Are wind farms shading each other?

Wind farms can take power from each other. (Photo: MR1805 / istock)

Wind turbines brake the wind behind the rotors and can take the power to the following turbines – because of this well-known effect, individual wind turbines are set up at certain minimum distances from one another. But how far does this shadow effect affect wind farms? According to a study, wind farms that are miles apart can influence each other. The yield from parks in the slipstream of other systems can be significantly reduced as a result.

Wind power is an important pillar of the energy transition. But although the wind blows almost constantly in areas suitable for wind farms, such systems quickly reach their performance limits. The reason: Wind turbines generate electricity from the kinetic energy of the wind – they have to slow it down. This means that each turbine slows down the wind speed and thus reduces the driving force for the following wind turbines. But how far does this so-called wake or lag effect go?

Julie Lundquist from the University of Colorado in Boulder and her colleagues have shown that it is not just tightly packed turbines within a wind farm that can drive each other. The braking effect actually seems to be carried over from wind farm to wind farm. For their study, the researchers examined how the electricity yield of a large wind farm in West Texas changed after another system was installed in the immediate vicinity. With the construction of the second wind farm, the first system was now in the slipstream of this new system. Would this affect their productivity?

Large trailing zone

In fact, it turned out that in the observation period from 2009 to 2015, the electricity production of the old wind farm fell noticeably – by an average of five percent. These losses meant annual financial losses of around two million US dollars, Lundquist and her team report. Both the comparison with a nearby wind farm, but not in the slipstream of the new facility, and model simulations confirmed that the observed effect was actually due to the braking effect of the other wind farm.

According to the simulations, the strength and range of the wake effect also depend on the prevailing conditions in the atmosphere. Under certain atmospheric conditions, the effects can therefore extend up to 50 kilometers, in the case of offshore plants even further. “Almost 90 percent of all wind farms in the USA are within 40 kilometers of another wind farm. And that means that all of these systems could be affected by wake effects, ”write the scientists. With a view to Germany, Stefan Emeis from the Karlsruhe Institute of Technology comments: “The effect is also important for the expansion of offshore wind farms in Germany. Despite the logistical boundary conditions in the North Sea, one should try to increase the distances between the individual wind farms in order to keep mutual shadowing as low as possible ”.

Source: Julie Lundquist (University of Colorado, Boulder) et al., Nature Energy, doi: 10.1038 / s41560-018-0281-2

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