TVA has eight contracts with eight wind farms for the purchase of 1,242 megawatts of energy. The majority of the wind contracts are the result of a TVA request for proposals issued in December 2008. The other contracts are as follows:
In November 2011, EDP Renewables North America LLC began supplying 104 megawatts from its Pioneer Prairie Wind Farm in Howard and Mitchell counties in Iowa. An additional contract for 55 megawatts also began delivering energy in January 2012 from the company's Lost Lakes Wind Farm.
In January 2012, ENEL Green Power LLC began supplying 201 megawatts from its Caney River Wind Farm in Elk County, Kansas.
NextEra Energy Resources LLC supplies 315 megawatts of wind energy:
A wind energy system transforms the kinetic energy of the wind into mechanical or electrical energy. The output of a wind turbine depends on the turbine's size and the wind's speed through the rotor. Wind turbines being manufactured today have power ratings from 1 to 3 megawatts. These can be used as a single unit or grouped together to form large-scale wind farms such as the ones with which TVA contracts.
The capacity factor, or productivity, of a wind turbine normally ranges from 25 percent to 50 percent, although higher capacity factors can be achieved during windy periods. The capacity factor is determined by comparing actual production with the amount of power that would have been produced if the turbine were able to operate at maximum output 100 percent of the time.