With key changes to environmental protection regulations, it’s important to consider bat curtailment as part of this.

When developing a wind farm project, one criterion for the environmental acceptability concerns the avifauna impact study. Turbine positions are not controlled to be on migration corridors nor on local species’ hunting territory. In some cases, compensatory actions can be offered to obtain the administrative authorization.

During the operational phase of a project, the French governmental order of August 26th, 2011, on establishments classified for environmental protection (ICPE), imposed a long-term follow-up to estimate the impact of wind turbines on bird and bat fatalities. Until now, post-construction avifauna studies have not lead to any restriction. However, with environmental regulations getting more drastic, reading of avifauna studies will lead to more severe impacts on existing wind farms in the near future.

With that in mind, this article aims to improve knowledge on bat curtailment and demonstrate the financial impact of changes in regulations, with effective solutions to minimise the corresponding loss of revenue. The article also has a strong focus on the French market and regulations.

Background on bats

Europe has more than 30 different species of bats, which are all protected by law since 1981. This animal has an important role in the ecological balance since one bat can eat up to 600 insects per night.
Bats use the echolocation system for their spatial orientation. In this way, they are particularly sensitive to variations in pressure that could sometimes lead to fatal barotrauma.

Bat reproduction cycle

With only one birth per year and two migration periods, bats have a reproduction cycle that makes the species vulnerable. However, this is counterbalanced, thanks to their average long lifetime (~30 years).

bat curtailment - bat cycle reproduction

Interaction with wind turbines

On the basis of rotating movement, wind turbines create important air displacements, which are associated with large pressure variations. Thus, the risk of collisions and barotrauma for bats increases as the wind energy sector extends. Consequently, this has lead to increasing concerns and changes in regulations to preserve the species from extinction and has prompted bat curtailment action.

Changes in regulations

In some French regions, wind farms under development must comply with the bat curtailment plan enforced by the local administration Decree. In the near future, results from ICPE studies for operational wind farms will lead to similar measures.

In this context, it is important for asset owners to anticipate financial impacts and be aware of the solutions available to prevent loss of revenue. Several approaches have already been explored to design ultrasonic systems that are able to keep bats away from wind turbines. However, results were not satisfactory enough to develop such solution at an industrial level.

Therefore, the bat curtailment plan seems to be the most effective solution that is systematically chosen by the administration.

Bat Curtailment – Case study

The standard curtailment plan that can be easily imposed consists of increasing the wind turbines cut-in wind speed to 5 m/s or 6 m/s when bats are the most active. For example, early at night and/or when environmental conditions are compliant with bats’ operating mode (no rain, low wind, temperature above 12°C). This type of curtailment plan reduces bat mortality by more than 50%. In some cases, results from this avoidance strategy can reach 90% of success.

However, without any additional sensors, this type of curtailment plan can have a detrimental effect on budget with a production loss between 3% and 4% per year.

Standard case

As an example, the following distribution and hourly profile are considered to estimate the loss of revenue, due to increasing cut-in wind speed to 6 m/s, from April to October, between 7pm and 2am (this time window is wide enough to systematically cover the first 4 hours after sunset of the concerned semester).

It leads to production losses of about 3%.

Optimised case

All wind turbine manufacturers are working on modules, integrating sensors to curtail wind turbines at times and environmental conditions with high risk of bat mortality. Some companies, specialised in environment, are also working on this type of technology to compete with turbine manufacturers. Now, assuming that the wind farm is equipped with a dedicated bat system that enables real-time turbine control, the production losses will be reduced to less than 1.0%.

Initial investment for this type of system is estimated to be around €30k per wind turbine. In some cases, the installation can be limited to only one turbine. If you would be interested in installing such a module, Greensolver could help you estimate the balance between the CAPEX costs and the return on investment, depending on the production profile of the concerned asset. In parallel, Greensolver could also be of assistance during the negotiation phase.


The protection of wild fauna, with a particular focus on bats, is an increasing concern. It is worth the consideration of wind turbine operators and owners, as regulations are getting tougher. In the coming years, there is no doubt that the environmental agency will impose more severe restrictions for bat curtailment.

How can Greensolver help?

In this context, it is important to find the most adapted system to minimise loss of revenue. With many years of experience in operating wind farms, and the constant quest for innovative solutions, Greensolver can assist you finding the right system adapted to your site at lower cost. Do not hesitate to contact us.