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

**Francesco Papi , Alberto Nocentini, Giovanni Ferrara and Alessandro Bianchini \***

Department of Industrial Engineering, Università Degli Studi di Firenze, via di Santa Marta 3, 50139 Firenze, Italy; fr.papi@unifi.it (F.P.); alberto.nocentini@stud.unifi.it (A.N.); giovanni.ferrara@unifi.it (G.F.) **\*** Correspondence: alessandro.bianchini@unifi.it

**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.

**Keywords:** wind turbine; pitch; stall; aerodynamics; engineering codes
