A review of surface engineering issues critical to wind turbine performance

Abstract

Wind turbine performance can be significantly reduced when the surface integrity of the turbine blades is compromised. Many frontier high-energy regions that are sought for wind farm development including Nordic, warm-humid, and desert-like environments often provide conditions detrimental to the surface of the turbine blade. In Nordic climates ice can form on the blades and the turbine structure itself through a variety of mechanisms. Initial ice adhesion may slightly modify the original aerodynamic profile of the blade; continued ice accretion can drastically affect the structural loading of the entire rotor leading to potentially dangerous situations. In warmer climates, a humid wind is desirable for its increased density; however, it can come at a price when the region supports large populations of insects. Insect collisions with the blades can foul blade surfaces leading to a marked increase in skin drag, reducing power production by as much as 50%. Finally, in more arid regions where there is no threat from ice or insects, high winds can carry soil particles eroded from the ground (abrasive particles). Particulate-laden winds effectively sand-blast the blade surfaces, and disrupt the original skin profile of the blade, again reducing its aerodynamic efficiency. While these problems are challenging, some mitigative measures presently exist and are discussed in the paper. Though, many of the current solutions to ice or insect fouling actually siphon power from the turbine itself to operate, or require that the turbine be stopped, in either case, profitability is diminished. Our survey of this topic in the course of our research suggests that a desirable solution may be a single surface engineered coating that reduces the incidence of ice adhesion, insect fouling, and protects the blade surface from erosive deterioration. Research directions that may lead to such a development are discussed herein.

Introduction

Wind energy is a renewable power source that produces no known significant atmospheric pollution. Currently the worldwide capacity of installed wind energy stands at more than 40,000 MW with a 30% growth rate predicted over the next decade. Maintaining such growth necessitates research into the management of economic and environmental risks associated with the operation of large-scale commercial wind ventures. Wind turbine technology has a unique technical identity and subsequently has unique demands in terms of methods used for design [1]. A focal variable critical to the economic optimization of wind power production is the evolution of the wind turbine blade. Fundamental to the efficient extraction of power from the wind are the structural and aerodynamic properties of the blade. Until relatively recently it was enough to design blades with a desirable aerodynamic profile and a durable yet responsive structure. However, with the expansion of wind infrastructure, an increasing number of turbine installations have pushed their way into three distinct climatic zones, icy Nordic environments, humid regions that support large insect populations, and desert environments with sand-laden winds. Each of these environments can create significant operational issues for a wind farm; critical to the comprehension and potential resolution of all three issues are the composition, specifically the surface properties of the turbine blade. Currently, most manufacturers employ epoxy or polyester matrix composites reinforced with glass and/or carbon fibres; though polyester and glass fibres remain the material of choice due to their lower capital cost, despite the superior mechanical properties of epoxy and carbon fibres. A compatible gelcoat is also typically applied on the finished blade to improve surface erosion resistance. The wind energy industry presently faces three major challenges concerning the surface engineering of blades: ice adhesion and accretion on the turbine blades and supporting structure, insect accumulation on blades, and the erosion of blades by sand and water droplets. We have yet to uncover much literature that addresses the surface engineering issues facing wind turbines in a holistic sense. This is likely due to the complexity associated with a multidisciplinary challenge that calls on expertise from materials science, aero-, thermo-, and structural-dynamics. We endeavour to provide details of the current challenges confronting the industry, then discuss present solutions, and propose potential research directions.