Birds and Turbines: Designing Offshore Wind-farms to Prevent Bird-strikes

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Home / Birds and Turbines: Designing Offshore Wind-farms to Prevent Bird-strikes
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A new study suggests that offshore windfarms can be designed to minimise the risk for bird-strike. Image by greenfinger

Wind power represents a growing part of the renewable energy industry, and it has its supporters and critics.

Experts have expressed concerns about the threat that offshore wind farms may present to marine wildlife, particularly birds.

Now a new study has taken a fresh look at this potential problem.

Wind Energy Growing in Europe

For the United Kingdom and other nations in Northern Europe, wind power is a key part of their renewable energy strategy.  The shallow basin of the North Sea offers the opportunity to build large arrays offshore.

When the London Array started generating electricity in 2013, it was the largest offshore wind farm in the world, covering 40 square miles. This array is scheduled to double in size in the near future.

Previous research has implied that any bird entering the array at a height swept by the spinning turbine blades carries an equal chance of being hit. Estimates resulting from such figures have been widely used by the wind energy industry when carrying out impact assessments for new wind farms.

New Study Reviews Risk to Birds

This new study by Dr. Alison Johnston, and a team from the British Trust for Ornithology (BTO), has used new statistical methods to analyse previously collected data on the flight heights of marine birds. They have concluded that not all birds will be at the same risk of collision.

Dr. Johnston told DecodedScience: “This new approach to analysing the data enables us to model the average flight heights of birds in far greater detail than was previously possible.

Even for birds which often fly at the turbine heights (for example Eider duck and Greater and Lesser Black-backed gulls), most will fly at the lower part of the rotor blade area, where the circular nature of the blade area will give them a greater chance to miss the sweep of the turbine blades. Other species such as Puffins, usually fly below the height of the turbine blades, putting individual birds at low risk of collision.

Turbine Design Affects Risk of Bird-Strike

Using the distributions of flight heights, the study examined the impact of two aspects of turbine design on the collision risks for 25 species of seabirds.

Firstly, they found turbines designed with hubs higher above the sea surface reduced the collision risk for all species, as more birds would naturally fly underneath the turbine blades.

Secondly, the risk of bird strike depended on the size of the turbines used. Larger diameter turbines can be spaced further apart, while still producing the same energy output as a larger number of smaller turbines in the same area. The larger gaps between the individual turbines would allow more birds to pass through the wind farm unharmed.

JohnstonTurbineSpacing

Using larger turbines can allow wider gaps for birds to pass through. (a) = 80m rotors, (b) = 90m, (c) = 126m. The numbers in the top-right corner of each diagram represents the number of turbines of each size required to generate 30MW. Image courtesy of Johnston et al. (2014)

According to Dr Johnston, “With these new models, it is now possible to examine the impact of different turbine designs on the estimated number of bird collisions. For example, turbine arrays could be designed with fewer and larger diameter turbines and hubs located higher above the water surface. This would reduce the risk of collision for marine birds, for the same power output.”

Birds and Turbines: Further Study Needed

It’s possible that the model could be applied in other parts of the world, though further work is still needed to verify these results.

Dr Johnston reminded DecodedScience “The data in this study came from boat surveys, which did not take place at night or in rough sea conditions. Further research is required to determine whether birds fly at different heights in dark conditions or stormy weather.”

Nevertheless, this study already suggests that the risk of bird strike could have been overstated in the past, and could be further reduced by using fewer, larger, and taller turbines.

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