LONDON • Britain is set to build the biggest wind farm in the world, one that will power more than a million homes, just as worldwide investments in renewable energy hit an all-time high.

Spanning more than half the size of Singapore at 407 sq km, the 1.2-gigawatt Hornsea Project One will be built 120km off the coast of Yorkshire in northern England.

When it is completed by 2020, it will have 174 wind turbines each 190m tall - about the height of Marina Bay Sands in Singapore.

Danish developer Dong Energy said on Wednesday that it has decided to construct the farm, although it declined to say how much it is investing. But it had said earlier that it will pump £6 billion (S$12.3 billion) into the Humber region by 2019.

RenewableUK, which represents Britain's wind power industry, said the farm will bring multiple benefits to the country, such as creating 2,000 jobs and generating inward investment.

"This offshore wind farm will play an important part in meeting our Paris climate commitments, but will also help create the new energy infrastructure this country desperately needs," said its deputy chief executive Maf Smith.

Britain was among 195 countries to sign the historic agreement in Paris last year to cut greenhouse gas emissions and limit the rise in global temperatures to less than 2 deg C.

Dong Energy was given a subsidy contract by former energy secretary Ed Davey in 2014 for which it will be paid four times the current market price of power for every unit of electricity it generates for 15 years, reported The Telegraph newspaper.

But according to the National Audit Office, the British government spending watchdog, the project will add £4.2 billion to energy bills, as homes and businesses will have to fund this through green levies on their bills.

Britain has been the world leader in offshore wind energy since 2008, with a current capacity as much as that of the rest of the world combined.

According to RenewableUK, the total offshore generating capacity in British waters provides almost 15 terawatt-hours of electricity per year, equivalent to the electricity consumption of more than 3.5 million homes.

By 2020, offshore wind farms will supply between 8 and 10 per cent of the country's electricity a year.

Britain's geographic location and strong wind conditions make it a prime candidate for hosting wind farms. The three largest wind schemes in the world are there - one off the Kent coast, one off the coast of North Wales and one off the coast of Suffolk. Their capacities range from 504 megawatts to 630 megawatts.

There are nearly 70 operational wind farms in the world, mostly in Europe. Britain has 28 and a total of 1,465 wind turbines in its waters.

Offshore wind farms cost more to run, as they require more robust and bigger wind turbines than onshore farms.

Last year, Britain's government stopped subsidising onshore wind generation, turning its support instead to siting wind farms out at sea, in part because of land use objections by locals.

As windspeeds at sea are more consistent, offshore wind turbines tend to be more productive compared to their onshore counterparts.

To carry the wind energy from the Hornsea Project One farm to land and into the national power grid will require 900km of cables, about the distance of Singapore to Hat Yai in Thailand.

Dong Energy has rights to Hornsea Project Two and Three, which could potentially produce another 3 gigawatts of power.