There are many issues that a wind developer must consider when siting a wind project, but one that has become increasingly pressing in the U.S. is the effect of turbines on local wildlife. The wind industry takes great pride in contributing to a clean energy future and will protect species across the globe from climate change, but at the local level, turbines do have an impact on wildlife, including causing the fatality of birds and bats.
The wind industry takes these consequences seriously and is continuously working toward minimizing its impact. In recent years, bats have emerged as a critical focus for the wind industry, as there are several threatened and endangered North American bat species whose territories overlap with existing and forthcoming wind development sites. Although wind turbines do cause bat fatalities, it is the horrific disease white-nose syndrome (WNS) that has caused the drastic reduction in many hibernating bat species. Mortality from WNS can differ by site and species, but some bat hibernation sites, also known as hibernacula, in the Northeastern U.S. have seen 90% to 100% mortality rates, making bat conservation a crucial issue for wind developers and operators.
WNS is caused by a white fungus (pseudogymnoascus destructans) that grows on a bat’s nose and wings, disrupting both its hydration and its hibernation cycles and ultimately leading to its death. The disease was first detected in North America in 2007 at four sites in New York state and, less than a decade later, has been confirmed in 26 states and five Canadian provinces. Hibernating bats are most affected by WNS due to the cold and humid conditions in their hibernacula, which promote the growth of the fungus. Once present, WNS can spread rapidly among hibernating bats, which retreat together.
However, even before WNS devastated the North American bat population, the wind industry was taking proactive steps to lessen its impact on wildlife by addressing the issue of bat mortality as a result of wind plants. In 2003, the Bats and Wind Energy Cooperative was formed by Bat Conservation International, the U.S. Fish and Wildlife Service (FWS), the American Wind Energy Association, and the National Renewable Energy Laboratory. The goal of this consortium is twofold: to better understand the causes of bat fatalities and to find ways to minimize them.
An important milestone in the wind industry’s efforts occurred in 2012, when the FWS produced the Land-Based Wind Energy Guidelines. The guidelines were created to “provide a structured, scientific process for addressing wildlife conservation concerns at all stages of land-based wind energy development. They also promote effective communication among wind energy developers and federal, state, and local conservation agencies and tribes.”
The guidelines use a tiered approach, with increasing levels of data collected at each tier, to better characterize the risk to species of concern, such as bats. After each tier, the developer consults with the FWS to determine next steps. These can range from abandoning a project altogether to proceeding to the next tier without further data collection – all based on the level of risk. This iterative approach allows developers to increase investment incrementally and in proportion with the level of risk surrounding the project.
The first three tiers – preliminary site evaluation, site characterization and field study, and impact prediction – are addressed in the preconstruction phase. As the developer moves through the tiers, the data collection becomes more specific – from the landscape scale using publicly available information to site-specific measurements of species-of-concern presence.
For bats, this can include acoustic studies that are used to determine bat activity on-site, as well as mist-netting studies, in which a sample of bats is captured by biologists to characterize the species composition in the area. It is important to note that although adherence to the guidelines is voluntary, that does not relieve the developer of the responsibility of complying with laws and regulations, including the Endangered Species Act, which covers threatened and endangered bats. At the end of Tier 3, the developer can estimate the risks posed to endangered species, and if the risk of mortality is high, the developer must choose whether to abandon the project or to pursue a permit with the FWS.
Although there are over a dozen listed bat species in the U.S., the three species that are most likely to be impacted by wind plants are the Indiana bat (myotis sodalis), the northern long-eared bat (myotis septentrionalis) and the Hawaiian hoary bat (Lasiurus cinereus semotus). The map shows the range of each of the species and its concurrence with wind energy plants in the U.S.
Because wind plants do not intend to take bats, which is defined by the Endangered Species Act as meaning “to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect or attempt to engage in any such conduct,” there is a path to receive what is called an incidental take permit (ITP) from the FWS for threatened and endangered species. The ITP is meant for activities such as wind energy generation that are otherwise lawful but result in the “incidental take” of a listed wildlife species. This permitting mechanism is not unique to wind and covers all activities that may impact listed species. To receive an ITP, an applicant must show the FWS the following:
- Taking will be incidental;
- The applicant will, to the maximum extent practicable, minimize and mitigate the impacts of the taking;
- The applicant will ensure that adequate funding for the plan will be provided;
- Taking will not appreciably reduce the likelihood of the survival and recovery of the species in the wild; and
- Other measures, as required by the secretary, will be met.
The plan the applicant creates to show the FWS these steps is called a Habitat Conservation Plan (HCP). An HCP outlines the three major efforts, known as the “mitigation hierarchy,” that will be implemented by the developer:
1. Avoidance – How will the developer avoid take of the endangered species through micro-siting of the turbines to avoid known hibernacula and create buffers from preferred habitat and known roost trees?
2. Minimization – How will the wind plant be operated to minimize, to the maximum extent practicable, the levels of bat take at the wind plant?
3. Mitigation – If unavoidable take remains after avoidance and minimization efforts have been implemented, how will the developer compensate for the loss? This is known as “compensatory mitigation” and, for bats, can include funding conservation projects such as gating, which protects important hibernacula, and purchasing conservation easements on suitable habitat.
The HCPs are reviewed by the appropriate local FWS Field Office. If the HCP is deemed sufficient to protect the species, an ITP that allows the wind plant to take a limited number of endangered species over the fixed life of the wind plant is issued.
Clearly, this entire process can be quite time- and resource-intensive. For wind developers, time is of the essence, so it is typically not feasible for the developer to wait for the issuance of the ITP to commission the wind plant. In these cases, the project is issued a Technical Assistance Letter from the FWS that allows for operation of the wind farm, under specific operational constraints, until the issuance of the ITP and implementation of the HCP. The goal is to operate in such a way that no significant impacts occur to the listed species.
For wind plants, that typically means increasing the turbines’ cut-in speed (when they start generating power) from the original equipment manufacturer standard level of 3.0 m/s-3.5 m/s to 6.9 m/s, which the FWS considers take avoidance. This level of curtailment typically applies during the fall migration (August to October) but, depending on the risk profile and location of turbines, can also be applied during the summer months. An increase in the turbine cut-in speed is an effective mortality minimization tool because bats are less active at higher wind speeds.
However, the power losses from curtailing at this level are significant and impact wind plant revenue during its first, critical years. Once the ITP is issued, a lower level of curtailment is typically implemented (4.5 m/s-5.5 m/s) to reduce, but not eliminate, the take of bats at the wind plant.
Post-construction mortality studies are conducted during the first several years of wind plant operation. These mortality studies involve human searchers, who walk transects around a number of sample turbines looking for bat and bird carcasses.
The intensity of these search efforts varies based on the level of risk of impacts to species of concern and the required probability of detection required. For low-risk projects, a “roads and pads” search protocol may be used, in which only the access road to and gravel pad around the sample turbines are searched. For high-risk projects, large plots ranging from 50 meters to 80 meters around the sample turbine are cleared and searched. The search process is very labor-intensive and incurs a very significant cost to the project. The results of these searches are used to generate an estimated take level for the wind plants and are used to validate that the predictions of bat mortality and impacts on the habitat of the species of concern, both estimated in Tier 3, were correct.
Through the efforts outlined previously, the wind industry has actively reduced its impact on bats. Often, this minimization comes with a relatively small price tag, as is the case with the industry’s voluntary best management practice of feathering a turbine’s blades before the cut-in wind speed is reached. This drastically reduces the rotational rate of the blades before the turbine makes power and can reduce operating wind turbines’ impacts on bats by as much as 30% without significantly affecting generation. Unfortunately, the turbine curtailment required to reduce endangered species take risk does require a significant decrease in the amount of renewable energy generation.
Brogan P. Morton is product manager at Hinesburg, Vt.-based Renewable NRG Systems. He can be reached at email@example.com.