Solar extinction measurement system based on digital cameras. Application to solar tower plants

In Concentrating Solar Power (CSP) technologies, direct solar radiation is reflected from a concentrating system to a receiver, where it is transformed into process heat. In particular, in solar tower plants, the phenomenon of atmospheric extinction between both systems must be studied since the radiative losses can be important due to the increasingly large distances in the gradually larger plants. Large distances are necessary in order to measure the extinction since, in reduced distances, it can be undetectable. However, the great uncertainty of some available instruments and/or the monochromaticity of others, make it possible to affirm that, at present, there is no experimental device that allows a credible measure of solar extinction to be carried out. Nowadays, digital cameras are used in many scientific applications due to their ability to convert available light into digital images. Their broad spectral range, high resolution and high signal to noise ratio, make them an interesting device for extinction measurement. The aim of this work is to present the description of a novel measurement system for solar extinction at ground level based on two digital cameras and a Lambertian target. The first experimental results show that the system can measure solar extinction in the bandwidth 400-1000 nm with an accuracy of less than an absolute ±2%. This measurement system is currently running on a daily basis at Plataforma Solar de Almería.