WindVision using largest-ever land turbines

WindVision will install 11 of Enercon GmbH's 6-MW, E-126 model wind turbines. To date, six of the 11 turbines are in place. Although officially rated at 6 MW, the E-126 turbine is more likely to reach 7 MW in productive use.

Each turbine consists of a massive rotor with a diameter of 126 meters, and is mounted on a 198-meter concrete tower. The wind turbines are so large that specialized equipment had to be designed and constructed to enable them to be installed. The world's largest crawler crane, capable of lifting 1,600 tons, was developed specifically to lift the rotor assembly, which weighs more than 350 tons, in one step.

Enercon has incorporated several new features into the E-126 turbines. The optimized blade design includes a spoiler that extends to the rotor hub and the complete assembly is supported on a pre-cast concrete base that is 29 meters in diameter and contains more than 1,400 cubic meters of concrete and more than 120 tons of reinforcing steel.

The supporting tower is made up of a series of 35 prefabricated rings, which are glued together on-site. Because of the enormous size of the towers, which are more than 14 meters in diameter, the first five rings are made in three segments each, which are then glued together to form a complete ring. The next 25 rings consist of two segments each, while the final and top-most five rings are a single piece.

Unlike wind turbines supplied by competing companies, most of which use a gearbox in the nacelle to increase the revolution speed of the generator, the Enercon turbine does not use a gearbox. Instead, Enercon has placed the generator at the largest part of the nacelle, claiming that this is more efficient and provides longer life with fewer moving parts.

The wind turbines are being connected to the grid in Harmignies, about three kilometers away from the windfarm, which is located on a 7.5-square-kilometer plateau that provides good wind conditions with no obstacles. In total, the turbines will require a total of 11 kilometers of underground cabling to make the grid connections.

Enercon justifies the size of the E-126 turbines on the basis of economy of scale. The company states that while building a single large 6-MW turbine is expensive, three 2-MW turbines require three support towers and contain three times as many potential failing parts.

The windfarm was first planned in March 2003, when extensive consultation began with the municipal authorities. Over the following 12 months, individual meetings and group meetings were held with landowners and tenants and an environmental impact assessment study was completed, which identified two possible alternatives — a high number of lower-capacity turbines, or a low number of high-capacity turbines, with the latter option being preferred.

Final adjustments were made to the proposed windfarm, following the environmental impact assessment and permitting process, resulting in the current 11-turbine proposal. It is a testament to the thoroughness of the consultations with local authorities and the population that not a single objection has been filed against the granting of the permits to build the park.