Energy

Electricity through osmosis: Japan opens landmark osmotic power plant

Electricity through osmosis: Japan opens landmark osmotic power plant
A desalination plant in Fukuoka has been connected to a new kind of osmotic electricity generator.
A desalination plant in Fukuoka has been connected to a new kind of osmotic electricity generator.
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A desalination plant in Fukuoka has been connected to a new kind of osmotic electricity generator.
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A desalination plant in Fukuoka has been connected to a new kind of osmotic electricity generator.

Imagine generating power not from sunlight or wind, but from the simple mixing of fresh and salt water. This is the quiet promise of osmotic energy, a renewable energy source generated where river meets ocean. The idea has been around for decades, but only now is it flowing into real-world use.

The principle behind osmotic potential is deceptively simple. When fresh and salt water are separated by a semi-permeable membrane, water molecules naturally move across the barrier to balance the difference. That flow builds up pressure strong enough to spin a turbine. No combustion, no emissions. And unlike wind or solar, there is no dependence on weather or daylight, making it capable of running continuously.

The first real push came in 2009, when the Norwegian company Statkraft built one of the world’s first prototype osmotic power plants. The four-kilowatt demonstration model proved the concept could generate electricity, but due to costs the technology mostly lingered in labs and small pilots.

Now, for only the second time since development of those prototypes, a full-scale facility has opened in Fukuoka, Japan. Built by a consortium including the National Institute for Materials Science and local partners, it’s the world’s second osmotic power facility designed for continuous output following the launch of another plant in Denmark in 2023. While considered modest in scale, it will generate around 880,000 kilowatt-hours per year – enough to power 220 households or offset the energy needs of a desalination plant.

What sets the Fukuoka facility apart from any prior iterations of the technology is not the amount of energy it generates, but how it applies physics to infrastructure. By pairing with a desalination plant, it taps into concentrated brine waste that would otherwise be discarded, creating a sharper salinity contrast than rivers naturally provide. Those stronger gradients boost efficiency and grounds osmotic generation in existing systems rather than the lab.

Still, hurdles remain. Pumping losses and membrane fouling can erode efficiency, and advanced membranes are expensive.

“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," said Professor Sandra Kentish of the University of Melbourne in a recent interview with The Guardian. "This means that the net energy that can be gained is small.”

Precisely the sort of challenges that pushed companies such as Statkraft to shutter its prototype after a few years.

While the Fukuoka facility doesn’t claim to have solved all of the issues, it shows that osmotic power can be folded into real-world infrastructure. Advances in membrane and pump technology are reducing the losses, Kentish noted, and Japan’s use of concentrated brine from desalination increases the energy available. That integration marks an engineering milestone – and underscores the core attraction of osmotic power: its reliability.

Unlike solar or wind, osmotic power can run continuously wherever fresh and saltwater meet; at estuaries, desalination plants, even inland salt lakes. Researchers say the global potential is vast, potentially one day rivaling hydropower if costs continue to come down. The launch of the Fukuoka plant signals renewed interest in exploring this emerging energy source.

And while osmotic power may never match the scale of solar or offshore wind, parity isn’t required for impact. As energy grids diversify, steady background renewables will matter more than ever, especially when they can plug into existing infrastructure.

In Fukuoka, salt and fresh water are already driving turbines, turning a long-studied concept into a working source of power. A modest step, showing osmotic power edging closer to real-world relevance.

Sources: Science Japan, The Guardian

10 comments
10 comments
TechGazer
Doesn't seem like a good bet for river/sea situations, due to fouling. However, there might be strong chemical solutions as waste from industries that might make economic sense to exploit. Assuming that dilution is the solution to disposing of that waste. The chemical waste probably has less potential for biological fouling.
SamH
I see difficulties in getting your fresh water and salt water into the one location in sufficient volume to generate enough electricity. A damn is kind of doing the same thing but harnessing the energy differently. Rivers get progressively salty as they near the ocean so do you end up piping water from distant locations?
martinwinlow
When are we going to stop wasting all this time, talent, effort and money on these ridiculous and equally pointless 'white elephant' projects? I'm sure there is a very good reason (probably many) that the Norwegians did not run with this idea when they tried it. Why keep on trying to reinvent a wonky wheel?!! We've been doing the same for 50 years trying to make hydrogen work as a replacement for fossil fuels and that's just as patently daft! You only have understand the - pretty basic problems - and then 'do the math'! It isn't rocket science!
Aside from the simple fact that PV is easily now the cheapest way to generate electricity, what on Earth is the point in generating vast quantities of useless salty water from not quite so vast quantities of fresh water when half the countries on the planet are already short of fresh water - some critically so? Spend the money on battery storage instead and stop this idiotic nonsense!
Brian M
'and unlike wind or solar, there is no dependence on weather '
Of course that is not strictly true, rivers depend on the weather/climate for its water, no rain, less flow or even no flow
The truly independent, predicable and reliably sources are things like tidal barrages and geothermal energy (at least in human timescale terms).
Like solar and wind it could work as part of a mix, although it doesn't seem that cost efficient.
harry van trotsenburg
It is done also in the Netherlands: Blue Energy - De Afsluitdijk https://deafsluitdijk.nl/projecten/blue-energy/
Techjunkie88
An interesting tech for very specific locations with a supply of highly saline water. I'm not sure I get the logic of teaming with desalination plants though, as surely then you are using your product (fresh water) to supply the energy and a quick review of the literature suggests that you cannot get out what you put in - desalination can cost 3kWh per m3 of water (https://www.chunkerowaterplant.com/news/water-desalination-station), whereas reverse osmosis generates less than 1 kWh per m3 of flow (https://doi.org/10.1016/j.enconman.2020.113504). Nevertheless the article about SaltPower linked to is worth a read, and the LCOE could between 10 to 20 cents per kWh when combined with geothermal projects from highly saline aquifers.
rgbatduke
It seems that the real problem is that they are relying on mechanical means to generate the electricity. This "shouldn't" be necessary -- if there is an energy differential, it should be possible to directly extract electricity from it via a specially engineered membrane. Both sodium and chlorine ions "want" to get to the other side of the barrier -- if one has two barrier membranes, one of which will pass sodium ions through nanoscale pores but retain chlorine ions (which is almost twice the size) one SHOULD be able to establish a direct osmosis-to-electric potential transformation in a fully passive system. The human body does something a bit like this with its neural sodium channels, but it doesn't have the osmotic energy to draw on -- it actually has to oppose it via biochemical energy.
I don't THINK that this will violate any laws of thermodynamics -- there is no Maxwell Demon involved, only differentially permeable membranes actually driven by osmotic pressure. Best of all, if one neutralizes the ions as they pass through the separated membranes via electron transfer (a driven electric current) they change size! Neutral sodium per se is actually larger than neutral chlorine, which will prevent it from establishing any sort of detailed balance back-flow as long as the fresh water is constantly refreshed to maintain the pressure.
WONKY KLERKY
I note: From image of ye plant shewn, no apparent use made of its 'flat' roof area for PV panel fix. Q: Artists rendition (presumably of early proposal for scheme) / snap proper?
Trylon
It makes no sense to use it to drive a desalinization plant. Here you are using energy to desalinate water and then you're going to waste that newly desalinated water to generate electricity by passing it through the membrane to dilute the newly concentrated brine? Sounds like somebody's idea of a "perpetual motion machine" to me.
Rustgecko
This keeps a few academics in a job, but don’t sell your shares in nuclear, windmills or hydro yet.