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Iberdrola Renewables, BWEC ground-breaking bat study shows more than 70 percent reduction in bat mortality

Iberdrola Renewables, BWEC ground-breaking bat study shows more than 70 percent reduction in bat mortality

Click here  for a PDF version of this press release.

May 12, 2009

GARRET, Pa. — The first year of a ground-breaking effort to study the interaction between bats and wind turbines at the Casselman Wind Power Project shows that turning off the turbines during low wind periods reduced bat mortality by more than 70 percent.

Iberdrola Renewables, the owner of the Casselman wind farm, partnered with independent conservation group, Bat Conservation International (BCI), for wildlife data collection at the southwestern Pennsylvania wind power project.

BCI's work is being conducted through the Bats and Wind Energy Cooperative (BWEC -, which is a coalition of the American Wind Energy Association (AWEA), the U.S. Fish and Wildlife Service, the National Renewable Energy Laboratory and BCI. The cooperative's work focuses on identifying and addressing potential wind energy impacts on bats.

From late July to mid-October 2008, Iberdrola Renewables, working with BCI researchers, conducted a controlled experiment in which selected wind turbines at the Casselman project were stopped during relatively low wind-speed nights in the late summer and early fall. This represents the first U.S.-based effort reporting the effects of shutting down turbines on reducing bat deaths.

"Shutting down turbines at certain wind speeds during periods when bats appear most vulnerable at this Northeastern US wind farm may have the potential to be a cost-effective way to reduce the impact on bats during their late summer migration season," said Andy Linehan, wind permitting director for Iberdrola Renewables. "As responsible stewards of natural resources, Iberdrola Renewables looks forward to a second year of the study to confirm what appears to be very good results with modest generation lost."

Although it was crucial for this study, curtailing turbine operations is not likely to be the complete solution to reducing the impact on bats in all circumstances or locations, but it may be a practical solution at some northeastern US sites where elevated bat mortality has been a concern, company officials said. This study is one of a series of collaborations with BWEC at five Iberdrola Renewables sites.

The results of the 2008 Casselman study were reviewed by BWEC's scientific advisory committee before being made public.

Dr. Ed Arnett, conservation scientist at Bat Conservation International and program coordinator for the Bats and Wind Energy Cooperative, led a team of scientists that tested increasing the minimum wind speed necessary for turbines to begin spinning and producing electricity into the power grid. "We hypothesized that bat fatalities could be lowered substantially by reducing the amount of turbine operating hours during low wind periods when bats are most active. We found that bat kills were reduced from 53 to 87 percent on any given night at turbines that were partially curtailed during low wind nights compared to those that were fully operational" said Arnett.

The Casselman study has wider implications for the wind energy industry as a whole.

"AWEA is a founding member of the Bat Wind Energy Cooperative, and we are glad to see this very encouraging step in identifying ways to reduce impacts of wind energy on bats," said Laurie Jodziewicz, AWEA Manager of Siting Policy. "We see this partnership as being a valuable resource not only for Iberdrola Renewables, but also for the entire wind energy industry."

The Casselman Wind Power Project, located in Somerset County, also marks an important environmental first for the state of Pennsylvania by putting a former coal mine to productive use. Eight of the project's turbines are located atop infill from a surface mine. In total, the 23 turbines at this wind power project will generate 34.5 megawatts (MW) of clean, renewable energy and contribute jobs and tax revenue to the local community. Typically a 34.5 MW wind project can generate power for more than 10,000 homes, according to the American Wind Energy Association's calculation.

Iberdrola Renewables is the world's leading provider of wind power with 9,642 megawatts in operation as of March 31, 2009. The company has made multiple commitments to wildlife, becoming the first US wind power company to adopt an Avian and Bat Protection Plan at all its wind farms and the first wind power company in the world to use Merlin Avian Radar Systems to curtail power generation during certain conditions at a Texas project. The complete study can be seen here.

Art Sasse, Director, Communications & Brand, Iberdrola Renewables, 503-796-7740
Paul Copleman, Media Relations, Iberdrola Renewables, 207-641-2805
Ed Arnett, Bat Conservation International, 512-327-9721
Laurie Jodziewicz, AWEA, 202-383-2516


Additional Resources:

  • To view a video story on the Casselman Wind Power Project, visit
  • B-roll of the Casselman Wind Power Project, coal mining activities and bat data collection
  • Print-quality still images of wind technicians at work, coal mining activities and bat data collection

About Avangrid

About Avangrid: Avangrid, Inc. (NYSE: AGR) aspires to be the leading sustainable energy company in the United States. Headquartered in Orange, CT with approximately $44 billion in assets and operations in 24 U.S. states, Avangrid has two primary lines of business: networks and renewables. Through its networks business, Avangrid owns and operates eight electric and natural gas utilities, serving more than 3.3 million customers in New York and New England. Through its renewables business, Avangrid owns and operates a portfolio of renewable energy generation facilities across the United States. Avangrid employs approximately 8,000 people and has been recognized by JUST Capital in 2021, 2022, 2023 and 2024 as one of the JUST 100 companies – a ranking of America’s best corporate citizens. In 2024, Avangrid ranked first among utilities and 12 overall. The company supports the U.N.’s Sustainable Development Goals and was named among the World’s Most Ethical Companies in 2024 for the sixth consecutive year by the Ethisphere Institute. Avangrid is a member of the group of companies controlled by Iberdrola, S.A. For more information, visit


About Iberdrola: Iberdrola is one of the world's biggest energy companies and a leader in renewables, spearheading the energy transition to a low carbon economy. The group supplies energy to almost 100 million people in dozens of countries. With a focus on renewable energy, smart networks and smart solutions for customers, Iberdrola’s main markets include Europe (Spain, the United Kingdom, Portugal, France, Germany, Italy and Greece), the United States, Brazil, Mexico and Australia. The company is also present in growth markets such as Japan, Taiwan, Ireland, Sweden and Poland, among others.

With a workforce of nearly 40,000 and assets in excess of €141.7 billion, across the world, Iberdrola helps to support 400,000 jobs across its supply chain, with annual procurement of €12.2 billion. A benchmark in the fight against climate change, Iberdrola has invested more than €130 billion over the past two decades to help build a sustainable energy model, based on sound environmental, social and governance (ESG) principles.

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