TECHNOLOGY FOR CHANGE

World's First Osmotic Power Plant Yields 24/7 Renewable Energy

R. Colin Johnson | Date: 11-24-09 | Comments

Unlike solar, wind, wave and other sources of renewable energy, osmotic power plants harness a source of energy that is constantly available--fresh water streams running into the sea--thereby enabling sustainable, renewable power plants that produce constant, uniform electricity, all day, every day.

The world's first osmotic power plant officially opened today in Tofte, Norway, providing sustainable, renewable electricity generation 24/7.

Unlike solar, wind, wave and other sources of renewable energy, osmotic power plants harness a source of energy that is constantly available--fresh water streams running into the sea--thereby enabling sustainable, renewable power plants that produce constant, uniform electricity, all day, every day.

Osmotic power generation harnesses the chemical energy locked in the gradient between salt water and fresh water by using an osmosis process. This pilot plant was designed by Statkraft (Oslo) to produce 10 kWatts of energy, but the Norwegian renewable energy company plans to expand that to a full-scale osmotic power plant capable of producing continuous 25 megawatts.

"Our pilot facility is a significant step toward the commercialization of a game-changing renewable energy source," said Stein Erik Skilhagan, vice president of osmotic power at Statkraft, "The global production potential of osmotic power could exceed 1,600 TWh, or the equivalent to half of Europe's entire energy demand."

Osmosis is a process by which water moves through a membrane which blocks other particles, which is how it is used to purify water. For osmotic power it works in reverse, with osmosis drawing fresh water through the membrane to mix with salty water, thereby increasing its pressure which can be harnessed to drive electricity turbines.

"The core process is a lot like desalination in reverse," said Rick Stover, chief technology officer of Energy Recovery, manufacturer of the key component to the osmotic power generator, called a pressure exchanger. "In desalination you are separating fresh water from salt water, but in osmotic power you are combining fresh water with salt water."

The pressure exchanger works similarly to a heat exchanger, essentially transferring the increased pressure from the salty outflow from the osmosis membrane to the fresh-water diluted output so it can drive a turbine. Without the pressure exchanger, the efficiency of the process would be too low to create full-scale osmotic energy generators.

"The pressure exchanger transfers pressure from a high-pressure stream to a low-pressure stream with 98 percent efficiency," said Stover.

Energy Recovery's pressure exchanger devices are currently installed in desalination plants worldwide, where they serve a similar function in increasing the efficiency of the osmosis process. Desalination plants discharge water that has higher salt content than the original sea water, piping the fresh water produced into cities for drinking.

Osmotic power plants, on the other hand, discharge fresh water diluted with salt water in exactly the same proportions as would have happened naturally when the stream flowed into the sea anyway.

Statkraft plans to build plants where fresh water is already dumping into the sea, but the output of desalination plants could also be used even more successfully, since their output is twice as salty as seawater, thereby doubling the energy generation capability, which is proportional to saltiness.