The windmill token, also known as the wind turbine token, allows the player to place a Windmill. Before the full release, you could place as many as you wanted, given you have enough power, this however was changed just before Love was released on the 25th of March 2010.
It is important to note that for a brief period of time at morning and evening, the windmills shut off for about a minute. Don't freak out, they come back on, but if you're counting on them for powering something that must always be on, consider other power sources, or the use of a Power Deposit. When raiding enemy settlements that are powered by windmills, it can be a good idea to wait until dusk or dawn to attack, to take advantage of the brief break in their defences.