What is inter-seasonal heat storage?

One of the frustrations of solar power in the UK is that there’s a lot of seasonal variability. It’s cold at the moment and so this is when my household uses the most energy. It unfortunately coincides with the point in the year when the solar panels generate the least power, thanks to the short winter days and lots of cloud.

Come May and June the situation will be inverted. The solar will be producing generous quantities of power that I don’t need. It would be so useful to be able to store a...