In this Q&A, Professor Iain Bomphray, director of the Lightweight Manufacturing Centre (LMC) part of the University of Strathclyde and Dr Sabrina Malpede, ACT Blade CEO, discuss with Ed Hill a project to design and build a new ultra-lightweight composite wind turbine blade.
The new blade developed by Edinburgh-based ACT Blade, as part of a project comprising industry, academia and backed by Innovate UK, involves replacing the traditional heavier glass fibre design used for wind turbine blades with a lighter composite structure, wrapped in a sail-like textile. Intended to produce up to 9% more energy than conventional blades, the protypes built by the project also lower manufacturing costs by as much as 30% and can be fitted to existing wind turbine towers to produce more energy.
Q) How did the LMC first get involved with this project?
Bomphray: The team at The Lightweight Manufacturing Centre (LMC) was asked to be part of a consortium brought together to support an ACT Blade funding bid with Innovate UK. Along with the AMRC in Sheffield, and the Offshore Renewable Energy Catapult (OREC) in Blyth, the LMC brought the capability to manufacture the blades onsite in Scotland, which was beneficial to the ACT Blade Team based in Edinburgh.
Making the first prototype informed the thinking for not just the subsequent blades, but also the move from prototype to full production, incorporating lessons learnt and other novel technologies. We were able to use this exercise as a benchmark from which to further optimise both the blade and the manufacturing performance and to underpin the business case for future programmes.
Q) What are the technical challenges of designing, testing and manufacturing this kind of blade?
Bomphray: With something like a wind turbine, where the economic returns are governed by the performance of turbine and weight plays a large factor in that, there is always pressure to reduce the quantity of the material and push that as far as you can safely in the design.
The technical challenges are considerable. Qualification of blades by physical testing is extremely arduous as they have to go through an accelerated lifecycle before the design is deemed to be fit for purpose and able to be mounted onto a turbine.
There is also the difficulty in achieving the balance between risk and reward. ACT Blade’s novel concept has the potential to offer some very significant improvements in performance and the challenge with a prototype is to understand how much of this to realise at this stage. In order to push this as far as possible, a number of intermediary stages were undertaken to minimise this risk and increase our confidence in our approach.
Q) Why is this blade cheaper to manufacture? How do the new materials make it lighter and improve performance?
Bomphray: A conventional wind turbine blade has a hard-exterior surface that defines the aerodynamic shape of the blade and these blades are typically made in two shells and two or three shear webs that are glued together to form the complete hollow blade.
When bonding the two shells together you need to have a sufficiently wide edge to be able to apply enough adhesive to enable a strong joint. This joint usually occurs on the leading and trailing edge of the blade.
This thick edge is in a place on the blade that doesn’t contribute a lot to the bending stiffness of the blade. It’s the stiffness that prevents the blade from colliding with the tower as the blade deforms under the wind pressure used to turn the turbine and generate the electricity.
The ACT Blade concept resolves this by having a simple tube, a spar, with ribs that define the aerodynamic profile and an engineered textile that is pulled over the assembly, like pulling a sock over your foot. Another benefit with the engineered textile is that it eliminates a lot of the cost from finishing and painting the blade. These processes are expensive, labour intensive and time-consuming.
The ACT Blade offering is that the spar can be largely universal, covering a range of turbines from different manufacturers, and that they can be assembled relatively easily onsite, enabling a different business model.
Q) Can you tell us a bit more about the core material?
Bomphray: The core material for this version is glass fibre and will remain so until the blade lengths become much larger, where a small percentage of carbon fibre may be strategically added. The LMC, together with colleagues in the University of Strathclyde, is also engaged in a national programme to look at the recycling of glass fibre, for example from end of life wind turbine blades, and then reprocess it into a material fit to be reintroduced into product.
Q) How is it produced: traditional prepreg/vacuum infusion, hand lay-up or heated tooling processes? Can this be easily be upscaled?
Bomphray: Resin infusion was the most robust and cost-effective manufacturing solution and various combinations and proportions of candidate materials were simulated and trialled.
From experience, heated tools can offer in the region of 75% savings in energy consumption compared to oven curing for components of this size and construction. These cost savings are factored into any business case to understand whether the higher costs of heated moulds are justifiable and at what production volume.
Q) How do you achieve a suitable surface finish without finishing or painting?
Bomphray: The surface finish of the spar is not as critical as it might be with conventional blades as the spar is covered with the textile. That said, it still has to be sufficiently smooth so as not to damage the textile. This can be achieved with a high-quality mould surface. The quality of the mould surface being translated to the moulded part that is produced from it. The textile will effectively provide a protective barrier for the spar.
Q) What interest is there from the wind turbine OEMs? Is it easy to retrofit them to existing wind turbines on land or at sea?
Malpede: A lighter blade can be longer than existing blades. So retrofitting on existing turbines is interesting to wind farm owners/energy companies as they can produce more energy from the same turbine. Definitively the interest in retrofitting exists on land and offshore. In both cases, the operational costs to maintain the new blades is very important in the decision-making process.
OEMs are in the race to reduce the cost of energy and so the cost of the turbine. We believe the ACT Blade can be a possible solution to their current challenges, by offering a lighter longer blade, produced using cheaper and flexible manufacturing processes.
Q) Does less weight also mean less stress on the generating mechanics of the turbine?
Bomphray: Yes. It’s really important that the gearbox isn’t loaded beyond its fatigue limits and lighter blades help ensure this is the case. Parity in weight with the incumbent blade can provide an opportunity for the more efficient ACT Blade option to be marginally longer, hence, providing a larger swept surface area which can capture more wind and ultimately energy.
Q) What was the collaboration like between all the parties involved?
Bomphray: The collaboration worked really well. We were all engaged with the process and the aims and it was very collegiate and rewarding to be part of.
The manufacture took place at the LMC and was supported by engineers and technicians alike. We bought equipment, adapted our facility and trained staff explicitly to undertake this programme. As an engineer, I get a real kick from making things, so it’s good to see all of these actions, processes and decisions combine to make something substantial and innovative.
Q) Is the wind power industry keen to adopt new ideas and advances and could it benefit from adoption of more advanced composite materials?
Bomphray: The industry continues to be innovative, but it is also highly regulated and new solutions find high barriers not only because of very strict certification rules, but also because lots of choices are made on the basis of previous track records.
So, while the industry is seeking solutions to reduce the costs of energy, the implementation can be slower. This puts smaller companies in a good position to capitalise on this, especially if they can access appropriate support and funding. Every so often a small company with a big idea can make a difference.
Industries such as Renewables need cheaper carbon composite materials, preferably from renewable sources, and this has to be the main push. We are on the cusp of dealing with large numbers of decommissioned turbine blades. We need coherent strategies to reclaim and reformat the composite materials used in their construction to enable them to be used again in other products. Like recycling aeroplanes and turning them into drinks cans. The LMC is actively involved in both of these activities.