Development and testing of a three‐dimensional ballistics model for bat strikes on wind turbines

Abstract

Bats colliding with spinning wind turbine blades result in bat mortality. Carcass surveys at individual wind turbines vary from daily to once a week and from large cleared plots to only the road and pad area. A physics‐based model is proposed to guide carcass surveys, for designing curtailment studies to detect treatment fatalities and for improving fatality estimates by accounting for unsearched areas. The model considers the effects of carcass size, weight, and drag, and it accounts for the turbine rotor size and rotation rate to simulate the trajectory of a carcass after it is struck by a wind turbine blade. A carcass parameter is defined as the ratio of drag force to body weight, which accounts for the relative effect of bat biophysical and aerodynamic characteristics. By applying restrictions on carcass survey and turbine yaw data, a limited sample of bat fatalities was obtained, and the analysis revealed that bats fall downwind of wind turbines, indicating wind drift significantly influences carcass fall trajectories. The new ballistics model includes the effect of wind drift on fall trajectory of a carcass. The model was used to investigate the sensitivity of carcass fall trajectories to variability of the input parameters. The tests showed that larger values of the carcass parameter, that is, when drag dominates, such as for small carcasses, resulted in larger downwind drift, whereas large carcasses with smaller carcass parameter values resulted in larger distances within the rotor plane. The relationship of wind speed and RPM was found to influence the carcass downwind distance more compared to the within rotor plane distance. Using carcass survey data, turbine operation data, and wind speed records, for seven bats surveyed the day after colliding with a wind turbine, modelled back‐trajectories were used to identify the likely strike location on the rotor. The model can be improved by validating the modelled trajectories with the recorded bat‐blade strikes in thermal videos. It should be noted that the findings of the present study are based on the bat fatalities that met strict criteria leading to small sample size and hence requires further evaluation for testing the robustness of the model.

Accounting for the Fraction of Carcasses outside the Searched Area and the Estimation of Bird and Bat Fatalities at Wind Energy Facilities

“…We start by assuming that the animal is killed upon impact with the turbine blade and that the wind is blowing horizontally (with no vertical component) and normal to the plane of the blades. Like Prakash and Markfort (2021) and Hull and Muir (2011), we ignore the wake effect behind the turbine, but we do include wind shear.…”

“…The final position of the carcass on the ground is (x, w) when y = 0. This set of governing equations is similar to those used by Prakash and Markfort (2021) but allows wind speed to vary with carcass position, thereby enabling the accommodation of wind shear and wake effect. Like Prakash and Markfort (2021) and Hull and Muir (2011), we ignore the wake effect.…”

“…This set of governing equations is similar to those used by Prakash and Markfort (2021) but allows wind speed to vary with carcass position, thereby enabling the accommodation of wind shear and wake effect. Like Prakash and Markfort (2021) and Hull and Muir (2011), we ignore the wake effect. We do account for wind shear through the Wind Power Law, or w (y) = w (y n ) • y/y n a , where w (y) is the wind speed at y meters above the ground, y n is the height of the nacelle, and a is the Hellman coefficient (Counihan 1975).…”

“…In addition, we assume that the cross-sectional area of the carcass presented to the wind (A) and the drag coefficient (C d ) are constant, so the term 0.5 C d Aρ/m (Prakash and Markfort (2021); Hull and Muir (2011)) simplifies to 9.807/y T 2 after noting that the terminal velocity is the vertical velocity at which the wind resistance equals the force of gravity so there is no longer any vertical acceleration. In other words, terminal velocity, {y'_T}, is the velocity such that ρ/2C d A/m • y T 2 − g = 0 from Prakash and Markfort's (2021) equations 3 and 4 with no acceleration in the horizontal directions, giving ρ/2C d A/m = G/y T 2 = y. Thus, the terminal velocity, which is relatively easy to measure and is relatively well-known, is used in lieu of the product of parameters with largely unknown values (C d and A).…”

Experiments and Analysis of a Nonlinear Sickle‐Shaped Cantilever Beam Piezoelectric Energy Harvester for Wind Energy Harvesting

“…Therefore, the use of a clean energy source that can provide real-time power to these types of electronic devices has great market value and social benefits. Harvesting energy from the environment to wirelessly charge such electronic devices directly is one of the effective ways, including solar energy, [3,4] fluid, [5,6] mechanical operations, [7,8] human [9,10] and animal [11] activities, etc. A large number of energy conversion devices and technologies have been researched today to harvest energy from these environments, including thermoelectric, [12,13] electrostatic, [14,15] triboelectric nanogenerator, [16,17] and piezoelectric.…”