Optical study of diffraction grating/Fresnel lens combinations applied to a spectral-splitting solar concentrator for space applications

This paper presents a new design of a planar solar concentrator with spectral splitting of light for space applications. This concentrator spectrally splits the incident light into mainly two parts. Each part is then focused onto specific spatially separated photovoltaic cells allowing for independent control of respective cells' output power. These advantages of both spectral splitting and light focusing are combined here because of a specific diffraction grating superimposed on a Fresnel lens. The theoretical principle of the optical design is presented with optimization of each element and improvement steps including optimization of grating period evolution along the lens and testing of two kinds of gratings (a blazed and a lamellar one). First numerical results are presented highlighting the possibility to design a concentrator at about 10× or more for each cell with an output power larger than that of a classical concentrator focusing on a GaAs single junction cell and less than 10% of losses for tracking errors up to ±0.8°. Some experimental results are also presented.