It comes with 101-metre rotor diameter and either a 99- or 135-metre hub height. The rated power is calculated at a favourable 12m/s, making it a medium wind-speed turbine, but Enercon Belgium representative Bernhard Fink claims the rotor-blade design is efficient and, together with a high tower, it is also suitable for low wind-speed conditions.
The rotor blade has Enercon's characteristic winglet tip and unusual airfoil shape that widens from a slender outer section towards the centre spinner. Enercon claims that the aerofoil has achieved an aerodynamic power coefficient close to or even beyond the maximum 59.3%, known as the Betz limit. "Total system efficiency and all measured losses in the generator, power converter, controls, bearings and cables together reflect this value," adds Fink.
Enercon's direct-drive wind turbines use the company's in-house manufactured and electrically excited ring generators. Unlike nearly all its competitors, which use the more compact and lighter neodymium-based permanent-magnet generators, Enercon has not been affected by the recent price explosion of neodymium, a rare earth element.
Air-cooling has been standard Enercon technology until a 3MW water-cooled E-82 model was introduced in 2008. And from the first 1.5MW E-66 all successor airand water-cooled models up to 3MW have been fitted with a generator of around 5.3-metre outer diameter. Innovative E-101 generator-design features include load-optimised cast components for the stator instead of a fabricated welded steel structure. Also, both the stator and rotating part are water cooled.
The E-101 design has also considered logistical challenges. "The market increasingly demands larger more powerful turbines, but our objective was to retain the recognised E-70 and E-82 transport and logistics standards in the E-101. This explains the unchanged generator outer dimension," says Fink. "We further designed the concrete-steel 135-metre tower as a concrete bottom section comprising multiple coning rings with a standard 57-metre tubular-steel section in three individual parts on top."
The solution enables the use of small, inexpensive cranes for assembling the concrete tower and a bigger crane for the steel parts, nacelle and rotor. "Most importantly, our capability to install complete wind turbines within one-week has been retained," he adds.
Set against competing 3MW turbines, the E-101 - with a 250-tonne top-head mass - is not a lightweight concept, but this difference can be attributed to design philosophy. "In case of any doubt about a certain load for instance, we always choose to build in an extra safety margin even if it gives a small weight penalty," says Fink.