W(watt) ratings very rarely tell you how much power a turbine will produce. Most small turbines are advertised with a given W rating or output. For example, a turbine might be called 500W, 10 kW, 5 kW or 25 kW (1000 w = 1 Kw). The rating describes the rated capacity of the turbine at a particular wind speed. A 10 kW turbine might produce 10 kW at a 40 MPH wind speed. A 25 kW turbine might produce 25 kW at a 36 MPH wind speed. These numbers do not tell you how much power the turbine will produce at the average or more realistic wind speed at your location - or any location for that matter. There are few, if any, locations where small wind turbines will be installed where the average wind speed is 25 or 30 MPH. Most locations where small turbines will be installed have average wind speeds in the 4-10 MPH range.

Two 500 W turbines might also produce completely different power outputs due to the rotor diameter. One has a 4 foot diameter rotor and the other an 8 foot diameter rotor. Both have 500 W generators. The 8 foot turbine has twice the swept area of the 10 foot turbine. It will therefore produce twice the power of the smaller rotor turbine. The 500 W rating tells the prospective customer nothing about the turbine's capacity to produce electrical power.

Another factor to consider is what is considered a “Small” turbine. Most small turbines are anything but “Small” and require large mounting supports 20’ to 30’ high and could boast 10’ to 14’ diameter rotors. The start up speed for these units might be significantly above your average wind speed in your installation area.

Unfortunately, Watts is a key word in marketing a wind turbine to the general market. Some states and funding agencies require these ambiguous ratings. This only encourages manufacturers to attach large (less efficient) generators to small diameter rotors in order to secure a market and funding advantage. This practice both unfairly prejudices a particular turbine but misleads the consumer to spend more money on the wrong product for their needs.