PHOTOSYNTHESIZING ROOFING MATERIAL
This is my wildest idea and would probably require giant strides in technology but here goes:
Did you ever notice how much cooler it is under a tree than under any other sort of roof or covering? My theory is that this is because conventional roof coverings absorb and then radiate heat/energy downward producing a space that while it may be shaded, is not much cooler than the surrounding area. Trees on the other hand are absorbing the energy and using it for photosynthesis. Since the energy is being used and directed to the nourishment of the tree, heat does not radiate downward and it produces a much cooler space beneath.
My idea would be to produce a roofing material that is embedded or covered with photosynthesizing material. The material would absorb the sunlight/energy and produce sugars or perhaps even electricity that could be collected or used elsewhere, thereby removing the energy and preventing it from radiating down to the area below the roof.
I see this as a possible covering for homes, businesses, permanent patio covers in homes or parks, etc. When used in buildings it should dramatically reduce cooling costs and, if it is possible to convert the output to electricity, it could even offset some of the cost of installation.
Reward: Installation of the material on my house and any future homes I move to.