The world’s largest wind facility, called the London Array, which uses Siemens equipment and cost almost $3 billion, was recently inaugurated off Britain’s east coast. With 630 megawatts of capacity, it is comparable to or bigger than conventional generators.

Far larger projects, like one called East Anglia, which might be more than 10 times the size of the London Array, are under discussion for off the British coast.

Siemens figures there are about 3.3 gigawatts of offshore wind power connected to the grid in Europe. That is similar in size to a large contemporary nuclear power station. The company also expects the global market to grow 20 percent a year for the next few years, but that will depend on many factors, including costs and government support.

Offshore wind has advantages beyond the presence of sea breezes. The seabed is relatively cheap real estate, and much larger wind farms can be built there than on land. The vast expanses available at sea allow economies of scale that may bring down costs.

In addition, sea-based wind farms are less likely to set off aesthetic or environmental objections than land-based ones. Although there is worry that their fast-turning rotors may put seabirds at risk, particularly on foggy days, and grumbling that the big white pinwheels spoil views, they are being placed farther and farther out to sea to partly quell the complaints.

Siemens acquired a foothold in the industry by buying the Danish company Bonus Energy in 2004. Since then, it has been scaling up the turbines and trying to streamline their installation. The company is a global leader in the offshore business, with 1,200 turbines fully installed and another 1,200 on order, costing several million euros each. Major competitors include General Electric, Vestas and Chinese companies.

On an installation called Riffgat that Siemens is now finishing off Borkum, Germany, one of a chain of sandy islands that run along the German and Dutch coastlines, it managed to cut turbine installation times to 14 hours — no small feat for units that have rotor diameters of 120 meters and weigh 250 tons.