Desalination using marine renewable energy sources

The focus of this project is the desalination of seawater using renewable energy. The availability of fresh water is one of today's greatest challenges as well as reducing greenhouse gas emissions and embracing a low carbon future. Traditional desalination plants contribute to a significant amount of global emissions. Addressing these concerns, desalination powered by renewable energy is very promising; however it needs further development in order to replace plants that powered by fossil fuels. Marine renewable energy sources are particularly attractive, as both the energy source and raw material are found in the same place.

There are a vast amount of renewable energy sources that can power a desalination plant, including wave, tidal and wind power. However, these are primarily used to generate electricity. If this electricity were to be used to power the desalination plant, much of the energy would be lost through conversion. Using renewable energy to power the desalination process directly, would lead to much higher efficiencies.

Desalination technologies include thermal, physical and chemical processes. Thermal and physical processes have been more widely used, the first one utilising a change in phase and the second involving a physical barrier, most often a membrane, through which the water passes and the salt is retained. Thermal processes include vapour compression, flash and multiple effect distillation. Reverse osmosis and electrodialysis are examples of membrane processes.

Reverse osmosis is currently the most popular method of desalination, where the change in osmotic pressure is used to drive water through a membrane which retains the brine. The most favourable aspect of this technology is its low energy requirement of 2-5 kWh/m3, depending on whether brackish or seawater is used. However, following the initial investment, the cost of a renewable energy desalination plant is very low and waves for example, carry large amounts of energy. This shows that there's room for consideration of other desalination techniques such as mechanical vapour compression. Additionally, a current issue with wave powered reverse osmosis is the intermittent supply of energy, while a constant supply is required for the optimum operation of the membranes.

Currently, renewable energy powers 1% of all desalination plants, most of which are photovoltaic reverse osmosis plants. Many other technologies need more advanced research and development before reaching the stage of commercial applications. The particular combination of equipment for this project and whether it will be a membrane or a thermal process, powered by wind or waves, will follow after detailed research. The aims of this project are to identify the most beneficial combination, calibrate a mathematical model, identify appropriate control strategies, estimate the cost and efficiency of the system and finally, to identify the key technological challenges.