Evaluation of Linear Fresnel Reflectors
Abstract
We determine the thermal efficiency as a function of temperature for a large number of Linear Fresnel reflectors (LFRs) published in the literature, whose main geometrical and optical parameters are available. The thermal efficiency function combines properly the geometrical, optical and thermal properties of the LFR when those systems make part of a solar plant. The first part of the paper (Sections 2, 3 and 4) describes the methodology to obtain that function for the linear “aplanatic” Fresnel reflector, as well as the calculation of its annual energy absorbed for a region in the Brazilian Northeast. Results of the thermal efficiency function at normal incidence of various linear “aplanatic” Fresnel reflectors is presented showing that for DNI as high as 800 W/m², different LFARs tested can reach thermal efficiency between 59% and 77%. We also demonstrate that practical high-performance LAFR designs can achieve annual energy absorption efficiency as high as 61% at concentration values of 35. The second part (Section 6) synthetizes the thermal efficiency of the selected geometries at normal incidence. Results show that temperatures as high as 390 °C can be achieved with thermal efficiency between 60% and 75% for most part of geometries selected. A discussion is made about the choice of the probability function that governs the interval angle of light rays reaching the concentrator.
Keywords
Concentrating Solar Power, Fresnel Concentrator, Linear Fresnel, Solar Concentrator, Thermal Efficiency.