Saving bats and generating more power: Acoustic data is the key
August 12, 2021
EchoPITCH? is a smarter framework for wind turbine curtailment that reduces downtime and bat fatalities
In the global race to carbon reduction and net zero commitments, demand is soaring for renewable energy, especially wind power. As wind energy generation capacity grows, so does the opportunity and duty for the industry to reduce impacts to vulnerable wildlife¡ªespecially bats.
This is a topic that I have explored previously. While new technologies have emerged in past years, a one-size-fits-all solution to this problem doesn¡¯t exist. Likewise, regulatory requirements to reduce bat fatalities vary among regions.
What we have learned during this time is that designing a smart-curtailment program will minimize energy loss while achieving meaningful risk reduction in bat fatalities.
Stantec supports the development of renewable energy by using smart curtailment with EchoPITCH.
What is the risk?
Although bats use ultrasonic echolocation pulses to avoid obstacles and capture prey, they appear unable to avoid fast-moving turbine blades and may even be attracted to wind turbines.
The risk associated with bat mortality is threefold. First, there is the obvious impact on bat population levels. Second, fatalities of rare bat species can have immediate regulatory effects and result in night-time shutdowns until lengthy permitting processes are complete. And third, there is the potential for reputational damage for individual facilities or organizations and the wind energy industry due to the perceived risks to wildlife.
One effective method to minimize bat mortality risk is to curtail turbine operation at night below an increased cut-in speed (the speed at which turbine rotors start to spin and generate power) by pitching the turbine blades parallel to the wind direction. This practice prevents turbine rotation. When cut-in speed is increased over broad seasons (e.g., May-September), the practice is known as ¡°blanket curtailment.¡±
Although blanket curtailment cut-in wind speeds from 5.0-6.9 metres per second (m/s) can be highly effective at reducing bat fatalities, it can result in the loss of 90-500 or more megawatt-hours per turbine per year, depending on the cut-in speed and local wind regime. Multiply this amount for a 50-turbine wind farm and the associated energy losses can be substantial.
Wind farm operators are increasingly required to apply blanket curtailment strategies as part of the permitting process or in response to fatalities for regionally protected or rare bat species. Maintaining vulnerable bat species¡ªlike the hoary bat¡ªmay require more widespread use of curtailment and other minimization strategies.?
Acoustic bat detector on top of a turbine nacelle.
A smart approach to curtailment
In 2019, my team received funding from the United States Department of Energy and Â鶹´«Ã½¡¯s Greenlight Program. Greenlight is part of our Innovation Office to help our employees realize an idea that benefits us, our clients, and our communities.
We used this funding to reanalyze data collected on behalf of two clients to explore the link between bat activity exposed to turbine operation and fatality risk. The data allowed us to simulate smart-curtailment strategies compared to blanket alternatives. We also refined our understanding of the distribution of bat activity in the aerosphere. The result of this work is EchoPITCH?.
The premise of EchoPITCH is that operators can identify key times when they should curtail turbine activity to lessen risk to bats. By identifying these key timeframes, operators curtail for shorter periods, increasing power generation and total turbine uptime over a blanket curtailment strategy. Ideally, turbine curtailment would occur only when bats are active. EchoPITCH uses site-specific patterns in bat activity to minimize both the amount of bat activity exposed to turbine operation and the amount of energy loss from curtailment.
With EchoPITCH, curtailment will no longer be defined in terms of cut-in speed but using risk-reduction goals.
How does EchoPITCH work?
We use passive acoustic bat detectors to measure the distribution of bat activity as a function of temperature and wind speed and how these vary in time and space.
Decades of research at wind farms have established that certain patterns in bat mortality are highly consistent, namely the seasonal distribution of fatalities and the association with lower wind speeds and warmer temperatures. While fatality monitoring provides the bulk of what we know about bat mortality at wind farms, they do not tell us the exact time at which fatalities occur. Acoustic detectors mounted on turbine nacelles allow us to pinpoint the temperature and wind speed when bats are active in the rotor zone of a turbine. With this information, we can:
- Establish the seasonal distribution of bat activity as determined by temperature and wind speed
- Measure species-specific acoustic exposure of bat activity to turbine operation with and without curtailment
- Predict the cost and effectiveness of any curtailment strategy
- Provide operators with increased turbine uptime
We use customized software to evaluate turbine operation, visualize the distribution of bat activity, and calculate the reduction in exposure and energy loss for curtailment alternatives. Often, we use an agency-recommended blanket curtailment strategy to establish a baseline target for risk reduction and then determine whether that same target can be achieved with less energy loss.
Instead of focusing only on the cut-in speeds or parameters of the curtailment strategy, EchoPITCH helps to pinpoint goals for bat-mortality reduction and how best to achieve them. Based on trials and simulations conducted at commercial wind energy projects, EchoPITCH allows project operators to generate more energy while achieving equivalent reduction in risk to bats.
EchoPITCH uses commercially available bat detectors and can be implemented using turbine-control systems already in place at a wind farm. Typically, one season of data is required to design the smart-curtailment strategy, with at least one more season of acoustic monitoring to document effectiveness.
This graph represents a ¡°target¡± level of exposure associated with blanket curtailment below 5 metres per second (m/s).
Acoustic exposure provides a better metric of the effectiveness of curtailment strategies than standardized carcass monitoring, at a mere fraction of the cost. This provides a viable method for periodic follow-up monitoring, representing an ideal metric to manage risks to bats.
Wind energy is set to be a large source of power for many nations working toward achieving net zero. Meeting demand requires increased development of wind farms and turbine updates. By mitigating both risks to bats and bat fatalities through technology, operators are addressing environmental stewardship practices and managing associated reputational risk.
The skies ahead
Through current and past work with clients across North America, we are helping to collect data and incorporate EchoPITCH into adaptive-management frameworks. A peer-reviewed manuscript was published in The Wildlife Society Bulletin in December 2021.
With EchoPITCH, curtailment will no longer be defined in terms of cut-in speed but using risk-reduction goals. Broader use of smart curtailment will lower impacts to bats and increase the amount of renewable energy generated across the globe, helping to meet net zero goals.
EchoPITCH? is a trademark of Â鶹´«Ã½.