Japan has brought its first osmotic power plant online in Fukuoka, marking the world’s second such facility and the first in Asia.
The Fukuoka District Waterworks Agency said the plant began operations recently and is expected to produce 880,000 kilowatt hours a year, power that will be fed to a desalination facility serving the city and neighbouring areas.
Describing osmotic power as “a next-generation renewable energy source that is not affected by weather or time of day and emits no carbon dioxide”, the agency framed the startup as a step towards round-the-clock clean electricity.
“I feel overwhelmed that we have been able to put this into practical use. I hope it spreads not just in Japan, but across the world,” said Akihiko Tanioka, professor emeritus at the Institute of Science Tokyo, via Kyodo News.
The Fukuoka site is only the second power plant of its type in the world, and is expected to power roughly 220 Japanese households, Dr Ali Altaee of the University of Technology Sydney told the Guardian.
The technology’s recent momentum follows the world’s first commercial-scale installation in Mariager, Denmark, which came online in 2023.
How the Fukuoka plant works
Osmotic power plants harness the same principle as osmosis: water moving from a less concentrated solution to a more concentrated one across a semipermeable membrane. At Fukuoka, electricity is produced from the salinity gradient between two streams placed on either side of a semipermeable membrane.
On one side, there is concentrated seawater created by extracting fresh water; on the other, treated water from a sewage treatment facility. The membrane allows water to pass but blocks impurities. As water naturally moves towards the saltier side, pressure builds and is used to spin a turbine, which then drives a generator.
The agency emphasises that this approach avoids the intermittency of wind and solar and, at the point of generation, does not emit carbon dioxide, per Kyodo News.
Global context and current hurdles
The Fukuoka facility follows the first plant in Denmark (2023). It comes after pilot-scale demonstrations in Norway and South Korea, with research groups also building prototypes in Sydney (University of Technology Sydney), Spain, and Qatar, according to the Guardian. While the idea is simple, scaling has been difficult.
As Prof Sandra Kentish told the Guardian: “While energy is released when the salt water is mixed with fresh water, a lot of energy is lost in pumping the two streams into the power plant and from the frictional loss across the membranes. This means that the net energy that can be gained is small.
“It is also noteworthy that the Japanese plant uses concentrated seawater, the brine left after removal of fresh water in a desalination plant, as the feed, which increases the difference in salt concentrations and thus the energy available.”
From idea to deployment: a brief explainer and what’s next
The concept behind osmotic or 'blue' energy has been in development for decades. In 1954, RE Pattle first theorised the potential to harvest energy from the mixing of fresh and saltwater. In the 1970s, Professor Sidney Loeb, co-inventor of reverse osmosis desalination, developed the framework for pressure-retarded osmosis after observing the natural mixing of the Jordan River and the Dead Sea.
One of the big barriers has been membrane cost and efficiency, because large surface areas and high pressures are required, and pressure-related and frictional losses erode net gains.
Recent advances aim to tackle those constraints. Hollow-fibre forward-osmosis membranes developed by Toyobo are designed to allow water molecules to pass while rejecting salts and impurities, improving overall efficiency in modern setups. These were used in the world’s first fully functioning osmotic power plant in Denmark.
In parallel, emerging approaches such as Ionic Nano Osmotic Diffusion from French startup Sweetch Energy use bio-sourced raw materials and nano-osmotic diffusion principles to enhance ionic selectivity and reduce losses, pointing toward more scalable blue-energy capture.