Flexible rubber blades for tidal turbines

A study published in Nature by engineers from the University of Edinburgh and Michelin shows that tidal turbine blades made of flexible rubber with a stiff internal steel spar can generate as much electricity as conventional turbines that rely on active pitch control, while reducing the rapid load fluctuations that cause fatigue damage by up to 29%. The blades automatically bend and flatten their curved profile as currents strengthen, shedding excess load without hinges, bearings, or actuators. Researchers 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. Cameras filmed the blades changing shape as they spun. Combining measurements with simulations of a full tidal cycle, the team found the rubber-bladed turbine produced the same total energy yield as a rigid blade with active pitch control under the same conditions. Because rubber has a density similar to water, the blades can be made neutrally buoyant, further limiting load fluctuations. Computer simulations of a 20-meter (66-foot) turbine suggest the blades could be similarly effective at commercial scale, and early calculations indicate 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, and international projections estimate more than 300 gigawatts could be generated worldwide by 2050. However, fast-flowing tidal channels are among the harshest places to build a machine, and today's largest turbines rely on expensive, failure-prone pitch control systems with motors, sensors, and bearings that are difficult to maintain underwater. Professor Ignazio Maria Viola of the University of Edinburgh's School of Engineering, who co-led the study, said the 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 the blades adapt to the flow, rather than relying on complex mechanical systems to withstand harsh ocean currents." Bertrand Daval, vice president of research and development for composite solutions at Michelin, said the research shows how Michelin's expertise in rubber under heavy, repeated loads can help tackle one of the toughest challenges in renewable energy. Michelin has filed a patent on the technology, and the university holds related patents. The work remains at the research stage, and further development and testing would be required before any potential industrial application or commercialization.