The Offshore Energy Podcast

Episode 9 - In the Shadows of Giant Turbines

• Ian Voparil & Jim Bennett • Season 1 • Episode 9

Share episode

Send us a text

In this episode, hosts Jim Bennett and Ian Voparil delve into wake effects in offshore wind energy, exploring how they influence turbine efficiency and ocean circulation.  We are joined by Jessica O'Connor from DNV and Dr. Kaus Raghukumar from Integral Consulting and together, we unpack the implications for farm layout, system controls, project economics, and even the ramifications for policy.  Our discussion highlights the need for innovative modeling to optimize offshore wind projects and further scientific exploration of the coupling between the atmosphere and oceans.

• Discussion of wake effects and their significance 
• Impact on energy production and cost efficiency 
• Role of turbine placement in maximizing output 
• Implications for ocean currents and marine ecosystems 
• Advanced modeling techniques for predicting wake interactions 
• Future trends in turbine design and environmental considerations 
• Importance of integrating scientific knowledge into policy decisions 
• Encouragement for continued research in offshore wind energy

Speaker 1:

Hey everyone, did you know that the success or failure of an offshore wind project could come down to a key factor that you might not expect Wake effects. A spinning turbine often slows down the wind, can mess with the strength and consistency of the wind. For a project under design, it can be a game changer. It's one of the trickiest and least well-known challenges in wind farm design. So why does that matter? Well, let's dive into it on the Offshore Energy Podcast right now.

Speaker 2:

I'm Jim Bennett and I have over 40 years of experience developing energy in the ocean. I'm Ian Valpero and I've spent the last 20 years developing offshore energy projects around the world, and this is the Offshore Energy Podcast.

Speaker 1:

Hello Ian, are you there hey?

Speaker 2:

Jim, how are you? I am fantastic. Good afternoon. Happy Valentine's Day, jim.

Speaker 1:

Oh, that's right, it's Valentine's Day. I've already got a dozen roses taken care of.

Speaker 2:

That's right. There are things to take care of before Valentine's Day and I'm glad to hear you have.

Speaker 1:

I think we both still have some snow on the ground, although I have a lot less down here in Virginia than you have up in Maine.

Speaker 2:

Yep, Jim, it's still winter up here, so I've been dreaming of hot, sunny days and warm, breezy nights. In other words, I've been dreaming about more solar and wind power too. Nice transition, huh. In 2024, the European Union saw more power generated by solar and wind than from fossil fuels. In the US, wind and solar generate about 18% of our power. Currently, China and even Saudi Arabia are growing their solar and wind industries at a fast clip because every nation around the world expects their energy demand to grow over the next few decades, and solar and wind, particularly onshore and on land, are faster and cheaper to develop than power plants using fossil fuels in most parts of the world. Now, not every nation cares about the decarbonization value of solar and wind. They just want inexpensive, reliable, predictable energy in time to meet their nation's demands. Jim, your teaser really piqued my interest, because I don't know a lot about wake effects in and around wind farms and I certainly don't know about them offshore in the ocean. But if they affect power output so much, I'd sure love to learn more.

Speaker 1:

Well, we're very fortunate that we have a couple of people here today that will help us work our way through this, because it is a very technical issue and it is very much more involved than I know my background is sufficient for, so maybe we could introduce our guests.

Speaker 2:

We have joining us today Jessica O'Connor from DNV, and we've got Kaus Raghu Kumar from Integral Consulting too. How are you guys?

Speaker 3:

Doing great. Thanks, Ian.

Speaker 4:

I'm good, Thank you Thanks.

Speaker 2:

Ian and Jim, would you like to do a quick introduction? Tell our listeners why you are fantastic to have on this. Jessica, why don't you go first?

Speaker 3:

So I am the business development lead for DNV's Offshore Wind Advisory Services in North America. Most folks are familiar with DNV's involvement in project financing, due diligence and project certification. Involvement in project financing, due diligence and project certification. I sit on the advisory side. I support developers, oems and other agencies in offshore wind projects. My background is 18 years in the wind industry and really my experience has always been where the wind meets the machine and that is in site suitability, site-specific mechanical loading and energy resource assessments. That's the topic we're talking about today and as business development lead now I'm completely focused on offshore wind and it's a really fun project for me, as well as moderating our offshore wind training program.

Speaker 2:

Sounds like just the right background to help Jim and I navigate this space. And Kaus, it's great to see you again. Kaus, how about your background and why you've been invited to join us here?

Speaker 4:

I'm a physical oceanographer and underwater acoustician. At Integral Consulting, I work on a variety of problems related to environmental effects of marine energy that range from, say, changes in ocean circulation around offshore energy structures to underwater sound radiated by these structures. I use tools such as in-situ measurements, acoustic propagation model, large-scale physical circulation models whatever tool suits the job. And the question we're asking really is what effects, if any, positive or negative, arise from offshore energy installations.

Speaker 2:

The topic of our podcast today is going to be around wind, wake effects and interactions with the ocean, so I'm so glad we have you guys both here. For many of our listeners, this seems a little bit like a technical podcast, right, jim, and I often don't dive into technical details.

Speaker 1:

I'd like to note that in the development of the program early on, there were a lot of technical issues that we simply weren't able to fully address, and this is certainly one of them. In fact, the first time I heard about it I was kind of rolling my eyes. I said you know, the ocean's pretty big place and the airspace above the ocean and the wind, they're pretty big spaces too. It's kind of hard to believe it would have an effect. Well, I got educated over some time and it's one of these issues that has a very strong technical basis. But that technical basis feeds into the development of policy and it feeds into how decisions are made about what areas offshore can be offered appropriately and how they should be configured. So it's another example of where the technical feeds into the policy structure.

Speaker 2:

I've heard anecdotally that these wake effects amongst turbines and between turbines can be really quite significant. Correct me if I'm wrong, but I've heard things like 10 to 20%. Am I in the right ballpark there?

Speaker 3:

Very close. We say that the inter-array wake effects can be about a 10% reduction or up to 10% reduction of energy production and then an up to 30% reduction in array-to-array effects.

Speaker 1:

Definitely significant and that goes to the point about the education that I got is that this is not a small thing, it's a big thing. It's a very big thing in terms of wind farm design. That's right. Terms of wind farm design that's right. Given that information, let's ask the basic question why do wakes?

Speaker 3:

matter. What is at stake here? And, jessica, maybe you could help us with that a little bit. Yeah, sure, really, it all comes down to dollars and cents. It impacts directly the levelized cost of energy and this impacts that by impacting our grid planning, project financing and then, of course, eventually the cost to the rate payer and so wakes. They can both reduce the amount of energy but also increase the mechanical loading in the wind turbine. So when we're planning for our project, we want to maximize for wind production and minimize for mechanical loading, and that is an iterative process. Process and both of those things throughout that iterative process directly affects our development expenses, our capital expenses and our operations expenses.

Speaker 2:

Okay, so walk us through this conversion of wind through a turbine into mechanical energy and then an output of power that ultimately gets sold into the grid.

Speaker 3:

So in a very simplistic form, first we want to find what the energy is in the free stream, so pretending that there are no wind turbines in there. We want to take publicly available long-term data, whether it's measured or it's reanalysis data, and that gives us that free stream wind speed. We apply that to the wind turbine's power curve and then from there we have an energy yield value. But then we need to apply the losses, and there are losses like electrical losses, availability so we know that O&M is going to create a certain kind of availability.

Speaker 3:

And then wakes, and there are basically three kinds of wakes. One is that turbine to turbine interaction. The next, which has had a lot of research, is blockage. And then the third is array-to-array wakes, and for offshore wind it is much more of an impact because of that atmospheric stability. On land we have more of an unstable situation where the atmosphere is able to mix, but on the ocean we do not. It stays quite stable and so those long-distance wakes travel a lot farther. So from wind energy 1.0, onshore wind, and we need to improve our measuring and modeling techniques.

Speaker 2:

When you said blockage, that was something it's not a term that I'm familiar with in this context.

Speaker 3:

As the wind approaches a very large array, it kind of slows down. So it's kind of like when you put your foot in the water and a wave is coming towards your foot, it kind of slows down before it hits your foot. And that's what's happening in the atmosphere is the wind slows down before it meets the array, and that loss can be up to 4% of energy production.

Speaker 1:

How do you deal with the uncertainty and the losses that are associated with the wind resource in the context of an offshore wind project?

Speaker 3:

We want to maximize the energy, minimize the loading. Both can be affected by wakes. So we want to maximize the energy by maybe having larger rotors, having more wind turbines within the array, putting the wind turbines in the most energetic locations. But then we want to minimize the loading. So that means we need to spread out the wind turbines and maybe reduce the rotor size. But then when you're introducing wakes, those larger rotors also bring down the energy. So it's this very delicate balance of rotor size, spacing, location and then even your controls algorithms, so different kinds of pitch schedules and yaw schedules to treat the wakes or make the wakes act differently within their ray.

Speaker 2:

Jessica explain pitch and yaw for those of us who don't always work in three dimensions.

Speaker 3:

Yeah. So a pitch is when the wind turbine blade is spinning back and forth to catch the wind in a very particular way. So the blade is like an airplane wing and it is affected by the wind. It has drag and lift. Well, that airfoil as it changes, as it changes how it faces the wind, it changes how fast the blade is spinning around. So we want to change the pitch in order to have the wind turbine spinning at different speeds. Yaw is when the whole nacelle is going from north to maybe west.

Speaker 3:

And that is changing usually with the direction of the wind speed, the freestream wind speed, and for the case of wakes you might want to be a little bit off kilter so that the wakes meander kind of differently and don't hit the wind turbines directly downwind that or downwind that makes a lot of sense to me.

Speaker 2:

So when you're thinking about the potential for wake effects, so when you're thinking about the potential for wake effects, you're thinking about the spacing between individual turbines in a wind farm, where you put them, you're thinking about if you're maximizing power output, you're thinking about how an individual turbine is oriented facing into the wind or perhaps slightly off the wind if there's something behind it, and you're also determining how to orient the blades in respect to the wind. I mean, there are so many different levels of control here that it must be a lot of complexity for an operator to deal with.

Speaker 3:

And I actually have one more control that we have and that is the location of these arrays. So, like in the New York byte, the wind speed is directly north and south and all of the arrays are aligned north and south. Now there isn't a whole lot we can do about that, but we do know that there's going to be these long distance wake effects because of the way that they're arranged, so there could be that planning. That happens a little bit earlier in the development state.

Speaker 1:

So you're saying that that was one of the earliest leases that we issued, and I think what I'm hearing you say is that, in the absence of more thorough knowledge about wake effects, we probably have an array and a configuration which might be less than optimal.

Speaker 2:

Yes, that orientation of the farms that was done from a I'm sorry from a regulatory perspective, right, because it wanted to be predictable for ship traffic, or from a regulatory perspective right, because it wanted to be predictable for ship traffic or it was more than regulatory.

Speaker 1:

but yes, it was a lot of different factors involved and what I'm hearing is that the factor about wake effects, which definitely was considered in later leases, maybe didn't play as thorough a role as it should have.

Speaker 3:

Yeah, and in fact just after the New York bite auction, that's when a lot of the research about long distance wakes really started to come out of Europe, and so there wasn't a whole lot of information about the types of modeling that could actually capture what those wake losses could be. But now we do know a lot better those wake losses could be. But now we do know a lot better. And we also have all of these other site constraints beyond the wind resource that we need to consider, so it's a much bigger picture.

Speaker 2:

And Kals, we want to bring you into this conversation too. We've been discussing how turbines can impact the flow of wind, and you know all about how the flow of wind affects the movement of the oceans, the surface currents. Can you explain to our listeners some of the key factors in those interactions?

Speaker 4:

With an offshore wind farm, the awakes that are created in the lee of each wind turbine. They kind of accumulate over the size of the wind farm and the end result is that, like the wake behind an array of wind turbines, can be tens to or to close to 100 kilometers or more. The question we've been asking at INEGRAL is whether this region of reduction behind regional wind speed reduction behind a wind farm, can this reduction affect wind-driven ocean circulation? Because fundamentally, surface circulation or surface movement of water masses in the ocean is wind-driven and if there's a reduction in wind speed from whatever, process would this affect surface circulation?

Speaker 2:

Does this potential you know the wake effects of turbines have a real potential to be significantly important to the ocean, or is it just lost in the noise that the ocean signals?

Speaker 4:

Essentially, if the physical scale of the wake behind a wind farm is on the order of several tens of kilometers at typical latitudes where wind farms are currently being installed, then the circulation at those scales is affected by the Earth's rotation and the change in circulation does start to feel rotation-related effects. So one example is typically when winds blow in a near constant speed or direction over the ocean's surface, it leads to a transport of surface waters and, counterintuitively, the direction at which those surface waters are transported is not downstream of the wind but at an angle to the wind. And if the surface waters are moving offshore, it's replaced by cool, deep, nutrient-rich waters from deeper water, which then leads to a pretty thriving ecosystem in some regions of the world. So it's a question worth asking is whether the changes in ocean circulation at the surface, for whatever reason, can affect that ecosystem.

Speaker 2:

I'm also thinking of, like the coast of California. Isn't that one of these ecosystems where we do see that that's the way it often works?

Speaker 4:

Exactly. There's really two different effects. One is, yeah, as you mentioned, when, like on the coast of California, where the winds predominantly blow from the Northwest to the Southeast, this wake if offshore wind farms were to be located off the coast of California, the wake will be to the south and the movement of surface waters to the right or offshore in California it does lead to what's called an upwelling ecosystem, where you have really rich and by rich I mean rich in nutrients surface waters which would support a pretty healthy ecosystem. The other effect is when you have, as you go, say, from east to the west or west to the east, horizontally along the surface of the ocean. If you were to encounter a change in wind speeds, that gradient can also drive a movement of surface waters and either upwelling of deeper waters or downwelling of deeper waters, which can have both a positive and a negative effect offshore winds been around for a while in the North Sea, and so is that a similar situation over there, or how can we judge where in the world this should be?

Speaker 2:

you know, studied enough of potential exploration.

Speaker 4:

Yeah. And so as long as you have. Uh, uh, uh wakes behind the wind farm, uh behind an offshore wind farm, you can expect there to be wake-driven effects to ocean circulation.

Speaker 4:

The question is, just how strong is that signal of the wind farm driven ocean circulation effect above the noise of general ocean circulation or changes in ocean circulation due to climate change or warming of ocean or the general warming of ocean temperatures? So in some cases where you have a really clean signal so the modeling studies that have been done off of California do have a characteristic of a really clean signal because the winds tend to predominantly blow in one direction and you can run the models over a long enough time that you can start to see signals that emerge above the noise. It's a lot easier to see the effect. In other cases, like the North Sea, the signal might get mixed by several other confounding factors and you might not even see that signal above the noise.

Speaker 1:

Okay, so how do we bring this all together? Tell us about the modeling, if you would, between the oceanographic models and their interface with the meteorological models, so that we feel like we're in a pretty good position to know what's actually going on out there.

Speaker 3:

So there are two ways that we need to understand this, or two methods to understand this, and that is through measurements and through modeling, and the measurements feed into the modeling and actually likewise the modeling feeds into the measurement schemes. So first, with measurements for offshore wind, we are deploying a floating lidar or a buoy that has lidar on it, and then for Klaus, it would have a bunch of and he'll be able to speak to this better than I would oceanographic measurement equipment below the sea surface, and so it's really great when a state deploys this. That way, a developer can take that data and then do their own modeling, both using linear flow model, but then also computational fluid dynamics and other types of mesoscale modeling and Kaus. I know you know some more about some modeling, so I'll let you take it from there.

Speaker 4:

So the same model, same atmospheric model, which are used to predict wake losses or wake effects behind wind turbines, also provide what are known as the forcing fields, or one of the inputs that go into ocean circulation models, which is wind speeds or wind stresses at the ocean surface. So essentially, the way these studies are conducted is you run an ocean circulation with atmospheric fields in the absence of wind turbines over a long period of time, and then you go back and introduce turbines into your atmospheric model, compute the wind fields and then you rerun your same ocean model over the same period of time with this modified wind field and you can then start to look at effects of any.

Speaker 3:

And that is actually how we observe that there are wake effects in the energy production. So we can measure the production before any other wind turbines or arrays are nearby and then when they are installed. So we're introducing those wind turbines. We then know what those losses end up being and therefore we're able to calibrate our models.

Speaker 2:

Jessica Kaus, are we talking spreadsheet modeling that I can do or are we talking about much more detail? When you talk about these mesoscale models?

Speaker 3:

It's a lot of Bernoulli's equations. A major model that is used for measuring wake effects in a much more computational, heavy way is computational fluid dynamics, so some sort of flow model. But then you want to take into consideration all of the atmospheric parameters that affect the wind speed and how the wind interacts with different surfaces, and that's when we're looking at the wind research, weather research and forecasting tools. So WARF is what we call it, and at DMV we couple those two types of models and that gives us a very complicated scheme of data that I am not an expert in, but it has been validated against the wind projects in Europe. So I find it exciting. Though it's not exactly my expertise, I do like listening to those in my team.

Speaker 4:

I do like listening to those in my team. Yeah, the mathematics that go into either the mesoscale atmospheric models or the ocean models are actually identical but they differ in that they can make different simplifying assumptions to be able to solve these equations in a computationally efficient and timely manner. So, for example, in an ocean model you take in temperature, you take in salinity distributions in the ocean and you see how differences in temperature and salinity affect density of the ocean. And when you have changes in density then it can lead to water masses flowing from regions of higher pressure to lower pressure, with pressure differences being driven by changes in density, for example.

Speaker 2:

In the future, as we expect to see turbine sizes increasing, particularly offshore, would you expect wake effects and ocean interactions to become more pronounced or less pronounced?

Speaker 3:

It's definitely a push and pull. So you are able to extract more energy out of the wind when you have a larger swept area, but that larger swept area is also taking the momentum out of that wind speed and taking the energy out of the wind for the next winter. Right the wind turbine downstream, but also having newer designs in blade lengths and airfoils and all the different ways that we try to improve our wind turbines, it actually also introduces a level of uncertainty and investors don't like uncertainty. So it's a push and pull of. We want to maximize how much we get out of the energy, but we also want to minimize risk.

Speaker 2:

We know you're each involved in R&D efforts and additional science programs to help the offshore wind industry get better, more efficient, more environmentally responsible and more affordable. Where do you see these key next steps of improvement coming from?

Speaker 3:

Through operations. So the more we have wind turbines operating, such as in the North Sea, we're learning so much like the long-distance wakes on how the wind turbines can survive in ocean conditions and how different designs are affected in ocean conditions, and so the more we expose our technology in these different environments, the more we're going to learn about how they should be designed, built, installed, operated be designed, built, installed, operated, and there's innovation and improvement in that regard.

Speaker 4:

Yeah, and then in terms of modeling environmental effects, there's two main directions where a lot of research is currently being done or needs to be done. The first is better. The first is better modeling, or understanding what the wake behind the structures themselves are. As a colleague once told me, flow around a cylindrical structure is one of the most well-studied problems in fluid mechanics, but as soon as you add stratification, no one seems to know anything. So that's currently an active area of research. Vineyard Wind actually is funding a study called Ocean Wakes, which is looking at this particular problem specifically. The second area of research is looking at this feedback between the ocean onto the atmosphere. So essentially running or developing atmospheric models that take into account changes in surface roughness at the bottom and changes in temperature at the bottom, which can affect the weight loss calculations that Jessica is interested in.

Speaker 3:

Actually, that's a really good point because when I was talking about the free stream wind, that free stream wind is affected by the surface roughness. And even though Ian said that the ocean is flat, it does have a roughness to it. It's flatter than land, but it still has a roughness to it. It's flatter than land, but it still has a roughness, and we do need to know that. And likewise with the temperature, we can make assumptions as to what the surface of the ocean, surface temperature is, but the more we're able to measure and model it, the better we can model the atmospheric conditions and, ultimately, the wake effects.

Speaker 1:

I can't help but look at it from a public policy standpoint. It's not just the accumulation of the knowledge in a way that leads to better technical decisions, but it also is the use of the knowledge to make better policy decisions, and decisions about things like area ID and what works and what will work best.

Speaker 3:

And I can advocate for both DNV's efforts in measurement and modeling and House's integral modeling and measuring. That all of that affects uncertainties. The better we get at measuring, the better we get at modeling, the better we can reduce the uncertainty and the cheaper it would be to borrow that money and then ultimately bring down the cost of energy.

Speaker 1:

The program is working the way it was supposed to work. We do not know we're not pretending to know everything. There are so many areas and this is one of them where we're learning things and feeding that back into the decision-making process. So we have our ups and downs. We have our political changes, if you will. That's going to have an effect on things. Have our political changes, if you will. That's going to have an effect on things. But overall, we're feeding information back into the process to make better decisions on a technical basis and make better decisions on a policy basis.

Speaker 2:

Thank you, guys, but we normally end with any last drops in the ocean for our listeners and that's a chance to just mention any other things around the offshore energy topic that might be going on in your world as our guests. Jessica, would you like to go first? Any last drops for this week?

Speaker 3:

Sure. So, going off of what Jim said about policy matters in the federal government, we're seeing a lot of change in policy and funding toward the things that we care about. So I'm going to say let's watch the states. Watch what the states are doing funding research and development, having plans for offtake and then even having potential offshore wind development in the state waters. So I say, watch the states wind development in the state waters.

Speaker 4:

So I say, watch the states. The first, following on Jessica's comment about the states, is California, for one just passed Assembly Bill 472. That includes the development of ports to service offshore wind in their definition of infrastructure and to essentially incorporate offshore wind development into infrastructure planning. The second drop is kind of a shout out to this National Academies panel which released a report on potential effects of offshore wind on the ecology of the Nantucket Shoals. I was lucky enough to be a part of that academy panel and that report is out and in the public domain for those who want to look it up.

Speaker 2:

Hey, great, we'll include a link in the show notes.

Speaker 1:

Well, I've already repeated what would constitute my last drops the points about look to the states, the points about the definition of infrastructure. These are great points and I'm going to turn it right back to you, ian, as far as a last drop is concerned.

Speaker 2:

Ian, as far as a last drop is concerned, I've got two last drops. One is a recent report you may have seen. Texas's main grid operator, ercot, forecasts that the state's growing demand for power could surpass its existing available energy supply beginning in not 10 years, not five years, but next year during the summer. So that's awfully interesting to look at. Here comes fast renewables to the rescue, I have a feeling. And second, I just wanted to say if at any point during this podcast I mentioned the Gulf of Mexico, of course I meant the Gulf of America.

Speaker 3:

You're on the record there.

Speaker 1:

Ian, I think we need to ask our listeners to give us some feedback. Tell us if we're in the right place here, tell us what you're thinking about the podcast and what we might want to be doing better, and, if you have topics, send them to us. And, like today, the opportunity to have such great special guests like we just had in Jessica and Klaas it would be terrific. I hope you've enjoyed participating and I really do appreciate you joining us. Yeah, thank you guys.

Speaker 3:

Yeah, thanks for the opportunity.

Speaker 4:

Yeah, thanks for the invite.

Speaker 2:

And until we meet again on the next Offshore Energy Podcast.