Osmotic energy, created by the difference in salinity between river water and seawater, is emerging as a promising source of renewable electricity. Unlike wind or solar, this form of power is steady, carbon-free and naturally available wherever rivers meet the sea.
“Osmotic power is clean, completely natural, available 24 hours a day in all coastal areas, can be turned on almost instantly and modulated very easily,” explains Nicolas Heuzé, co-founder of Sweetch Energy, a company working to bring this technology to scale.
The World Economic Forum recently highlighted osmotic power as one of the 10 emerging technologies to watch in 2025; it is currently being reviewed by the Forum’s Global Future Council on Energy Technology Frontiers.
In France, a demonstration facility known as OPUS-1 began testing at the end of 2024 on the Rhône estuary. The pilot site is designed to show how osmotic systems can operate under real-world conditions.
At the facility, pipes channel freshwater and seawater. A controlled flow, through selective membranes, enables the generation of an ionic current — the core mechanism behind converting osmotic energy into electricity.
If replicated more widely on the Rhône estuary, such facilities could deliver up to 500 megawatts of carbon-free electricity, which could power more than 1.5 million people, according to Sweetch, a World Economic Forum Technology Pioneer. That is equivalent to the population of Marseille in southern France and its metropolitan area.
On geographic opportunities: Sweetch says it is exploring similar opportunities in North America and Asia, where osmotic resources are significant.
According to estimates from the Dubai Future Foundation, osmotic systems could eventually generate nearly a fifth of global electricity needs – around 5,177 terawatt-hours (TWh) annually.
“Globally, and particularly in salt-rich areas like Australia and the Middle East, where access to brackish or seawater exceeds access to freshwater, these power systems hold huge potential for baseload energy and clean water production,” says Dr Katherine Daniell, Director of the Australian National University’s School of Cybernetics.
Beyond licensing processes and effective environmental and social impact assessments, there are relatively few hurdles – which are technical and economic in nature – to broad adoption once sufficient financial investments are made into osmotic power systems.
From lab to generation
The concept of osmotic power systems is not new.
“It has been on the radar screens of academics and industrial companies since the 1950s,” says Heuzé.
Each year, nearly 30,000 TWh of osmotic energy – more than the world’s electricity demand – is released by deltas and estuaries, according to Sweetch.
Attempts were made in the 1970s to harness this osmotic energy, which would otherwise dissipate but were not commercialized as the membranes – used to generate the ionic current needed to produce electricity – were inefficient and produced only small amounts of electricity.
But new scientific breakthroughs and material patents have increased the potential viability of osmotic power systems in recent years, Daniell said in an interview with The Innovator.
Sweetch Energy’s technology was inspired by the technological breakthrough of a team in the physics laboratory of France’s l’École Normale Supérieure directed by Lydéric Bocquet.
Instead of focusing uniquely on the materials used to make the membranes, it looked at nanofluidics. The first experiments use a unique nanotube placed at the intersection of two reservoirs of salt water and clear water during the ionic transport.
The most important lesson learned from these experiments was to propose a different route for membrane design based on optimal osmotic transport at nanoscales, says Heuzé. “In a nanotube, you can make the pores 100 times bigger than previous pores, which means the ions can circulate much faster, making it easier to scale,” he says.
Competitive in renewables
Heuzé and co-founders Bruno Mottet and Pascal Le Melinaire approached Bocquet about commercializing the technology and Sweetch Energy was launched in 2015.
The team spent the next six years developing a new membrane that could replicate the efficient nano diffusion created in the lab, with materials that were low-cost, sustainable and easy to industrialize.
The result was a new type of nanoporous membrane: INOD (Ionic Nano Osmotic Diffusion) membrane, made from natural materials found everywhere on Earth and widely used in other industries. Combined with proprietary electrode systems, these membranes combine high ion selectivity and high ion transport, allowing more energy to be produced.
INOD membranes are now being used in the first pilot site to produce osmotic energy in France’s Rhône delta.
The objective is to produce electricity 24 hours a day and reach a cost of €100 per megawatt hour by 2030, competitive with main baseload sources such as nuclear, coal and gas (except gas in the United States) and cheaper than other renewable energy sources coupled with batteries.
Others are also trying to scale up osmotic energy. Japan’s first osmotic power plant began operations on 5 August in Fukuoka, a southwestern prefecture.
The Fukuoka District Waterworks Agency expects the power generation plant to produce 880,000 kilowatt-hours of electricity annually. The power will be used in a desalination facility that provides fresh water to the city and neighbouring areas.
An EU-funded Danish company, SaltPower, founded in 2015, already generates power using the super-concentrated salt solutions that well up from geothermal sites.
Beyond energy
Once the technology scales, utility companies might develop hybrid renewable systems that combine osmotic power with wind, solar and hydro technologies, enhancing local energy resilience.
Osmotic power has implications that go beyond electricity. Osmotic power technologies could enable new approaches to desalination while recovering critical resources like lithium during the process, according to the Dubai Future Foundation. It says this could create interconnected systems where water management, energy production and resource extraction become deeply integrated.
These applications suggest that osmotic systems could play a broader role in sustainable resource management, linking energy, water and materials in new ways.
While challenges remain, such as environmental assessments, regulatory frameworks and scaling infrastructure, the science and early pilot projects show that osmotic energy may soon complement wind, solar and hydro as a reliable source of renewable power.