1Agricultural University of Athens, Engineering Department,
²Austro Control Ltd., Austria

The lack of fresh water is a phenomenon often met in many islands and coastal areas through out the world. This fact inhibits social and economic development and this results in many cases, the people to leave their place and seek for a better life in the nearest city. Locally available renewable energy sources can in most of the times, supply the necessary energy for the operation of desalination systems and produce fresh water from sea or brackish water.

Existing technologies such as multi-stage-flash-evaporation (MSF), multi-effect evaporation (ME) and vapour compression (VC) distillation are the most characteristic and are generally cost-effective in large scale since the unit cost of product water is lower. They are mainly used to supply municipal drinking water and are relatively commercial. Other thermal processes such as freezing, membrane distillation and solar humidification usually have a lower quality energy requirement. Low-grade thermal energy can be used from sources as solar collectors or industrial waste heat. These processes are cost effective in medium- to small-scale systems. They are principally used to supply community or household drinking water supplies.

Such technologies require high infrastructure for securing electricity supply and system maintenance. Thus there is a need for an autonomous desalination system operating away from the electricity network and exploiting local renewable energy sources.

The present paper regards the development and application of a solar distillation system completely autonomous suitable for remote areas. Solar collectors supply the necessary heat energy for evaporating brackish or seawater. The salty water evaporation takes place under pressure lower than the atmospheric one (about 0.5 bar) thus lowering the boiling temperature and increasing the rate of evaporation. All auxiliary systems such as pumps, circulators, control system are energised by photovoltaics.

A prototype system was installed within the EC CRAFT programme in Greece. The system comprises of solar collectors of heat pipe type, having a surface of 90 m², photovoltaics of about 5.5 kWp with battery bank of 600 Ah (48 V) and a DC/AC inverter 48/240 V. During the first system operation under low solar radiation conditions the fresh water production was between 0.5 to 0.7 m³ per day.