Beam-down linear Fresnel reflector prototype: Construction and first tests

Abstract

A novel beam-down linear Fresnel reflector prototype, that gathers solar irradiance close to the ground by aiming it to a high focus, and redirecting it linearly towards the ground, has been designed and constructed. Its design considers the shading between adjacent mirrors and the spillage in the solar receiver, and uses flat mirrors to reduce costs. The prototype consists of forty 5.5 cm wide mirrors for the primary reflector, and eighteen 5 cm wide ones for the beam-down, resulting of 3.16 m in the transversal plane, 1.6 m in the longitudinal plane, and 1.8 m high. The solar field was characterized, and the built geometry was compared with the design one, by comparing the expected positions and inclinations of the mirrors with the real ones, and by simulating using Monte Carlo ray-tracing to grasp its potential. The solar field was taken outside, in the Universidad Carlos III de Madrid campus (40° N, 3° W), Spain, to perform 6 different on-sun tests, which were compared with simulations under similar conditions. It was able to achieve an average solar concentration of 6.41 suns with an optical efficiency of 29.14 %, measured between July 3rd and 4th 2023, over a 10 cm wide receiver.