Only seven years ago prime minister boris johnson scoffed at wind turbines. they would not pull the skin off a rice pudding, he sneered. now, he says offshore turbines will make enough electricity to power every home in the uk by 2030. his newfound enthusiasm is justified. costs have fallen steeply. the goal of 40 gigawatts of offshore capacity he trumpeted on tuesday looks achievable.

It is still ambitious. some 30gw of extra capacity would have to be installed this decade. that could require 2,500 turbines, the equivalent of one installation every weekday. that involves 50bn in capital investment, calculates aurora energy research.

That should be forthcoming. while there is no longer any expectation of direct subsidies, a government price guarantee makes investing in wind attractive. the appetite of investors can be gauged by the soaring share prices of industry leader orsted, fellow danish group vestas wind systems and spanish-german siemens gamesa.

There are also grounds for claiming that offshore wind output will exceed domestic electricity consumption. at present, uk households consume about 104,000 gigawatt hours of electricity per year. if there is 40gw of offshore wind capacity, and the turbines operate at 40 per cent of peak capacity on average, they would produce 140,000 gwh per year.using a 40 per cent capacity factor may be an underestimate. the average output of the next generation of turbines some the size of the shard, londons tallest building is 50 per cent of their peak capacity.

For sure, 40gw would not always be enough to meet peak electricity demand. it would work best in conjunction with energy storage devices. but offshore wind is much less variable than onshore wind and solar. it can generate electricity at all times and tends to produce more in windier winter months.

Wind power has not always lived up to hopes. witness the failed ambitions of us oilman t boone pickens who, like mr johnson, believed his country was the saudi arabia of wind. but the conditions are good for the uk, already a world leader in installed capacity. its climate, geography and the cross-party ambition to address climate change should keep the wind at the industrys back.

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