According to the researchers, tweaking the size of the membrane could help generate electricity much more cheaply than ever before.
PRO was first developed in the early 70s as a way to turn osmotic pressure into electrical power. It involves using a very large semipermeable membrane to allow a solvent, such as fresh river water, to flow into a more concentrated and pressurized solution, such as sea water. Salt molecules pull the fresh water through the one-way membrane and cause an increase in pressure, which is harvested by a turbine to generate power.
The huge amount of fresh river water running into seas and oceans throughout the world makes PRO a very promising prospect. Norwegian electricity company Statkraft, who built the first PRO prototype power plant, estimates that as much as 1,600 TWh per year could be generated in this way. In addition, the same technique could also be used to recover energy from brine, the mildly salty water which is a byproduct of water desalination plants, with an even higher energy output.