Abstract
An often-overlooked source of marine renewable energy is the energy available from salinity gradients. The potential resource for the osmotic pairing of fresh water and seawater is estimated at 2.6 TW. Several concepts have been proposed. Obviously, any scheme to desalinate seawater can be operated in reverse. Recent developments in pressure-retarded osmosis, vapor compression, reverse dialysis and hydrocratic generation are highlighted. Commercial barriers prevent necessary investment. The power available in salinity gradients will be exploited, but not without substantial investment.