This summer five wind turbines are being towed out into the North Sea, where they will be the first ever floating offshore wind farm. The turbines, built in Norway this year, have been dragged across the ocean to Scotland, where they will start working just off the coast. The project — known as Hywind Scotland — cost a total of NOK 2 billion (£193 million, or $253 million). It is expected to generate enough power for 20,000 households when it starts producing energy later this year, 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 why an idea once dismissed as "crazy" is coming to life. Slides View As: One Page

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

They are designed to sit on the surface, with about 180 metres above water and 80 metres submerged. The turbines can drift in all three dimensions on the water's surface, and will be held in place by anchors on the sea bed. Long cables will carry electricity back to shore.

The wind farm will be in the North Sea, around 30km off the Scottish coast.

Here is a turbine being towed through the North Sea by a tug boat. 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.

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

Here they are being assembled at Stord, southwestern Norway.

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

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