Not Wind, Not Solar: Japan's Renewable Project Makes Energy From Saltwater

Wind and solar power are both well established sources of renewable energy, but for nations with plenty of coastline, a promising emerging technology called osmotic power offers another possibility. Osmotic power involves generating electricity from the natural interaction between saltwater and freshwater, and Japan has turned the intriguing idea into a working power plant. The technology uses a membrane that separates saltwater from freshwater. The membrane allows water molecules to pass through from the freshwater side into the saltwater side, while blocking most of the salt. This movement, known as osmosis, increases the amount of water on the saltwater side, creating a pressurized flow that can be used to drive a turbine connected to a generator, producing electricity.

Japan, a country that's no stranger to exploring new energy technologies, began operating the osmotic power facility in the western city of Fukuoka in 2025 using concentrated brine left over from seawater desalination alongside treated wastewater. Rather than simply discarding the water streams, the plant uses the difference in their salt concentrations to generate power. One of the features of the technology is that the process doesn't depend on an abundance of sunshine or wind, as it can, in principle, produce electricity whenever the two water streams are available.

It's important to recognize, though, that generating electricity from osmosis comes with its own challenges. The facility has to use energy to run its equipment, and the special membranes need to work efficiently and affordably if the process is ever to become commercially viable. Japan's project is a notable real-world demonstration of the technology, but the bigger question is whether osmotic power can generate enough electricity at a competitive cost to make a difference beyond a single facility.

A striking feature of the new osmotic power plant in Fukuoka is the way in which it uses existing infrastructure. The facility combines concentrated brine left over from seawater desalination with treated wastewater, recovering energy from water streams that would otherwise be discarded. It's expected to generate around 880,000 kilowatt-hours of electricity a year, equivalent to the annual consumption of around 300 Japanese households.

But scaling up the system remains a challenge. Researchers have pointed to energy losses from pumping water through the plant and friction across the membranes, which reduce the amount of electricity that's available to use. It means that improving membrane and pump technology will be important in the quest to make osmotic power commercially viable. Generating power is one thing, but it has to be produced cheaply enough to compete with other energy sources — a challenge that next-generation geothermal power is also working to overcome.

Osmotic power may have its greatest near-term potential not as a rival to wind and solar farms, each of which already excels in efficiency, but as a way to recover additional energy at facilities that already process large amounts of water. With that in mind, coastal regions with a lot of desalination infrastructure, such as parts of the Middle East, could find the technology particularly useful. Japan has demonstrated what the technology can do. The next step is to make it efficient and affordable enough for wider adoption.