Wind Mills are types of generators that utilize the energy of the wind to produce EU. They are the most unstable and unpredictable type of generators, depending greatly upon both placement and some luck, because when the chunks load there is a random (with minimum and maximum limits) base value for the wind, value which maintains stable as long as the chunks are kept loaded and the Wind Mills are at high (150+) Y levels.
On practice it's possible to have Wind Mills generating 1.5 EU/t or 2.5 EU/t each depending on luck. If it's raining or thundering that average output (EU/t) won't change significantly (< 10%) as long as the chunks don't unload. Knowing this, it's possible through some tries of loading and unloading the chunks with the Wind Mills to get a constant high EU output using chunk loaders.
It is advised to dismantle a wind mill with a wrench or electric wrench. Wind mills will drop a Generator when broken with a pickaxe.
Minimum power is 0, Maximum is 11.46 (y: 255, obstructions: 0, and thundering),? Maximum safe is 4.98 (y: 147, obstructions: 0, and thundering). Maximum safe, with 2 cables, is 4.98 (y: 149, obstructions: 2, and thundering). Maximum safe, with 2 cables, is y = 191 if you wish to ignore high wind and rain storms.
Calculation is: power = s * (y - 64 - c) / 750; 's' is Wind Strength, 'y' is Block Height, and 'c' is number of blocks (not including the windmill itself) in a 9x9x7 area around the Wind Mill.
Power has a 50% (* 1.5) increase if it is thundering, 20% (* 1.2) increase if it is raining.
If the power is higher than 5, there is a 0% to 0.1292% chance (chance based on power) to change the windmill to a generator and drop 0 to 4 iron ingots.
At high Y levels without many obstructions the Wind Mills can stop generating energy if there is raining or thundering, although this is an indication that there is a high probability of the Wind Mills to get converted into Generators with thundering.