Osmotic Power

The osmotic pressure between salted and fresh water as well as between water of different salinity varies. Osmotic power takes an advantage of this circumstance and among others, one method of generating energy by utilizing the disparity in the osmotic pressure of differently salted water is the Pressure-Retarded-Osmosis (PRO). In PRO, seawater is pumped into a pressure chamber in which the pressure is lower than the osmotic pressure difference between fresh or lower salted water and water of high salinity. Fresh water or water of low salinity flows through a semipermeable membrane and by doing so, it increases the pressure within the chamber. Due to the increased pressure a turbine can be spun in order to generate energy.

An absolute advantage of osmotic power is the fact that it is renewable. Apart from that, there is no risk to run out of salt, because the process of producing osmotic power does not consume any salt but it just utilizes it in order to force water to move. Furthermore, osmotic power is a very clean sort of energy which can be generated with only a minimal environmental impact. The amount of heat that occurs during the process of producing osmotic power raises temperature less than half a degree Celsius. Therefore, the effect on marine organisms is relatively small. However, the huge costs that accrue due to the process of generating osmotic power are an absolute disadvantage. In fact, the production of osmotic power is about 36 times as expensive as conventional energy-producing processes. Besides, lowering the plant into the deep sea is very difficult and there is also a problem with the protection of marine organisms from the turbine.

Currently, a full-scale commercial osmotic power plant is being developed by the Norwegian company Statkraft. This plant will be able to supply enough energy for almost 10.000 households and it is supposed to put into service by 2015. As far as the development of a full-scale commercial osmotic power plant is concerned, the biggest challenge can be seen in the design of a membrane which draws enough water through in order to create an effective pressure to spin the turbine. Since Statkraft became involved in the development of a full-scale commercial osmotic power plant in 1997, the design of the membrane has been improving over and over again. The power plant being developed by Statkraft will be of the size of a large football stadium.