By Peter Greaves, Principal R&D Engineer for Blade Structures
The wind turbine blade is the point where a mass of engineering, policy and environmental ambitions meet, and these ambitions are growing. How can we tackle the need for bigger, better performing, more resilient and more sustainable blades?
This is a topic that I’ll be going into more detail in my session at ORE Catapult’s Wind Turbine Blades Week later this month. But for now, here are a few engineering feats that I believe we’ll begin to see in the next generation of offshore wind turbine blades.
Wind turbine blades have now pushed through the 100m barrier, and they will continue to grow for some time, driven by the substantial reductions in levelized cost of energy which turbines with higher power ratings achieve. As they continue to grow the industry must address new challenges around manufacturing, sustainability, reliability and cost – many of which cross more than one of these categories!
Wind turbine blades are currently made from a combination of glass and carbon fibre reinforced plastics (GFRP/ CFRP), and these are unlikely to be replaced any time soon – no other class of materials can provide the strength/stiffness to weight ratio and excellent fatigue properties at the costs and scale needed for wind turbines.
These materials have traditionally proven hard to recycle because it is difficult to separate the glass/carbon fibres from the thermoset plastic matrix, but now several companies are developing matrix resins which can be broken down to allow the fibres (and in some cases the matrix) to be recovered at the end of the turbine life. Others are investigating the use of bio-resins and wood fibres to reduce the dependency of blades on oil and the carbon footprint associated with blade manufacture (carbon fibres in particular have a very high global warming potential but they are necessary to make 100m+ blades viable). Most of the big blade OEMs are now aiming for completely recyclable blades for their next generation designs.
The manufacturing process for current blades is typically based on vacuum assisted resin transfer moulding (VARTM), which involves sandwiching dry fibres between a blade mould and a vacuum bag and then sucking resin into the gap between the bag and the mould. The resin then solidifies (cures) over time to create the finished part.
This manufacturing method has been around for a long time and is still used for the current generation of blades, but it is very much at the limit of its applicability – the process results in a lot of waste, is very labour intensive and can suffer from quality control issues. It is also very challenging to ensure that the resin penetrates all the way through the extremely thick laminates required for 100m+ blades to make contact with all the fibres as the blade infuses, so for next generation blades it is likely that some degree of automation will be necessary to address these manufacturing challenges.
Blades are currently made from several components: two load bearing spar caps resist the main aerodynamic loading, two or more shear webs to transfer load between the spar caps and two aerodynamic shells to catch the wind would be fairly typical. These parts are bonded together with adhesives during the manufacturing process.
However, it is rare that the blade is split up into multiple parts along its length. This may change in the future, as manufacturing sites for ultra large blades become more difficult to find and the cost of the huge moulds required for the blade shells skyrockets. Breaking the blade up into segments has other benefits as well – different tips could be applied at different sites to tailor the blades for specific wind conditions, and more advanced manufacturing processes such as additive manufacturing could be applied to this tip component to allow aerodynamic concepts which would be impossible with conventional manufacturing processes to eke extra AEP out of the turbine without increasing the blade length.
It’s a very exciting time for wind turbine blades at the moment, as the manufacturing techniques and materials that have got us this far are reaching their limits and big changes in how blades are made will inevitably happen in the next few years.
To learn more about what the future of these next-generation turbine blades could look like, make sure you register today for our Wind Turbine Blades Week event series on the 16th – 20th May.