By their nature, wind turbines are placed in exposed positions and snow and ice is always a threat in colder climates. The build-up of ice on a turbine blade will affect its performance and may lead to damage and even catastrophic failure. Ideally, the accumulation of ice should be stopped at the moment of creation. To overcome this problem, the DeICE-UT system will operate in two modes; anti-icing and de-icing.
Existing passive solutions to the ice build-up problem include; special coatings applied to the surface of the wind turbine blade to reduce the adhesive properties of the ice, painting the turbine blade black to enhance solar heating and applying chemicals to the surface to lower the freezing point of water. None of these is entirely satisfactory. Coatings are not totally effective in hindering ice formation, the solar heating effect only works in bright sunny conditions and chemical applications are problematic at height and are pollutants.
The most common active solution is to creat a thin film of water under the ice with thin-foil electrical resistors embedded in the blade. This process can consume 12% of the turbine’s nominal power output. Another active solution is to circulate hot-air within the blade, but GRP blade material is a thermal insulator and to melt the ice may consume as much as 15% of turbine output. Pulse Electro-thermal De-Icing is another active solution that claims to use less power by sending pulses of current through the heating elements, but there are no commercially available systems. Finally the Electro Expulsive Separation System de-icing device passes currents through wires glued on to the surface of a blade causing them to interact electromagnetically, creating slight movements that shake off the ice. The manufacturers claim very low power consumption, but the system has only been tested on the leading edges of small aircraft blades.
Active Pitching is a solution that doesn’t need an external device or supply. It relies on rotating the blades through their centreline axis to a point when the leading edge of the blade faces the airflow beyond a certain angle, causing turbulent flow and forces that shake off the ice. Of course there is a risk of damage to the blade.
The DeICE-UT project aims to overcome the limitations relating to the Anti-icing / De-icing of wind turbine blades by integrating two technologies which use low cost components that require relatively low energy and have the potential to achieve both anti-icing and de-icing at temperatures down to -20°C. The two technologies are Low Frequency Vibration and Guided Wave Ultrasonics.
The DeICE-UT project seeks to build on previous research and the initial investigations of the SME consortium. The project has 9 partners from 6 EU member states, including five SMEs. The SMEs include high technology organisations manufacturing composite parts (Floteks), high power ultrasonic transducers (Smart Materials) and electronic amplifiers and instruments (BS-Rotor and DTK). In addition, Tureb, as a large enterprise that provides customer support to the world's infrastructure markets in the fields of power generation will act as the initial route to market. The project is supported by three Research organisations; Brunel University (UK), which is providing expertise in numerical modelling, West Pomeranian Technical University (Poland), which is providing expertise in hardware for arduous conditions and TWI (UK), which will be developing the techniques and acting as project coordinator.
The DeICE-UT system concept is illustrated in Figure 1. The two techniques are activated from two sets of transducers placed inside the turbine blade. One set is placed centrally along the blade at distances calculated to give maximum vibration. Another set is in the form of an array that propagates guided ultrasonic waves around the leading edge of the blade. The technical objectives are to optimise two these techniques to prevent ice formation and remove ice.