Outlining proposals for mounting 1.5 MW turbine units either on traditional lattice pylons or, as illustrated, specially developed tubular towers, KEMA points out that the conversion of just 3% of the Netherlands 26,000 pylons would be sufficient to achieve the Dutch government's target of 1500 MW installed capacity by 2010.
"The size of current wind turbines and the intervening distances in a wind farm accords with the pylon distance in a high tension network," says De Vries. The current generation of 1.5 MW wind turbines with a hub height around 80 metres and a rotor diameter of 70 metres can easily accommodate cables, he says. "The vane tip turns around 45 metres above ground level, and a 150 kV pylon is 35 metres high, making it possible to combine both functions."
With grid connection accounting for some 13% of total investment in a wind farm and with over-ground connections 20 times cheaper than underground, project cost savings will also be significant, says KEMA. Nor is it necessary to wait for the replacement of existing high-tension networks. The study concludes that the premature conversion of the existing network would also cut the price of wind energy.
Grid reliability would not be compromised by the combi-pylons, says De Vries. "Extensive risk analyses show that the reliability of the power connection is not considerably harmed and the chances of a broken blade leading to a broken connection are much smaller than other chances of connection failure."
De Vries reports considerable interest from the Dutch power companies and the government.