Renewable energy-driven innovative energy-efficient desalination technologies

Globally, the Kingdom of Saudi Arabia (KSA) desalinates the largest capacity of seawater but through energy-intensive thermal processes such as multi-stage flash (MSF) distillation (>10kWh per m³ of desalinated water, including electrical and thermal energies). In other regions where fossil energy is more expensive and not subsidized, seawater reverse osmosis (SWRO) is the most common desalination technology but it is still energy-intensive (3-4kWh_e/m³). Both processes therefore lead to the emission of significant amounts of greenhouse gases (GHGs). Moreover, MSF and SWRO technologies are most often used for large desalination facilities serving urban centers with centralized water distribution systems and power grids. While renewable energy (RE) sources could be used to serve centralized systems in urban centers and thus provide an opportunity to make desalination greener, they are mostly used to serve rural communities off of the grid. In the KSA, solar and geothermal energy are of most relevance in terms of local conditions. Our group is focusing on developing new desalination processes, adsorption desalination (AD) and membrane distillation (MD), which can be driven by waste heat, geothermal or solar energy. A demonstration solar-powered AD facility has been constructed and a life cycle assessment showed that a specific energy consumption of <1.5kWh_e/m³ is possible. An innovative hybrid approach has also been explored which would combine solar and geothermal energy using an alternating 12-h cycle to reduce the probability of depleting the heat source within the geothermal reservoir and provide the most effective use of RE without the need for energy storage. This paper highlights the use of RE for desalination in KSA with a focus on our group's contribution in developing innovative low energy-driven desalination technologies.