The most common classification of CPV- modules is by the degree of concentration, which is expressed in number of "suns". E.g. "3x" means that the intensity of the light that hits the photovoltaic material is 3 times than it would be without concentration.
Here are some examples of concentrator technologies and examples for both line and point concentrators. Although there might be differences in execution or materials used, most designs will follow one of those concepts..
A Fresnel lens, named after the French physicist, comprises several sections with different angles, thus reducing weight and thickness in comparison to a standard lens. With a Fresnel lens, it is possible to achieve short focal lenght and large aperture while keeping the lens leight.
With the high concentration ratio in a Fresnel point lens, it is possible to use a multi-junction photovoltaic cell with maximum efficiency. In a line concentrator, it is more common to use high efficiency silicon.
Here, all incoming parallel light is reflected by the collector (the first mirror) through a focal point onto a second mirror. This second mirror, which is much smaller, is also a parabolic mirror with the same focal point. It reflects the light beams to the middle of the first parabolic mirror where it hits the solar cell.
The advantage of this configuration is that it does not require any optical lenses. However, losses will occur in both mirrors. SolFocus has achieved a concentration ratio of 500 in point concentrator- shape with dual axis- tracking.
Low concentration photovoltaic modules use mirrors to concentrate sunlight onto a solar cell. Often, these mirrors are manufactured with silicone-covered metal. This technique lowers the reflection losses by effectively providing a second internal mirror. The angle of the mirrors depends on the inclination angle and latitude as well as the module design, but is typically fixed. The concentration ratios achieved range from 1.5 - 2.5.
In a luminescent concentrator, light is refracted in a luminescent film, and then being channelled towards the photovoltaic material. This is a very promising technology, as it does not require optical lenses or mirrors. Moreover, it also works with diffuse light and hence does not need tracking. The concentration factor is around 3.
Furthermore, this concentrator does not need any cooling, as the film could be constructed such that wavelenghts that can not be converted by the solar cell would just pass thru. Hence, unwanted wavelenghts would be removed.