Flexible rubber blades for tidal turbines

A study published in Nature demonstrates that tidal turbines fitted with flexible rubber blades can generate as much electricity as conventional designs that rely on complex active pitch-control systems. Engineers from the University of Edinburgh and Michelin designed blades made of flexible rubber with a stiff internal steel spar running from root to tip. As currents strengthen, the trailing edge bends and flattens the blade's curved profile, automatically shedding excess load without hinges, bearings, or actuators.

The team tested a 1.26-meter (4.1-foot) model turbine at the University of Edinburgh's FloWave Ocean Energy Research Facility, a 25-meter (82-foot) circular tank that recreates turbulence found at real tidal sites. Submerged cameras filmed the blades changing shape as they spun. Combining measurements with simulations of a full tidal cycle, researchers found the rubber-bladed turbine produced the same energy as a conventional turbine with active pitch control under the same conditions, while reducing rapid load fluctuations that drive fatigue damage by up to 29%. Because rubber has a similar density to water, the blades can be made neutrally buoyant, further limiting load fluctuations.

The approach could eliminate the costliest and most failure-prone parts of tidal turbines. Pitch-control systems—motors, sensors, and bearings that twist blades away from strong flows—are expensive, difficult to maintain underwater, and a major source of breakdowns. Professor Ignazio Maria Viola of the University of Edinburgh's School of Engineering, who co-led the study, said: "Tidal energy is one of the most predictable renewable resources we have, but the sea is so unforgiving that turbines have needed complex machinery just to survive it. Our blades do that job on their own. By simply bending, they shed excess load and smooth out damaging fluctuations, while producing just as much energy."

Dr. Zhehong Zhang, co-first author, said the idea is to let blades adapt to the flow rather than relying on complex mechanical systems. Bertrand Daval, vice president of R&D for composite solutions at Michelin, said the company's expertise in rubber under heavy, repeated loads can help tackle one of the toughest challenges in renewable energy. Computer simulations of a 20-meter (66-foot) turbine suggest similar effectiveness at commercial scale, with early calculations indicating full-size rubber blades could potentially exceed the 20-year service life expected of current turbines. The U.K. aims to install 1 gigawatt of tidal stream capacity by 2035, enough to power around 1 million homes, while international projections estimate more than 300 gigawatts could be generated worldwide by 2050. The work remains at the research stage; Michelin has filed a patent and the university holds related patents.