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.
