Performance enhancement of parabolic trough collectors by solar flux measurement in the focal region

Characterization of the optical performance and detection of optical losses of parabolic trough collectors are very important issues in order to improve the optical efficiency of these systems and to ensure the desired quality in solar power plants. Therefore two methods of measuring the solar flux in the focal region were developed: PARASCAN (PARAbolic Trough Flux SCANner) is a solar flux density measurement instrument which can be moved along the receiver axis. The sensor registers the flux distribution in front and behind the receiver with high resolution. The resulting flux maps allow to calculate the intercept factor and to analyse the optical properties of the collector at the finally interesting location, i.e. around the receiver. The camera-target-method (CTM) uses a diffuse reflecting Lambertian target and a calibrated camera which takes pictures of it. The target is held perpendicular to the focal line surrounding the receiver. With the resulting images of this fast and easy method it is possible to visualize the paths of the reflected rays close to the receiver and to detect local optical errors. Both methods are described in detail. Latest measurement results gained at the Eurotrough-II prototype collector built on the Plataforma Solar de Almería (PSA) in Spain are presented and consequences are discussed.