Impact of turbulence and blade surface degradation on the annual energy production of small-scale wind turbines

Abstract

Small-scale horizontal axis wind-turbines (SHAWTs) are acquiring relevance within the regulatory policies of the wind sector aiming at net-zero emissions, while reducing visual and environmental impact by means of distributed grids. SHAWTs operate transitionally, at Reynolds numbers that fall between (Formula presented.). Furthermore, environmental turbulence and roughness affect the energetic outcome of the turbines. In this study, the combined effect of turbulence and roughness is analysed via wind tunnel experiments upon a transitionally operating NACA0021 airfoil. The combined effects cause a negative synergy, inducing higher drops in lift and efficiency values than when considering the perturbing agents individually. Besides, such losses are Reynolds-dependent, with higher numbers increasing the difference between clean and real configurations, reaching efficiency decrements above 60% in the worst-case scenario. Thus, these experimental measurements are employed for obtaining the power curves and estimating the annual energy production (AEP) of a 7.8-kW-rated SHAWT design by means of a BEM code. The simulations show a worst-case scenario in which the AEP reduces above 70% when compared to the baseline configuration, with such a loss getting attenuated when a pitch-regulated control is assumed. These results highlight the relevance of performing tests that consider the joint effect of turbulence and roughness.