A "simple" Thermal energy storage. Might deserve its own thread..
What Im thinking is:
Concentrate sunlight with e.g mirrors or a Fresnel lens guided through a window to heat up a mass bellow. The reflective surface acts like a cone above the black body to reflect any stray light down again.
The whole black body could be carbon, I have been considering t it, since it have very good conductivity and ok specific heat. However it is an expensive material and far from the most environmental friendly. (Im trying to go somewhat abundant and eco-friendly)
So my thinking is to use one material as a surface black body material to absorb the light and conduct the heat down as effectively as possible. Maybe som kind of carbon/graphite would be good for this since its only a small amount. It sure can take the temperature.
Then Im thinking to have a storage material of something like magnetite, high temp concrete, aluminum oxide (all got different pros and cons)