The dynamic simulations were carried out using Matlab/Simulink. The implementation of the thermodynamic model of a plant with 7 stages is depicted in the figure below. The model of a stage with all heat flows is collated to a single block, including thermal inertia. For an easier usage the evaporation area, quality of insulation, spacing between evaporator and condenser and the water volumes can be defined in a menu mask. Supplied heat energy, i. e. from a solar collector and ambient data are put in on the left. A scaling factor defines the quantity of brine entering the system.

The model had to be validated with measurement data from the unit in connection with a flat plate collector. The comparison of the simulation and the measured data can be seen in diagram figure 7. The accordance of simulated and measured data is very good. Differences in temperatures are mainly due to the uneven temperature distribution in the stages. So it occurs that a sensor is nearer to the cold seawater input and so measures a lower temperature.

With the help of a validated complete system, it is possible to predict the performance of the unit in other climatic regions. As an initial prognosis, the simulation was performed using weather data from Sidi Barrani on the Egyptian Mediterranean coast. The average daily production over a period of one year of a 1 m2 model with a 4 m2 flat plate collector is shown in Figure 8. The daily production is seen to be between 20 and 60 kg/d, depending on the time of year. The average yearly production achieved by the unit reached 47 kg/d.

In order to reduce the energy requirements even further, an additional system to recover the heat from the condensate and the discharged salt water, especially designed for solar thermal desalination units, is now being investigated with the financial support of RWE Aqua (Thames Water). Initial attempts have already shown very promising results.