Analysis of heating systems to mitigate ice accretion on wind turbine blades

Abstract

<p>Ice forming on wind turbine blades can cause loading imbalance and reduce power production of the turbine. Heating systems that prevent or remove ice on wind turbine blades are one of the more promising solutions to mitigate ice accretion. Methods to apply heat include direct application through electro-thermal resistance heaters mounted on the external surface of the blade or by indirect heating by forcing hot air through a channel along the leading edge of the blade. Heating systems for aircraft blades have become standardized and in some cases compulsory on aircraft to preserve human life; however, the technology is not directly transferable to the blades on wind turbines. The relative power of the anti-icing or de-icing system is critical to providing a cost benefit of having the system.</p> <p>This thesis investigates the heat transfer involved for electro-thermal and hot air heating strategies. An appropriate range of operating conditions and blade constructions are considered in order to characterize the effectiveness of both systems. A numerical model is developed to solve the one dimensional, differential heat transfer equations. The heater power required to prevent ice accumulation (anti-icing) on wind turbine blades is determined for electro-thermal heating. Anti-icing with hot air is shown to be unrealistic for a practical range of operating conditions.</p> <p>The low conductivity of the blade core creates a bottleneck for the de-icing system. It is shown that alternative core materials (Nomex/aluminum honeycomb) can reduce this effect. Electro-thermal and hot air de-icing each have their advantages and cannot be equally compared. In this thesis the suitability of each system has been analysed for a range of operating conditions and wind turbine constructions; the designer can then implement the most suitable strategy for their individual application.</p>