While the planned revision of Germany's renewable energy law aims to make development of sites with low wind unprofitable, German turbine manufacturers are demonstrating that if turbines are built high enough, viable wind speeds can be found at inland sites otherwise ruled out. Nordex has announced its first wind station to use machines on 100 metre steel towers. At the Zilsdorf wind station of three 2.5 MW turbines on 100 metre towers, the average wind speed at hub height is nearly 7 m/s, compared with 6.6 m/s when measured 20 metres lower. The extra 0.04 m/s represents a potential 6% improvement in output. Further, wind turbulence caused by obstacles at ground level is 25% lower at heights between 60 metres and 140 metres compared with at a height of 40 metres or lower. This reduces stress on the machines, points out the company. Enercon enthuses about the advantages of its 114 metre towers. "The height of the hub, not the length of the blades, is the deciding factor for output," at inland sites, says the firm. Five E66 1.5 MW machines now installed on 114 metre towers at Windpark Diepholz are expected to produce 5% more electricity than if 98 metre towers had been used.
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