The growth of the US wind industry has led to new challenges for wind turbine foundations, an often overlooked but critical component. ONYX Insight's Ian Prowell, a structural engineer with extensive wind industry experience, describes how early foundations were designed for smaller 1-1.5 MW turbines with a 20 year lifespan. Now, many sites are being "repowered" with larger 2-3 MW turbines, reusing and adding decades more fatigue loading to the same decades-old foundations. Prowell discusses common foundation types, construction methods, failure modes, and monitoring techniques to ensure adequate remaining life during repowering campaigns. Proper foundation assessment before repowering could prevent costly collapses and save project owners millions.



Allen Hall: I'm Allen Hall, host of the Uptime Wind Energy Podcast. Foundations are a topic that we received several requests for, and honestly, foundations are not discussed enough. Buried beneath the earth, these massive foundations supporting our wind turbines have to remain steady year after year in some tough conditions.



And yet, wind turbine foundations have a great track record. However, As the wind industry expands and turbines grow, new challenges are emerging that demand innovative solutions. So I'm looking forward to our discussion with our guest, Ian Prowell, Principal Engineer with ONYX Insight. And Ian has a Ph. D. in structural engineering plus years of experience in the renewables industry. Ian, welcome to the program. Thank you. 



Ian Prowell: Great to chat with you, Allen.



Allen Hall: So we have something in common, just to kick this off you went to UCSD.



Ian Prowell: Yeah, I did my master's and PhD there.



Allen Hall: Yeah, so we just visited that campus. It's quite lovely. It's a good place to get your master's and doctorate from.



Ian Prowell: Yeah, yeah. Some people do have problems with focus. The waves call and they end up surfing and 



Allen Hall: getting back on the topic of wind turbine foundation. So, Ian, you have a number of years in wind turbine foundations and what's been happening on the scene.



Can you just give us a brief history, like where we are today and sort of how we got to where we are? 



Ian Prowell: In terms of history, I mean, what you see with current wind turbines, say megawatt plus machines. Generally we're talking about late nineties and on early foundations, we kind of had some basic design philosophies and some ideas on how to do it.



But earlier we relied a lot on behavior, concrete and sheer and intention. There were some issues that came up as things went by and we learned due to some collapses that that wasn't something we could rely on. And so, yeah, as we're moving forward, turbines are getting bigger. Loads are getting higher.



Fatigue loads are getting much higher as we get higher capacity factors, larger rotors, so forth. And so we really have foundations now that are driven by fatigue. That's a major design concern. And we have kind of. Multiple generations of foundations where early on those foundations had initial design philosophies.



And as we learned more, those philosophies were updated. And so generally kind of era by era, we're getting more robust foundations, but also it's introducing new challenges. As loads get higher, the foundations get larger. So for example, concrete pours can be very difficult. They could go on for 10, 12 hours or more.



And that's, that's very challenging for the individuals out there working and maintaining good practice while pouring that concrete for that long of a period. 



Allen Hall: And were there a consistent set of designs used back in the nineties and early two thousands? Or, or what drove those designs? Were they just.



Professional engineer by professional engineer, designing them. And because it's not, doesn't seem to be a 



Ian Prowell: standard. In the U S there's kind of two things coming in here. We have U S building code.