For many years the capital of the United Kingdom’s offshore oil and gas industry, Aberdeen, Scotland, is in the midst of an energy transition that is transforming the North Sea from a fossil-fuel basin into the world’s center of offshore wind power.

With oil prices down to around $50 a barrel, as many as 50 North Sea oil and gas fields could be shut down this year, according to industry consultant Wood Mackenzie. Even if crude rebounds to $85 a barrel, oil companies are likely to abandon 140 North Sea fields over the next five years, the company says.

That contrasts sharply with the building boom in offshore wind turbines. Europe added a record three gigawatts of new offshore wind capacity in 2015, most of that in the North Sea. About 3,000 offshore turbines, totaling about 10 gigawatts of installed capacity, are operating there already. Annual additions are expected to average four gigawatts through 2030, bringing wind power to more than 60 gigawatts of capacity. In terms of output, offshore wind power accounts for about 1.5 percent of Europe’s total electricity generation today. That figure will rise to 7 percent by 2030, according to WindEurope, a Brussels-based industry association.

Offshore turbines are beloved by many politicians, but whether they can provide clean, economical energy is doubtful.

The scale of these projects continues to grow. The Gemini project, off the coast of the Netherlands, will have 150 turbines totaling 600 megawatts of capacity when it’s completed next year. Grander schemes are in the works: late last year, Britain’s secretary of energy and climate change greenlighted the vast Dogger Bank project, which will cover 360 square miles off the northeast coast of Scotland. Dogger Bank will comprise 400 wind turbines with a capacity of 1.2 gigawatts, enough to power two million homes.

Offshore wind is booming despite the fact that electricity demand in Europe is flat and even declining in some countries. In Germany and the U.K., renewable energy is expanding more rapidly than aging fossil-fuel plants are being shut down (see “Germany Runs Up Against the Limits of Renewables”). The resulting overcapacity has slashed the wholesale price of electricity, from about 60 euros ($68) per megawatt-hour three years ago to around 30 euros ($34) today. The cost of energy from offshore wind turbines is more than 100 euros ($114) a megawatt-hour. Power from onshore wind farms costs much less—60 ($68) to 70 euros per megawatt-hour—but new onshore installations have been blocked, largely because of objections from local communities.

“There is no logical business case [for offshore wind] without the politics,” says David Reiner, assistant director of the Energy Policy Research Group at the University of Cambridge, “and that’s the only rationale as to why we’re willing to pay so much more for offshore rather than onshore.”

That means these mammoth wind farms are essentially being financed by governments. Northland Power, a Toronto-based company that is the lead developer on the 2.8-billion-euro ($3.2 billion) Gemini project, signed a 15-year agreement to supply power to the Dutch grid at 162 euros ($184) per megawatt-hour, far above the price it could get selling electricity on the wholesale market. The wind farm “absolutely would not have been built” without government price support, says Boris Balan, Northland’s director of business development for Europe.

Such largesse, naturally, has attracted opposition. Local governments along the coast of the Netherlands are resisting offshore wind farms within sight of their towns, and late last year a coalition of opposition parties in the Dutch parliament blocked a bill that would have provided additional support for new offshore wind turbines. Michael Pollitt, an economics professor at the University of Cambridge, calls governments’ enthusiasm for offshore wind “clearly unwise.”

Still, the boom shows no sign of slowing. Offshore wind investments in Britain will total more than 20 billion pounds ($30 billion) from 2010 to 2020, said Hugh McNeal, the CEO of RenewableUK, at an offshore-wind conference in Manchester on June 21. In Aberdeen, a rough-hewn port city of 200,000 that has thrived for two generations on the oil wealth from drilling platforms far out to sea, the wind-power revolution promises a new source of economic activity to replace the declining oil industry. That transition was underlined in December, when Britain’s highest court rejected an appeal by a resort developer who tried to halt the construction of a relatively modest, 11-turbine wind farm within sight of his golf course and luxury hotel on the Aberdeen coast. The developer: Republican presidential candidate Donald Trump.