Why Are Floating Wind Turbines So Huge?

With the recent news of China producing one of the largest wind turbines yet, with a rotor diameter of 260 meters (853 feet) and a rating of 18MW, it got me wondering why they’re so big. They’re almost defying imagination at this point. Bigger is always better in the world of wind. The reason is simple: we can harness more wind with bigger rotors to produce more energy.¹

But onshore turbines have their limits. To meet these challenges, engineers have been moving offshore. However, we only have so much coast to work with, and the most powerful winds are in the open ocean, where the water is much deeper. What if we could push the boundaries further?

The wind industry is currently doing just that, which is why floating wind turbines are suddenly so huge. By sending these skyscraper-sized floating structures out to sea, we can take advantage of faster, more consistent wind. That still leaves some big questions, so let’s address the elephant (or maybe the turbine) in the room. Why are floating wind turbines gigantic in the first place? And can the scale of floating wind be practical for meeting the planet’s energy needs?

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Is floating wind…overblown?

Despite how fantastical the concept of floating wind might seem, offshore wind turbines are going through quite the growth spurt. Earlier this year, the Danish company Vestas swept away the competition with its prototype offshore turbine V236-15.0MW. A name that rolls right off the tongue. It’s now the tallest turbine in the world. For comparison, here’s the 300-meter (or 984-foot) Eiffel Tower…and here’s a V236 turbine at 280 meters (or 919 feet).²

These burgeoning advances come as the world grows big on big turbines, and rationale for them all comes down to math. Before we describe how these behemoths can be buoyant, though, we have to establish just how large these things are.

To help wrap your head around their size, we’ll begin with the closest reference we have: ourselves. The average human height across the globe is roughly 5’5”, or about 1.7 meters.³ A one-story building is about 4.3 meters tall. De Noord, a Dutch national monument, is the tallest traditional windmill in the world (and a restaurant). It stands at 33.3 meters.⁴⁵

Zoom out from grinding flour to generating power, and you’ll see how turbines have advanced from landscape to landmark. Since the turn of the century, US-based turbines have increased in hub height (from the ground to the middle of the rotor) by about 66%. Consequently, as of 2021, the average US-based wind turbine is 94 meters (308 feet) tall, or slightly above the height of the Statue of Liberty’s torch.¹ Don Quixote wouldn’t stand a chance.

Here’s where it starts to kick into high gear. Maximizing wind’s potential requires that we blow up the size of turbines even more. And for many countries, hitting clean energy targets also means hitting the beach — but to build turbines, not sandcastles. Scoring big air is easier when you have fewer obstacles in your way.

Enter “offshore wind,” which refers to two types of tech. There’s the “fixed-bottom” turbines that you’d spot in the shallows, like the continental shelf of the North Sea, and the floating towers in waters more than 60 meters (197 feet) deep. Yes, float. More on how that works later.

Recently, the China State Shipbuilding Corporation (CSSC) announced its undertaking one of the most massive turbines yet, the H260-18MW. With a rotor diameter that spans 260 meters (853 feet), its swept area comes out to 53,000 square meters (or slightly over 570,000 square feet).⁶ That’s equivalent to about 10 American football fields.^{7 1}

You’re probably wondering: why go to such extremes? Wouldn’t it be easier to station smaller, easier-to-handle turbines in larger groups than the other way around? The answer lies in wind energy’s non-linear growth rate. You can’t chart the effects of tweaking turbine measurements in a straight line. That’s because slight increments cause big jumps in productivity. Mathematically, the power equation for a wind turbine shows this superlinear growth, as the available mechanical power is equal to half the air density multiplied by the wind velocity cubed and the radius squared:

P = 12v3R2

If that’s Greek to you, like it is to me, don’t worry. The gist of it is that as you broaden the radius of a turbine, you can generate greater factors of power.⁸

Let’s use the CSSC’s record-breaking rotor as an example. Their 2017 wind turbine started at a radius of 85.5 meters. In just 5 years, they’ve been able to improve the efficiencies of all power and mechanical components, as well as increasing the radius to 130 meters, upgrading its capacity from 5 MW to 18MW.⁹

The power equation also explains the necessity of continuously elevating turbines’ height. Generally, as you head higher into the sky, the wind speeds up. The faster the wind that you’re working with, the more power you can generate. This is especially crucial because wind velocity in the mechanical power equation is cubed. If you double the wind speed, you octuple the energy output.¹⁰

Even a tiny shift in wind speed can propel superlinear gains. A turbine spinning in a 6.7 m/s (15 mph) wind can generate twice as much energy as another in a 5.4 m/s (12 mph) wind.¹¹ With numbers like that, setting up floating wind turbine platforms deeper into the ocean, where wind speeds are generally higher, starts to make more sense.¹²¹³¹⁴

At the world’s first commercial floating wind farm, Hywind Scotland, each of its five Siemens SWT-6.0-154 turbines manage to stay stable with a towerhead mass of around 350 tons, atop a spar-buoy with roughly 6,060 tons of ballast, in waters 95 to 120 meters (311 to 393 feet) deep. These babies surf the waves at a hub height of 98 meters (322 feet).^{15 16 17 18}

These proportions sound pretty…well…quixotic. But the results are very real. When you widen a turbine’s swept area, you enable it to capture more wind and generate more power. One gargantuan turbine can do the job of many.⁹

Take the Haliade-X, manufactured by the US-based company General Electric. It can provide enough energy for a UK household…with one rotation. I’m sure its 220-meter rotor and max height of 260 meters might have something to do with that.¹⁹ To put those numbers into perspective, the largest passenger plane, the Airbus A380, flies with a wingspan of 80 meters.²⁰

And offshore wind isn’t just skyrocketing in size — it’s shooting up in popularity as well. According to German technology company Siemens, 2021 saw global offshore wind capacity expand by a record 18 GW. That brings us to about 51 GW of collective capacity in total.²¹

Why offshore? Location, location, location. Wind speeds are higher and more uniform off the shore than on land.²² On top of this, we usually like to settle down relatively close to the coast. According to the United Nations, about 40% of people around the world live within 100 km (60 miles) of the sea.²³

In the US’ case, the majority of the population is concentrated in states that border either the ocean or the Great Lakes.²⁴ As a result, almost 80% of the country’s electricity demand stems from these areas. This makes offshore wind turbines particularly convenient because their proximity allows for shorter transmission lines.²⁵

Another advantage of offshore turbines in the US is that the winds available on land tend to strengthen at night, when consumer demand is low. Offshore wind projects can strategically place seaside turbines where wind speeds peak during the afternoon and evening, right alongside demand.²⁵

Offshore wind also helps avoid “wind shadow,” the type of drag that reduces the speed, and therefore the amount of energy captured, each time you add another turbine.²⁶ Sailors actually have a term for this phenomenon too: “bad” or “dirty” air. Getting caught downwind of another boat reduces your own vessels’ power, slowing you down.²⁷ And just as wakes trail behind boats as they zip through the water, the wakes of turbines ripple through the air. According to the National Renewable Energy Laboratory [NREL], this can disrupt wind farm production, reducing its potential energy by about 10%.²⁸

Developers on the ground do their best to circumvent this effect by spacing out turbines, which means covering more land.²⁷²⁶ But with the vast expanses of the ocean at our disposal, combined with colossal turbines that can do more work in smaller groups, offshore wind can more easily steer clear of this problem.

Overall, seafaring turbines have a significant edge over their landlubbing counterparts, and offshore wind can certainly make for quite the catch. The DOE estimates that just 1% of offshore wind’s potential could power nearly 6.5 million homes.²⁹ And in a 2019 report, the International Energy Agency estimated that the technical potential of turbines deployed in less than 60 meters of water is 36,000 TWh per year. That’s more than enough for all of us, considering that global electricity demand is about 23,000 TWh per year.³⁰

But fixed-bottom turbines can only go so far. Shallow water isn’t distributed evenly across the world, and some locations are already fully booked or inaccessible.³¹ Beachfront property has never had a reputation for being easy to obtain.

About 80% of offshore wind resources circulate in water deeper than 60 meters anyway.³¹ For example, the West Coast of the US doesn’t have much of a continental shelf to work with. In California, once you go offshore, you quickly run into waters over a thousand meters deep.³² The powerful wind we want also lies above deep water off the coastlines of places like the Great Lakes, Japan, and the Mediterranean Sea.³³ Where fixed-bottom isn’t feasible, floating is the way to go. And making use of these areas would be no small feat. The IEA also calculated that floating turbines could produce enough electricity for the entire world 11 times over in 2040.³⁰

How do we get there? With boats. That’s a major benefit of floating turbines: assembly in a port rather than out in the ocean itself. The specialized vehicles needed to install fixed-bottom turbines, like jack-up and dynamic positioning vessels, are both expensive and hard to come by. But with floating turbines, once constructed, workers can tow them where they’re needed rather than struggle with installation onsite.³⁴

Boats also underpin the physics behind how turbines taller than world wonders can defy gravity. The same principles that make the operation of oil tankers possible apply to floating wind. In fact, the oil and gas industry’s nautical experience is exactly what floating turbines rely on. Some iterations of floating turbines stand atop spar buoys just like the ones that have supported offshore drilling for decades.That’s why it’s no surprise that a Norwegian petroleum company, Equinor, founded Hywind Scotland in 2017 using its own spar buoy designs.³³ It wasn’t exactly navigating unfamiliar waters.

Whether the offshore wind industry can stay afloat is another question. Like with most emerging technologies, the cost of floating wind turbines is…steep. The infrastructure needed to mass-produce them doesn’t exist yet, and most projects are only just now getting started. According to a September 2022 White House brief, “Globally, only 0.1 GW of floating offshore wind has been deployed to date, compared with over 50 GW of fixed-bottom offshore wind.”³⁵ Advocates for floating wind argue that industrialization is key to driving down costs.⁸

For right now, though, floating wind turbines need about double the funding of fixed-bottom ones. According to the NREL, expenses related to the turbines themselves are identical; it’s the installation and increased amount of material needed for the foundations that jack up prices.³⁶ The DOE estimates that turbines without sea legs cost about $30 per megawatt hour and fixed-bottom wind turbines cost about $80. Meanwhile, floating wind hovers at around $200 per megawatt hour.³⁷

Plus, the monstrous submarine cables connected to floating turbines aren’t just far from land: they’re far from cheap. As you can imagine, burying an electrical cable into the seafloor requires a boatload of insulation and meticulous engineering. I’ve touched on how astronomically expensive these networks of thick cords can get in a previous video about macro vs. micro power grids.

With all that in mind, you could say it’s much harder for floating wind developers to keep from blowing the budget.

The environmental impacts of floating turbines are another prominent concern. Oceanographers haven’t yet established a concrete base of the repercussions of…all those concrete bases on marine ecology. We do know that offshore wind farms can act as artificial reefs that attract sea life, but whether this causes negative ripple effects is unclear.³⁸

Researchers from the US National Oceanic and Atmospheric Administration note that potential consequences include the introduction of noise pollution, electromagnetic fields that can disrupt the behavior of aquatic animals, and increased vessel traffic, which might mean increased vessel strikes.³⁹ It’s also difficult to determine how dangerous turbines are for birds in general, especially between species.⁴⁰ The mystery won’t last forever, though: there are promising ways to mitigate those effects.

But if one thing’s for certain, it’s that the theoretical possibilities offered by floating wind are nothing to blow off. The Vestas V236-15.0 MW, is currently installed at the Østerild Test Center in Western Jutland, Denmark. After it passes its exams, the plan is for it to graduate to the Frederikshavn Offshore Wind Farm in 2024. A single turbine can produce 80 GWh per year, or enough to power about 20,000 European households.² If just one of these turbines can power tens of thousands of homes, then what could we achieve by moving from handfuls to hundreds?