How Efficient Are Solar Cells?
There is a common but mistaken notion that solar cells never produce more energy than it takes to make them. While the expected working lifetime is around 40 years, the energy payback time of a solar panel is anywhere from 1 to 30 years (usually under five) depending on the type and where it is used (see net energy gain). This means solar cells are net energy producers and can “reproduce” themselves (from 6 to more than 30 times) over their lifetime. In addition to optimizing the production processes, work is also being done to increase the level of efficiency, in order to lower the costs of solar cells. However, different loss mechanisms are setting limits on these plans. Basically, the different semiconductor materials or combinations are suited only for specific spectral ranges. Therefore a specific portion of the radiant energy cannot be used, because the light quanta do not have enough energy to activate the charge carriers. A certain amount of surplus photon energy is transformed
