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Giant industrial wind turbines represent an existential threat to birds, bats, bees and a veritable host of other insect species. For just about anything on the wing, their 50-60m blades represent the end of the line. And the carnage is measured in the thousands of tonnes.

A few weeks back we covered some German research on the issue: Bug’s Life: Bees & Other Flying Critters Being Wiped Out By Wind Turbines

Here’s a couple of further reports on the wind industry’s insect demolition Derby.

DLR studies interactions between flying insects and wind farms

DLR

Interview with Franz Trieb

26 March 2019

For 25 years, Franz Trieb has worked in the Energy Systems Analysis Department of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). The department of the same name at the DLR Institute of Engineering.

Dr Trieb, how does one come up with the idea of investigating the impact of wind farms on flying insects?

Franz Trieb: A comprehensive assessment of German energy scenarios based on a large number of indicators, which we carried out in 2017[1], revealed that the compatibility of wind farms and flying insects during the migration of insects to new breeding grounds was still an open question. Initial research has shown that the remains of flying insects on rotor blades can lead to large reductions in the efficiency of wind turbines and have motivated the establishment of a global cleaning industry for rotor blades. For this reason, we conducted a study on the subject, drawing on interdisciplinary expertise in the fields of entomology, atmospheric physics, wind energy, aerodynamics and DNA barcoding – a method of species identification based on DNA sequencing.

What was the starting point for your study?

Trieb: An extensive body of technical literature currently shows that large swarms of flying insects also seek high, fast air currents. They allow themselves to be carried by the wind to distant breeding grounds. Observations and measurements have been able to detect high insect concentrations worldwide at altitudes between 20 and 220 metres above the ground – the very same altitudes occupied by the rotors of wind turbines. The phenomenon of insect strikes can reduce the power output of wind turbines by up to 50 percent – this has been the subject of extensive research in both theory and practice. So far, however, the consequences of insect collisions with wind turbine rotors on the insect population and the ecosystem have not been investigated.

What approach was used in your study? How did you proceed?

Trieb: First, we conducted extensive research, collecting and evaluating existing scientific data. Based on this data, we created our own model calculation. On the one hand, this model calculation is based on an average insect density of around three creatures per 1000 cubic metres of air at the level of the wind turbine rotors. This figure was based on regular insect catches over Schleswig Holstein by entomologists between 1998 and 2004[2]. On the other hand, for our model calculation, we extrapolated the volumetric flow, that is, the ‘air throughput’ of all the wind farms in Germany. Here, there are around 30,000 wind turbines with a total rotor area of around 160 square kilometres, which with a nominal wind speed of 50 kilometres per hour reach an average of 1000 nominal full load hours during the insect flying season from April to October. By simply multiplying these numbers, we calculated a seasonal air flow rate of about eight million cubic kilometres – that is more than 10 times the total German airspace up to a height of two kilometres. If one multiplies the insect density and airflow rate, then around 24,000 billion airborne insects fly through the rotors in Germany each year.

A simple approximation of the resulting damage can be derived from studies by Sandia National Laboratories on the contamination of rotor blades by flying insects. Four factors are multiplied with each other: the ratio (five percent) between the blade surface visible from the wind’s direction and the circular area swept by the rotor blades; the average proportion of the polluted blade area on both sides of the rotor blades totalling around 80 percent relative to the visible blade area; the so-called collection efficiency for winged insects averaging 40 percent; and a ratio between median relative blade speed (45 metres per second) and nominal wind speed (14 metres per second) of about 3.2. According to the figures, on average, about five percent of the creatures flying through a running rotor get hit. This amounts to approximately 1200 billion insects per year. These figures only consider creatures that leave visible residues on the rotor blades.

What conclusions can be drawn from your model calculation?

Trieb: Our model calculation points to an aspect of wind energy that has not yet been comprehensively researched. Approximately 1200 billion flying insects are struck each year as they fly through the rotors of wind farms in Germany. Such a large number of affected insects could be a relevant factor for the stability of the insect population and could thus influence species protection and the food chain.

DLR

This summary is from their research report.

Interference of Flying Insects and Wind Parks

Deutsches Zentrum für Luft- und Raumfahrt Study Report

Franz Trieb

30 October 2018

Summary

The study investigates possible coherence of flying insect losses recently discovered in Germany and insect impingement on the rotor blades of wind turbines.

Evidence from literature confirms that migrating insects select fast air streams above the turbulent surface layer of the atmosphere for the purpose of efficient displacement to breeding grounds. Wind farm developers select sites with strong winds and install high towers with rotors just above the surface layer in order to optimize the energy output of their wind turbines. As a result of this coincidence, large numbers of flying insects can be expected in wind farms.

Model calculation of the amount of insect biomass that traverses wind rotors during operation provides a first estimate of the order of magnitude of 24,000 tons of insects crossing the German wind park throughout the summer season. Based on conservative model assumptions, five percent of the insects flying through a rotor could be actually damaged. The related loss of 1,200 tons per year since more than fifteen years could be relevant for population stability.

Species flying at critical rotor heights between 20 and 220 meters above ground level in addition to those already found within this study should urgently be identified by DNA meta-barcoding of the deposits that are regularly found on rotor blades. In addition to that, wind farms should be enabled to recognize approaching insect swarms and to react accordingly for their protection and conservation.

Deutsches Zentrum für Luft- und Raumfahrt Study Report