| Popis: |
Shockley and Queisser have shown that systems based on single junction PV cells are limited to a system efficiency of 33%. This restriction results from the mismatch between the photon energy of the incident sunlight and the inability of a single junction device to optimally convert the broad incident spectrum. One approach to overcome this difficulty is to incorporate multiple PV cells with different bandgaps that are optimized to convert different parts of the incident spectrum to electrical power. Spectrum splitting configurations distribute incident photons onto several single bandgap PV cells that are spatially separated. Although, systems with different methods and geometries have been proposed, optical systems relying on reflective filters have not been compared to transmissive ones. Since reflection-type films are primarily based on the interference of reflected waves from optical interfaces, systems based on these filters do not have dispersion losses. Dispersive spectrum splitting systems rely on optical elements that use diffraction or refraction for spectral separation. The dispersion from a single broad band optical element can be used for spectral separation. The geometrical relationship between focusing power, the degree of dispersion, the system aperture, and the PV cell aperture and position can be used to tailor the spectral shape of the incident spectrum into each of the PV cells comprising the system. In this paper, the effects of dispersion introduced by transmission type filters are presented compared to reflective filters. |
