If you attend a lot of conferences like I do, you’ll be aware of the growing use of mobile phones to take pictures of interesting slides in a presentation. It’s a bit annoying, I know, but I was one of the worst offenders at the Global Wind Summit in Hamburg last month.
There are certain subjects and certain presenters that always make us want to use our phones to capture a particularly important point they’re making or a particularly stunning fact. There are a lot of important points and stunning facts being made about offshore wind right now, so much so that offshore really rather dominated the event.
One of the presenters the wind energy conference circuit especially likes to hear from is John Korsgaard, a senior director at LM Wind Power, nowadays part of GE. Mr Korsgaard oversees test and evaluation at the blade builder.
Given the fast growth in the size of offshore wind turbines, and the need for ever-larger blades for those turbines, what Mr Korsgaard has to say about blade length, how big blades might become and technical barriers to the production of longer and longer blades is of interest to all of us, not just LM Wind and GE.
At the wind summit in Hamburg, Mr Korsgaard spoke alongside representatives from research house MAKE and turbine manufacturer Senvion’s chief technology officer Servet Sert.
In a nutshell, MAKE anticipates that the market will see 15-20-MW turbines by 2030 and highlighted the cost reduction potential of 12-15-MW units that are already under development. Mr Sert described the development of Senvion’s 10-MW monster – which has already morphed into a 12-MW unit with growth potential beyond that – and highlighted some of the challenges in developing such a huge turbine. First and foremost is increased blade length, and the need for new control systems for such a large turbine.
‘Is there a limit to blade length?’ was the subject Mr Korsgaard was tasked with talking about. The cost of a blade is about 6-8% of the overall cost of a turbine, he said. Longer and longer blades are going to be more and more expensive, but they can help reduce the levelised cost of energy and a relatively small increase in blade length can significantly increase annual energy production.
LM Wind has produced an 88.4-m blade and is going to develop a 107-m blade for GE’s Haliade-X. He said the first blade for the Haliade-X will be produced by the end of the year. Mr Korsgaard highlighted some of the challenges involved in building such massive blades: they include aerodynamics and the fact that longer blades mean a significant increase in mass. Like Mr Sen he highlighted the challenge of control systems for very long blades and the need for new, advanced control systems that can reduce loads.
As blades get longer and longer so their mass becomes more and more of an issue. That issue is one that LM Wind has addressed by using new materials, such as carbon fibre. Its new 5.3-MW onshore turbine, Cypress, makes extensive use of carbon and has a novel two-piece blade design. However, carbon fibre has issues of its own said Mr Korsgaard – it’s a conductor, so if you go down that route lightning protection is more of an issue.
I have been waiting for a two-piece blade to come along, and now it has. If you’ve ever watched one of those videos of blades being transported from production facilities to the point of assembly you’ll know why two-piece blades are needed. What role will they one day play offshore? A two piece blade would be easier to build, transport and install offshore, if it were technically suited to the harsh offshore environment. A 20-MW turbine with a 250-m rotor diameter is perfectly feasible, Mr Korsgaard said. Might we see a two-piece offshore blade before long?
Towards the end of his presentation, Mr Korsgaard put up a slide showing a graph of the growth in blade length. The growth curve went all the way up to 140 m. Up went the iPhones and the cameras.
Is 140 m where LM Wind sees the limit of blade growth using current technology? Does it anticipate a need for even longer blades? What kind of technology might it be working on for even longer blades? Rest assured, I think LM Wind Power will be making us whip out our cameras for a long time to come.