Renewable energy sources reduce our dependence on fossil fuels and help curtail the emission of greenhouse gases. But they are not all beyond reproach when it comes to climate change: The widespread use of those technologies can have negative impacts on the environment.
When wind turbines are used to harvest energy, they change the air flow in the atmosphere near Earth’s surface. That change, in turn, reduces wind speeds, which affect the exchange of heat and moisture between the air and the ground. And the turbines’ influence is not limited to their immediate area: The effects can be detected hundreds of kilometers away.
Previous large-scale studies simulating the global climate impacts of wind energy have assumed an unrealistic number and distribution of wind turbines. On a smaller scale, models of single wind farms don’t yield any information about nonlocal effects. To find a middle ground, Lee Miller and David Keith at Harvard University simulated the effects of large-scale wind-power generation on surface air temperatures across the continental US.
To make their model realistic, the researchers simulated turbines in the windiest parts of the country. In the figure, those areas are inside the black lines and roughly correspond to the locations of wind farms operating today, which are indicated by the circles. The 0.46 TW of power generated in the simulation is approximately enough to supply the entire country with electricity. They then looked at the air temperature 2 m above the ground across the entire simulation area.
At that rate of energy generation, Miller and Keith’s simulation predicts that average air temperatures would increase by 0.24 °C across the country and by 0.54 °C in the wind-farm region. The effect of turbine-driven mixing is more pronounced at night when there is a larger vertical temperature gradient in the atmosphere. Interestingly, not all areas saw increased temperatures: Some places along the East Coast actually became slightly cooler.
Although the overall heating effect from wind turbines is small compared with the fossil fuels they replace, it is 10 times as large as what the authors predict from solar panels. In a related study, Miller and Keith also found that unlike solar panels, the areal density of power generated by a wind farm decreases as the farm’s size increases. The decreased production efficiency with increased energy generation is caused by interactions between turbines and the atmosphere. (L. M. Miller, D. W. Keith, Joule, 2018, doi:10.1016/j.joule.2018.09.009.)
