Main and principal criterion for a trough collector is its ability to concentrate sunrays effi­ciently and economically on the absorber tube in order to heat the thermal fluid. It is obvi­ous that the knowledge of the flux distribution on the absorber tube is very useful to assess and improve the collector. The objective is to analyze the influence of different parameters of the collector geometry on the collector output. One approach has been made with the PARASCAN (PARAbolic through flux SCANner) system [3, 4], which measures the solar flux distribution at a distance of about 10 cm around the absorber tube along its longitudi­nal axis, resulting in 2-dimensional flux distribution maps. It has a high spatial resolution and provides the result for a 3.5 m long focal area between two absorber tube supports. Figure 5 shows a plot of a PARASCAN measurement.

For fast and easy flux distribution analysis the Camera-Target-Method shown in Figure 6 can be used. With this method the flux distribution on a plane perpendicular to the receiver axis can be visualized and sunrays, which pass the absorber tube, can be detected. The digital pictures taken of the diffuse reflecting target are evaluated basing on long-time ex­perience with indirect flux density measurements. Quantitative results of intercept values over the length of large collector areas are possible.

Both methods allow for checking and documentation of proper trough collector alignment and intercept factor impact on receiver performance data. The results of this technique help to quantify the effects of tracking accuracy on the collector performance [4].