Building a windmill involves buying a windmill kit. The windmill will have sails, a shaft on which to affix the sails, a pole to mount them and several electrical devices, and must be carefully situated. These need to be properly affixed and wired so that current is created. The pole must be firmly planted in the ground.
How to build a windmill
The sails are affixed firmly to the shaft, which is itself attached to the top of the pole. Some windmills have a single pole while others come on a small tower. Ensure that the fastenings are firm and tight, so that the sails will not spin off. A dynamo should be firmly affixed to the shaft so that when it rotates and produces electricity. There should also be a tail-fin which makes the windmill rotate into the wind.
Siting the windmill
For maximum effect, the windmill must be located in a place where there is an average wind-speed of 9mph at least and where there are no long windless periods. It must be located with due regard to the safety of inhabitants of the dwelling/site, who might be injured if it collapsed or a blade came off.
Using the electricity
Essential among the parts of a windmill are the batteries. Ideally, there will be 12 batteries linked together so that the maximum power output will be stored. Between the batteries and the windmill will be a transformer. This is necessary because a dynamo produces A.C. [alternating current] which runs back and forth whereas a battery stores D.C. [direct current ] which only runs in one direction. The transformer converts AC to DC.
A cut-off device
You will need sufficient batteries to power your appliances while other ones are being charged. A regulator will be included to control the flow of current. There will be a cut-off device which can switch off the current if the windmill runs too fast, e.g. in a storm, as the current produced at such a high rotation might burn out the batteries. To run standard domestic devices off the batteries, you will need an invertor to take the current back to AC. This may come with the kit.
Safety is important. The windmill must be firmly fixed into the ground and all parts properly affixed, as you do not want it to fall or spin off in high winds. This can cause fatalities or structural damage. The pole must be well-concreted into the ground to the manufacturer's prescribed/specified depth with properly made concrete. All electrical parts must be kept safely under cover in a dry place so that water cannot affect them.