A leading manufacturer of offshore wind turbines is collaborating with experts in Denmark’s Fast Track project to find solutions to leading edge erosion and wants to develop a new standard for blade protection to benefit the whole industry
The offshore wind industry is developing rapidly and expanding worldwide. One of the keys to its success is the development of larger and more powerful offshore turbines. 8-10 MW turbines are becoming the norm, but much larger units are in development. With the development of larger and larger turbines comes need for longer and longer rotor blades.
However, there is an issue with which the industry has long wrestled, one that has affected blades since the early days of the industry, when blades were much shorter. Harsh weather conditions lead to a phenomenon known as leading edge erosion.
Blade leading edge erosion is a problem onshore and offshore but erosion is accelerated offshore due to environmental conditions. It affects the aerodynamic performance of the blade, which leads to reduced efficiency, reliability and availability, as well as increased operations and maintenance activity.
Blade leading edge erosion also reduces the generating capacity of a wind turbine and hence of a windfarm as a whole. If severe, it can also affect a blade’s structural integrity as water ingress and UV light exposure can lead to structural damage. All of this proves costly for offshore windfarm owner/operators through lost power generation and revenue.
Fast Track project
To address the issue and try to find potential solutions, Siemens Gamesa’s surface treatment and corrosion team has joined several industry experts in the Fast Track project – an initiative supported by Innovation Fund Denmark – to improve materials and protective coatings, and thus reduce maintenance costs and extend the lifetime of wind turbine blades.
The Fast Track partnership provides services to the materials engineering sector and was set up to meet the needs of Danish industry. The aim is to put the right people together across fields to give them access to materials engineering solutions, to simplify the process of solving materials engineering problems and make that process more efficient.
In response to the challenge, Fast Track brought together a number of organisations active in the sector, including Siemens Gamesa, Hempel, Terma, Elplatek, FORCE Technology and DTU, Aalborg University, and Teknologisk Institut.
As Kasper Bondo Hansen, who heads up the Fast Track initiative explained, longer blades have a higher tip speed. It can exceed 350 km/h. Strong offshore winds accelerate water drops and particles that meet the leading edge of the wind turbine blade at extremely high speed.
“This regular mechanical impact on the leading edge of the blade results in severe material degradation over time,” he said. Harsh weather conditions also lead to erosion of surface coatings, which reduces the turbine’s annual energy production. “Erosion is one of the most critical degradation mechanisms occurring on wind turbine blades, as it requires non-operational downtime due to costly on-site repair work,” he explained.
Despite the deficiencies of existing coatings, they remain among the most important ways to protect a blade from erosion. Existing solutions consist of glass fibre reinforced epoxy protected by a paint system, but this kind of protection can degrade rapidly – in two to seven years of the turbine’s operation – depending on conditions. Hence, the offshore wind energy industry is looking for new ideas to improve leading edge protection, ideas that can withstand physical impact and protect the blade coating in the long run.
The Fast Track project kicked off in 2016 and is due to be completed in mid-2019. Various technologies are being addressed in materials research projects and sub-projects and Mr Bondo Hansen believes that improvements are on the way.
The leading edge protection effort is one of the sub-projects. Its aim is to investigate material properties and erosion mechanisms using innovative techniques that combine analysis of failure modes with real-life experience, accelerated testing and lifetime modelling.
“In this particular project we want to free ourselves from conventional thinking and be open to innovative ideas. New thinking about materials and processing will enable us to set new standards and, if possible, redefine the concept of leading edge protection,” he explained.
“Promoting a competitive process environment across the industry will help us to provide a stepping stone for future innovation, something that Siemens Gamesa will lead,” he said. “Doing so will enable the industry to develop new-generation blades that will have inherently better properties.”
Ane Saelland Christiansen, a specialist engineer at Siemens Gamesa, said the company’s surface treatment and corrosion department is part of a team developing a new standard for corrosion protection for offshore wind turbines. “Hopefully, the deliverables from Fast Track will be incorporated into new product coating processes.
“We would also like to establish standardisation and certification for more suitable product and process specifications, new methods of assessing adhesion strength, and establish a long-term solution to leading edge erosion,” she concluded.
Offshore blade access
However good future leading edge protection systems are, access to rotor blades offshore will continue to be required but it is a time-consuming and expensive business. However, a Scottish company, Span Access Solutions Ltd, is developing an innovative way to access the blades that could save £1.05Bn (US$1.37Bn) across the current European fleet of offshore windfarms.
The £830,000 Innovate UK-backed project Blade Access System and Working Environment (BASE) project aims to develop a tower-mounted blade access system and habitat to provide a stable working environment for technicians undertaking blade maintenance. Such a concept could reduce maintenance costs and minimise turbine downtime and lost revenue while increasing the quality of repairs and performance upgrades, it is claimed.
An example of an alternative access and working at height solution developed by Span Access Ltd
Span Access, based in Kinross and Methil, is a specialist in alternative access and working at height solutions and will work in partnership with the Offshore Renewable Energy (ORE) Catapult, Turner Access Ltd, Turner Iceni along with Dundee and Robert Gordon Universities to adapt their patented product suite to a solution for offshore wind.
The Span Access product is a purpose built, modular access platform technology for working at height and its flexible, adaptable systems can be designed to accommodate improved access to any challenging blade design. The BASE project aims to create an optimised prototype access solution for offshore windfarms, which will be demonstrated at ORE Catapult’s 7-MW Levenmouth Demonstration Turbine in Fife.
The repair of blade damage and/or installation of performance upgrades is typically undertaken using rope access technicians and access platforms suspended from the turbine nacelle. The length of turbine downtime, and hence lost energy production, using this approach is high and the quality of repairs are often difficult to manage in highly variable weather and working conditions.
Span Access managing director Ross Turner said the BASE solution will be faster to deploy and more flexible to use than traditional suspended platforms. This should mean that revenue lost from forced turbine shutdowns associated with blade maintenance will be substantially reduced. “We’ll be able to control the temperature and humidity within the habitat, increasing the weather windows for performing maintenance and improving the quality of complex repairs that require stable environmental conditions for curing materials,” he explained.