Renewable energy has been called impractical for its small scale and large expense compared to conventional power production methods. Now, one area of development is answering those criticisms by getting very big to cut costs. New offshore wind facilities now going online are equal in size to the largest gas- or coal-fired power stations. The world’s largest wind facility, the London Array, located off England’s east coast, produces 630 megawatts of capacity, equal to traditional fossil-fuel power generators. And a project 10 times that size to be located nearby is in the planning stages. Siemens, the German power systems company, estimates that there are now 3.3 gigawatts of offshore wind power connected to the European power grid. That capacity is equal to the output of a large nuclear power station. And the global market for offshore wind power is expected to grow 20 percent a year for the next few years. The economies of scale in building very large wind power plants offshore i