Economic comparison of small solar-powered desalination plants

The objective of this paper is to find the most convenient solution to supply water to remote coastal areas by comparing the economics of different configurations of small solar powered desalination plants. Three desalting technologies have been investigated: (1) Reverse Osmosis, (2) Multi Stage-Flash and (3) Multiple Effect Distillation. In line with the philosophy of the present approach, the RO processes are powered by a photo-voltaic plant, while the MSF and MED processes both use solar collectors as the heat source (hot water instead of steam) and photo-voltaic panels as electrical power sources. Two different plant operational modes have been considered: a first one based on a 24-h freshwater production, and a second one based on freshwater production only during irradiation hours. Performance data have been obtained via a modular simulation code, CAMEL (c), developed by the Authors' group at the Department of Mechanical and Aeronautical Engineering of the University of Roma-1 "La Sapienza". The cost of the distillate production is calculated taking into account both fixed (solar, desalting and energy storage devices) and operating costs (chemicals, spares, maintenance and energy). Labour costs are lumped into the fixed costs. The study shows that PV-powered RO processes operating only during irradiation hours represent the most convenient solution. To evaluate the real convenience of adopting a solar RO plant configuration, two additional alternatives have been investigated: a first one that satisfies the design daily water request by tankering, the second by a RO plant powered by a Diesel engine. It turns out, that the last alternative is the most economically convenient solution in the assumed current socio-economical contest (remote areas, semi-desertic sub-tropical regions).