Desalination, Vol.137, No.1-3, 7-13, 2001
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 wind energy. Such a plant will serve small isolated communities in remote areas devoid of water resources. A specially customized code was built to simulate 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 water lever of the reservoir as well as the current state of charge of the accumulators. Depending on these two variables, a logical decision tree is built to decide whether the cumulated wind and solar energy production can satisfy 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 special considerations regarding the design philosophy in order to reach a state as close as possible to a maintenance-free system. In view of this consideration, several layers of back-up were built into the system such as a diesel generator (whose use is to be kept to a minimum). Also, the system has been designed to operate at about a 33% service factor. Two-day battery storage autonomy has also been provided. The desalination plant uses reverse osmosis technology. The plant has a maximum product capacity of 9 m(3)/d in view 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 wells. 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 years. The system was successfully erected and has been continuously operated producing 3 m(3)/d. Experimental measurements are now in progress, and a comparison to theoretical predictions is presented. The time schedule for the whole project consisted of 6-8 months, including many changes required during construction.