In this episode of the Uptime Podcast with Allen Hall, we discuss how lightning strikes affect wind turbine blades, what protection most turbines have, and how effective it is. Wind turbines operate in some of the toughest conditions on earth, and there are a lot of myths about how frequent, how damaging and how powerful lightning strikes on these machines can be. Lightning protection expert Allen Hall dispels some myths about improving uptime in the renewable energy business.
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Podcast Transcript
Dan: Welcome! This is the first episode of the Uptime Podcast. I’m your co-host Dan Blewett and I’m here with lightning protection expert Allen Hall. Allen, how are you?
Allen: Great Dan, how are you?
Dan: Doing well here in self-isolation in Washington DC, and you’re out in Massachusetts right?
Allen: Out in western Massachusetts. It’s a snow storm right now. We’re supposed to get 6 to 8 inches of snow today, so self-isolation is going to happen no matter what. It’s still in the midst of winter over here. At least there’s sunny weather south of us, but up here we’re all buried in our holes trying to survive the winter.
Dan: DC’s not too bad, and that’s what’s been kind of eerie about the whole coronavirus thing. There’s been some really nice days recently, and it’s 65 and sunny and there’s not a human to be seen. This is so weird especially for this time of year where everyone’s excited for spring, and you just want to be outside on those days. But it’s just a ghost town.
Allen: Yes, we see a lot of people running up and down the street jogging when the sun does come out. Even when it’s mildly warm they’ll be up and running down the street, but they’re self isolating when they’re running even. So instead of seeing the normal packs of college kids running down the street you’ve spread out. So there you’ve got to be careful when you’re driving down the roads because they’re self isolating when they’re running too.
Dan: So here on the Uptime Podcast our goal is to talk about the wind turbine industry and how we can keep these crazy big machines operating. Obviously they keep getting bigger every year. Some of the challenges that these are facing are being in some of the harshest conditions, like in the middle of the ocean, up on mountain ranges, in the snow and the rain and the sleet. This whole theme of Uptime. If you’re a wind farm operator working in the renewable energy sector, keeping these machines running is a huge challenge. Obviously, we have the technology to produce tons and tons of electricity, but can we actually keep them running 24/7 or as close to it as possible? So Allen, my first question for you today, because you’ve been in the lightning protection industry for two plus decades, what does the common person not know about wind turbines? And as they keep getting bigger and bigger and bigger – now they’re soaring, I know GE’s new turbine is now over eight hundred feet, which is crazy – how do we keep these things protected from lightning specifically?
Allen: Well, as they get taller they become more and more of a lightning rod. I think even the layman can kind of see that. If you have any wind turbines that are around your home or business, you’ve watched them get taller and bigger and produce more energy. Each one’s producing more and more energy as we go along. That’s for economy of scale. You want to produce the maximum amount of energy in the smallest amount of footprint. So what’s happening now is as we’re getting taller and taller blades and turbines is that they’re becoming lightning attractors in a sense. They’re actually triggering a lot of lightning events, and the issue with that really is if we’re starting to trigger lightning events they’re becoming less random. So if a thunderstorm is coming through you’re starting to approach more than 50% probability some of those turbines are going to be struck just based on their size. They’re so high, and we’re also putting them in places where they stand out more. Obviously around us we’re placing them on mountaintops, which makes a lot of sense. That’s where the wind is. But off the coast of Massachusetts and all around the world we’re putting them in the ocean so they’re definitely the tallest thing around, and it’s just causing more and more lightning strikes. As we’re hearing about a lot of downtime just because lightning is damaging the blades.
Dan: So talk a little more on this concept because I think this was a misconception for me just as a person new to the industry. You’re saying that these are causing lightning strikes, rather just being in the wrong place at the wrong time?
Allen: Yes, the common philosophy forever was if lightning struck your house, your car, your airplane, anything it was qualified as an act of God. That was pretty much the case if you had me playing golf in the middle of nowhere and lightning hit you, it’s kind of an act of God. What’s happening now is we’re getting so tall that as those storm clouds come over there full of charge, even if lightning would not normally happen, the proximity of a grounded gigantic object starts to trigger that process. Even though there may not have been a lightning strike before the storm got near the wind turbine field, the wind field tends to cause it to start. So what we’re seeing is a lot of good videos and things taken in the last 10 years, a lot of it over in Spain. But we’re seeing triggering of lightning events coming from the wind turbines reaching out into those clouds, physically putting electrical energy into the air, and traveling up to the cloud and discharging the cloud. So it’d be kind of like rubbing your feet on the carpet and touching a doorknob. It’s a similar thing that helped start that process.
Dan: Those are streamers. So streamers originate from ground objects and they reach out to step leaders, is that right?
Allen: Yes. So what happens is you have a lot of electrical charge at the tips of the blades as the electric field gets stronger and stronger. You start to ionize the air getting little things called streamers, which are just electrical discharges and then they start to form into bigger things. And bigger things become things like step leaders which are ionized channels that start to reach out in the air. So when you see a lightning strike out in the real world, not in movies but in the real world, what you’ll see is these charge channels that send a flash. All that is just charge stored up in the atmosphere as the electric charges are trying to get from point A to point B. That’s what we’re seeing a lot of on wind turbine blades is that the blade is starting that charge and reaching out to those clouds to discharge that cloud. So it’s a really unique phenomena. We spent a lot of time back in the 1920s and 30s, when we started building big steel buildings much higher than we had in the past. Those things were getting struck, and we didn’t know a lot about it. And if you look back into old papers and things you’ll see that General Electric instrumented the Empire State Building. Then we kind of forgot about all that. And then we started making wind turbines and reliving the Empire State Building testing and phenomena. It’s just the problem with wind turbines if you’re in the Empire State Building you’re in the middle of New York City. If something were to happen, you can probably get to it pretty quickly and repair it. If you’re out in the middle of nowhere in the ocean or you’re on a mountaintop with the wind turbine, it’s going to take a little while to get that thing repaired.
Dan: It seems nightmarish to have to go repair some of these turbines. In gale force winds in the middle of the ocean… it seems like a terrible ordeal.
Allen: It takes a lot of a lot of training. A lot of safety training because you can think about the risks involved in climbing out onto these things. There’s a lot of things that can go wrong. I’m always shocked at how good the industry is on the safety record for people working on wind turbines. They do a really good job of doing it. It’s just a really difficult job. In our company we’re trying to help minimize the times they got to go out there to fix some lightning damage. That’s what we’re focused on because it is just dangerous no matter how you look at it. If you’re hanging from a rope several hundred feet in the air, and you’re trying to fix this blade, it’s not an easy job to do.
Dan: Especially considering that these turbines are placed in environments, especially in the ocean, where there’s just a constant flow of wind. I mean being up on a rope while it’s blowing 35 mile-per-hour winds, that seems like the time when you don’t ever want to be up on a rope. But that’s the reality a lot of times.
Allen: Well, they try to limit the times they’re not going to be out there when it’s really windy. So there will be select times they can get out and go do those things. I think the kicker is, if you’ve ever tried to work on a car while hanging from a rope, it’s like that. You just can’t walk over to the tool box and get a tool. It’s got to be on you and you don’t really have any leverage either because you’re not really attached to the thing. So it’s like levitating while trying to try to fix your car.
Dan: Do people fix cars via ropes?
Allen: Well, if there was someone in the world that could do it it’d be a wind turbine blade repair person. Because if you ever watch them work, it’s really amazing. Just the coordination and attention to detail and the thought process that goes into it before they even get onto the blade.
Dan: Oh yes. Talking about a common job like painting your house, the biggest thing is prep. If you do your prep right everything else goes very smoothly. But I mean they’re going to be up there for a couple hours at least, I would assume, for some of these more complex repairs. They’re going to have to have multiple batteries for their drill and their sander and all of these tools. They have a lot of stuff, I mean there’s a lot of stuff.
Allen: You have a lot of equipment hanging off you also. You’re the one bringing the equipment in, you’re the one taking the equipment out. It’s a complicated thing, no doubt.
Dan: So when these turbines get struck obviously the blades are the closest thing to the heavens so they’re going to take– more often than not–the lightning strikes. But the nacelle gets struck. How would you break down the percentage of strikes on these turbines?
Allen: I think the data– and I have been looking at data over the last couple of weeks– does tend to vary because you’re not getting full industry data. It’s also going to depend on where you are located in the world. But it’s roughly from what I can see, 80 to 90 percent blades, 10 to 20 percent in nacelles. So if you think about the back of the nacelle you have instrumentation, pointy objects, hanging off the back of the cell. Then once in a while those things will get struck, and it’ll miss the blade. But for the most part as these blades get bigger and taller the nacelle strikes are going to go down, and the blade strikes are going to go up accordingly because the blades are so much higher. So much higher than the nacelles.
Dan: But I think what’s really interesting is–and this I didn’t know until just recently– is that the lightning’s not going to attach to just the exact point when it hits. You know we think of lightning as being when it hits a tree and it splits a tree. Or it hits a lightning rod and that’s where it goes in. But turbine blades are moving a hundred plus miles per hour so it’ll be initially attached on the tip but then that blade is still moving. So then it’ll be attached to a second point and maybe even a third. Speak a little bit on how these actually attach to these moving blades.
Allen: Well the thing to think about is typically during a thunderstorm there are winds. So the wind turbine is actually generating power in most cases, unless the winds get too high and then they automatically shut down. But those blades are turning at a speed that is longer than the lightning event. So what will happen a lot of times is, it’ll strike one blade and then as a blade rotates around down to the bottom it’ll jump to the next blade that’s popping up in the air. That is pretty typical of the bigger lightning strikes, and so you’ll actually see damage on two blades instead of just one. And obviously short lightning strikes, little strikes, will take mostly on one blade. But I’ve seen images and videos of them jumping over to second blades and it’s pretty common looking at the data. Obviously we don’t sit around 24 hours a day, 365 days a year, watching turbines. But the data that’s coming back indicates that the blades are moving fast enough that you’re going to hop from one blade to another. So a lot of the blades, if you look at them, have similar damage to them. It isn’t like one blade has taken a big strike so the other two haven’t. All three have some level of damage to them.
Dan: And that’s, I think, where a lot of problems occur because on every blade that rolls off the factory floor, the lightning receptor is pretty close to the edge of the blade but not all the way to the tip. So if the initial strike is out there the tip, which makes sense because it’s going to be the farthest point up towards the sky, it might hit the receptor and flow through the down conductor then to the ground through the rest of the metal body. But if it’s got that second attachment point then then what happens?
Allen: Well, if it jumps over to the other blade, if that’s what you’re asking, it starts the process all over again. We see this in airplanes quite often because the airplanes are moving at such a high speed. It will attach to the nose of the airplane, and as the airplane starts flying forward, the lightning channel is fixed in space. So the lightning channel tries to find the next spot to attach to and then the next spot to attach to and the next spot to attach to. So every attachment has its own physics, local physics to it, about where it’s going to attach to. So it may have hit the receptor on blade one but when it starts looking for blade two, it’s going to go anywhere it possibly can find. It may not find the receptor on blade two before it finds the down conductor or some structural weakness in the blade and decides to go through it. So it’s like rolling the dice all over again, so you want to increase your likelihood that it doesn’t go anywhere but the receptor no matter which direction it’s coming from. Whether it’s starting there or it’s being swept into it, you want to get it to those receptors. We see that when, in a lot of cases especially in the restrike situation, it doesn’t necessarily go to the receptor. The physics are a little bit different, and I think that’s what’s driving it is the physics get a little bit different. Once you have an established lightning channel and lightning energy running it down into a blade, when it jumps in the next blade it’s more of a localized effect instead of a universal effect. So you get different different kinds of lightning environments and lightning requirements. On the aircraft side, maybe you’d bring up aircraft as an example. On the aircraft side they actually have two separate lightning tests that’ll run – the initial lightning attachment to the airplane and then the subsequent attachments to the airplane because the physics are different. We don’t really do that on wind turbine blades. We look at the initial attachment and hope for the best. I think the aircraft industry has learned from that over time, and the wind industry is starting to pick up a lot of those things as they figure out what’s happening in the field.
Dan: As the blade moves it gets initially struck on the receptor, on the tip. Then it moves a little bit, and it takes a second strike, say it’s further down the same blade. So that’s where a lot of the damage is going to occur, am I right? Because it will puncture and go through to the down conductor that’s hidden beneath inside the blade?
Allen: So there are two places where blades are really susceptible. Anywhere there’s the big copper down conductor running inside the blade, and then a lot of times they have something we call a receptor block. So the actual receptor screws into a big aluminum or steel block that’s mounted inside the inside the blade. The receptor block is physically much bigger than the actual receptor outside. You see this kind of coin size receptor on the outside, then you see this twelve inch by twelve inch or six by six block of metal that’s sitting on the inside. So that receptor block is just as attractive as the receptor itself in some cases. So lightning tends to get to those receptor blocks and tends to get to that down conductor cable. In order to do that it’s going to blow through the structure of the blade which causes all kinds of damage.
Dan: But initially off the factory floor the blade dielectric is enough to keep that insulated, is that right?
Allen: Yes, if you go test a new blade, which is what we tend to do. We tend to take a new blade off the floor and then go off and run a lightning test on it. We do the same thing for aircraft by the way. An aircraft will make a plastic part, it’s just rolled off the factory line. We’ll take it out for lightning testing. It’s perfectly new, it’s pristine, and we go test it. It looks great because the dielectric, the actual physical nature of the plastic material is still pristine. It hasn’t been stressed electrically over time, so a lot of times you get a great test result. Then as you put that product into service it seems to degrade over time. What we’re seeing is that just being exposed to multiple lightning events or electric events, electric charge events or electric field events will degrade the plastic materials and so they’re not as strong as they once were. So you ran a lightning test that qualified your blade to meet the IEC specs. You’re not going to get that same performance out in the field. That degradation of the dielectric and weathering is going to do that to you. In a lot of cases you’ll see a lot of great advertising come out that says, “We’ve done the lightning test. We’ve done the IEC testing. Everything’s great!” And then a year later you hear about a lightning strike that blew a hole in the blade. That’s why.
Dan: And then do things like rain erosion and temperature fluctuations hasten the process of the blade dielectric eroding?
Allen: Anything that eats into the blade degrades the blade. Be it hot/cold, mechanical stresses, or rain erosion. Rain erosion is a big one because it actually physically eats away at the outside structure of the blade. That removes some dielectric material and makes the blade electrically weaker.
Obviously there’s a big push right now to make the blades more durable for rain erosion and being out in the ocean where the blades are getting beaten up. That degrades the lightning protection also. So again we’re seeing differences in what we test in the lab versus what’s happening in the field just because of that.
Dan: And that makes sense. For me as a layman to the electricity world–it’s hard to think of something being electrically porous. But for me I’m just visualizing it as actually having holes where the electricity can actually go through. But it isn’t really like that, but in a sense it is, right?
Allen: Yeah, yeah. In the power industry they learned a long time ago to not make things out of plastic because they change their nature over time. If you go out on the street and look at the light pole or the pole that’s powering your home or apartment complex whatever you’re living in, you’ll see that a lot of the components are made out of ceramic. They’re made out of a glass ceramic material. That’s why. Those materials don’t really change structure over time, and they can handle the weathering. But they’re also particularly brittle. And they’re heavy too so you can’t make wind turbine blades out of those things.
Dan: It could hit a bird and shatters or something.
Allen: It’s the wrong material. But it just tells you that you don’t see a lot of plastics being used in the power industry, and that’s why. Because those things tend to degrade with heat, temperature, UV, you pick it. Plastics do change substantially over time, and this is a division of labor typically that happens on the engineering side. Say we all go to school, we crank out electrical engineers, and we all understand electricity and all that cool stuff. And then we create mechanical engineers, and they all understand the stresses and the loads and the materials and all that kind of great stuff. And never the two shall meet. In the lightning world you’d better be good at both of those or better have an understanding of both of those, because you’re dealing with materials, and you’re dealing with electricity. And that’s where the handoff becomes a little murky. A lot of times the mechanical engineers get involved or structural engineers get involved on the lightning side because the structural aspects and materials aspects are so important. And the electrical guy is just running a test. Somewhere you have got to meet in the middle, and I think that’s part of the reason why we’ve had so much difficulty over time. It’s just been that sort of separation of labor and the way we train engineers, but as time goes on one thing about the human condition is you learn from your mistakes. So we’re adapting everything, and we’re starting to see a lot of changes happen in the wind turbine industry. We’re starting to be a little more cross-functional, particularly in lightning. In my opinion, we’re starting to see more of the electrical people taking on some understanding about what the materials are. And that’s a good approach. A lot of mechanicals tend to be at least somewhat electrical savvy, not that they can create a circuit or make a microprocessor or anything. But they understand the energy effects of lightning and what it does to materials. So we’re getting there, it’s not a fast process but we’re getting there.
Dan: Well, one of the things we’re going to talk about in our next episode is all the new waste that’s being produced, because we’re getting to the point where a lot of these wind turbines have been around for a long time. They’re starting to come out of service with some severe damage. You have to take a whole blade out of service. What are we doing with this stuff? We’ve been facing that with cell phones and electrical waste. It’s funny how our species is creating more huge piles of trash, but this is a growing concern for the wind turbine industry. They’re just now starting to figure out what they can and can’t do, and how they can maybe repurpose some of these.
Allen: It’s similar to a lot of different industries. Especially the airlines right now are taking big time hits, and the aircraft manufacturers are taking big time hits. What’s going to happen is they’re going to park airplanes. They will take airplanes out of service because they’ve met their service life. On an airplane a lot of that material is going to be recycled and made into something else. A lot of it’s made out of metal and parts of the airplane can be reused or used as replacement parts on other airplanes. So those airplanes are recycled forever, and you’ll see them sitting in bone yards in the desert and recycled. A blade doesn’t work like that. Once it has met its service life it’s really hard to extend it. I’ll give you a good example. The B-52 has been around since the mid 50s as a United States bomber aircraft. It has been around a long, long time. They will retrofit those things to keep them flying, and the same thing is true of some commercial airlines. A lot of airplanes have been around a long, long time because it’s more efficient to try to keep that thing in service than to throw it away. On the wind turbine side we haven’t really gotten there yet. Blades get structurally degraded, and that’s pretty much it. They’re going to end up in a landfill. The trouble is that the way we designed blades 20-30 years ago, they’re not really recyclable, so we’re struggling. So the more we can keep blades in service, the less we’re going to be putting them in landfills, and I think that’s a good thing to be thinking about.
Dan: Well, Allen, great first episode. Next week we’re going to tackle this a little more in-depth – wind turbine blade recyclability. What are some things we can potentially do with these massive things that are getting bigger and bigger. One blade is now the size of a 20-story building, it’s getting up there. Tune in next week for the Uptime podcast again where we talk about everything wind turbines, renewable energy, and lightning strike protection. Allen, thanks again!
Allen: Thanks Dan, stay warm next week.
Dan: I will! See you next week.
