Solar energy powered high-recovery reverse osmosis for synchronous seawater desalination and energy storage

Abstract

Solar energy is clean and sustainable to power our continuously developing society, but the intermittency and unpredictability lays a barrier on its direct connection to the grid. Seawater desalination is an effective path to consume dynamic solar energy to produce fresh water and stable salinity gradient energy simultaneously. Thus, a self-diluted 2-stage reverse osmosis with high recovery ratio is proposed to consume the renewable power from a dish solar Stirling engine to achieve more water production and energy storage. Based on theoretical derivation, system performance is evaluated under ideal membrane property and enough membrane area condition. The influence of hydraulic pressure difference and diluted fraction ratio on water production and energy storage performance are investigated. A performance optimization is further conducted and the corresponding performance are evaluated. Results revealed that self-diluted 2-stage configuration can improve the maximal recovery ratio from 25%, 57% and 70% to 39%, 62% and 72% under the maximal bearable pressure difference of 4, 7 and 10 MPa. Maximal salinity gradient energy of 3.84 MJ can be stored with an overall energy efficiency of 8.42% while desalinating 1 cubic meter seawater of 0.6 M. Theoretical analysis indicates that novel configuration is potentially an effective method to improve the upper separation limitation, which further produces more water and stores more solar energy in the desalination process of finite amount of source seawater.