Wind Farms Prove Themselves in Practice

A recent news item on the Dutch BNR Nieuwsradio covering the results of German-American research by the Max-Planck Institute on the efficiency of wind generation published in the scientific publication PNAS has caused surprise and concern among the Dutch wind energy industry.

With a new political debate on wind energy in the Netherlands planned for this Thursday, Dolf Elsevier van Griethuysen and Hans Timmers from the Netherlands Wind Energy Association, NWEA, are responding to the recent BNR Nieuwsradio news item with an article in the Dutch newspaper NRC Handelsblad.

While NWEA are not challenging ministry, they would like to point out it is not applicable to Borssele wind farm. In their view the news is a misinterpretation of the results of the research and damaging the image of the Netherlands’ offshore wind sector and wind energy in general.

According to the BNR Nieuwsradio news item the results of the Max-Planck Institute research, headed by Lee Miller and others, showed that wind power generation is calculated to be 80% less productive than previously thought. This is explained to be a result of the wake effect, where the first turbines in line of the wind direction absorb the main share of the wind, leaving the turbines positioned behind to be less productive. As a result the maximum output would be 1.1MW per km².

The news item takes the Borssele offshore wind site as a case study. The Borssele total output, 1,400MW, would be calculated from four sites, total area of 344 km² having a planned 350MW each. This is a possible 4MW per square kilometre over the entire area. When calculating subsidies the Dutch Government uses a figure of 4000 hours per year, 45% of the total possible output, which when factored in translates to an effective power output of 1.6MW per km².

However, according to the two NWEA spokesmen the background of the research and its results should be explained in further detail. The research is based on a theoretical model which looks at the ‘worse case scenario’; the maximum generation per square metre in an area of 100,000km², more than twice the size of the Netherlands where every possible space is used for installing turbines. This is a situation which they compare to be as likely as ever reaching -273°C or Absolute zero, the lower limit on the thermodynamic temperature scale.

First of all they explain that it is hardly likely for wind farms of that size to be planned either on land or offshore. The entire North Sea and European continent would have to be covered densely with turbines to get even close. Secondly the wake effect is already taken into consideration when designing the wind farm layout, leaving enough distance between the turbines to minimise the wake effect. The wake will have a certain level of effect, but much less than the report predicts as further back in a wind farm the wind level is boosted by higher air currents.

Even Miller states already himself in the research that the generation is not affected in smaller areas, providing as an example an area that is 50 times larger than the Dutch province Flevoland which is already densely covered by wind turbines.

A fact which is even more conclusive, though, is based calculations from existing wind farms in the North Sea which shows that in general the annual power generation is even higher than expected.

“In conclusion, therefore, there is no reason to doubt the current stated expected power output of the existing and planned offshore wind farms,” said in a statement.