There is a pressing environmental need to reduce global greenhouse gas emissions through technologies that are capable of extracting energy from the environment whilst being non-polluting and sustainable. New advances in wind energy technologies for improving aerodynamic performance of vertical axis wind turbines (VAWTs) has been the focus in the 21st century. The book presents both numerical and experimental wind tunnel approaches to provide a detailed understanding of the aerodynamic performance of the small-scale wind turbines under unsteady winds. Computational Fluid Dynamics (CFD) models validated against the experimental data are utilized to provide additional insight into VAWT behavior. The experimental design setup and use of a wind tunnel-based performance testing assembly is described in detail. The apparatus are described for the various components of the testing rig including the rotor assembly, the measurement assemblies, the braking system assemblies, and the development of the data logging program. The analysis is key for wind energy stakeholders to inform investment requiring designs for wind turbine blades, reflecting realistic unsteady wind operating conditions.