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Most wind turbines are designed to face the wind, following the “Danish concept” established in the 1980s. This design features three blades positioned upwind to maximize energy production by continually facing the wind.
Now researchers from the National Renewable Energy Laboratory (NREL), in collaboration with the Technical University of Denmark (DTU), set out to challenge this concept by exploring what happens when wind turbine blades are turned around.
In their experiment, NREL and DTU researchers reversed the rotor of a 1.5-megawatt research wind turbine at NREL’s Flatirons Campus in Colorado. They also repositioned the wind vane and nacelle (which houses the gearbox) and rewired the generator to spin in the opposite direction. This experiment is part of the Big Adaptive Rotor (BAR) project, funded by the U.S. Department of Energy’s Wind Energy Technologies Office, which aims to advance land-based wind turbine technologies and find ways to reduce costs, particularly by developing lighter and more flexible blades.
Although the final results of the study are expected later in 2024, preliminary findings suggest that the potential benefits of downwind operations do not outweigh the drawbacks.
“There has been for decades this ongoing discussion in the research community about whether turbines should all be upwind,” said NREL wind energy researcher (and project lead) Pietro Bortolotti. “The turbines we started with in the 1980s, when this standard was set, were very different than what we deploy today. They were much smaller and had chunkier blades, chunkier towers.”
“We conducted this experiment for two reasons: to study the techno-economic feasibility of downwind turbines and to utilize this very new instrumentation from DTU that can measure the performance of pressure distributions on a turbine blade,” Bortolotti added.
“We did something that nobody thought that we could do, which was to spin a fairly big wind turbine outfitted with a large set of instrumentation that recorded a broad spectrum of aeroacoustics, loads, and pressure data,” Bortolotti concluded. “This 1.5-megawatt turbine is small compared to modern installations, but still, it’s a big beast, and spinning it downwind safely without breaking a single bolt was a big achievement.”
