Alameda County – Projects designed to improve the efficiency of wind-driven energy production in the Altamont Pass Wind Resource Area (APWRA) came with an unanticipated impact – an increase in bat mortality.
While scientific experts are hesitant to even speculate at this point why they’re finding more bat carcasses near the new turbines than they did with the old turbines, those involved are aiming to create a reliable and repeatable means for studying and reducing the rate of deaths.
The Altamont County Wind Repowering Technical Advisory Committee (TAC) and NextEra Energy Resources – the owners and operators of the Golden Hills Wind Farm – are engaged in an effort to reduce bat mortality caused by the newest generation of wind turbines.
During the June 25 TAC meeting, representatives from NextEra agreed to modify its operations to reduce bat fatalities, but stopped short of agreeing to monitor the impacts of the changes.
“Golden Hills proposed to make changes to the turbines’ operations during the peak fall migration season for bats, consistent with the Program Environmental Impact Review (PEIR),” said Renee Culver, senior manager of environmental services at NextEra Energy Resources, in an email to The Independent. “Golden Hills did not propose to conduct monitoring at this time, because results based upon dog search teams, compared to the PEIR threshold, would result in no useful scientific data about the efficacy of the adaptive management efforts in the fall. Dogs are many times more effective at locating bat carcasses and portions of such carcasses, and thus any results will simply not correlate to the existing PEIR threshold.
“Golden Hills continues to request that the TAC work with Alameda County to develop a scientifically sound threshold based upon best-available information. While the TAC members during the meeting demanded that Golden Hills conduct monitoring this fall, the use of dog search teams is very expensive, and such costs are not warranted without a real-world threshold for comparison.”
Culver’s position rankled members of the committee. While TAC and NextEra are in agreement that the methods to determine original fatality rates were insufficient at best, TAC members remained firm that monitoring must take place.
“NextEra has exceeded the threshold, so NextEra needs to decide what they think it’s going to take to reduce fatalities,” said Douglas Leslie, an environmental consultant and TAC member. “NextEra is in the best position to design a monitoring program that will measure the reduction in bat fatalities that occur as a result of implementing whatever measures they decide to implement.”
Leslie noted that bat deaths became an issue across the U.S. when the larger, newer generation turbines were built.
Doug Bell, also a TAC member and wildlife program manager with the East Bay Regional Park District, said in an email to The Independent that an estimated 3 million bats were killed by wind farms across the U.S. in 2019. That estimate, he said, is likely undercounting actual bat mortality by a significant factor. He added that a bat fatality crisis may already be in progress.
While the objective of limiting bat deaths due to wind turbines may sound simple enough, the complexities can be staggering.
The conditional use permit issued to NextEra for the Golden Hills repowering project required creation of an adaptive management plan (AMP) for bats. Determining if the new turbines are killing more or less bats than the first-generation turbines requires understanding how many bat fatalities were associated with those original turbines. The draft AMP states that the threshold value for bat mortality was “poorly formulated” and there is no “reliable information from the APWRA to effectively represent pre-repowering fatality rates for any bat species or bats as a group.”
Bird mortality, which also continues to be a challenge for wind farm operators, has been studied more extensively. With more data available, better mortality thresholds were developed.
“There’s a straightforward baseline for bird (mortality), which has historically been the issue in the Altamont – birds, not bats,” Leslie said. “There is a baseline for birds because a lot of monitoring was done at the old generation turbines … The problem is that either the methods used to estimate the number of bats (killed) at the old generation turbines were wholly inaccurate, or, more likely, the old generation turbines didn’t kill a lot of bats, so it wasn’t considered an issue. There’s no baseline for bats like there is for birds.”
Beyond establishing a threshold for bat mortality, monitoring the count of bats killed presents another layer of complexity. Bell explained that multiple factors influence the number of bat carcasses recovered by searchers. Weather, grass height, terrain, the frequency of the searches and the use of trained dogs can dramatically influence the success rate in locating bats killed by turbines.
The more efficient means of locating dead bats can lead to more accurate counts and a more comprehensive understanding of a true mortality rate. But to do so creates an apples-and-oranges comparison of the new monitoring techniques compared to the techniques used to formulate the original bat mortality threshold.
The wind energy industry got its start in Alameda County, and specifically in the Altamont area in the late 1970s. With memories of the energy crisis earlier in the decade still fresh, there was a desire to reduce the country’s dependence on foreign oil; wind power was part of the wider strategy to achieve that goal.
Cool marine winds coming off the Pacific Ocean funnel through the Altamont Pass where they meet the warmer air mass of the Central Valley. These conditions create strong, predictable winds that made the APWRA a desirable location for the generation of electrical power from wind. While energy production varies on a day-to-day and season-to-season basis, the ability to create electricity is nearly constant.
The APWRA was established in 1980, and by the mid-1990s, it was the largest wind farm in the world with approximately 7,200 turbines generating power. As the technology related to energy production from wind improved, an effort to repower the wind farms in the Altamont got underway in 1998. NextEra engaged in the repowering effort. The Golden Hills Project removed 775 aging wind turbines and replaced them with 48 1.97 megawatt (MW) turbines in 2015. The project, which covers 4,500 acres, was planned to generate 85.92 MW per year.
NextEra agreed to revise the draft AMP to address TAC concerns. The revised draft is expected to be reviewed at a future TAC meeting.
“The Golden Hills Wind project continues to deliver renewable energy while participating in and supporting the best scientifically-sound and economically-viable ways to minimize the effects of turbines on bats,” said Bryan Garner, director of communications at NextEra. “Golden Hills values the collaborative process and will continue to take part in both Alameda County and TAC discussions around this complex issue.”