NOISE TUNING FOR URBAN SITE

Technical improvements have made wind turbine operation ever quieter in recent years. But still, some good wind locations have been barred from development because noise emissions at the nearest occupied buildings would exceed legal limits. Now, thanks to a new electronic sound regulation system, a 500 kW Enercon E40 machine was installed in early March on a disused coal tip in the middle of the town of Hamm in North Rhine Westfalia.

The sound regulation system is the first of its kind in the world according to the Ökozentrum in Hamm on whose property the E40 is sited. It was developed by the Department for Electronic Innovation at Magdeburg University, led by Professor Klaus-Dieter Buschkamp. The principle on which the system operates is simple. If sound from the turbine measured at the nearest house, 150 metres, away exceeds the level of background noise monitored at a site 1000 metres from the turbine, the electronic system automatically cuts in, curtailing machine output by adjusting the rotor's angle to the wind, thus reducing noise. "Annual power generation will only be reduced by around 0.06% and for this small sacrifice the turbine was licensed and could be installed," says project planner Winfried Arand of engineering office J Hartmann in Unna.

Installation of the wind turbine on the unstable coal tip also posed a challenge. The foundations required 16 instead of the originally planned eight 16 metre concrete piles, while trucks transporting the tower sections had to be towed up the slag heap with caterpillars in order to spread the load. The plateau of the coal tip measures only 38 metres across so that room for manoeuvre was extremely limited. A 250 tonne crane was used to bolt together a 400 tonne crane on the plateau which then heaved the nacelle on to the tower. The smaller crane subsequently arrived on the scene for a second time to dismantle the larger one. Since there are around 60 other coal tips suitable for wind turbines in North Rhine Westfalia, the experienced gained so far should stand all involved in good stead for future projects.

Not only the installation but also the ownership structure of the DEM 1.4 million Hamm turbine is unusual. A wing of the Evangelical Church, Kiwi, owns 52% of the project; a 33% stake is owned by 69 private investors while the remaining 12% belongs to the town of Hamm. While Kiwi's aim is "to maintain and care for the world created by God," Hamm sees the project as a vital contribution to its identity as "an ecological town of the future."