From our Scandinavian Desk
Translation of
“Mølleparker: Skyggevirkning mærkes fem kilometre borte”, published by Per
Andersen in Eltra magasinet, Nr 4., June/July 2005.
Turbine parks: Shadow effect is felt five kilometres away.
By Per Andersen, Head of Information, Eltra
The wind is reduced
considerably between the first and last turbine in a turbine park. One should
therefore ensure that turbines don’t stand “behind each other” with respect to
the prevailing wind (westerly).
But the distance between turbines
should also be made greater than the 7 to 10 times rotor diameter which has
until now been common. (Between 550 and 750 metres in the parks at Horns Rev and
Nysted).
“The shadow effect is greater than what we have assumed”, said
Engineer Claus Perstrup at ENERGI E2’s Technology day (17th May) when he went
through the results of a “lee project” which Risø, Elsam and ENERGI E2 had
undertaken together at Nysted Offshore Wind Park, near Falster.
40 percent is lost
“With some wind directions,
production falls from 100 to 60 percent from the first to the last turbine in a
row. We have also measured a reduction in wind of 1 m/s about 2 km on the other
side of the park. Five kilometres from the park the lee effect gives a reduction
of 1/2 [i.e.0.5??] m/s. So the design of the park – the ground plan- is
itself of much greater significance than expected”.Claus Perstrup: “Until now we have considered the bringing ashore of output as the most important constraint on the size of offshore wind parks. But the shadow effect appears to be just as big. It is important that the ground plan of the park is designed for optimal production conditions – and not according to appearance. Nysted Park would thus produce more if the ground plan had been turned 90 degrees. And then one should probably make the distance between turbines greater – and make the parks smaller. It could possibly pay to refrain from building some of the turbines planned for a given park”.
1,000 plants of 900 MW
ENERGI E2 is the world’s fourth largest wind player with regard to operational management. Four years ago the company had no wind plants, but today it owns and/or operates about 1,000 plants with a total capacity of almost 900 MW in Denmark, Spain, Sweden and Greece. The company is engaged in large offshore wind projects in England, in the German Bight, in Spain and in Norway. Head of Production, Poul Erik-Borch, leader of the maintenance section: “Offshore wind parks are a challenge. We aim at robust systems and the optimisation of preventative maintenance so that we can decide for ourselves when we will service them. We also employ independent, competent staff who are always available during the best of summer weather when conditions are calm and who think it good to take time off during winter and in periods of bad and windy weather”.
