Wind turbines are already the size of a skyscraper – is there a limit to how big they can get?

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In 2023, about 100 miles off the coast of northeast England, the world’s largest wind turbines will begin generating electricity. This first phase of Dogger Bank offshore wind farm development uses General Electric’s Haliade X turbine, which stands more than a quarter kilometer high from the sea surface to the highest point of the blade tip.

If you place one in London, it will be the third tallest structure in the city, taller than One Canada Square in Canary Wharf and only 50 meters shorter than The Shard. Each of its three blades would be taller than Big Ben’s clock tower. And Dogger Bank will eventually have about 300 of these giants.

Comparison of large wind turbine and famous buildings

Comparison of large wind turbine and famous buildings

It has been just two decades since England’s first viable offshore wind farm was built on the north Wales coast. Each of its turbines could produce 2 megawatts (MW) of electricity under ideal conditions, which was considered huge at the time. In contrast, the Haliade X can generate 13 MW of electricity and is only a year or two away from 15 MW turbines.

So why are turbines growing so fast, and is there a limit to how big they can get? In short, the first answer is to reduce the cost of energy, the second is that there should be a limit – but no one has put a figure yet.

Big turbines, cheap electricity

Just five years ago, the offshore wind industry had hoped to reduce energy pricing from new projects in UK waters to less than £100 per megawatt-hour by 2020. Even at this level, projects could rely on government subsidies to make them economically viable compared to other types of electricity generation.

But in fact, costs have dropped so quickly that offshore wind farm developers soon committed to selling their electricity at much lower prices. Today developers are building wind farms like Dogger Bank, where they are committed to keeping prices under £50 per megawatt hour. This makes offshore wind competitive with other forms of power generation, effectively eliminating the need for subsidies.

The most important factor in reducing these costs was the turbine size. Larger than ever turbines hit the market faster than nearly everyone in the industry expected.

Dogger Bank offshore wind map

Dogger Bank offshore wind map

Blades can’t spin very fast

Theoretically, turbines could continue to grow. After all, a larger blade draws energy from the wind over a larger area as it rotates, which generates more electricity.

But there are some engineering constraints. One of them has to do with erosion caused by the blades colliding with raindrops and sea spray. For current designs, the speed of the blade tips should be limited to 90 meters per second (this runs just under 200mph) to prevent erosion. Therefore, as turbines get larger and their blades longer, their rotors must rotate more slowly.

As a result of having to slow down the rotor, the blades have to deflect the wind more to generate the same amount of power. This results in greatly increased forces over the entire turbine. We can overcome these high forces, but only by increasing the turbine weight and cost. And this means that the point where the turbine becomes unprofitable – the point where the extra cost is no longer worth it for the value of the extra electricity produced – is reached much sooner than if the blade tips are allowed to go faster.

Also, the longer the blades become, the more flexible they become. This makes it difficult to fully control the aerodynamics of the wind flow around them and ensure that the blades do not crash into the turbine tower in extreme wind conditions.

Logistics restrictions

Still, engineering challenges like this could perhaps be resolved in the longer term. This will mean that the size of wind turbines will be more constrained by production, installation and operational issues than by any physical limitations in turbine design.

Even moving the blades and towers from the factory to the construction site and installing the turbine when you get there presents enormous challenges. Big Ben size knives must be shipped as one piece each. This requires huge ports, giant ships and cranes that can operate safely and reliably on the high seas. This is where the limit will most likely come from.

wind farm under construction

wind farm under construction

You can see these limits in practice in the UK, surrounded by windy, shallow seas that are perfect for power generation. Even so, the UK will likely miss its ambitious goal of more than tripling its offshore wind capacity by 2030.

This is not because of the lack of technology or offshore fields. On the contrary, the industry will not be able to produce turbines fast enough and the port infrastructure and number of installation vessels, suitable cranes and skilled workers will not be sufficient.

Therefore, if the UK is to maximize the benefit to its economy from what has been a fantastic success story so far, the focus now needs to shift from simply cutting costs to developing employee skills and the offshore wind supply chain.

I’m sure the turbines will grow, but I suspect it’s at a slower pace than we’ve seen in recent years. And would anyone care if the turbines were deployed 100 miles offshore? After all, the public won’t be there to see them.

Read more: Why is a sunken island the perfect place for the world’s largest wind farm?

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This article has been republished under a Creative Commons license from The Conversation. Read the original article.



Simon Hogg is Ørsted Professor of Renewable Energy at Durham University. Ørsted is a leading developer of offshore wind farms. Professor Hogg is President of the Energi Coast Innovation Group ( Awarded research funding for projects by offshore wind industry partners and the UK government research council.

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