Land-based wind turbines with flexible rail-transportable blades – Part 1: Conceptual design and aeroservoelastic performance

Abstract

Abstract. This work investigates the conceptual design and the aeroservoelastic performance of land-based wind turbines whose blades can be transported on rail via controlled bending. The turbines have a nameplate power of 5 MW and a rotor diameter of 206 m, and they aim to represent the next generation of land-based machines. Three upwind designs and two downwind designs are presented, combining different design goals together with conventional glass and pultruded carbon fiber laminates in the spar caps. One of the five blade designs is segmented and serves as a benchmark to the state of the art in industry. The results show that controlled flexing requires a reduction in the flapwise stiffness of the blades, but it represents a promising pathway for increasing the size of land-based wind turbine rotors. Given the required stiffness, the rotor can be designed either downwind with standard rotor preconing and nacelle uptilt angles or upwind with higher-than-usual angles. A downwind-specific controller is also presented, featuring a cut-out wind speed reduced to 19 m s−1 and a pitch-to-stall shutdown strategy to minimize blade tip deflections toward the tower. The flexible upwind and downwind rotor designs equipped with pultruded carbon fiber spar caps are found to generate the lowest levelized cost of energy, 2.9 % and 1.3 %, respectively, less than the segmented design. The paper concludes with several recommendations for future work in the area of large flexible wind turbine rotors.

Big Adaptive Rotor Phase I (Final Report)

“…Readers interested in more details are invited to read the following two papers: "Land-Based Wind Turbines with Flexible Rail Transportable Blades -Part I: Conceptual Design and Aeroservoelastic Performance" (Bortolotti et al 2021b) and "Part II: 3D FEM Design Optimization of the Rotor Blades," (Camarena et al 2021) submitted to Wind Energy Science in the first half of 2021. The next subsections summarize the design approaches discussed in the two journal articles and provide a more technical look at the five wind turbine designs.…”

Big Adaptive Rotor Phase I Final Report

“…To quantify the change in capacity factor and LCOE associated with the turbine configurations studied, the analysis relies on hourly time series wind-speed data from NREL's WIND Toolkit 10 . The toolkit data can be briefly characterized as a national mesoscale wind-resource data set that includes meteorological data for more than 1.85 million locations in the contiguous United States.…”

“…Please note that the next paragraph from the original text was removed for clarity 9. Please note that some paragraphs are skipped here for clarity, and for citations in excerpt, please reference the original publication 10. The development of the Wind Integration National Dataset (WIND) Toolkit (https://www.nrel.gov/grid/windtoolkit.html) was funded by the Wind Energy Technologies Office within the US Department of Energy's Office of Energy Efficiency and Renewable Energy, and was created through the collaborative efforts of NREL and 3TIER (which has since been acquired by Vaisala-http://knowledge.vaisala.com/3TIER, accessed 1 September 2019).…”

Land-based wind turbines with flexible rail-transportable blades – Part 2: 3D finite element design optimization of the rotor blades

“…All blades had a total length, L, of 100 m. Further detail of the BAR concepts and initial design optimization is found in Part 1 (Bortolotti et al, 2021). Since the use of traditional aerospace carbon fibers has contributed limited benefit to wind turbines due to high cost, a new low-cost carbon fiber (Ennis et al, 2019), referred to here as heavy-tow (HT) carbon fiber, is also evaluated.…”

“…This was performed first, whereby a preliminary blade design was created. Further details are presented in Part 1 of this two-part series (Bortolotti et al, 2021).…”