Huge turbines are making the cost of electricity from offshore wind less and less expensive, but the cost reduction process is not over yet.
Earlier this year the Offshore Renewable Energy Catapult began testing the world’s longest blade for an offshore wind turbine at its facility in Blyth, Northumberland.
The 88.4-m blade, developed as part of XL-Blade, an EU DemoWind-funded project that aims to reduce the cost of offshore wind by designing, validating and deploying the world’s largest offshore wind turbine blade, was built by LM Wind Power.
88.4 m is a big blade, very big, but larger blades are already being developed for the huge 12 MW turbine GE Renewable Energy is developing, the Haliade X, which will have 107-m blades, also from LM Wind Power.
It is not that long ago the company launched the LM 88.4. In fact, it was introduced to the market as recently as June 2016, but it has sometimes been suggested that around 120 m might be the limit for blade size - at least with current construction techniques - because as blade length grows, so weight becomes an ever-greater issue.
But is 120 m the limit? LM Wind Power’s test and validation centre director John Korsgaard does not think so. He told the Global Offshore Wind conference in Manchester in June he did not believe that LM Wind or the industry as a whole is approaching the end of the line when it comes to blade length and growth in size of turbines.
In fact, in the discussion after his presentation on blades for multi-megawatt offshore turbines, he told delegates that if ways could be found to reduce the mass of a blade, he did not rule out one day being able to produce a 200-m unit. That’s a 200-m blade, not a rotor with a diameter of 200 m, or the 220-m rotor of the Haliade X.
When Mr Korsgaard first joined LM Wind Power, the company built 12 m blades. Now, it has produced the world’s longest blade, the one being tested at the ORE Catapult as part of the EU-funded project.
At 88.4 m, the blade will achieve a significant reduction in the levelised cost of energy (LCoE) by means of lighter construction and a more predictable operational expenditure through reliability-driven design.
A blade of the size Mr Korsgaard envisaged would present some huge technical challenges. The 107-m blade for the Haliade X has about 50 tonnes of material in it. Building blades that size is challenging and much of the work involved requires manual labour. But a far larger unit?
How would a blade that size be transported, let alone lifted into place on an offshore turbine? What kind of turbine might we be talking about? Almost certainly not a bottom-fixed unit, that's for sure. A floater? Perhaps.
Blades of that size would be subject to severely fluctuating wind loads and present an enormous challenge when it comes to a control system. As the size of offshore wind turbines has grown, so longer blades have imposed greater and greater forces on drivetrains.
Apart from weight growth, manufacturing, transportation and the loads that massive blades would be under, material costs would be a huge issue.
As ORE Catapult’s research and disruptive innovation director Dr Stephen Wyatt noted here “Producing ever larger turbines means manufacturing even longer blades – something which pushes current technology to the very limit. As such, these longer blades will need to be constructed using new designs, materials and new construction and manufacturing processes – and these new blades will need to be tested and validated.” The British organisation is already helping companies working on potential solutions.
Will we ever see a turbine with a 200-m blade? Would it be affordable? Maybe, maybe not. By the time the technology is available to produce one that size, it is possible the industry may have gone through another revolution. We might all be talking about kites or other forms of airborne offshore wind rather than blades.
Mr Korsgaard’s statement should not be interpreted to mean that a 200-m blade is likely to be built soon, or that several years of research and development would not be required to make it a reality. But it does emphasise the massive sense of confidence in the industry that technical challenges can be overcome, and that reductions in the LCoE from offshore wind – although already impressive – are far from over.