Siemens installed two colossal offshore wind turbines this week, demonstrating technology that could have a significant impact on the economics of wind power.

The German company has been developing the turbines, which produce double the maximum power output of its current models, for several years. It has been testing the technology on land, and installed the first ones offshore with the help of a new ship designed specifically for the task. The turbines feature test blades that are 60 meters long, but Siemens intends to employ world-record 75-meter blades eventually.

Yet for offshore wind power to compete with fossil fuels, wind turbines may need to get even bigger. The new turbines generate six megawatts of power in good wind. Several companies are designing 10- and even 15-megawatt machines with 100-meter blades. These blades would reach two-thirds of the way to the roof of the Empire State Building. The push to supersize wind turbines is part of an effort to reduce installation and maintenance costs, which can be far higher than the cost of the turbines themselves. The pictures in this slideshow give a sense of just why installation is so costly.