All wind farms disturb habitat with their grading, foundations, fences, roads and other changes made to the land. Birds and bats can be hit by rotating blades of turbines.
Although the potential for harm still exists if birds and bats fly directly into a Vertical Axis Wind Turbine (VAWT) rotor, Wind Harvest International anticipates that VAWTs will be friendlier to wildlife than Horizontal Axis Wind Turbines (HAWTs) because:
- VAWTs can be placed in existing wind farms, reducing the need to build new ones in undisturbed habitat.
- VAWTs are three-dimensional and closer to the ground than traditional HAWTs, which should make them easier for birds and bats to see. These animals evolved to detect three-dimensional objects that are the height of trees, unlike traditional turbines that are two-dimensional and reach heights of 60m to 140m above ground level.
- VAWT blade-tip speeds are in the 50-80 mph range, whereas HAWT blades are often traveling at 150-200 mph. The lower tip-speeds of VAWTs reduce the likelihood of creating “barotrauma” that bats face with HAWTs.
Few VAWTs have operated for extended periods, and there are no known studies on how they affect birds and bats. It will take time to determine if VAWTS operate with less impact on wildlife than HAWTs. WHI will participate in this research by using detection and recording systems and hiring independent scientists to validate how birds and bats interact with its G168 VAWT Systems.
Because renewable energy does not rely on mining for its fuel, it is significantly less harmful to wildlife. If large, renewable energy projects are installed on farmland, harm to habitat is minimal. But when they are built in wild lands, the related infrastructure degrades habitat quality.
In terms of habitat loss, integrating VAWTs into existing wind farms may be the least damaging, large-scale energy source currently available. In locations such as California, where wind farms are sited on rangeland or in deserts rather than on farms, erecting VAWTs in the understories of HAWTs results in minimal habitat loss. New roads, fences, meteorological mast towers are not needed. In “capacity factor enhancement" projects, VAWTs in wind-farm understories eliminate the need for new transmission lines and the habitat damage that accompanies their slices through the landscape.
When wind turbines are appropriately located, they have negligible negative impacts on birds and bats. The hills and ridgelines on which many wind farms are installed have relatively poor quality habitat to attract or sustain many species.
A major exception to the inherent suitability of hills and ridgelines for wind farms concerns birds of prey. Here, these species use the higher wind speeds to soar and gain lift. These species can have a difficult time seeing and avoiding HAWT rotors. This may be caused by genetic variations within certain species; vultures, for example, have blind spots in their visual field that prevent them from seeing objects—such as wind-turbine blades—that are directly in front of them. Moreover, many birds of prey that hunt from hundreds of meters above ground have eyes that focus in the ten-meter zone as they track small, running animals. These birds can completely miss seeing the two-dimensional rotors of the HAWTs as they fly down for the kill. 
Why VAWTs Should Be More Bird-Friendly than HAWTs
VAWTs, like WHI’s G168 VAWT Systems, should avoid the problems stated above in the following ways, and thus be more wildlife-friendly, especially to eagles, condors, hawks, other soaring birds.
Closeness to the ground
Blades on HAWTs can sweep a circle anywhere from 20m to 150m (65 to 492 ft) above ground level, whereas blades on Wind Harvest International’s G168 VAWT with a standard-sized tower start at 4m (13 ft) above ground level and top out at 18m (59 ft). Because of this dramatic difference in height, VAWTs are out of the flight paths of high-flying birds of prey and most migrating birds. Condors and eagles, with their eyes focused on the ground, will have their view interrupted by VAWTs in this near-ground space.
There is a lot yet to be discovered, including whether birds like hen harriers and kites look up from their hunting in time to see the spinning, tree-sized turbines downwind. It may be that a subsonic whistle or other sound needs to be triggered when the motion-detection camera and computer detect this type of bird.
Unlike HAWT blades, which rotate in two dimensions and lack depth, VAWTs rotate in three dimensions, with horizontal arms attaching their center shafts to their rotating blades. An array of VAWTs shares similarities in shape and size to a row of tall trees. Whether coming straight into a row of closely spaced VAWTs or flying down toward them, birds and bats should be able to recognize the three-dimensionality, moving blades and blade arms in time to avoid them.
Lower Blade-Tip Speeds
Blades of WHI's variable-speed VAWTs will have a tip speed of 40 to 90 mph, compared to the HAWT tip speeds of 120 to 200 mph. In general, birds are good at resolving rapid movements and most species should not have trouble seeing the rotating vertical-axis blades.
When birds are detected in the vicinity, systems like DTBird can quickly slow down VAWT blade tip speeds to five to fifteen miles per hour, and thus make the blades more easily seen, tracked and avoided.
WHI will use its resources and grants to develop the scientific knowledge needed to reduce and even eliminate the potential for harm our turbines could create. WHI will do its best to use this website to share what is known about VAWT impacts on wildlife. We appreciate help from anyone in finding and sharing information that will advance this goal.
Traditional turbines can harm bats in two ways. These nocturnal, flying mammals can fail to “hear” the rotating blades and fly into them. Bats are also susceptible to “barotrauma” and tissue damage resulting from sudden changes in air pressure created by HAWTs’ fast-moving blades. The best method to protect bats is to not install projects in bat habitat or in their migration routes.
Presently, little is known about how VAWTs may impact bats.
- Most VAWT blades rotate at less than half the speed (30-100 mph) of HAWT blade tips (150-200 mph). The slower-moving blades may be easier for bats to echolocate and avoid.
- The slower speed of VAWT blades could reduce or eliminate bat exposure to barotrauma.
- VAWT blades rotate in completely different ways than HAWTs, and bats may well be able to anticipate the blades’ direction and path.
- Because they can be placed closer to the ground, VAWTs may be at a height significantly lower than some bat migratory routes.
Using new technology that can detect bat species by their “chirps” and calls, VAWTs can be programmed to slow or shut down before bats fly into their rotors. Wind Harvest International is committed to researching and understanding how different species of bats detect and are affected by VAWT rotors.
Detection & Avoidance
Real Time Bird and Bat Monitoring and Collision Avoidance
DTBird is a system that combines real-time, high-definition image analysis to detect birds with collision risk mitigation actions: emission of warning sounds or by stopping the turbine. This technique can be adapted for use with rows of VAWTs. The DTBird high-definition cameras survey 360 degrees around turbines, detecting birds in real time while recording and storing videos and data. Installation and operational settings can be adapted to any target species. Any actual bird collision is recorded and then can be viewed online in videos with sound.
Collision avoidance measures include warning sound emissions. These can be adapted for target species, and triggered when the VAWT is operating and the cameras’ analysis units detect birds of a certain size or flight pattern. Data from an experimental test in Sweden in 2015 showed that the DTBird system triggered avoidance behavior in 88% of cases where a bird was on a collision course with the wind turbine. 
Independent of the sound emission, DTBird Stop Control module can also trigger a signal to stop the VAWT according to predefined bird collision risk situations.
To confirm how well the DTBird system works with WHI VAWTs, Underwriters Laboratories (UL) will measure how quickly the system can detect drones mimicking birds of different sizes and speeds at different distances and angles as they approach. This third-party validated data will be important in securing project permits in bird-sensitive areas.
Similarly, DTBat is a system that automatically surveys the airspace around wind turbines, and optionally, reduces the collision risk by triggering the wind turbine to stop when it detects bat activity in the area. Other research organizations have used bat-chirp recognition software to create bat acoustical recording devices capable of turning off a turbine or emitting dissuasion events if bats come too close to wind turbines.
The collection of data with automatic recording systems will also provide a great deal of information on how different species and types of birds and bats notice and avoid VAWTs.
WHI plans to use the detection and modules of DTBird with its VAWTs in locations where bird and bat populations may be at risk.