Japan’s new osmotic power plant turns saltwater into clean energy

Japan has launched its first osmotic power plant in the city of Fukuoka, marking a significant step in renewable energy innovation. This facility is only the second of its kind in the world and is designed to produce around 880,000 kilowatt-hours of electricity annually. That’s enough to help power a local desalination plant that supplies fresh water to Fukuoka and nearby communities.

According to Dr Ali Altaee from the University of Technology Sydney (UTS), this output is equivalent to the electricity used by about 220 Japanese households. He explained that while osmotic power is still a developing technology, it has one big advantage over solar and wind—it operates continuously, day and night.

“It relies simply on the mixing of fresh and salt water, so the energy flow can continue day and night, providing a steady source of electricity.”

How osmotic power works

Osmosis is the natural process where water moves through a semipermeable membrane from a less concentrated to a more concentrated solution, trying to balance both sides. Imagine a cup divided by a thin membrane: freshwater on one side, salty water on the other. The freshwater moves toward the salty side to even out the concentration.

Osmotic power plants use this same principle. They separate freshwater and seawater with a special membrane. When water moves toward the saltier side, it increases pressure that can be converted into electricity.

At the Fukuoka plant, freshwater—or even treated wastewater—and seawater are placed on either side of a membrane. The seawater side builds pressure, and some of that water is channeled through a turbine connected to a generator, producing renewable power.

A growing global effort

The Fukuoka facility follows the world’s first osmotic power plant built in 2023 in Mariager, Denmark, by SaltPower. While both plants operate on similar principles, Japan’s version is larger. Research projects and pilot systems have also appeared in Norway, South Korea, Spain, and Qatar.

Dr Altaee mentioned that UTS in Sydney had built its own prototype before the Covid pandemic interrupted progress. The team hopes to restart the project with future government funding.

Challenges and breakthroughs

Despite its potential, scaling osmotic power remains complex. Professor Sandra Kentish from the University of Melbourne pointed out that a lot of energy is lost when pumping water into the plant and during its movement through the membranes.

“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,” Kentish said. “This means that the net energy that can be gained is small.”

However, new advances in pump and membrane technology are helping to reduce these inefficiencies. The Japanese plant also uses concentrated seawater left over from desalination—known as brine—which increases the difference in salt levels and boosts energy production.

Looking ahead

Both Kentish and Altaee agree that Japan’s osmotic plant signals a major step forward. It proves that osmotic power can be applied on a larger scale, contributing to clean and continuous renewable energy.

Altaee noted that similar facilities could be built in Australia, especially around New South Wales and Sydney, where salt lakes offer natural potential for osmotic energy.

“We have salt lakes around New South Wales and Sydney that could be used as a resource and we also have the expertise to build it.”