Solar Energy ArticlesEnergy Losses in a Solar Panel Visible light is just a small fraction of the larger electromagnetic spectrum. The entire electromagnetic spectrum is composed of a lot of wavelengths that are capable of showcasing the different energy levels. In this article, we are going to explore the losses in a solar panel, due to such properties exhibited by light. It is not a rare phenomenon that light can be separated into its constituent wavelengths. The light that hits the solar panels and the silicon crystals at a sub-atomic level is composed of different energy levels. There is a minimum energy requirement for an electron to get knocked off the valence band into the conduction band. This corresponds to the generation of an electron hole pair. If the photons do not have the minimum energy to knock of an electron, its energy will go waste and would not affect the electron in any way. This means that the photon will just pass away through the silicon crystal of the solar panel without producing any electrical equivalent of energy output. This will give an impression as if the solar cell were of transparent nature with a photon just passing through it. The minimum energy that needs to be imparted to an electron for knocking it off and create a hole thereby is specified in electron Volts (eV). Solar panels, which are equipped with solar cells made up of crystalline silicon typically, have this energy rating defined as 1.1 eV. This is also called as the band gap energy of a material. The study of quantum physics states that the photons carry limited number of energy packets. There might be other photons with sufficiently higher energies striking an electron. But due to its discrete nature of energy, the extra energy possessed by photon is lost after completing the work of generating an electron hole pair. Thus we see that, at the sub-atomic level, the energy of a photon is non-reusable. On top of it, to make it worse, no matter how much quanta of energy is carried by the photon, it can exactly knock off only one electron. In short, a photon can collide with and excite only one electron no matter if it has energy to knock off 2 or more electrons. These limitations of quantum physics pose a lot of restrictions and constitute of losses in a solar cell. The above stated minimum energy requirement and also the extra-energy photons constitute alone of 70% of the energy losses in a solar cell. Now it’s a possible thought to occur in anyone's mind that there must be some way to lower the band gap. Or a solution might be there where choosing a material with low band gap could help minimize the losses. But this does not happen. This is due to the unfortunate dependence of the strength of the electric field on the band gap energy of an electron in the material of solar cell. Lower the band gap, lower the voltage produced at the output even if we are making a provision for the lower energy photons to produce an electrical equivalent of energy. Hence in the industrial applications of solar panel manufacturing, the optimum band gap of the single material in a solar cell is chosen to be 1.4eV and it is a compromise between these two conditions stated above. Then there are also other losses. The electrons lose significant amount of energy in overcoming the electrical resistance subjected to it by the connecting wires of the external circuit. Also, internally silicon opposes the flow of current due to collision of electrons with immobile ions. This is because silicon is a semiconductor and different from metals. It does not contain a pool of readily available electrons. To minimized these losses, the solar panels have a metal sheet covered on to the rear end while the front end is left covered with glass for allowing maximum transparency and injection of photons into the solar cells with least effort. Related articles
|
|
| 28 Church Road, Stanmore, Middlesex, London, UK. HA7 4XR. |
|
| enquiries@solarenergyhome.co.uk | |