Reverse Osmosis using Renewable Energy: System Design and Technoeconomic Optimization for Distributed Desalination

Freshwater use in energy generation, manufacturing, and agriculture has resulted in a significant increase in global water demand. Desalination is a technology solution that augments freshwater reserves by treating saline sources using an energy input. Reverse osmosis (RO) is a mature membrane-based technology for seawater desalination, but centralized systems consume significant amounts of energy that contributes to the cost and carbon footprint of the product water. This has led to an emerging interest in coupling RO with renewable energy sources (RES) at a distributed scale to treat inland saline sources, like brackish groundwater or oil and gas produced water. However, the intermittency of solar photovoltaics (PV) and wind is a challenge given that conventional RO is a constant pressure process designed to operate continuously and maximize uptime. Batch Reverse Osmosis (BRO) is a novel variable pressure process that has been demonstrated to operate at higher water fluxes, higher water recovery, and with lower energy input. These attributes make it suitable for a renewably paired system, but this has yet to be investigated. This research (i) develops an analysis framework for RO driven by intermittent RES, and (ii) evaluates the performance of BRO compared to conventional RO.
The system design comprises four subsystems: energy generation (RES), energy storage (battery), RO (conventional and BRO), and water storage (tank). The RO energy consumption and flux are obtained using the solution-diffusion model. System operation over one year is simulated, and techno-economic modeling and optimization techniques are applied to identify subsystem sizes that yield the lowest levelized cost of water (LCOW). This framework is also applied to other energy resources (wind, hybrid, and grid-connected), feed salinities (brackish and produced water), and water demand profiles (constant and agricultural). For PV-RO, the analysis reveals that the higher flux operation of BRO can (i) increase direct use of renewables by 40%, (ii) reduce energy storage needs by 94%, and (iii) reduce curtailed electricity by 6%. BRO can also (iv) reduce brine production 16% by operating at higher recovery, or (v) reduce membrane area or energy system size 10% by operating at a lower specific energy consumption. These attributes result in a total LCOW reduction of 1-14% for BRO compared to conventional RO. Overall, this work identifies key design tradeoffs in RES-driven RO systems to enable sustainable water production.