The Economic Infeasibility of Salinity Gradient Energy via Pressure Retarded Osmosis

Pressure retarded osmosis (PRO) harvests the chemical potential difference between water sources of two different salinities and has been widely researched as a source of low carbon energy. This study identifies the cost-optimal design and operation using a nonlinear programming model to minimize the levelized cost of electricity (LCOE) of a PRO system for specified process and financial parameters. Our model includes a detailed finite difference module-scale model that considers the pressure drop along the module, nonconstant solution properties, local mass transfer coefficients, and equipment inefficiencies that previous analyses lacked. Under realistic case specifications and present-day costs, the expected median LCOE ranges from $2.37/ kWh (seawater draw) to $0.11/kWh (Dead Sea draw). The optimistic case specifications, which assume significant improvements in process performance with no additional increase in cost, lower these median costs to $1.00/kWh (seawater draw) and $0.05/kWh (Dead Sea draw). These estimates exclude variable pretreatment costs and are likely to underestimate the actual LCOE. Membrane costs and maintenance are the primary cost components for all cases. Comparing the LCOE and capacity factor of PRO to other low carbon energy sources suggests that reductions in PRO component costs are unlikely to make PRO cost competitive with renewable energy technologies.

Automated summary

This study identifies the cost-optimal design and operation of Pressure Retarded Osmosis (PRO) system to minimize the levelized cost of electricity (LCOE), considering various factors and providing expected LCOE for different scenarios. The research finds that membrane costs and maintenance are the primary cost components for PRO systems, and reducing PRO component costs is unlikely to make it cost competitive with renewable energy technologies.