The massive farms harnessing an invisible force
Share on Linkedin
(Credit: Alamy)
Huge offshore wind turbines require feats of engineering to construct. But the resulting power is both clean and cheap – and the UK is investing so much, it is now the world leader.

There is nothing out here to highlight the scale of these machines. A blue-grey sky hangs behind the enormous structures; the boat we are on, 4 miles (7km) offshore from Liverpool, bobs excitedly up and down on the swell of the sea. We’ve come to the Burbo Bank Extension wind farm to see an engineering marvel: the largest wind turbines in the world.

When one of the turbine’s blades swings to its highest point, it reaches 195m (640ft) – making these structures nearly twice as tall as Big Ben. The diameter of the turbines’ three colossal blades is greater than that of the London Eye. As the huge wings sail by, cutting the air, they make a gentle swooshing sound.

The very first offshore wind farm was a Danish project. But Britain now leads the world. The largest offshore wind farm on Earth is the UK’s London Array, a massive site of 175 turbines in the outer Thames estuary. Up to 5.2GW of electricity are provided by the country’s offshore turbines – almost as much as the rest of Europe’s sea-based wind farms put together, with more than two-thirds of continental Europe's capacity. Beyond Europe, the rest of the world’s offshore wind totals just a few gigawatts.

Industry insiders say the significance of tapping the power provided by coastal winds ever more cheaply should not be underestimated. In December 2016, the World Economic Forum reported that as the cost of producing wind turbines has fallen by more than 30% in the last three years, the cost of electricity from wind power has fallen to $50 per megawatt hour on average worldwide, without subsidies. That’s half the cost of coal.

The cost of electricity from wind power has fallen to $50 per megawatt hour on average worldwide, without subsidies – half the cost of coal

Even offshore wind, specifically – which requires especially difficult engineering and rugged structures – still is cheaper than nuclear power per megawatt hour.

As a result, Germany, Denmark, the Netherlands and others are investing in wind and countries like China and South Korea are beginning to take an interest, too.

Burbo Bank is a demonstration of just how quickly offshore wind has evolved. The original wind farm, built just 10 years ago, comprised 25 3.6MW turbines – enough capacity to power about 80,000 homes. The Burbo Bank Extension boasts 32 8MW turbines, providing nearly three times the old farm’s capacity.

An offshore substation at Burbo Bank (Credit: Chris Baraniuk)

An offshore substation at Burbo Bank (Credit: Chris Baraniuk)

“It’s a big difference,” says Benj Sykes, vice president and head of asset management at the Danish firm Dong Energy, which installed the Burbo Bank Extension. “And I think that’s testament to the progress in technology over the last 10 years.”

A single rotation of one of those giant blades, he says, could power an average British home for 29 hours. Spinning at their fastest, the blades rotate nearly 30 times per minute. But there are limits to how much force these giant rotors can harness. If spun too fast, the motion could damage the turbine, so the blades are designed to lock in place when a gale picks up.

But turbines need to be maintained once they are constructed. As they are far from shore, that can be difficult. In Liverpool, teams of shift technicians tend to the lonely structures of Burbo Bank. “It’s the exact same thing you do to your car,” says supervisor Justin Monaghan. “When it breaks down, you go in and find out what is wrong.”

Depending on the problem, Monaghan and his team might fix or replace electrical gear, hydraulics or moving parts. Each structure has its own barrel of food and water inside just in case the weather changes suddenly and a technician has to wait it out.

Because offshore wind turbines sit so far from land, maintenance can be difficult (Credit: Chris Baraniuk)

Because offshore wind turbines sit so far from land, maintenance can be difficult (Credit: Chris Baraniuk)

Right now, that’s an extremely rare occurrence thanks to detailed forecasts and careful monitoring of the weather while workers are out on the turbines. But living on site at an offshore wind farm may soon be part of the job. The next landmark project for the offshore wind industry is Hornsea, off the north-west coast of England. The site itself will be far from shore: 120km away. Instead of being ferried back and forth, up to 150 technicians will live in offshore accommodation, not unlike those who work on oil platforms.

When completed in 2021, phase one of Hornsea’s construction alone will make it the largest offshore wind farm in the world with a capacity of up to 1.2GW. Depending on planning for the final stages, the entire farm could have 4-6GW of capacity when completed in the mid-2020s – enough to power more than four million homes, or roughly 15% of all the homes in the UK.

Far out

Even more remote projects are already being brainstormed by developers. There is a proposal to build an artificial island in the middle of the North Sea with hundreds of turbines encircling it.

How do you install an offshore turbine?

You can’t build on water. But you can drive long piles down into the seabed to provide a foundation.

The depths at which this is done vary greatly – the deepest in Europe being around 40m. There are plans to develop floating offshore wind farms at even greater depths, though, with one such project recently given planning permission in Aberdeen.

Once a foundational pile is in place, however, a ‘transitional piece’ that brings the structure above sea level is added.

Finally, the turbine itself, and each of the three blades, is winched into place.

Power lines to the Netherlands, Germany, Denmark, Norway, Belgium and Great Britain could divide the electricity between them. Capacity estimates vary, but some range from 70-100GW – more than all of the nuclear power stations in France put together.

A wind farm like that would take decades to plan and construct, however, and for now it remains a relatively distant prospect.

Instead, most expect the UK to continue its investment in offshore wind simply by building up wind farms on a similar scale to those already in existence. “There is huge potential,” says Joel Meggelaars of trade body Wind Europe. “The UK and the North Sea is a very windy region.” Meggelaars explains that the load factor of British turbines – the amount of energy actually produced – is unusually high. In December last year, offshore turbines in the UK clocked an average load of 68.2% of total capacity. For many offshore farms elsewhere, the figure is often less than 50%.

The bigger turbines get, the better the power output. While 8MW may be the current maximum, Meggelaars expects this to roughly double in 10 years.

The bigger turbines get, the better the power output (Credit: Chris Baraniuk)

The bigger turbines get, the better the power output (Credit: Chris Baraniuk)

Turbines can stand in remote spots for as much as 25 years with ongoing maintenance. Unlike solar energy, of course, they also provide power during the night – so long as it’s windy.

There are downsides to offshore wind, however. As well as being costly to install and maintain, the turbines may have a detrimental impact on wildlife. Critics say that they are particularly disruptive to colonies of birds like gannets and kittiwakes, and a proposed extension to London Array was blocked in court due to the threat posed to seabirds.

Others say the vibrations of the turbines could disorient whales. However, beyond the noise of installing the piles that the turbines are placed on – which is very loud – it is not known how harmful sound generated by the normal operation of the machines may be.

One poll found that 73% of the public supported offshore wind farms

But many in Britain already have their sights set on a future increasingly powered by offshore wind. There’s more public enthusiasm than land-based farms, too. Despite some complaints that they tarnish sea views, there is evidence that a majority of people are in favour of them. One poll in 2016 found that 73% of the public supported offshore wind farms.

Despite their benefits, offshore wind turbines have downsides, including being disruptive to birds (Credit: Chris Baraniuk)

Despite their benefits, offshore wind turbines have downsides, including being disruptive to birds (Credit: Chris Baraniuk)

“They’re a bit less obtrusive when they’re offshore, they’re a bit further away,” points out Monaghan. “They’re not in the back of your garden whizzing away.”

For now, Britain’s turbines seem to satisfy many of the requirements we have of renewable energy. They’re clean, they don’t get in the way of ordinary people, and they give a boost to local industry. The long-term advantages and disadvantages may soon become clearer. But for now, the new blades at Burbo Bank spin on, the power they generate flowing into the grid.

This story is a part of BBC Britain – a series focused on exploring this extraordinary island, one story at a time. Readers outside of the UK can see every BBC Britain story by heading to the Britain homepage; you also can see our latest stories by following us on Facebook and Twitter.

Join 600,000+ Future fans by liking us on Facebook, or follow us on Twitter, Google+, LinkedIn and Instagram.

If you liked this story, sign up for the weekly bbc.com features newsletter, called “If You Only Read 6 Things This Week”. A handpicked selection of stories from BBC Future, Earth, Culture, Capital, Travel and Autos, delivered to your inbox every Friday.

Around the BBC