On the Use of Modern Engineering Codes for Designing a Small Wind Turbine: An Annotated Case Study

Abstract

While most wind energy comes from large utility-scale machines, small wind turbines (SWTs) can still play a role in off-grid installations or in the context of distributed production and smart energy systems. Over the years, these small machines have not received the same level of aerodynamic refinement of their larger counterparts, resulting in a notably lower efficiency and, therefore, a higher cost per installed kilowatt. In an effort to reduce this gap during the design of a new SWT, the scope of the study was twofold. First, it aimed to show how to combine and best exploit the modern engineering methods and codes available in order to provide the scientific and industrial community with an annotated procedure for a full preliminary design process. Secondly, special focus was put on the regulation methods, which are often some of the critical points of a real design. A dedicated sensitivity analysis for a proper setting is provided, both for the pitch-to-feather and the stall regulation methods. In particular, it is shown that stall regulation (which is usually preferred in SWTs) may be a cost-effective and simple solution, but it can require significant aerodynamic compromises and results in a lower annual energy output in respect to a turbine making use of modern stall-regulation strategies. Results of the selected case study showed how an increase in annual energy production (AEP) of over 12% can be achieved by a proper aerodynamic optimization coupled with pitch-to-feather regulation with respect to a conventional approach.

Design Loads in Small Wind Turbines: a Detailed Comparison Between Pitch and Stall Regulation

“…As the difference of weight between the two towers is roughly 3400 kg, an additional vertical force of more than 33.2 kN is expected. While not completely general, this result is of interest for a future optimization of SWTs, since the need for a stiffer (and heavier) tower is often needed in the design phase to adapt it to the different resonance frequencies, as discussed in [6]. Together with tower and blades, the drivetrain is an element subject to relevant forces, and so the analysis of the peak loads is worth to be performed, especially for the low-speed shaft directly connected to the rotor (Figure 8).…”

“…In fact, designers are often forced to compromise on peak performance, to ensure smooth power regulation above rated windspeed. Therefore, from an energy capture standpoint, stall regulation often causes lower Annual Energy Production (AEP), as investigated in [6]. The lack of a blade pitching system has implications in the turbine loading too.…”

UNICO: an open-source controller optimized for stall-regulated wind turbines

“…The stall-control-oriented implementation of the controller was tested on the open-source UNIFI 50kW RWT designed by the Wind Energy Group at the University of Florence [13]. It is a horizontalaxis, fixed-pitch stall-regulated turbine.…”

Recent Development in the Design of Wind Deflectors for Vertical Axis Wind Turbine: A Review

“…Small-scale wind power generation is not as popular as large-scale wind power; searching for "small winds" in the database of MDPI found 59 research articles, only, compared to 900 for "wind power" or "wind energy" for the same period from 2010 to 2019. Lack of interest towards small wind systems for decades resulted in highly counterproductive VAWTs, lower efficiency, and hence, high costs per kilowatt [57,58]. The development of smart grids and distributed energy systems is spurring renewed interest in small energy again.…”