Operation experience of a solar- and wind-powered desalination demonstration plant

The present work outlines the designing, erection and operation process of a stand-alone desalination plant powered by both solar photovoltaic and win d energy. Such a plant will serve small isolated communities in remote area s devoid of water resources. A specially customized code was built to simul ate the operation of the installation in order to allow appropriate choice of components specifications. Site meteorological data were used to enhance prediction capabilities. The code continuously updates the instantaneous w ater lever of the reservoir as well as the current state of charge of the a ccumulators. Depending on these two variables, a logical decision tree is b uilt to decide whether the cumulated wind and solar energy production can s atisfy the load of the plant or additional energy must be provided from the accumulators or an auxiliary diesel engine generator. The process control system for such an installation must allow for operation in isolated areas where qualified maintenance personnel are scarce or remote. These are speci al considerations regarding the design philosophy in order to reach a state as close as possible to a maintenance-free system. In view of this conside ration, several layers of back-up were built into the system such as a dies el generator (whose use is to be kept to a minimum). Also, the system has b een designed to operate at about a 33% service factor. Two-day battery stor age autonomy has also been provided. The desalination plant uses reverse os mosis technology. The plant has a maximum product capacity of 9 m(3)/d in v iew of future needs, even though it is designed to currently produce only 3 m(3)/d. The inlet water is to be provided fi om on-site brackish water wel ls. The local water quality is approximately 3500-5000 ppm corresponding to brackish water. The system has been designed based on the premise that the average on-site wind velocity is about 4-5 m/s and an insolation level of about 5-5.5 kWh/m(2)/d. The expected life-span of the plant is about 15 yea rs. The system was successfully erected and has been continuously operated producing 3 m(3)/d. Experimental measurements are now in progress, and a co mparison to theoretical predictions is presented. The time schedule for the whole project consisted of 6-8 months, including many changes required dur ing construction.