The E-66 was based on a unique 'gearless design developed by Enercon for a 500 kW machine, already used successfully in over 1,400 installations. Attaching a ring generator directly to the rotor hub offers several advantages.

"There are fewer moving parts, and they move slowly, so maintenance costs are greatly reduced," says Martina Kuhlmann, Enercon's assisstant manager. "But the real difference is in the conversion efficiency. Intermediate gearing wastes energy in friction and, more importantly, allows the blades to move at one, or sometimes two, fixed speeds. Without a gearbox there is no such restriction."

Electronic controls adjust the speed of the E-66's rotor continuously by making slight changes to the pitch of its blades, in order to maximise power yield even in low winds.

Constructed from epoxy, the blades were designed in co-operation with Enercon's Dutch partner, Aerpac. The 68 m prototype was erected in December 1995 at Enercon's premises in Aurich.

A year after the end of the 12 month pilot test, the E-66 went into series production. Since then, 90 machines have been installed.

Each produces3-4 million kWh a year - saving large quantities of fossil fuels, and around 5 million kg of CO2 emissions.