We are currently going through a time where the search for clean and renewable energies It is the absolute priority. In this path the main assets are the solar and wind energy. We have been talking about them for a while and we are more than aware that they have a clear problem: both depend on the weather. If we are on a cloudy or windless day, they do not produce energy and, therefore, electricity.

This has led to a desperate search for efficient ways of storage of the surplus. And at peak times, with the sun beating down, more energy is generated than necessary. Until now the alternatives were enormous lithium batteries and, given how heavy, expensive and demanding in materials they are, work is being done looking for other options.

But beyond storage, there are other avenues of research open that are aimed at searching other alternatives to the solar energy and wind that do not depend as much on external situations as these two. One of those alternatives that is proposed as a solution is the osmotic energy, a constant and predictable source.

What is osmotic energy?

Osmotic energy, also known as blue energy, is a renewable energy source that is obtained by taking advantage of the difference in salinity between fresh water and salt water. When a river flows into the sea, fresh water meets salt water and a large amount of energy is released, since nature tends to balance salt concentrations. If at that point we build a plant that captures that energy in a controlled way, we will have a constant energy source.

In its classic version, the process is relatively simple. The fresh water, that of a river, is conducted through a tube and crosses a membrane towards the compartment where the salt water, that of the sea, is found. This transfer increases the volume and generates pressure, and that pressure is used to move a turbine that generates electricity, just like in a small hydroelectric plant.

The idea, by the way, is not new: it has been researched since the 1950s. The problem was always the same, that the membranes cost too much for the few watts they delivered. The pilots that were built in Norway and the Netherlands stayed between 4 and 50 kilowatts, and the industry ended up shelving the matter a decade ago.

Sweetch Energy and its INOD Technology

Traditionally, two main methods have been investigated: pressure retarded osmosis (PRO) and reverse electrodialysis (RED). However, the high cost and low efficiency of membranes slowed their development for decades. The innovation of Sweetch Energy, with its INOD® technology (Ionic Nano Osmotic Diffusion), has arrived to change everything.

The key is in the improvement of membranes, which makes them more efficient, durable and cheaper, solving the main obstacle that prevented this technology from taking off. And here comes the twist: INOD® technology uses a physical phenomenon, nano-ionic osmotic diffusion, to generate a ionic current directly through their membraneswithout the need for any turbine. The ions move, the electrodes collect that current, and there is electricity.

INOD® is based on a physical phenomenon discovered in the laboratory of the École Normale Supérieure in France by the team of Lydéric Bocquet, research director of the CNRS and one of the world’s leading names in nanofluidics, who identified the effect at the beginning of the last decade and founded the company in 2015 to bring it to the market.

The membranes are manufactured with materials of biological originabundant and already used in other industries, which makes them much cheaper and more sustainable. And the jump in performance is brutal: Bocquet himself estimates it at almost 20 times what previous osmotic plants achieved. This technological advance is what has allowed us to go from laboratory prototypes to an industrial demonstrator like OPUS-1.

The Rhône Project: Roadmap to 500 MW

The demonstrator plant OPUS-1, located at the Barcarin lock in Port-Saint-Louis-du-Rhônebegan its tests at the end of 2024, right at the exact point where the Rhône ends its career and meets the Mediterranean. The project is being developed together with CNR, the Compagnie Nationale du Rhône, which produces no less than 25% of French hydroelectric energy.

At the plant, fresh water from the Rhône and salt water from the Mediterranean are channeled into modules containing hundreds of stacked INOD® membranes. The controlled flow of ions through these selective membranes generates an electrical current that the electrodes collect and send to the network. No moving parts, no turbines, no noise.

Unlike solar or wind power, this process does not depend on the weather and can work 24/7, offering constant and reliable “baseline” electricity. The plant returns water to the estuary without creating chemical waste, because water is the only ingredient in the process.

Another advantage that is often overlooked is the terrain. According to the company itself, a megawatt-scale osmotic station needs about 1,500 square meters, about 60 times less surface area than an equivalent solar installation. The energy is in the water, not distributed over an entire field.

The OPUS-1 demonstrator plant is the first step of an ambitious plan. And the goal is to install a series of plants along the Rhône estuary in the next decade and, with them, reach a capacity of 500 MW. This energy could supply more than 1.5 million people, a figure similar to the population of Marseille and its metropolitan area.

The numbers of the delta are enough to dream about: the CNR itself calculates that the osmotic resource of the mouth is around 4 terawatt hours per year, a third of what all the river’s dams already generate. And the company’s economic objective is to reach 100 euros per megawatt hour in 2030, a price that would put it on par with nuclear or gas, and below other renewables accompanied by batteries.

In addition, the project has collaboration with Rockwell Automationwhich focuses on digital transformation and intelligent plant control. For facilities like the plant in the Rhône, these strategies achieve real-time visibility, optimize energy consumption, reduce operating costs and improve process efficiency and quality.

An energy for the future

The potential of osmotic energy is enormous. The World Economic Forum has named it one of the 10 emerging technologies to follow in 2025, and estimates by the sector suggest that it could cover up to 20% of global energy needs. The Dubai Future Foundation’s estimate is that osmotic systems could generate about 5,177 TWh per year, almost a fifth of current global demand.

The Rhône plant is not the only one. Japan opened its first osmotic power plant in Fukuoka in August 2025, with a capacity to produce 880,000 kWh per year, taking advantage of brine from a nearby desalination plant. That works with the classic method, that of pressure and the turbine, and its production powers an office building. The French goal is about 4,500 times higher.

It is advisable, however, to be honest with what remains to be demonstrated. None of the cost figures are yet validated on an industrial scale, and although osmotic energy does not depend on the sun or wind, it does depend on the flow of the river, which varies with the seasons and with droughts. The acid test will not come with the press releases, but with the first megawatt-scale station in the delta and the real price at which it delivers each megawatt hour.

Additionally, this technology can be combined with other sources. For example, using waste heat from nuclear plants or solar energy to heat water and increase the efficiency of the osmotic process, or integrating it into desalination plants to take advantage of its brine.