Wind Mill
Most simple, enviromentally clean, but not very efficient source of torque energy.
It's converting wind motion and wind is not very stable source.
Wind Mill is oscilating during the day cycle where in the night it's typically very low and during the noon at the highest.
The weather is affecting the wind too. Sand storms make the Wind Mill work on 200%, but the heat will almost shut it down.
More stable power source is Water Wheel for now even though drought caused by the heat has a negative effect on it also because it can weaken a Water source.
There will be more advanced power sources soon.