Abstract
The U.S. Department of Energy Wind Energy Technologies Office, and the National Renewable Energy Laboratory convened a workshop entitled the State of the Science and Technology for Minimizing Impacts to Bats from Wind Energy on Nov. 13–14, 2019.
The objectives of the workshop were to:
- Identify the current impact minimization measures that are, or can be, used to reduce bat fatalities at wind energy facilities
- Assess the current effectiveness of those minimization measures
- Identify and assess the research and development opportunities needed to optimize and improve the effectiveness of current minimization and deterrent technologies and inform the development of future solutions
- Identify potential emerging or novel methods for informing impact minimization measures at or around wind energy facilities.
Specifically, the workshop focused on deterrent and curtailment strategies. For deterrents, the discussion centered on the existing technology (e.g., ultrasonic deterrents, dim ultraviolet light, and texture coating), integration with wind turbines (either retrofitting or out of the box installation), effectiveness, validation studies, and cost (e.g., technology, installation, validation, and maintenance). For curtailment, the conversation was divided into blanket curtailment (i.e., based on time and wind speed) and smart curtailment (i.e., blanket curtailment plus additional variables such as temperature or bat activity).
The workshop included plenary presentations, panels, and breakout sessions to share data and stakeholder perspectives and engage participants. Although there are several priority topics related to bats and wind energy, this workshop focused the discussion on the current technologies and strategies that are, or can be, used to reduce bat fatalities at wind energy facilities, status of research and development of minimization measures, opportunities to optimize costs and improve effectiveness, and potential emerging or novel approaches to explore. This workshop took a holistic approach and discussed all aspects associated with advancing deterrent technologies and curtailment strategies, including the technological, biological, economic, and regulatory barriers faced by the wind energy and wildlife community.
Deterrents
The intent of deterrents is to reduce interactions between bats and wind turbines by ensonifying the surrounding airspace with an uncomfortable or disorienting stimulus (e.g., ultrasound), or altering the appearance of the wind turbine (e.g., dim ultraviolet light or texture coating). Given that deterrents allow wind turbines to operate normally, they also may be more cost-effective than curtailment (see below), particularly in regions with a relatively long period of risk or at facilities sited in low-wind regimes. Nevertheless, several unknowns regarding deterrents remain, including long-term durability, whether bats may become habituated to visual or auditory stimuli, what sound pressure level is required to deter bats using acoustic deterrents, if there are species-specific responses to deterrent stimuli, and adaptability of the deterrents to evolving turbine technology. Some of the cost, technology, regulatory, and validation considerations associated with assessing the effectiveness of deterrent technology include:
- The variety of deterrent technologies and their state of readiness. Nacelle-mounted ultrasonic deterrents have advanced to commercialization, but their efficacy is limited by the rapid attenuation of high-frequency sound and therefore cannot cover the entire rotor-swept zone of the current fleet of commercial wind turbines. Blade-mounted ultrasonic deterrents and other technologies (e.g., dim ultraviolet light and texture coating) are still in the early- to mid-phases of development and require further validation to demonstrate their effectiveness.
- The regulatory uncertainty. Risk of potential take of a state or federally listed species and lack of incentives may factor into decisions to host experimental studies for new technologies. Permitting requirements also may inhibit or delay studies.
- The advancement of technologies through the technology readiness level hierarchy. Research and development requires a systematic approach and allows vendors to identify failure points and system weaknesses early, in safe and low risk settings. However, it can take years to move a technology through the hierarchy.
- The expensive nature of validation studies. In addition to the cost of mortality and/or behavioral monitoring, operations staff time to support studies, clearing and maintaining research plots, hardware and software associated with the technology, and maintenance of equipment should be factored into budget planning.
Curtailment
Although deterrents rely on a behavioral response from bats to reduce interactions with turbines, curtailment alters turbine operations in response to risk factors (e.g., temporal, weather, or evidence of bat activity). Early studies observed that bats are more active during lower wind speeds and incidence of fatality was noted to be highest during late summer and early fall. These data indicated a relatively narrow window of risk based on wind speed, time of year, and time of day (i.e., night) and the potential to reduce risk by altering turbine operations (i.e., feathering turbine blades and raising cut-in speeds). This practice is commonly referred to as standard or blanket curtailment (aka operational minimization).
Blanket curtailment has shown significant reductions in fatalities, but it also reduces annual energy production and revenue, which could hinder the financial viability of wind farms in low wind class areas. Moreover, it is a relatively coarse approach that results in curtailment during times when bats may not be at risk. Smart curtailment strategies build on the foundation of blanket curtailment by incorporating additional weather variables or bat activity data as triggers for altering wind turbine operations. This approach is currently being evaluated for its ability to achieve the same level of minimization while reducing loss of annual energy production and revenue. As with deterrent technologies, it is necessary to consider the cost, technology, and regulatory and validation factors associated with assessing the effectiveness of curtailment strategies, some of which include:
- The expensive nature of validation studies. Similar to deterrent studies, validating curtailment strategies is expensive. The costs can include operations staff support for hosting studies, clearing and maintenance of research plots, mortality and behavioral monitoring to verify efficacy, installation and maintenance of hardware (e.g., acoustic detectors), updating supervisory control and data acquisition systems, and revenue loss associated with altered turbine operations.
- The variety of turbine hardware and software. Variation in turbine models and the wind regimes in which they are deployed influence both the cost and the feasibility of adopting curtailment. Currently, turbine models spanning more than 3 decades exist and are installed with varying supervisory control and data acquisition system capabilities. In some cases, this may limit the practicality of implementing more complex curtailment scenarios at some wind energy facilities.
- The regulatory uncertainty. Risk of mortality of threatened or endangered species factor into decisions to host experimental studies for new curtailment strategies. Permitting requirements also may inhibit or delay studies.
Communication
Communication is essential for large-scale, complex studies, and should begin early and be continuous throughout the project. The phrase “it takes a village” applies to these efforts as active participation by a diverse set of stakeholders is necessary for the project to be successful. Representatives from the technology provider, original equipment manufacturers, wind energy facility (e.g., permit managers, electrical engineers, mechanical engineers, supervisory control and data acquisition operators, and site managers), research team (e.g., field crew and statistician) make up the core group. A dedicated project manager is recommended to coordinate activities among all team members. It also is important to engage early with those outside the core project team, such as state and federal regulators.
Engaging in multistakeholder collaboratives (e.g., Bats and Wind Energy Cooperative and American Wind Wildlife Institute) can help facilitate sharing perspectives, building relationships, and discussing priorities. Networking activities such as workshops are necessary to disseminate study results and lessons learned as well as to address misperceptions. There also is an urgency to disseminate research findings more rapidly to keep pace with technology development.
Study Design and Monitoring Tools
A robust experimental design is crucial to avoid situations where inconclusive results are the product of the design rather than the strategy being tested. Experimental studies are designed to maximize detection of a treatment effect, as opposed to monitoring studies, which optimize detections of carcasses. In the early stages of planning, researchers need to articulate the objectives, clearly define the experimental units (e.g., site, turbine, night), response variable (e.g., total mortality by night or over a longer period), and sources of variation (e.g., detection probability affected by treatment). Another early step is to conduct a power analysis to determine whether the experimental design has the power to detect the desired effect. Commonly used experimental designs include a randomized block design or a completely randomized design. Each option has its advantages and disadvantages and the decision about which to choose must be weighed with other factors of the study.
The technologies and methodologies used for monitoring, such as acoustic detectors, thermal video cameras, radar, radio tags, and mortality monitoring, offer different benefits and can enhance our understanding of bat/wind turbine interactions. Nonetheless, it is important to understand the costs, limitations, and biases associated with each. The selection of technologies and methodologies used will depend on the study objectives, although, combining ≥2 tools (e.g., mortality monitoring and thermal cameras) may provide a more complete assessment of the strategy being tested.
Integration
For bats, minimization measures are primarily enacted during the operational phase, after the facility is constructed and generating electricity. Adopting minimization measures for long-term success requires integration with wind energy infrastructure, communication, and supervisory control and data acquisition systems. Key considerations for integrating technologies include location, potential structural changes necessary to affix the technology to the wind turbine, and data security. Operators must also consider aspects of the technology, such as maintenance, power requirements, monitoring, and regulatory requirements.
Greater collaboration across the supply chain will facilitate the integration of technologies with wind turbines. For example, when technology vendors work directly with original equipment manufacturers, the two parties can coordinate the seamless integration of wind turbines and after-market minimization technologies. These collaborations inform technology developers about potential constraints or opportunities for potential placement locations, power availability, and communication capabilities, and give original equipment manufacturers an opportunity to optimize future turbine designs for integrating monitoring or minimization technologies (e.g., providing dedicated space for equipment). They also allow for discussion of potential warranty concerns about installing new technology on a wind turbine or changing turbine operations. Improving communication and advancing partnerships across the supply chain and throughout the phases of research and development will further streamline the integration of wildlife impact minimization technologies. This requires increasing and accelerating information dissemination to current and new audiences and sharing lessons learned.
Behavior and Physiology
It is unclear why bats approach and interact with wind turbines. Certain species appear to be attracted to these structures, but the behavioral or physiological drivers remain unknown. These potential attractants likely vary by species and habitat conditions, and may not be mutually exclusive (i.e., it could be more than one attractant). Understanding how bats perceive wind turbines may help improve minimization measures. For deterrents, improving existing or developing new technology hinges on a better understanding of the species-specific responses to various stimuli. For curtailment, knowing the behavior and physiological drivers associated with bat activity may provide opportunities to optimize curtailment strategies.
Cost and Funding
Understanding project logistics and costs is critical to the success of a project but may not be fully understood by those who have not been involved in these large-scale studies. It is important to recognize and plan for the time and labor required. Given how expensive the experimental studies are, diverse funding mechanisms are needed to reduce cost barriers. Pooling funding opportunities is advantageous for large-scale projects so that no single entity bears all the financial burden. This has been successful in recent funding opportunity announcements by the U.S. Department of Energy Wind Energy Technologies Office, where government funding is combined with cost-share from project team members. Another recent funding mechanism is the Wind Wildlife Research Fund, which brings a multitude of industry partners together to collectively fund priority research.
Recommendations for Minimization Research
One of the workshop outcomes was to compare minimization priorities established by the Bats and Wind Energy Cooperative during the 5th Science Meeting in June 2018 with those of the November 2019 workshop. The Bats and Wind Energy Cooperative committee meets every 3 to 4 years to discuss the state of the science on a broad suite of bat and wind issues and to revise priorities. Using the 2018 Bats and Wind Energy Cooperative priorities for minimization strategies as a foundation, the workshop participants reiterated their relevancy and importance and voiced the need for additional priorities going forward.
To successfully advance deterrent technologies, stakeholders need to address major barriers (most notably species-specific efficacy), high costs of research and development, and lack of regulatory incentives to test new technologies. For curtailment, it is necessary to balance the conservation goals with renewable energy production. In addition, smart curtailment offers promising applications in certain situations, but continued studies on improving blanket curtailment to address remaining data gaps (e.g., fatality reduction at lower cut-in speeds, true cost of the lost energy production, contracting issues between the facility owner-operator and the offtaker who contracted for the energy to be produced, etc.) is warranted.