In the quest for new ways to generate low-emissions electricity, some innovators have come up with unlikely ways of generating clean power, including a new generating station in Japan that runs solely on seawater—and luckily, 70 percent of the surface of our planet is covered with the stuff! Although this new facility doesn’t produce a great deal of power, it is only the second of its kind on the planet, a proof-of-concept project that has already been put to practical use.

This novel power plant, used by the Fukuoka District Waterworks Agency to power a desalination plant that services the Japanese city of Fukuoka, generates electricity using the pressure that results from water’s natural tendency to flow from one side of a membrane to the other—in this case using the difference in pressure between fresh and salt water—through a process called osmosis, generating power from the movement of the water across a membrane.

The key to this process is that, due to it being denser than fresh water, salt water has a higher pressure than its less-saline counterpart by 2.36 percent. Under normal circumstances, if a body of water is divided into two sections by a semi-permeable barrier (our osmotic membrane) that only allows water through, and one side is saltier than the other, the fresh water will flow through the barrier into the salty side to even out the saltiness of the two solutions, since the salt itself can’t pass through the membrane.

Using water pumps, power generating facilities that use this principle slightly pressurize the salty side of the membrane, so that when the fresh water seeps over to the saline side it increases that side’s volume; it is this change in volume that is used to power the electric generators.

Although the amount of power generated by the Fukuoka facility isn’t very high—just 880,000 kilowatt hours annually, enough to power about 220 households—it can be used 24 hours a day, an advantage it has over renewables like solar and wind generation. Unfortunately, a great deal of efficiency is lost from the need to operate the pumps used to create the pressure differential, an engineering limitation that the process’s developers are working on.

“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,” University of Melbourne Professor Sandra Kentish explained. “This means that the net energy that can be gained is small.”

However, the Fukuoka facility offsets this limitation by using the leftover concentrated brine that is created by the desalination plant—a distinct advantage for a facility that extracts salt from water—”which increases the difference in salt concentrations and thus the energy available.”

Although the Fukuoka plant is only the second of its kind in the world—the first went online in 2023 in Mariager, Denmark—it generates nearly four and a half times more power than its Danish predecessor, and has the previously-mentioned advantage of having ready access to highly concentrated brine to help drive the osmosis process. As future osmosis plants increase in size, their power output is also expected to scale with the size of the facility.