Solar Sponge

Using sunlight to generate steam that can, in turn, be converted into electricity isn’t a new concept. But it’s also not very efficient, so existing systems employ a variety of mechanisms designed to concentrate the solar energy. Movable mirrors (or heliostats) that track the sun’s movement are capable of multiplying the collected energy up to 1000 times. Parabolic troughs increase the intensity by 60 to 80 times. And additives, like gold nanoparticles, increase efficiency, but still cannot boost performance above about 25%, and require intensely concentrated light.

Recently, researchers developed a material that would enable steam production with efficiencies up to 85 percent, using sunlight that is magnified by a factor of ten (and possibly less). This eliminates much of the cost, as lower magnification can be accomplished with inexpensive lenses rather than costly mirrors.

The idea is based on the same principle that turns a thin layer of water on a road into steam when exposed to sunlight. The material consists of a thin layer of graphite flakes on top of porous carbon foam, shaped like a disk and floating on the surface of a container filled with water. As the graphite absorbs heat from the sun, it creates a pressure gradient that pulls water up through the sponge. When it reaches the surface of the disk, the water readily turns into steam.
Inexpensive and efficient solar steam power could bring a wide range of essential and even life-saving technologies (such as desalination, refrigeration, sterilization and waste treatment) to areas of the world where sunlight is the only energy source.