but I now have a large mound and two ponds which would only fit in a big garden.
One thing I have found is that the store works best when the heating temperature range is not too much above ambient but it is not yet working long enough to measure heat losses at different temperature differentials. It means that the temperature is not high enough to use directly for underfloor heating but is good for heat pump input. I have about 85 sq' of solar panels dedicated to heating and a small VAWT currently being added , also for heating only. Increasing the panel area would have allowed the option of not using the heat pump but I was concerned that the heat losses could be excessive and the heat would not last over winter. It will be interesting to compare with a 300 sq' collector system.
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