The London Array

The London Array, 12 miles (20 km) off the coast of Kent, is currently the world's largest offshore wind farm. It features 175 turbines spread over an area of about 100 square kilometers. It is capable of producing 630 Megawatts of electricity, enough to power half a million homes. Generating that much electricity with coal would produce about 925,000 tons of carbon dioxide. Phase II will raise the capacity to 1,000 MW. This part of the North Sea is called the Long Sands, and the water is only about 80 feet (25 meters) deep.

Offshore wind farms offer certain advantages, such as, since people can't see them from their houses they are less likely to protest. The wind is also steadier. But the costs are very high, mainly for construction: right now these cost about three times what a comparable coal or natural gas facility would cost. Costs are starting to fall as the industry develops specialized ships and so on, but so far offshore wind still depends on large government subsidies.