Wave-powered desalination: resource assessment and review of technology

The growing scarcity of freshwater is driving the implementation of desalination on an increasingly large scale. However, the energy required to run desalination plants remains a drawback. The idea of using renewable energy sources is fundamentally attractive and many studies have been done in this area, mostly relating to solar or wind energy. In contrast, this study focuses on the potential to link ocean-wave energy to desalination. The extent of the resource is assessed, with an emphasis on the scenario of wave energy being massively exploited to supply irrigation in arid regions. Technologies of wave-powered desalination are reviewed and it is concluded that relatively little work has been done in this area. Along arid, sunny coastlines, an efficient wave-powered desalination plant could provide water to irrigate a strip of land 0.8 km wide if the waves are 1 m high, increasing to 5 km with waves 2 m high. Wave energy availabilities are compared to water shortages for a number of arid nations for which statistics are available. It is concluded that the maximum potential to correct these shortages varies from 16% for Morocco to 100% for Somalia and many islands. However, wave energy is mainly out-of-phase with evapotranspiration demand leading to capacity ratios of 3-9, representing the ratios of land areas that could be irrigated with and without seasonal storage. In the absence of storage, a device intended for widespread application should be optimised for summer wave heights of about 1 m. If storage is available, it should be optimised for winter wave heights of 2-2.5 m.