On a humid morning in Fukuoka, a coastal city in southern Japan, a new kind of power came online. Japan has launched Asia’s first osmotic power plant, which generates electricity by mixing fresh water with salt water.

“It’s a meaningful plan—the start of a plan, perhaps—in our response against climate change,” said Kenji Hirokawa, director of the Seawater Desalination Center, which runs the facility, as per Gizmodo.

Fukuoka’s plant is only the second of its kind worldwide, following one in Denmark that opened in 2023. Japan’s version is larger and marks a step forward for this little-used but promising renewable energy source.

The plant will generate about 880,000 kilowatt hours of electricity per year—enough to help run a nearby desalination facility and supply around 220 homes. That equals the output of two soccer fields of solar panels, but osmotic power keeps running day and night, in any weather.

What Is Osmotic Power?

Osmosis is the same process that helps plants draw water from soil and allows our cells to stay hydrated. Put simply, it’s the movement of water from areas with low salt concentration (like fresh water) to areas with high salt concentration (like seawater) through a special membrane.

Osmotic power plants put this passive movement to work.

Fresh water—or treated wastewater—is placed on one side of a membrane. On the other side is seawater, made even saltier by concentrating leftover brine from a desalination process. The difference in saltiness pulls the fresh water across the membrane, increasing the pressure on the saltwater side. That pressure is then used to drive a turbine, generating electricity.

“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,” Professor Sandra Kentish, a chemical engineer at the University of Melbourne, told The Guardian.

The process is completely renewable. It produces no carbon dioxide. And because oceans and sea are virtually boundless for this task, osmotic power is “a stable source of electricity generation that can operate 24 hours a day, for every day of the year,” Hirokawa told NHK (translated from Japanese).

Why Haven’t We Used This Before?

For something that sounds so elegantly simple, osmotic power has been stubbornly difficult to scale.

“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,” said Kentish.

The challenge lies in efficiency. Pumps use up power to move water into the system, and membranes can slow things down due to friction. These hurdles are not unsolvable, but they’ve kept osmotic power in the shadows of its other counterparts—wind, solar, and hydroelectric.

Still, research teams across the globe have kept the idea alive. In addition to Denmark and Japan, pilot projects have cropped up in Norway, South Korea, Spain, and Qatar. Australia paused its prototype plant at the University of Technology Sydney (UTS) during the COVID pandemic. But Dr. Ali Altaee, a specialist in water-energy systems at UTS, hopes it can be revived.

“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,” he told The Guardian.

Akihiko Tanioka, professor emeritus at the Institute of Science Tokyo and a pioneer in the field, showed visible emotion at the launch. “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,” he told Kyodo News.

Can the Tide Turn for Osmotic Energy?

Today, osmotic power contributes only a microscopic fraction of global electricity. But if technical challenges can be solved, researchers say it could eventually meet up to 15% of global energy demand by 2050.

That would make it one of the largest untapped renewable sources on Earth.

What gives osmotic power its unique edge is consistency. Wind slows and clouds can obstruct the sun. But rivers never stop running to the sea. Wherever fresh water meets salt water—estuaries, deltas, and coasts—there’s potential for power.

The Fukuoka facility is modest by global standards. But it is real and operating. And it is the first of its kind in Asia.

As the need for reliable clean energy grows, the simple act of mixing fresh and salt water could play a bigger role.