The Hurdle for Solar Energy

A lot of research in academic institutions is going into ways to harvest energy more efficiently and in a sustainable way. The obvious source of clean, unlimited energy is the sun, however,as is popular in the news, solar energy is not yet economically viable. My own research interests are in materials and methods to create cheap solar energy, so I will describe here the main scientific hurdles in the field and ways to address them.

Most solar cells are made of either Silicon or a derivative of a compound called Gallium Arsenide (GaAs). The basic principle on which the materials convert light to electricity is that they are able to absorb light of a certain wavelength (colour) and use the energy in the light to excite an electron to become free like in a metal. By 'freeing' many electrons in this way, electricity is produced and you can simply connect a device to the cell just like you would a battery. This brings us to the first problem with solar cells, that only certain colours of light can produce electricity. The chief way in which people are trying to solve this problem is by taking light of different colours and using certain chemicals to convert that light to the colour of light suitable for the solar cell. Another way of attacking this issue is to use different types of solar cells to convert different parts of the solar spectrum to electricity.

The next major issue with solar cells is that even with the right colour of light hitting it, only a certain amount of the incoming light actually excites electrons and of the fraction of electrons only some actually make it to the wires connecting to the device. In order to ensure more electrons actually make it to the device, the solar cell has to be a perfect crystal so that the electron doesn't lose any energy before going to the wires. Doing this is extremely expensive, which is also the last major issue with solar cells right now, they are too expensive! There are again two major approaches to solving this problem, one is concentrating the light onto a small solar cell, and the other is making cheaper solar cells at the cost of conversion efficiency.

In terms of concentrators, there are a lot of interesting advances being made to different ways of concentrating light that can be incorporated in urban buildings by essentially have light fall on a sheet and directing that light to the edges of the sheet where you place a solar cell. At the other end of the 'spectrum', cheap solar cells are being made out of plastics, however, the conversions efficiencies are extremely low (~4%) as opposed to silicon cells that can reach ~30% efficiency. Here again a lot of research is being done to increase the efficiency, and it seems to be a promising area of development.

While there is still some time before economically viable solar energy is available, what is important to realise is that at the end of the day, oil companies will need to be shut up. The actual biggest problem right now is creating political incentives to promote solar energy, and of course pushing in the opposite direction are the large oil companies. There has to be more political interest in investing in clean energy. The only government that is doing a good job right now is Germany, with excellent incentives to set up solar energy farms. Then again, if it wasn't for oil, perhaps Bush wouldn't have given the Iraqi people democracy?