Salt Water, Driving Osmotic Energy
2 min read
Using the salinity of the oceans to produce is an idea whose time has come in Norway, which boasts the world’s first osmotic plant. The technology is still being tested.
© J. HECKER / AFP - At the osmotic power plant in Tofte, Norway, electricity is generated when saltwater and fresh water meet.
Energy Based on the Principle of Osmosis
Osmotic energy uses the salt concentrated in seawater to produce electricity . The key element of this technology is a semi-permeable, double-sided membrane that lets water through but captures mineral salts. The membrane is in contact with freshwater on one side and seawater on the other. The salt molecules attract the freshwater, which migrates to the compartment containing salt water: this phenomenon is called osmosis. Driven by the movement of the water, a turbine generates power 1.
The success of this technology is based on high-performance membranes, which must have good wear resistance and the capacity to attract enough water to drive the turbine and generate power with optimal efficiency. They also, of course, have to be affordable.
An plant cannot be built just anywhere along the coastline. It needs to be close to reservoirs of fresh water and seawater. Consequently, the mouths of rivers are the only locations where such plants can be located. In practice, in an osmotic power plant, a network of pipes conveys freshwater and seawater into different chambers, separated by a membrane.
A Pioneering Plant in Norway
After a number of experimental facilities, Statkraft, a Norwegian electric utility specialized in , commissioned its first osmotic power plant in Tofte, Norway, in 2009. This is a prototype used to test the resistance of membranes over time and the feasibility of the technology. Two other projects are being developed, in Japan with a pilot plant in Fukuoka and in the United States.
Currently, 1 square meter of membrane provides output of 3 W. Statkraft works with theoretical osmotic pressure of 12 bars, the equivalent of a 120-meter drop. More adjustments need to be made to improve efficiency and reach the target of 5 W per square meter. At this stage, a 1 MW osmotic power plant would require 200,000 square meters of membrane. A power plant of this capacity (1 to 2 MW) is being considered for Sunndalsøra.
Sources:
- Ocean Energies - InterMines (french only)
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