During the design phase, a detailed model of the solar thermal plant has been developed in INSEL [2] and some simulations have been done in order to predict the energy produced by the solar thermal system [3]. Those simulations have been performed using meteorological data of the INSEL database. Performance analyses of the solar plant have been done with the monitored data for the period between March and June 2008 [4]. The results of the yearly simulated predictions and the measured data of 4 months of operation are shown in the table 1:

Several days with different operating conditions (solar irradiation, control strategy) have been simulated and compared with measurement data. The nomenclature used in the schema corresponds to the different sensors represented in figure 1. The measurement data used for the simulation are mean values calculated over 5 minutes time step. Those data were obtained from the monitoring system of the University of Applied Sciences Offenburg. Figures 2, 3 and 4 show the simulated and measured values for 3 different days.

Figure 2 (10th May) represents a sunny day with constant collector volume flow. The control strategy has been recently modified in order to reduce the electricity consumption of the collector pumps, figure 3 and 4 shows the results with the new control for both sunny and cloudy days.