A new research collaboration is using UK aerospace technology to develop a novel leading-edge protection system for offshore wind turbines. The proposed solution could eliminate the need for intervention related to rain erosion and pave the way for lighter wind-turbine blades and drivetrains.
Improving protection for offshore wind-turbine blades against erosion can significantly reduce turbine blade repair costs and loss of power production through maintenance downtime. It can also enable the development of longer, lighter turbine blades with higher tip speeds, reducing the cost of energy generated by each turbine over its operating lifetime.
Wind-turbine blade erosion is caused by a combination of the impact of water droplets and weathering, which degrades and removes the blade’s protective coating, exposing and compromising the blade’s underlying composite structure. This deterioration causes a reduction in aerodynamic efficiency and subsequently a loss in operational output of the turbine. This type of damage manifests itself as pitting on the blade’s leading edge and studies have shown that related erosion can result in significant drag increase as the blades turn, causing a reduction in energy output for each wind turbine.
Rain erosion is currently the leading cause of damage to wind turbine blades and is a particular issue offshore as blade lengths tend to be longer and tip rotation speeds higher than onshore wind turbines. It is a significant issue for both turbine manufacturers and owner/operators as they look to improve a blade’s operational life to match the 25-year active service life of the turbines.
Leading-edge erosion is now being reported within two years of a turbine’s operation offshore, with significant damage requiring intervention. One North Sea wind farm reported that the blades on all its 270 turbines were severely eroded within six years; many requiring structural repair onshore.
The Leading Edge for Turbines (LEFT) project, part-funded by Innovate UK, is a two-year, £1 million collaboration between Sheffield-based Doncasters Bramah and Performance Engineered Solutions (PES) Ltd, plus the Offshore Renewable Energy Catapult; the UK’s leading technology innovation and research centre for offshore renewable energy.
Doncasters Bramah is a specialist aerospace component manufacturer and will apply its expertise in supplying leading-edge erosion shields for aircraft and helicopters to solutions for the offshore wind industry. Meanwhile the PES design engineers are using their experience in component performance and composites optimization on the project. In particular this includes their understanding of lightweight materials, and aerodynamic design.
Doncasters Bramah manufacture civil and military aerospace components and assemblies, using a variety of forming and fabrication processes. One of these processes is called electro-forming, which is an electrodeposition based additive manufacturing process, similar in principal to electroplating. Parts are grown in a chemical bath onto a preformed mandrel to produce near net shape parts, removing the need for multi-stage forming operations associated with conventional metal forming techniques.
Although the process isn’t new, Doncasters Bramah is unique in the UK in being able to produce industrial products to aerospace specifications. Parts are typically electro-formed in a nickel cobalt alloy, which has a high tensile and yield strength, as well as a high hardness value compared to titanium and stainless steel. This makes it ideal for producing lightweight erosion shields.
Doncasters Bramah has been supplying leading-edge erosion shields for use on civil and military helicopter and propeller blades for over 15 years and is now looking at adapting this solution for use on offshore wind turbines. Benchmark rain erosion testing at ORE Catapult has indicated that this nickel cobalt solution could be expected to give 30 years protection when continuously tested to offshore wind specifications, far above other solutions currently available on the market. With a turbine lifetime of 25 years this solution could give a true lifetime protection against leading edge erosion.
Project LEFT will investigate and validate an optimal method of attaching such a solution to offshore wind blades, in addition to considering how to integrate the design of a nickel cobalt leading edge into the overall design and functionality of wind-turbine blades.
If successful, this project will lead to the introduction of a new product that provides significant benefits to the offshore wind industry:
- Research findings from ORE Catapult show metallic strip protection performs better than the current polymeric coatings and thermoplastic shields developed for this market, which typically have a maximum operating life of up to 16 years.
- Such an advance in erosion performance would not only lead to the introduction of larger, lighter blades but also to reduced turbine nacelle sizes through smaller sub systems.
- Turbine operators will also see a significant cost benefit through reduced repair costs, estimated to save around £1.3m per turbine during a typical 25 year service life, removing significant cost of operations and infrastructure and more importantly reducing significant risk to operators when carrying out this activity in the field.
- Prevention of leading-edge erosion will also ensure that aerodynamic losses are not incurred from blade damage, therefore ensuring power generation remains at rated capacity throughout the life of the turbine. Wind tunnel tests show that such erosion corresponds to a 2.3% loss in annual energy production per turbine.
- Together, these factors would further reduce the unit cost per kW that the wind sector provides, ultimately benefiting the consumer as energy demand increases.