I think the domestic applications are partly covered by phase change materials: waxes selected for a melting point at the desired temperature. So, for example,

I think the domestic applications are partly covered by phase change materials: waxes selected for a melting point at the desired temperature. So, for example, you can embed a 23C phase change material in the plaster of a room - giving the room a high apparent thermal mass at the temperature you want it to stay at. A phase change material formulated to melt at 60C can make a hot water tank much "bigger" for coupling with a solar thermal system. These days houses can and should be built with enough insulation that they need very little heating (in most climes). On the other hand there probably are valuable industrial applications for this sort of material, particularly now that we really want high efficiency. There might even be uses in neighbourhood or utility scale power project.