Reverse osmosis (RO) membrane desalination driven by wind and solar photovoltaic (PV) energy: State of the art and challenges for large-scale implementation

Highlights: • State of the art in wind and solar energy-driven RO is presented. • Challenges and potential solutions are outlined for large-scale RO desalination operated by mature renewables. • Variable operation is a promising operation strategy to directly operate RO plants with wind and solar power. • Recommendations and future research directions are outlined. -- Abstract: The use of Reverse Osmosis (RO) desalination has grown considerably in response to water scarcity. Despite steady improvements in efficiency, RO desalination remains an energy-intensive process. Numerous studies focussed on using mature Renewable Energy Sources (RES), such as wind and solar photovoltaic (PV) energy, to drive RO plants on a small scale. However, RES have not been used to drive large plants, except with a grid connection, due to the intermittency and fluctuation of such sources. Direct coupling of the RO plant to a RES requires variable-speed operation and/or modular operation to match the load to the available power. This review presents the state-of-the-art in wind and solar-PV powered RO to identify technical challenges and potential solutions regarding large-scale implementation. Recent studies using wind and solar-PV to drive RO are analysed while considering the plant configuration, operational strategy, control system and methods used to improve the plant adaptability to the RES. Technical challenges may include shortened membrane life and reduced performance of energy recovery devices. Potential strategies for incorporating modular and variable-speed operation in commercial RO plants are presented. Control strategies are reviewed, including Model Predictive Control, Neural Networks and classical Proportional-Integral-Differential feedback control. Recommendations are made on future research necessary for operation of commercial RO plant operation from renewable energy.