Acoustically Triggered Curtailment as a Strategic Investment for Wind Farms

How to Follow USFWS Voluntary Guidance for the Tricolored Bat

The Tricolored Bat (Perimyotis subflavus), once a common sight across North America, is now facing an uncertain future due to habitat loss, disease, and—we’re learning—mortality from wind energy development. Recognizing these threats, the U.S. Fish and Wildlife Service (USFWS) has proposed listing the species as endangered under the Endangered Species Act (ESA).

For wind farm operators, this means new regulatory risks and potential operational constraints. However, by proactively adopting “smart curtailment” strategies like Acoustically Triggered Curtailment (ATC), wind farms can mitigate bat fatalities while maintaining energy production efficiency. With ESA listing on the horizon, now is the time to implement solutions that balance conservation and business interests.

The Growing Regulatory Landscape: Why Act Now?

The proposed ESA listing will increase scrutiny on wind farms operating within the Tricolored Bat’s range. In anticipation of this, the USFWS issued Land-based Wind Energy Voluntary Avoidance Guidance for the Tricolored Bat (TCB Wind Guidance) in 2024, providing voluntary measures that wind farms can take now to implement practices that minimize bat fatalities.

The good news? Wind operators who proactively implement Acoustically Triggered Curtailment can minimize risks before they become mandates.

What Is Acoustically Triggered Curtailment (ATC)?

Traditional mitigation measures, such as Blanket Curtailment, require turbines to shut down during periods of heightened bat activity throughout the year, leading to energy loss. In contrast, Acoustically Triggered Curtailment leverages acoustic data to precisely adjust turbine operation only when necessary.

In their TCB Wind Guidance, the USFWS has laid out three primary options for wind energy facilities:

1. Blanket Curtailment (Option 1)

• A simple but costly approach, requiring turbines near Tricolored Bat habitat or migratory routes to shut down 30 minutes before sunset through 30 minutes after sunrise as well as under specific wind speed and temperature conditions.
  

2. Activity-Based Informed Curtailment (ABIC) (Option 2)

• Uses acoustic monitoring to develop predictive models and adjust turbine operation accordingly. Models are based on environmental conditions when bats are active, including at nacelle height. This is generally done with the help of an environmental consultant.

3. Real-Time Acoustic-Activated Curtailment (Option 3)

• Also known as Acoustically Triggered Curtailment (ATC), this is the most sophisticated method, using acoustic monitoring to detect bats and signal the SCADA in near real-time to feather turbine blades and pause rotation.
• Wildlife Acoustics offers this solution with our SMART (Song Meter with Analysis and Remote Transfer) System. Acoustically Triggered Curtailment is a flexible method that can work together with ABIC or Blanket Curtailment.
  

Why Choose Acoustically Triggered Curtailment (ATC)?

Compared to Blanket Curtailment or ABIC, Acoustically Triggered Curtailment provides a more refined approach that maintains energy production.

1. Cost-Effective Conservation

• Acoustically Triggered Curtailment minimizes downtime by adjusting turbine operations only when bat activity is detected, reducing energy loss 10-fold compared to Blanket Curtailment.

2. Proactive ESA Compliance

• ESA violations for unpermitted bat fatalities could lead to fines, legal actions, and project shutdowns.

• Wind farms that voluntarily implement Acoustically Triggered Curtailment now are well-positioned to avoid future compliance costs.

3. Flexible, Data-Driven Solutions

• Unlike Blanket Curtailment, Acoustically Triggered Curtailment mitigation is based on real-time conditions and site-specific bat activity.

• Operators can fine-tune curtailment parameters—such as levels of bat activity and the length of turbine pauses—to optimize efficiency and bat safety.

• Operators can also create more complex protocols combining Acoustically Triggered Curtailment with elements of Blanket Curtailment or ABIC, tailored to site-specific requirements.

How to Implement ABIC or Acoustically Triggered Curtailment (ATC)

Here are the steps to take for post-construction monitoring:

Step 1: Deploy Acoustic Recorders for Bats at Height

• Install bat recorders, such as the Song Meter SM4BAT FS or SMART Systems, including at least one microphone at nacelle height, on at least 15% of turbines, prioritizing those near bat habitats.

• Both Option 2 (ABIC) and Option 3 (ATC) require baseline data. However, if the intention is to implement an ATC protocol then it is most cost-efficient to use a SMART System for the data collection phase.

• While a SMART System incurs more up-front costs, these can be offset against the need for regular nacelle visits thanks to SMART’s remote data access capabilities.

Step 2: Develop an ABIC or ATC Plan

• For Option 2 (ABIC): Use collected predictor data to determine optimal wind speed and temperature thresholds for curtailment, tailored to seasonal changes.

• Collect baseline data for at least one full season to assess bat activity patterns and environmental data like wind speed. In areas with high concentrations of Tricolored Bat activity, this will mean one full year of data collection. In the meantime, implement Blanket Curtailment. As bat activity and weather conditions vary from year to year, an ABIC protocol should include regular reviews and refinement.

• For Option 3 (ATC): Following a period of recording to characterize turbine and other noises, the SMART System can be rapidly deployed for Acoustically Triggered Curtailment. An accurate ATC protocol requires a period of regular reviews and refinement.

A major advantage to ATC is that you can implement it faster than ABIC with the SMART System—no need for Blanket Curtailment or collecting baseline data before implementation (though it can be used with tapering Blanket Curtailment, if desired).

Step 3: Monitor and Report Performance

• For All Options: conduct post-construction mortality monitoring (PCMM) to assess the effectiveness of the curtailment strategy.

• Submit annual reports to your local USFWS field office, demonstrating compliance and effectiveness. Our SMART System generates log files via a secure online portal.

The Bottom Line

By implementing Acoustically Triggered Curtailment now, wind farm operators can:

• Reduce regulatory risks ahead of a potential ESA listing.

• Minimize energy losses compared to Blanket Curtailment and ABIC.

• Demonstrate environmental responsibility to stakeholders.

With the potential ESA listing of the Tricolored Bat, there’s no better time for wind farm operators to future-proof their projects. Acoustically Triggered Curtailment is not just a compliance measure—it’s a strategic investment in sustainable wind energy.

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For more info about USFWS Wind Guidance, click here.