Wind power, already the world's fastest-growing source of electricity, is picking up still more momentum. The wind industry in Europe -- the epicenter of wind power adoption -- expects that one-quarter of the continent's new electricity-generating capacity in the next decade will come from wind. To both spur and serve this demand, manufacturers are developing colossal new offshore wind turbines with blade spans that exceed the length of a football field -- including the end zones.

Today's largest commercial wind turbine has a blade span of 104 meters and produces up to 3.6 megawatts of electricity -- enough to power 1,000 average U.S. households. But in February, Repower Systems of Germany switched on a demonstration turbine near Hamburg that produces five megawatts and has a blade span of 126 meters. And General Electric is developing a design for a 70-meter blade, which translates to a total blade span topping 140 meters. GE doesn't yet have a timeline for building such a massive machine but believes a turbine of that size could produce as much as seven megawatts, says Jim Lyons, chief tech­nologist at GE Wind.