Development of a high concentration solar flux mapping system.

Abstract

The Group for Solar Energy Thermodynamics (GSET) is in the process of commissioning the Solar Energy Research Amplified Flux Facility (SERAFF), which is South Africa’s first solar furnace facility. SERAFF is situated at the University of KwaZulu-Natal’s Howard College campus and assumes an on-axis optical configuration, comprising a 9 m2 non-focusing heliostat reflector, a 3 m diameter paraboloidal dish concentrator and a test article platform. The facility was designed to aid research in the fields of high temperature materials testing, concentrating solar energy and solar thermochemistry. The concentrated radiative energy output of a solar furnace establishes the energy input to prototype receivers, reactors or materials that aim to be tested using the facility. The challenge is compounded by the temporal and spatial variation of SERAFF’s radiative energy output, influenced by weather-related and geometric factors. In this study, an indirect spatial flux mapping system is developed to characterise SERAFF’s spatial radiative energy output. SERAFF’s theoretical spatial radiative energy output is estimated through Monte Carlo ray-tracing techniques to provide benchmark performance parameters including total thermal power output, peak concentration ratio and focal spot size. The indirect system uses optical measurement techniques, in which spatial solar flux is measured via diffuse reflection off a Lambertian target using a digital CMOS camera through a neutral density filter and lens. Pixel intensities are calibrated against reference measurements acquired from a circular-foil Gardon gauge heat flux transducer. The calibrated CMOS camera can be used to measure values of radiative flux, incident at the focal plane from 0 kW/m2 - 468.19 kW/m2. Measurements were restricted to a brief testing period and are not representative of SERAFF’s peak operating conditions. Spatial flux measurements indicated a thermal power output of 3.83 kW, with a corresponding peak solar flux of 227.8 kW/m2 within a focal diameter of 250 mm. The study demonstrated successful integration of an indirect spatial flux mapping system into the SERAFF solar furnace.