Science News

A Window on Solar Power

Solar cells are expensive and difficult to produce, as they have to be made in a computer chip plant, so you want to maximise the amount of energy you can get out of each one.  One way is to concentrate the light onto a cell using relatively cheap mirrors, or lenses.  This means that several times more sunlight will fall on the solar cell so you can get more power out for your money.  However, the more you concentrate the light using lenses or mirrors, the more accurately you have to point them at the sun, meaning that these systems need expensive and high maintenance mechanical systems.  They also need costly cooling systems as they tend to waste a lot of energy as heat.

Now Michael Currie and colleagues from the Massachusetts Institute of Technology (MIT) have developed a system that will concentrate light whatever direction it is coming from.  They have taken a sheet of glass and covered it with a dye which absorbs light at one wavelength and then re-emits it at a slightly longer wavelength.  This re-emitted light is going in random directions and most of it gets trapped within the glass sheet by a process known as total internal reflection.  You could do something similar to this by adding some dirt to the surface of the glass.  This would scatter the light and some would get trapped in the glass but the dirt would also scatter the light in all other directions.  The MIT team’s dye is specially designed not to absorb the light which it has emitted, meaning that a huge amount of light is trapped in the sheet of glass, and you just put your solar cells around the outside.  Each cell produces about 10 times the amount of electricity they would do normally.

Another advantage is that you can pick the wavelength of light that your dye is producing to be the optimum wavelength for the solar cell to absorb.  This means that much less energy is wasted as heat in the solar cell so it doesn't overheat so easily, reducing the need for expensive coolants.

This system converts about 6.8% of the sun's energy which isn't great, but it should be much cheaper to make and you could use it wherever you have tinted windows in a building, so skyscrapers could generate electricity rather than just using vast amounts of it.

13th Jul 2008