Re-design of an upwind rotor for a downwind configuration: design changes and cost evaluation

Abstract

Abstract. Within this work, an existing model of a Suzlon S111 2.1 MW turbine is used to estimate potential cost savings when the conventional upwind rotor concept is changed into a downwind rotor concept. A design framework is used to get realistic design updates for the upwind configuration as well as two design updates for the downwind configuration, including a pure material cost-out on the rotor blades and a new planform design. A full design load basis according to the standard has been used to evaluate the impact of the redesigns on the loads. A detailed cost model with load scaling is used to estimate the impact of the design changes on the turbine costs and the cost of energy. It is shown that generally lower blade mass can be achieved with the downwind configurations of up to 5 % less than the upwind redesign. Compared to an upwind baseline, the upwind redesign shows an estimated cost of energy reduction of 2.3 % where the downwind designs achieve a maximum reduction of 1.3 %.

Challenges, opportunities, and a research roadmap for downwind wind turbines

“…With a reduction in blade mass, the costs of the nacelle system were also reduced by 1.3%, and the complete turbine capital cost reduction was 1.7%. However, the aeroservoelastic OpenFAST simulations returned a 1.2% lower AEP for the downwind rotor caused by the reduced swept area during operational loading, consistent with prior findings 17,18 . This is reflected in Figure 3, which shows the two power curves and the difference between them before rated power.…”

“…As for loads, recent numerical studies performed on a 2‐MW model with conventional aeroservoelastic models showed a decrease in the ultimate blade root flapwise moment, at the expense of an increase in fatigue loading 17,22 . Rotor thrust and tower base fore‐aft moments followed similar trends with lower ultimate loads but additional fatigue wear.…”

“…Other point design studies in the literature used medium‐fidelity aeroservoelastic models and also observed similar LCOE values, but with upwind designs slightly more cost‐effective than downwind. The studies were conducted on 2‐MW 17 and 10‐MW platforms 18 . In both works, the downwind configuration suffered from losses of a few percentage points in annual energy production (AEP), which were primarily attributed to the reduced swept area of the downwind rotors, which, when loaded, bend away from the rotor plane.…”

“…Additionally, the blade mass savings were found to be somewhat smaller, around 5–10% reduction, than in Ning and Petch 6 and Namura and Shinozaki 16 because of the need to retain some stiffness to avoid blade‐tower strike during operations at the cut‐out wind speed and other emergency shutdown maneuvers. The conclusion drawn by Wanke et al 17 is that downwind wind turbines might be advantageous in markets with high capital expenditure costs, whereas upwind wind turbines are likely to dominate in markets driven by minimum LCOE.…”

“…Compared to the most favorable studies for downwind wind turbines, which were conducted within WISDEM, 6,16 this study adds the impact of the rotor orientation on the drivetrain, updates the cost models to the latest models, 11,12 and includes aeroservoelastic simulations in OpenFAST. Compared to the other aeroservoelastic point designs, 17,18 this study includes additional parametric sweeps of key design details and also proposes some future topics of study that could show greater advantages for downwind wind turbines.…”