In the second half of the 90’s the FUKS-approach (function control without heat measurements) was developed in Germany as a cheap function control (<100€) [3]. This approach applies algorithms to measurement data and notices whether components function correctly. An overview of the developed algorithms is provided in table 3.2. The values in the algorithms could be adapted for other systems.

Several other algorithms were developed which can only be applied with additional sensors, e. g. resistance sensors for defect or inaccurate temperature sensors for the collector output or in the storage tank.

The method was for test purposes partially implemented in controllers of Esaa and Wagner. Several failures were recognized, but there were also false positives, detection of a failure while the system was functioning correctly. The approach stays cheap by using mainly sensors that are used for the control, however, with analysis and pressure measurements, the price may be slightly higher than mentioned. Although the method succeeds at detecting several failures in the lab, location of failures is limited, as can be seen in Table 3.2. Furthermore, there is no yield measurement, which could mean that large energy losses are not detected.