Abstract
Transmission gratings that combine a large diffraction angle with a high diffraction efficiency and a low angular and wavelength dispersion could be used to collect sunlight in a light guide. In this paper we compare the diffractive properties of polarization gratings and classical surface-relief gratings and explore their possible use in solar concentrators. It is found that polarization gratings and surface-relief gratings have qualitatively comparable diffraction characteristics when their thickness parameters are within the same regime. Relatively large grating periods result in high diffraction efficiencies over a wide range of incident angles. For small grating periods the efficiency and the angular acceptance are decreased. Surface-relief gratings are preferred over polarization gratings as in-couplers for solar concentrators.
Highlights
Solar energy is a promising response to the world’s growing energy demand
If the diffraction angle of a specific order is larger than the critical angle of the light guide that part of the transmitted light gets coupled into total internal reflection (TIR)
Using Finite Element Method (FEM) they verified Eq (9) and showed that the diffraction efficiency can be high for a broad range of incoming angles for thin polarization gratings
Summary
Solar energy is a promising response to the world’s growing energy demand. It is clean, reliable and by far the most powerful source of renewable energy. Producing a solar concentrator in this way requires structures that efficiently couple sunlight into the light guide. In this paper we study diffraction gratings as an alternative method for coupling sunlight into a light guide [5, 6]. If the diffraction angle of a specific order is larger than the critical angle of the light guide that part of the transmitted light gets coupled into TIR. For solar concentration this in-coupling mechanism should be made efficient. A relatively small grating period (or pitch size) is required in order to achieve a diffraction angle larger than the critical angle of the light guide material. We consider whether the gratings can be made with the required parameters
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