Extra-long single-piece wind turbine blades could be transported by rail to more locations and at lower cost than segmented blades if their manufacturing incorporated “controlled flexing”, according to researchers at the US Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL).
A new paper, “Land-based wind turbine with flexible rail-transportable blades”, argues that wind turbine blades of 100 metres and longer could be transported across the length of four railcars if they could bend enough to deal with the bends, twists and turns in railroad lines.
This would allow the installation of taller turbines, and the production of more energy, in areas of the country where wind speeds are lower, including the south-east of the US. The upper limit for transporting single-piece blades by rail is currently 75 meters.
Lowering the cost of transport and enabling rotors with a higher capacity factor could make more of these deployments economically feasible, the paper argues. It is co-authored by researchers from the NREL and Sandia National Laboratory.
Engineers at DNV GL in 2019 proposed on a conceptual level the controlled flexing of blades during rail transport. The new paper provides an in-depth investigation into the idea.
The scientists examined the potential for five designs of a 5MW wind turbine installed on a 140-metre-tall tower. Cutting the blade in two for transport was used as a baseline option based on existing technology, but resulted in higher costs than transporting a single-piece blade by rail.
Blades already possess some flexibility, allowing deflections of about 10% of the blade length. Under the US Department of Energy’s big adaptive rotor project (BAR), which produced the new study, flexibility would have to increase to 20% to allow for the rail transport of extra-long blades.
Nick Johnson, a mechanical engineer at NREL and co-lead of the BAR project, sees industry adoption of flexible blades about five years out.
“We're still in the process of fleshing out some of the details, some of the trade-offs associated with the technology,” he said.
“We have an industry advisory panel and have had great input and feedback from the members. They've kind of steered us in this direction. They think it's a promising idea, and certainly worthwhile as the impact could be significant,” he added.
The paper points out areas for further research, including the potential for blades even longer than 100 metres.