On-site focus alignment of a fresnel mirror field

Linear concentrating Fresnel collectors are available in various scales for providing solar thermal heat in the temperature range beyond 100 °C. For raising the flexibility in applying such collector systems on mounting sites with restricted space availability, the presented research project investigated the possibilities for adapting an existing Fresnel collector with a mirror surface of 22 m2 towards more compactness by using only one half of the mirror field. Therefore, the receiver was relocated and the focus alignment of the mirrors had to be adapted. The theoretical approach by geometrical calculation of the single mirror angles using MATLAB™ was successful, although the required effort for developing such an optical model was high. Furthermore, the resulting angle information obtained by the calculation is difficult to realise on the mirror field, because a high-precision goniometer would be necessary in order to adjust the mirror stripes accordingly. On the other hand, an experimental approach was analysed for realising on-site focus alignment of the single mirror field. The focussed beam of a conventional laser pointer was directed to each of the mirror stripes, while adjusting the corresponding mirror angle until the reflected beam impinged on the center of the receiver. In the end, the experimental procedure turned out to be favourable, because it is simple and reliable, and it requires much less effort. In this way, the adaption of the Fresnel mirror field was successful, as the concentration and the tracking is working as expected.