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This is the corrolary to the "home cold reservoir" idea.
Have a thermally insulated concrete container filled with a mix of meltable salts, buried underground.
Heat it by having a parabolic trough solar collector heat a pipe filled some sort of hydronic fluid that can withstand the high temperatures
(silicon oil, perhaps).
Circulate the hydronic fluid between solar collector and molten salt tank as long as the collector is producing higher temperatures than the temp of the salt in the tank.
A second loop of the same type of hydronic fluid moves heat from the tank to a heat engine (which generates electricity), and which is cooled by a third loop of hydronic fluid (low temperature, this time, so water should work ok), which heats the hot water tank and the house.
Depending on how hot the tank can get, it might even be reasonable to use the heat to cook with (route it via silicon oil hydronic fluid from the salt tank to the oven).
||Sort of baked. There's a patent on using tanks of
material with freezing points at around room
temperature (nasty fluids, most of them) to store
heat. The patent is sort of half baked, as I recall,
so maybe it's ok.
||If you use a material with a freezing point close to room temperature, it can only be used for heating; it can't be used for combined heat and power. Also, you'd need one heat heservoir for water heating, and another for heating the house.
||Oh, and the idea is sort of baked in an entirely different way -- it was inspired from the design of certain type of large scale solar power plant. Specifically one which uses parabolic mirror solar troughs to heat pipes filled with molten salt, which move heat either to a steam engine, or to a tank for overnight storage, to be able to produce energy both when the sun shines and partly through the night.
||Aside from the size, the only real difference between my idea, and the one which inspired it, is that I would use silicon oil to move heat to a tank of salt, instead of using salt as both heat store and as hydronic fluid. I made this substitution because silicone oil is liquid even when cool, and so it can be pumped through the pipes before the system has warmed up, or after it's cooled down.