The German wind energy sector leads its European peers by a good margin. Germany operates more than 28,000 wind turbines, and their total output of 50 gigawatts accounted for a 12.3 percent share of the country's entire electricity production in 2016.
Fraunhofer IWES is at the forefront of refining wind energy technology. The company and its partners are working on “SmartBlades2,” a joint project that tackles the BTC concept for wind turbine rotor blades.
A rotor blade has a large surface area that belies its slim appearance. Within that area, the strength of the wind can vary greatly and change quickly. The pressure on the blade that's pointing skyward could be very different from the pressure pushing at the other blade.
The rotor blades of conventional wind turbines are slow to react any change in wind strength. They are very rigid structures, so they cannot compensate for abrupt gusts of wind.
Wind turbine operators must turn the rotor blades away from the wind if the gusts are too strong. During the resulting down-times, the turbine does not produce any electricity. (Related: MIT researchers create device they claim can “generate electricity from air”.)
Wind turbines with BTC blade rotors can keep running even in gusty winds
Bend-twist coupling can compensate for the wind forces that act on the rotor blade on a constant basis. Every time the wind loads grow too much, the bend-twists automatically lower the forces affecting the blade and, ultimately, the entire turbine.
"The demonstrator BTC blade developed as part of this project is swept back whilst the blade tip is offset slightly to the rear in the direction of rotation. The 20-meter-long rotor blade is therefore able to rotate slightly around its own axis should strong gusts occur in order to mitigate the wind pressure to a certain degree," explained Dr. Elia Daniele, the IWES technology coordinator for BTC blades.
BTC rotor blades can be fitted on new wind turbines as well as existing ones. Using the new blades on new turbines allows designers to reduce the overall weight since the structure is subjected to lower loads.
Retrofitting BTC blades onto existing turbines will increase rotor diameter without having to replace other components. The retrofitted wind turbine will generate more electricity, which in turn results in more revenue.
Testing of BTC rotor blades is underway
Fraunhofer IWES will trial its new design on the test bench of the company's Bremerhaven facility, where the first bend-twist coupling blade – manufactured by SmartBlades2 project partner German Aerospace Center (DLR) – was installed.
Static tests will determine the blade's ability to withstand extreme loads, while dynamic tests will condense the structural stresses that would take place over its 20-year predicted lifespan.
Once the design completes bench tests in Germany, three new BTC rotor blades will be shipped to the Rocky Mountains in the U.S. for field testing. The blades will be installed on a research wind turbine operated by the National Renewable Energy Laboratory (NREL), another partner of the SmartBlades2 project.
The second phase will investigate the effectiveness of passive twisting in real life, open-air conditions. Each set of blades features the "Aeroprobe System" – pressure sensors that will measure the airflow dynamics around the rotors.
The high-tech sensors are supplemented by visible strands of wool. Other sensors inside the blade will measure acceleration while camera reflector systems will look for signs of deformation.
Power.news has more articles covering the breathtaking progress of wind energy tech.
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