Designing a flat beam-down linear Fresnel reflector, S. Taramona, P. Á. González-Gómez, J. V. Briongos, J. Gómez-Hernández, Renewable Energy, 187, 484-499, 2022, Online version,


A linear beam-down solar field consists of two reflections that concentrate the solar irradiation on heavy materials located on the ground. Several rows of linear Fresnel reflectors, which have the same width, aim the solar irradiation to a secondary mirror with a hyperbolic shape that redirects the solar concentration towards the ground receiver. This paper overcomes the main limitation of the previously proposed hyperbolic secondary reflector. A new secondary reflector composed by several fixed flat mirrors located at the same height is proposed. A model to calculate the optimal layout of this novel solar field, as well as the efficiency and concentration, is developed and validated against a Monte-Carlo Ray-Tracing software, obtaining relative errors lower than 15%. Two new dimensionless parameters are proposed to facilitate the design of the flat beam-down linear Fresnel reflector. The concentration, optical efficiency and receiver width can be easily obtained, without performing any simulation, as a function of the dimensionless parameters. This novel solar field can achieve concentration ratios of up to 31 and optical efficiencies of up to 60%, obtaining similar concentrations with better optical efficiency than a field using a hyperbolic reflector.