Wind power plants are cheap and perfectly clean, but they generate a very low amount of power. They're great for early or small towns, especially when you're trying to keep the city green.
The biggest problem with wind power plants is physical space. The base plant itself is relatively the same size as the others, but to expand it with additional windmills, you'll be using a lot of physical space. It's up to you as mayor to decide whether you want to eat up the physical space for the sake of no pollution.
The other issue with power plants is the qualification to a wind power plant's output, specifically the wind speed. When you first place a wind power plant, you'll see how fast the winds are in your town. The lower altitude, the slower the winds, and the less power you'll output. At sea level, you'll often see less than the 10 mph winds you need for 3 MW. High altitudes can lead to faster winds, but you can offset slow winds with additional windmills. Every module has a fixed MW to wind speed ratio.
It's a viable strategy to start your town with a wind power plant, then destroy it and replace it with something bigger once your funds and power demands are higher.
Each Wind Power Plant can have a maximum of 24 total turbines. Wind power plants lower surrounding land values.