ABSTRACT
Heat engines are one of the means that generate electricity from a heat source. The effi ciency of these engines increases with the temperature of the source, which means that, for high effi ciency, we need high temperatures. Solar energy is a clean, renewable source of energy that can generate high heat if highly concentrated. Another possible way to generate clean electricity is by using solar cells. They are, however, expensive and it may be interesting to replace a large cell by a large optic combined with a small, highly effi cient and less-expensive solar cell. This again means a high concentration of solar radiation. These are just two examples of application for a high concentration of radiation with a small angular aperture (such as sunlight).
