Small wind turbines – When thinking of wind turbines one is often perplexed when trying to imagine how big they are. Perhaps one has seen a wind pump on a farm, so one has the idea that a standard wind turbine might be about 30 to 50 feet high.The short answer is that there is no longer any standard size for a wind turbine. The large ones used by the utility companies to generate power are truly enormous. Their rotor diameters can range from about 150 feet to about 500 feet, and the towers can be roughly the same size.
The most advanced types can produce about 5 MW (megawatts) of power.
A 5MW turbine can produce more than 15 million kWh in a year – enough to power more than 1, 400 households. The average U.S. household consumes about 10,000 kWh of electricity each year. Small wind turbines can indeed be very small. Some of them produce a mere 250 watts.
Wind speed is a crucial factor when estimating the turbine performance and this is usually done prior to construction. Generally an annual average wind speed greater than 9 mph is required for small wind turbines that are going to be used for electricity.
Small wind turbines capable of 10 kW are being used very successfully to produce enough electricity for individual homes and schools
A small wind turbine of this size can easily produce the 10 000 kWh required for the average home. An interesting example of wind power as used at a school is the 250 kW turbine installed at the elementary school in Spirit Lake, Iowa. This single turbine provides an average of 350,000 kWh of electricity per year, more than is necessary for the 53,000-square-foot school. Surplus electricity is fed into the local utility system and it is not unusual for the school to earn $5 000 a year in electricity sales! The school uses electricity from the utility at times when the wind does not blow. More info here