For the design of a solar-powered desalination system, the question of energy efficiency important, since the investment costs mainly depend on the area of solar collectors to be Also, the power consumption of the auxiliary equipment (for example the pump) which will be supplied by photovoltaic (PV) has an important influence on the total system costs. Therefore, the system design has to focus on a very good heat recovery function to minimize the need for thermal energy. Heat recovery can be achieved by an external heat exchanger or by an internal heat recovery function, where the feed water is used as coolant for the condenser channel. The internal construction principle respectively the spiral wound geometry of the MD module with integrated heat recovery is shown in figure 3.The technical specifications of the MD modules constructed by Fraunhofer ISE are:

• hydrophobic membrane, mean pore size 0.1 — 0.4pm

• height 450 — 800 mm

• diameter 300 — 400 mm

• membrane area 7 m2 — 12m2

• feed temperature at evaporator inlet 60 — 85 °C

• maximum feed volume flow 500 l/h

• specific thermal energy consumption 100 — 260 kWh/m3distillate

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distillate output 10-40 l/h