Osmotic energy and the future of power
Can nature’s flow fuel tomorrow’s grid?
Photo: Ilan Kelman
Where freshwater meets saltwater south of Tofte in the Oslofjord — it was once the testing ground for Norway’s bold but elusive pursuit of osmotic energy.
As our thirst for electricity appears to be insatiable, Norway has been seeking creativity through osmosis. Not just the absorption and mingling of ideas by experts, but also through “osmotic energy” experimented with in the stretch of water south of Oslo, appropriately named Oslofjord.
Where a river meets the ocean, so meet saltwater and freshwater. Fjords are natural junctions, being fed by rainfall runoff from the land and opening into the sea. The salt concentration changes from the rain and river’s freshwater to the ocean’s salty water.
A membrane can be placed between the two waters. Nature does not like this change in salt concentration, so water flows naturally toward the higher salt concentration, attempting to equalize them. This process is called “osmosis” and the water flow through the membrane can be converted into electricity.
The huge potential for this electricity is the good news. Consider the large number of places with interfaces between saltwater and freshwater. Drop a membrane there and reap the rewards.
The bad news is that it does not quite work at the scale desired. Despite years of investment, research continues to produce a workable membrane and system, particularly at the size required to traverse a fjord’s width. Then consider monitoring and maintenance. Not to mention the consequences for shipping, recreational boats, marine life, and the wider ecosystems of having a membrane across a river mouth or fjord — and having it decay or break.
The electricity generation plants and distribution systems have costs and impacts. Many of us already lament seeing and dealing with transmission lines, transformer substations, and electricity pylons throughout our cities. How many would support osmosis infrastructure development exactly where needed, which could be a fragile delta, estuary, or wetland?
Trials in Oslofjord were inconclusive. At Tofte, which sits at the south end of the fjord’s narrowest part, the energy company Statkraft — fully owned by the government of Norway and marketing itself as “Europe’s largest renewable energy producer” — tested osmotic energy. Using a design finalized in 2006, three years later, they built a 10-kilowatt osmotic energy power plant. In practice, it produced less than half the electricity it should have, reported variously as being enough to power a handful of Norwegian households or a handful of kettles. The total membrane area was 2,000 m2 which is about one-third larger than a standard NHL ice hockey rink.
Statkraft’s osmotic energy was called “pressure retarded osmosis” (PRO) and the Tofte plant was the first of its kind in the world to generate this electricity on its own. In 2013, Statkraft obtained a permit to scale up this plant for producing up to 200 times as much electricity by Sunndalsøra near Trondheim. They never proceeded with it, and they closed the smaller plant, because they did not find it economically viable.
Since then, osmotic energy in Norway has stalled while research into the technology of osmotic energy has accelerated. Membranes now use the latest nanomaterials while the electricity generation is starting to examine nanofluids, in which nanoparticles are suspended in the liquid. Despite these important advancements, successful large-scale commercialization remains elusive, although PRO is not the only technique for producing osmotic energy.
Reality must match marketing. For the Tofte plant, one video claimed it to be “free energy,” despite the cost of building, operating, maintaining, and decommissioning the membrane and the plant — on top of the cost to distribute the electricity to the locations where it would be used. Same with “pollution-free.” Osmosis does not produce direct emissions. All the accompanying infrastructure does, including membrane manufacturing.
Osmotic energy being labeled as “all-weather” needs to be taken with (pardon the pun) a grain of salt. If the waterway freezes (at lower temperatures than rivers due to the saltiness) or if storminess reaches quite deep, then how would the performance of electricity generation fare? Have the designs been checked for withstanding tsunamis?
Despite the setbacks of its osmotic energy experiment at Tofte, Statkraft continues to play a key role in Norway’s broader push for renewable innovation. As Europe’s largest generator of renewable energy, the company is part of a national landscape where experimentation with future-facing technologies remains central — even when projects, like osmotic energy, don’t yet deliver at scale. Norway, with its natural resources and strong research environment, continues to serve as a testing ground for energy solutions that could shape tomorrow’s grid.
Current efforts demonstrate an ongoing commitment to exploring new models and technologies. These include green hydrogen, advanced biofuels, and hybrid systems that combine wind, solar, and hydropower. Innovations in AI-driven energy trading and hydropower flexibility show how the focus remains not just on generating more electricity, but also on building smarter, more adaptive systems. While osmotic energy may not have lived up to its early promise, it fits into a pattern of continual experimentation that defines Norway’s role in the future of energy.
The baseline question remains: Why does our electricity appetite never seem to be satisfied? Kudos to those pursuing osmotic energy and other creative renewable supply systems for electricity and other energy forms. Let’s always prioritize innovation in reducing demand.
This article originally appeared in the August 2025 issue of The Norwegian American.
