TVA has nine contracts with nine wind farms for the purchase of 1,542 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 September 2010, EDP Renewables North America LLC began supplying 115 megawatts from its Pioneer Prairie Wind Farm in Howard and Mitchell counties in Iowa. Beginning in January 2012, an additional 83 megawatts was being supplied from the same facility. With that, TVA had contracted for all 198 megawatts of the facility's output, generated by 131 Vesta 1.65-megawatt turbines. An additional contract for 101 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, Kan. The power is generated by 111 Vesta turbines.
Invenergy LLC supplies 400 megawatts of wind energy:
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 40 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.