Feasibility study of energy storage by concentrating/desalinating water: Concentrated Water Energy Storage

Two scenarios of CWES are specified including a CWES system using reverse osmosis (RO) and pressure retarded osmosis (PRO), and a CWES system co-storing/generating energy and freshwater using “osmotic-equivalent” wastewater. A comprehensive case study is carried out with focusing on the configuration of CWES using RO and PRO. It is found that the limiting cycle efficiency of the CWES using RO and PRO is inversely proportional to the RO water recovery and independent of the initial salinity. Therefore, to balance the energy density and cycle efficiency of CWES, it is recommended to operate a system at lower RO water recovery with higher concentration of the initial solution. Detailed energy analysis of detrimental effects in mass transfer, e.g. concentration polarization and salt leakage, and energy losses of pressurisation and expansion of pressurized water, are studied. Finally, a preliminary cost analysis of CWES is given.