I am researching heat storage materials. Traditionally products such as sand or concrete can be used for "sensible" heat storage from solar, heat pump or even electrical means.
Phase change materials add to the sensible heat by latent heat absorption/release as the product reaches the change point and melts, when it absorbs energy. When it cools down again it re releases the energy as latent heat when the pcm solidifies. This mixture an be tailor made to a specific release temperature, resulting in a massive increase in heat capacity. Concrete ith PCM report increases in heat capacity of 2-300% with no volume change. I believe that sand could mic with pcms and produce even higher capacities, because unlike concrete, which is a tsructuual materialm dry sand has no need to maintain its structural integrity under load.
I am working on mixtures of conrete3 and pcms or sand and pcms which are heated with low grade heat from heat pumps, driven by cheap nightime electricity, and which collect and store 5 units of heat for every i unit of electricity.
If you have been involved in heat storage, concrete mix design or taken the plunge and produced a working solar heat storage system I would love to swap information