As the world faces the pressing need for sustainable solutions to combat climate change, the quest for innovative renewable energy sources is more critical than ever. One such promising avenue is osmotic power. French start-up Sweetch Energy is at the forefront of this technology, pioneering advances that could redefine the landscape of renewable energy.

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Osmotic energy is a lesser-known form of energy generation that captures the energy generated from the natural salinity gradient between freshwater and saltwater. 

This type of energy  – also known as “blue energy” – is generated through the natural phenomenon of osmosis. This occurs when water moves from an area of lower solute concentration (freshwater) to an area of higher solute concentration (saltwater) across a semipermeable membrane. When freshwater and seawater meet, a natural gradient in salinity is created, prompting ions to migrate from the saltier side to the less salty side in pursuit of equilibrium. The movement of water and ions generates a pressure differential that can be harnessed to produce electricity. The process resembles a “silent lightning strike” occurring continuously at the confluence of rivers and oceans.

The concept of osmotic power emerged in the 1970s but practical implementation faced significant hurdles for decades. The primary challenge was the inefficiency of the membranes required for effective ion exchange, a crucial process for energy production. Early projects yielded mixed results. 

While various initiatives explored osmotic power locally, achieving a viable scale of operation for industrial use proved difficult. For example, Dutch company Redstack installed a demonstrator in 2014, though it only operates at a small scale on a dike. Similarly, Norway’s Statkraft, a state-owned green energy company, launched a demonstrator in 2009, but ceased operations in 2013 due to concerns about economic viability and insufficient energy output.

Sweetch Energy, a French start-up founded by researchers Bruno Mottet and Lydéric Bocquet, has unveiled a potential game-changer in the realm of renewable energy. The company has developed an innovative technology known as Ionic Nano Osmotic Diffusion (INOD), which promises to unlock osmotic energy on a large scale. 

The hallmark of Sweetch Energy’s approach lies in its unique and highly efficient membranes. They are composed of biomaterial manufactured using advanced patented nanotube technology to create pores measuring just ten nanometres, thus providing superior ion mobility compared to conventional materials.

This innovative design holds the potential to reshape the landscape of blue energy generation. In terms of osmotic performance, Sweetch Energy’s technology could be around 20 or 25 W/m2, a significant leap compared to the 1 W/m2 achieved by previous membrane devices. Moreover, by utilizing a biosourced material readily available within the industry for their membranes, the company anticipates the cost of materials would be reduced to one-tenth of the current price, making it a truly energy-efficient and cost-effective solution.

Sweetch Energy’s ambitions extend far beyond the confines of its laboratory. For more than three years, the company has been taking significant strides to reach industrial-scale production of its osmotic energy modules. 

At the end of 2024, the company’s pilot plant, OsmoRhône, became operational. The facility is located at the confluence of the Rhône River and the Mediterranean Sea – a particularly saline sea – with plans to expand beyond France’s borders. The company has targeted this river because it offers the highest osmotic electricity potential in France, estimated at about a third of the total hydraulic energy produced on the Rhône (13 TWh).

The initial stage will focus on producing a small amount of power, starting at a few dozen kilowatts, with the intention of scaling up production gradually in the years to come. In the long term, OsmoRhône is set to have a production capacity of 500 megawatts – enough energy to power over 1.5 million households, equivalent to the population of cities such as Barcelona, Amsterdam, or Montreal. 

As production scales up and infrastructure develops, the costs associated with osmotic power are projected to decline, making it more competitive with other established renewable sources such as solar and wind energy. 

One of the most remarkable attributes of osmotic energy is that its production is permanent and independent of weather conditions. Unlike intermittent sources such as solar or wind power, osmotic energy relies on the consistent and predictable natural flow of freshwater rivers into saltwater seas offering a stable and reliable energy source.

If successful, the potential of osmotic energy could be transformative. In contrast to traditional hydroelectric or fossil fuel-based energy generation methods, it does not generate carbon dioxide emissions, making it a clean energy source. What’s more, during the osmotic process water returns to its original environment with minimal ecological impact. While further studies are crucial to comprehensively assess potential long-term effects, particularly concerning salinity alterations in the return water, the preliminary outlook remains promising.

The global potential of osmotic power is considerable, with estimates suggesting that osmotic energy has the capability to satisfy up to 15% of global electricity demand if adequately leveraged. In regions like Greenland, where the paradox of climate change is evident, the unprecedented influx of freshwater from climate change-induced melting glaciers could ironically provide the increased freshwater flow needed to generate more osmotic power. Simultaneously, the deployment of osmotic power could contribute to combating the very climate change fuelling glacier melt, highlighting the technology’s multifaceted potential to address both environmental and energy challenges on a global scale.

The scalability of this technology introduces the prospect of integrating it into existing energy infrastructures, creating a more diverse and resilient energy landscape.

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energy energy transition france osmotic energy