In the summer the windmills heated up the wind farm by 0.7˚C per decade and in the winter slightly less by 0.5˚C per decade. This is measured in relation to the region immediately around the wind turbines. The warming effect was particularly noticeable at night, but hardly or not at all during the day.
“This makes sense because during the night the ground gets much colder than the air a few hundred meters above the Earth’s surface and the windmills create turbulence causing the layers of air to mix,” explains Steven Sherwood (University of New South Wales, Australia). As a result, the soil warms up at night. See image 1: Roscoe Wind Farm Texas.