A wind farm is a large array of wind turbines designed for providing wholesale bulk electricity to utilities or an electricity market. This differs from a single or small handful of windmills typically setup to serve an individual or small enterprise.
Wind farms are usually owned by independent power producers which traditionally have sold their electricity to or by electric utilities. These facilities are grid-connected, meaning they are interconnected to the nationwide electricity transmission system. Wind farms vary in generating capacity from five to several hundred megawatts and may consist of wind turbines of the same or different models. The turbines are mounted on towers and often placed in arrays or clusters along ridge tops.
The wind turbine is the most prominent feature of the wind energy project. Other components may include anemometers (wind measuring equipment), an electrical power collection and transmission system (transformers, substation, and overhead or underground lines), control and maintenance facilities, and site access and service roads.
Wind turbines capture the energy of the wind and convert it into electricity. The primary components are the rotor, electrical generator and tower. As the wind blows, it turns the rotor, which in turn drives the generator and creates electricity. Upwind blades have the rotor facing into the wind, positioned correctly by a motor on top of the tower. Downwind turbines have the blades behind the tower, facing away from the wind, and are swung about by the same wind which drives the rotor.
The nacelle, mounted on top of the tower, houses the turbine's electrical generator. A generator's rating (in kilowatts or megawatts) measures its potential output. Its actual output is dependent on the speed, strength and constancy of wind in the chosen location. The amount of power in the wind is a cubic function of wind speed; thus wind turbines produce an exponentially increasing amount of power as wind speeds increase.
A wind turbine's blades typically begin spinning as the wind reaches 7mph. At 9 to 10mph, they begin producing electricity. Rated output (the capacity of the generator) is typically reached between 27 and 35mph winds. To avoid damage, most turbines shut down when the wind reaches 55mph. Because wind in many places is intermittant, turbines will seldom operate at their rated power output for long periods of time. Industry averages predict about 30% efficiency overall.
Wind turbines are typically mounted on tubular steel or lattice (open framework) towers. The tower's function is to raise the turbines high enough to intercept stronger winds that provide more energy. The height of the tower will vary depending on the location and elevation of prevailing winds. Towers in Genesee County must be approximately 450 ft to catch viable winds. Tubular towers are mounted on solid concrete footers 8 to 35 feet deep to prevent them being toppled by strong winds. Lattice towers typically use four smaller piers.
Large arrays of wind turbines require an extensive power collection and electric interconnection system. Power generated by each turbine is typically carried by low-voltage underground cables to pad-mounted transformers located throughout the wind farm. There may be one transformer adjacent to each wind turbine. Medium voltage underground cables carry the electricity from each transformer and deliver it to an underground or overhead collection line. Power is then transmitted to the wind farm's substation for further step-up to match the voltage of the line to which it is connected.
An operations control facility maintains two-way communication with each wind turbine. Through the use of integrated computer systems, it is possible for an operations control center to monitor and control wind projects in several locations. It is highly likely that no more than one control center will be constructed within the county.
A large wind project will require a maintenance facility for storing trucks, service equipment, spare parts, lubricants, and other supplies. The maintenance facility may be located on or off site. UPC Wind has an established bank of personnel and rotating truck schedule so that it uses one maintenance team for multiple projects.
There will usually be one or more access roads into a wind project, to be used for maintenance, repair and eventual decommissioning.