Sand

This article is interesting, reporting on progress in Finland using sand as the storage medium for green heat, so it can be delivered through a communal heating system some (considerable) time later. This is a key need in our local context, given the main Loch heating is in the summer but the main house heating requirement is in the winter. Heat pumps will work efficiently with source water above 5oC, but when the temp drops below that a heat store may be the right answer. Filled with sand, this approach is low tech(good) and cheap to procure. They potentially could be distributed to make heat transfer through the towns more efficient, with high heat available closer to where it is needed. Just like hot stone treatments….