Solar power: The third way. A new method of making electricity from sunlight has just been tested. AT THE moment, there are two reliable ways to make electricity from sunlight. You can use a panel of solar cells to create the current directly, by liberating electrons from a semiconducting material such as silicon. Or you can concentrate the sun's rays using mirrors, boil water with them, and employ the steam to drive a generator. Both work. But both are expensive. Gang Chen of the Massachusetts Institute of Technology and Zhifeng Ren of Boston College therefore propose, in a paper in Nature Materials, an alternative. They suggest that a phenomenon called the thermoelectric effect might be used instead and they have built a prototype to show that the idea is practical. Thermoelectric devices are not new. They are used, for example, to capture waste heat from car engines. They work because certain materials, such as bismuth telluride, generate an electrical potential difference within themselves if one part is hotter than another. That can be used to drive a current through an external circuit. The reason thermoelectric materials have not, in the past, been applied successfully to the question of solar power is that to get a worthwhile current you have to have a significant temperature difference.
