The world's first floating offshore wind farm started producing electricity off the Scottish coast on Wednesday.

Hywind Scotland, as the project is known, consists of five huge linked wind turbines which float over deep ocean water while loosely tethered to the sea floor.

They were constructed on land in Norway, and dragged across the North Sea earlier this summer before being moored off the Aberdeenshire coast.

The wind farm is expected to generate enough power for 20,000 households at full capacity according to Statoil, the Norwegian state energy company behind the project.

Take a look at the slides below to see how the turbines work, and how an idea once dismissed as "crazy" has come to life.

Here are the experimental turbines that form the floating wind farm.

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They are designed to sit on the surface, with about 180 metres above water and up to 80 metres submerged.

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The turbines can drift in all three dimensions on the water's surface, and are held in place by anchors on the sea bed. Long cables carry the electricity back to shore.

The wind farm is in the North Sea, around 30km off Scotland's east coast.

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Here's a turbine being towed across the North Sea by a tug boat.

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The floating technology allows the turbines to go in deeper waters.

They are huge — each turbine is 258 metres high — more than twice the height of Big Ben. Each blade is 75 metres long.

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They weigh 11,500 tonnes (11.5 million kg) each.

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Here they are being assembled at Stord, southwestern Norway.

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Building the turbines took six months and cost an estimated 50 to 70 million NOK (£4.8-6.7 million, or $6.3-8.9 million).

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The project received a "generous subsidy" from the Scottish government, the Guardian reported in June.

Leif Delp, Hywind's project director, told the BBC in July that more wind farms like Hywind needed to be built in order for such projects to be cheaper in the future.

"I think eventually we will see floating wind farms compete without subsidy — but to do that we need to get building at scale," he said.

Each turbine is designed to produce six megawatts of energy. Combined, the wind farm is expected to power 20,000 homes across the UK.

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The amount of electricity generated is currently not profitable, and the project still requires subsidies, but authorities expect it to get cheaper over time.

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Statoil hopes to reduce the cost of Hywind's electricity from €40 to €60 (£36 to £54/$47 to $70) per megawatt hour by 2030, the company said on Wednesday.

People thought Statoil's idea for a floating wind farm was "crazy" at first — but now it's happening.

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"Some people thought we were crazy when we put a giant wind turbine on top of a floating spar structure and towed it out to sea," Statoil wrote in a press release. "But it turned out to be the future, and the future is now."

Halvor Hoen Hersleth, Hywind Scotland's operations manager, said: "The next step is, of course, to go bigger and into new areas."