Osmotic energy can be harvested because saltwater and freshwater, separated by an osmotic membrane, can build up a large pressure difference of - theoretically - around 27 bar, which is equivalent to the potential difference of a waterfall about 270 meters high. Therefore, in principle, each cubic meter of fresh water that flows into the sea could produce 0.7 kWh of electricity. For example: the ten largest rivers in Norway could provide approximately 25 TWh of osmotic energy per year - or almost 17% of Norway's projected electricity demand in 2030.

The development of osmotic power plants is still in the research phase. There are several methods for extracting the potential energy released when freshwater meets saltwater. The methods that look most promising so far are pressure-retarded osmosis and inverted electro dialysis. Both techniques are membrane processes, closely related to those used for the desalination of seawater. The market for osmotic desalination is projected to grow in the next few decades, which should result in further development of sources of osmotic energy.