Can osmotic power compete with solar and wind on cost and scale?

The article explores the potential and challenges of osmotic power—specifically pressure retarded osmosis (PRO)—as a renewable energy source that harnesses the energy from the natural mixing of freshwater and seawater at river mouths. This process exploits the osmotic pressure created by salinity gradients, which theoretically could generate up to 5,000 terawatt-hours annually, comparable to global energy consumption. PRO systems work by allowing freshwater to pass through a semipermeable membrane into pressurized seawater, expanding its volume and driving turbines to produce electricity. However, to be economically viable, commercial systems must achieve membrane power densities of at least 5 watts per square meter, a benchmark that most current installations fail to meet, typically operating at 1 to 3 W/m². The main technical hurdle lies in the membranes themselves. Current thin-film composite polyamide membranes can only withstand pressures up to 15-20 bars before deforming, limiting the efficiency of energy extraction. Additionally, biof