Yes, I’m going to talk about Wind Turbines again. I love the things because they are such beautiful machines, and also because composites are one of the major enablers for the wind turbine industry.
Yes, those are people on top of that wind turbine tower, working on something inside the generator part of the turbine. And that isn’t even a very large turbine. These things can get really large. There is a company in China (Sany Renewable Energy) that has just released a 131 meter long wind turbine blade – that’s 430 feet for those of you like me that grew up with the English system of units. This new blade is for a 10 megawatt land based wind turbine installation in Germany – at least according to Composites World (https://www.compositesworld.com/news/chinas-sany-renewable-rolls-out-131-meter-wind-blade-?utm_source=Omeda&utm_medium=email&utm_campaign=CW+Today+2%2F2%2F2024). And, they are planning on using this same blade for their upcoming 15 megawatt offshore wind turbines where the wind speeds are higher and more energy can be extracted from that wind.
Of course, wind turbines have been getting larger and larger, because of the economics of wind energy. Making the turbines larger is something of a marginal cost increase partly because they rely on the same infrastructure as smaller turbines. There is also the ground effect that taller towers get away from, so the wind speed is more constant across the blade circle. So, if you can double the power output from a wind turbine with only about a 50% increase in cost, you end up way ahead. That is the major motivation for going larger and larger with wind turbine blades. These are of course gross estimates, but not far enough off to make a difference when it comes to decisions about size.
I wrote about this in a post a while back when I was talking about what I learned at the Carbon Fiber Conference in Salt Lake last year. It turns out that glass fiber for the flat part of the blades that takes all of the stress reached its maximum length potential a few years back, so everyone is going to unidirectional carbon fiber for the main structural part of the wind turbine blades – called the “spar cap”. This is the front and back flat part of the blade that is the main structural element to the wind turbine blades. It is this spar cap that makes the blades strong and stiff enough to resist the bending loads on the blades when the wind is blowing directly at the wind turbine disk.
So how big can wind turbine blades get. One of the largest ones that I was able to find was a blade that is 140 meters long – again by a company in China (Mingyang in Quangdong) revealing a 140 meter long blade – at least the design of it – in 2023 for their 18 megawatt offshore wind turbine.
In Europe, the largest blade built to date is on the Vestas (Aardus, Denmark) 15 megawatt offshore wind turbine. It is 115.5 meters or about 380 feet. That is still much longer than a football field. And they are still talking about making blades longer yet.
The answer to the question that I posed initially is a bit complex, primarily because as the industry matures, people that have been designing these blades have gotten more and more clever about how to save weight – which reduces the tension load at the hub of the blades – while maintaining stiffness of the blade – to resist bending and also fatigue.
I believe people have tried to estimate this many times, but every time someone makes an estimate of a size limit, someone comes up with a new, clever design and judicious use of lightweight composites. And, with the reduction in price for carbon fiber, and the motivation in the industry to create new product forms with more fibers in a tow bundle and higher density fabric forms, more and more of the blades will become carbon fiber to replace the glass fiber used today. This will enable even larger blades to be made in the future.
Another alternative is to rethink the design of the blade and the wind turbine itself. In a 2016 article in the MIT Technology Review (1), it was reported that researchers at the University of Virginia and Sandia National Lab were developing a 200 meter long wind turbine blade under funding from the Department of Energy’s ARPA-E Program. This program has actually produced some amazing results. These blades, however, were based on a rather different design. They were first a downwind blade versus the typical upwind blade of today’s turbines. These blades had flexible hinges along the length so that the blades could fold back in hurricane force winds to save the blade, but under normal conditions would be folded out and capture the wind rather effectively.
So, bottom line, they are going to get longer and longer until we finally get to the limits of the materials that we have available to make wind turbine blades. There will be more clever designs, and more application of lighter weight carbon fiber as the fiber cost comes down until the blades are all monocoque carbon fiber. Only then will we know what the limit is for blade length. I’m betting on a little shy of 200 meters for an upwind, traditional wind turbine, but I may be wrong about that. Only time will tell.
That’s about enough for this week. I hope everyone that reads these posts enjoys them as much as I enjoy writing them. As usual I will post this first on my website – www.nedpatton.com – as well as on LinkedIn. And if anyone wants to provide comments to this, I welcome them with open arms. Comments, criticisms, etc. are all quite welcome. I really do want to engage in a conversation with all of you about composites because we can learn so much from each other as long as we share our own perspectives.
I also wanted to add this week that I will be speaking at the SAMPE conference in Long Beach in May. I’m going to be talking about the subject that I have a passion for – composites sustainability. Maybe I can help shake up the industry a bit again, like what happened at the Carbon Fiber Conference in Salt Lake. One can only hope. Anyway, for anyone that is interested in materials and process engineering, SAMPE will be a great conference. And they will have a really great exhibit as well.
And, finally, I still need to plug my book, so here’s the plug. The book pretty much covers the watershed in composites, starting with a brief history of composites, then introducing the Periodic Table and why Carbon is such an important and interesting element. The book was published and made available last August, and is available both on Amazon and from McFarland Books – my publisher. However, the best place to get one is to go to my website and buy one. I will send you a signed copy for the same price you would get charged on Amazon, except that I charge $8 shipping. Anyway, here’s the link to get your signed copy: https://www.nedpatton.com/product-page/the-string-and-glue-of-our-world-signed-copy. And as usual, here’s a picture of the book, for those of you just tuning in.
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