Dec 31st 2011 - TO MAKE electricity from sunlight you can convert it directly, using a photovoltaic cell. Or you can use the heat of that sunlight to boil water, and then drive a turbine with the resulting steam. These are both established technologies. But there is, in principle, a third way: use heat directly, without steam or turbines. In this case, unlike a standard solar cell (which is sensitive to some frequencies of light, but not others), almost all of the incident energy is available for conversion. Yet unlike the boiling-water method, no messy mechanical processes are involved. Once set up, such a system could run with the minimum of attention.
Unfortunately, devices that turn sunlight into heat and then into electricity in this way do not get much warmer than boiling water when they are exposed to direct, unconcentrated sunlight. The reason is that at temperatures significantly higher than this the laws of thermodynamics dictate that they shed heat as fast as they absorb it. That has proved problematic, because a direct converter of this sort needs to reach 700°C to become properly efficient, and that is impossible without using special (and expensive) parabolic mirrors to concentrate the incident light.
Peter Bermel of the Massachusetts Institute of Technology and his colleagues, however, think they have found a way round this difficulty. As they describe in Nanoscale Research Letters, they have invented a way of concentrating the energy in the sun’s rays without the need for mirrors. It is, quite literally, a suntrap. read more>>>