Society often draws inspiration from nature. Leonardo da Vinci studied birds to design flying machines, while Velcro was inspired by burdock burrs clinging to a dog. This approach imitates nature’s designs, known as biomimicry, but also addresses key human challenges through innovative engineering. With the same intention, French deeptech startup EEL Energy sought to redefine how we harness energy from nature. But when delamination in its design threatened to halt progress, pultruded and pull-wound composites manufacturer Exel Composites was ready with a solution.

EEL Energy specialises in hydrokinetic machines, developing a patented undulating membrane that draws inspiration from the movements of fish tails. This biomimetic design captures kinetic energy from water currents, providing a sustainable method for generating electricity that is non-disruptive to aquatic ecosystems.

However, as EEL embarked on bringing hydrokinetic energy production to market, it faced significant challenges. The underwater environment is particularly demanding, necessitating materials that can withstand extreme stress and pressure.

“Hydrokinetic generation exerts up to 30 times more mechanical stress on equipment than wind energy production,” explained Xavier Peroutka, CEO at EEL. “Hydrokinetic generators can produce energy constantly throughout their life by leveraging the water currents in rivers or tidal flow. The predictability of hydrokinetic energy generation is needed by communities across the globe in a green revolution that threatens to leave the neediest behind.”

Collaboration to gain material expertise

To address the challenge, EEL sought out Exel Composites. The collaboration aimed to enhance the resilience of EEL’s membrane and refine its performance for harsh underwater conditions.

Initially, EEL reinforced its membrane with fiberglass, but this original design revealed a critical flaw: delamination. Under the harsh cyclic loading of the underwater conditions, the membrane underwent large deformations, inducing high strains in the structure. The strain caused the layers of the membrane to separate, allowing water to infiltrate and compromise its functionality.

Recognising the serious implications of this issue — where a failure of the membrane during operation could jeopardize the entire hydrokinetic system — EEL required a solution capable of withstanding the continuous mechanical stress required for effective operation.

Composite solutions form the sky to the sea

Exel used multiple layers of discrete carbon flat profiles — the same as those developed for wind turbine applications. These carbon fiber flats are stacked to create beams which were strategically integrated into the membrane. Three bars were placed across it at 50, 80, and 100 per cent of its length. This arrangement prevents bulging and limits overall deformation, ensuring the membrane maintains structural integrity and operates optimally.

“The key to success was recognizing that our carbon fiber flats, originally designed for wind turbine blades, could be repurposed for EEL’s hydrokinetic membranes,” explained Neil Dykes, research and development manager at Exel Composites. “These flats provide the stiffness and strength required to withstand harsh wind conditions, making them ideal for this application.”

EXE571 – From fish tales to energy trails – HN The mechanical properties of Exel’s carbon fiber composites (CFRP) were essential to the membrane’s success. With an E-modulus of approximately 120 GPa, CFRP exhibits higher stiffness than traditional glass fiber composites (GFRP), which is only a third of CFRP’s stiffness. This high stiffness ensures the membrane retains its shape under operational stress, preventing excessive deformation and energy loss.

CFRP’s tensile strength of 2500 MPa, compared to GFRP’s  1000 MPa, enables it to withstand greater forces without failure. Additionally, CFRP’s compressive strength, at 1500 MPa, is much greater than the 600 MPa typical of GFRP. This increased strength, combined with CFRP’s excellent fatigue resistance, ensures the membrane can handle the cyclic loading conditions experienced during operation, supporting up to 6000 full reversal cycles per day. This durability is key for maintaining high efficiency in energy capture over the long term.

Biomimicry can unlock innovative solutions by mimicking nature’s designs, a principle at the heart of EEL’s hydrokinetic generators. In collaboration with Exel Composites, the company has created a system that delivers sustainable, reliable power for remote communities and large-scale energy farms. As EEL advances towards commercializing its technology, powered by Exel’s cutting-edge carbon composites, the potential for revolutionising renewable energy is within reach.

 Exel Composites is one of the largest manufacturers of pultruded and pull-wound composite profiles and tubes and a pultrusion technology forerunner in the global composite market. Our forward-thinking composite solutions made with continuous manufacturing technologies serve customers in a wide range of industries around the world. You can find our products used in applications in diverse industrial sectors such as wind power, transportation and building and infrastructure.

Their R&D expertise, collaborative approach and global footprint set them apart from their competition. Theircomposite solutions help customers save resources, reduce products’ weight, improve performance and energy efficiency, and decrease total lifetime costs. We want to be the first choice for sustainable composite solutions globally.

Headquartered in Finland, Exel Composites employs over 600 forward-thinking professionals around the world and is listed on Nasdaq Helsinki. To find out more about our offering and company please visit www.exelcomposites.com.

To discover more about how composites can power renewable energy applications, visit exelcomposites.com.