Full modeling and experimental validation of cylindrical holographic lenses recorded in Bayfol HX photopolymer and partly operating in the transition regime for solar concentration.

Abstract

Concentrating photovoltaics for building integration can be successfully carried out with Holographic Optical Elements (HOEs) because of their behavior analogous to refractive optical elements and their tuning ability to the spectral range that the photovoltaic (PV) cell is sensitive to. That way, concentration of spectral ranges that would cause overheating of the cell is avoided. Volume HOEs are usually chosen because they provide high efficiencies. However, their chromatic selectivity is also very high, and only a small part of the desired spectral range reaches the PV cell. A novel approach is theoretically and experimentally explored to overcome this problem: the use of HOEs operating in the transition regime, which yield lower chromatic selectivity while keeping rather high efficiencies. A model that considers the recording material's response, by determining the index modulation reached for each spatial frequency and exposure dosage, has been developed. It has been validated with experimental measurements of three cylindrical holographic lenses with different spatial frequency ranges recorded in Bayfol HX photopolymer. Simulations of systems comprising two lenses and a mono-c Si PV cell are carried out with the standard AM 1.5D solar spectrum. Promising results are obtained when using the system with lower spatial frequencies lenses: a total current intensity equal to 3.72 times the one that would be reached without the concentrator.