Windmill Sails, Clearance, and Kinetic Dynamo Output
A Windmill with all eight sails fitted turns three times faster than a bare one, and that single upgrade is the difference between a decorative rotor and a real power source. The windmill produces no energy by itself: it feeds rotation to a 
Kinetic Dynamo, and the dynamo makes the Flux.
Building the windmill
Three crafts, in order:
Windmill Blade - three 
Treated Wood Planks and four 
Treated Stick, one blade per craft- Windmill - eight Windmill Blade arranged around a single
Iron Ingot in the centre 
Windmill Sail - five 
Tough Fabric, one sail per craft
Eight blades is the expensive part, and each blade is seven pieces of treated wood, so budget roughly a stack of treated planks and rods for one rotor.
Tough Fabric comes from industrial hemp, which is exactly what a Garden Cloche planted with 
Industrial Hemp Seeds produces. If you are running cloches already, sails are effectively free.
Fitting the sails
Sails are not part of the crafting recipe. Place the windmill first, then right-click the placed rotor with a Windmill Sail to add one. You can add up to eight, and each one visibly attaches to a blade. A fully sailed rotor is the Improved Windmill.
The speed maths is simple and worth internalising:
- A bare windmill runs at a 0.5 speed modifier
- Each sail adds 0.125
- Eight sails bring it to 1.5
That is a three-fold increase from sails alone, for forty tough fabric. Nothing else you do to a windmill comes close to that return.
Clearance matters more than height
The windmill checks the space its blades sweep through - roughly four blocks in every direction around the rotor, in the plane it faces - and it turns faster the more of that circle is empty. A rotor jammed against a hillside, a roof, or its own support tower is throttled by its own obstructions.
Practical consequences:
- Mount the rotor on a thin tower, not against a wall. The support should be behind the windmill, on the axis, not beside the blades.
- Leave a clear disc about nine blocks across in the plane the blades turn in.
- Do not build a decorative housing around it. Every block in the swept area costs you speed.
The biome also applies a modifier, so identical windmills in different biomes will not produce identical output.
Getting Flux out
The rotation feeds whatever rotation acceptor sits behind the windmill, and in practice that is a Kinetic Dynamo. The dynamo has its own output multiplier, which is then scaled by the rotation modifier of the attached water wheel or windmill. This is why the sail count is so decisive: it is not a small bonus on the end of the chain, it is a multiplier applied to the whole thing.
Connect a wire connector to the dynamo and run the power wherever you need it. A windmill is a constant, weather-independent generator, which makes it the cleanest early answer to keeping a Garden Cloche bank or a Crusher running overnight.
The water alternative
If your base is on a river rather than a hilltop, the Watermill is the same idea with a different rotor: four 
Waterwheel Segment around a 
Steel Ingot. It feeds the same Kinetic Dynamo and follows the same rule about keeping its swept area clear. Which one you build should come down to terrain, not to output - a fully sailed windmill in open air is a serious generator.
A checklist for a working setup
- Rotor placed on a slim tower with nine blocks of clear air in the blade plane
- All eight Windmill Sail fitted by right-clicking the placed rotor
- Kinetic Dynamo directly behind the rotor on the axis
- Wire connector on the dynamo, running to your machines
Miss the sails and you are running at a third of the output for the same amount of wood.
Covers the mod's in-game guide topics: