Bat Deterrent Systems
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NRG Systems is currently developing a pioneering, patent pending technology that will help support bat conservation – one of the most pressing issues facing the wind industry today.
As White-Nose Syndrome continues to ravage the populations of many hibernating bat species, the wind industry remains committed to lessening its impact on wildlife, including contributing to bat fatalities. While it is well researched that wind turbines cause mortality to bats, successful minimization methods have been implemented. Presently, the most effective techniques involve curtailment, which requires a reduction in energy generation. NRG Systems understands that this is not an ideal option for wind plant operators, so we have set out to develop Bat Deterrent Systems that could significantly reduce bat take without curtailment, meaning operators can produce more renewable energy more of the time while keeping all bats out of harm’s way.
Early trials of NRG's Bat Deterrent Systems have yielded positive results and we are currently field testing Systems with a variety of wind plant operators. Our Bat Deterrent Systems will be commercially available in 2018.
HOW IT WORKS
The deterrent system emits an ultrasonic acoustic field in the same range as bats’ natural calling frequencies. This interferes with their ability to receive and interpret their own echolocation calls and creates a disorienting airspace that is difficult to navigate. By jamming their echolocation systems in such a way, bats are discouraged from entering the treated airspaces and roosting locations. This concept is very similar to the practice of using white noise machines to mask unwanted sounds.
Bats emit a high frequency call that is dispersed throughout the atmosphere, then reflect off of objects, including their prey. As the call travels away from the bat it spreads, causing the initial energy emitted to cover a larger and larger area. In this example we see that the call reflects off a moth, and travels back to the bat. The echo return suffers the same spreading losses as the outgoing signal, so the returning echo is very faint compared to the initial call. Bats rely on hearing this echo to determine how long it took the call to reach the object and bounce back, which provides information about how far away the object is.
The NRG Bat Deterrent Systems create constant ultrasonic noise at the same frequency as the bat call. When a bat enters the airspace where the deterrent units are operating, the ultrasound from the deterrent units will be louder than the echo return the bat is listening for. This effectively “jams” the bats ability to hear its own return. If the bat can’t hear the echoes, it is unable to successfully forage and orient itself, so it chooses airspace without the ultrasonic noise.
Bat Deterrent System FAQs
As bats approach the turbine, the intensity of the ultrasonic noise gradually increases, leading them away from the areas where sound levels could affect their hearing.
Because bats have very good directional hearing and the ultrasonic noise gradually increases as they approach the turbine, they are able to avoid any airspace where they would completely lose the ability to orient themselves. During field testing of the Bat Deterrent Systems, which was conducted on ponds where bats congregate, the bats immediately move in the opposite direction of the ultrasonic noise and did not become disoriented.
Our Bat Deterrent Systems only cover the rotor swept area of the turbine, so the intensity of ultrasonic noise beyond this region does not affect the bats. Since the rotor tips of modern wind turbines do not swing below 40m above ground level, bats foraging below this level are completely unaffected and will not be pushed out of their natural habitat.
When wildlife get used to an unnatural visual or acoustic disturbance that is meant to keep them out of an area it is called habituation (imagine a bird perched on a scarecrow). Luckily, our Bat Deterrent Systems are not meant to simply annoy or frighten bats—the ultrasonic noise they emit actually interferes with their ability to orient and forage. Because bats rely so heavily on echolocation, they know to avoid any area that compromises this capability.
We thoroughly considered the unintended consequences of using ultrasonic noise for our Bat Deterrent Systems. There is no evidence that birds can hear ultrasound or that they are repelled by it, so we do not believe that our Systems will have an effect on any wildlife besides bats. During some of the field testing that we have conducted on ponds, herons and ducks have flown into and stayed in the areas covered by our deterrent devices, while the bats stayed away.
The current version of our Bat Deterrent System affects bat species whose call frequencies are between 20 kHz and 50 kHz. This covers all of the bat species found in North America, including endangered myotis species, and a vast majority of bats found in Europe.