Utility-scale solar photovoltaic (PV) power plants in the U.S. operated on average at roughly 25% of their electricity generating capacity, based on an average of annual values, from 2014 through 2017, Kallanish Energy reports.
Known as a plantâ€™s capacity factor, this percentage is based on the plantâ€™s power generation as a percentage of its summer capacity value for plants with a full-year of operation, as expressed in terms of alternating current (AC) power, according to the Energy Information Administration.
States in the Southwest U.S. tend to have better solar resources, and higher capacity factors, than those in the Southeast or Northeast.
Arizonaâ€™s utility-scale solar PV plants performed better than those in any other state, achieving a 29.1% capacity factor from 2014 through 2017, EIA reported. Arizonaâ€™s installed utility-scale solar PV capacity was 1,700 megawatts (MW) at the end of 2017, roughly 7% of the national total.
Utahâ€™s 900 MW of solar PV plants ranked second, with a 29.0% capacity factor. Californiaâ€™s utility-scale solar PV plants, totaling 9,400 MW, or 37% of the national total, ranked third with an average capacity factor of 28.4%.
By comparison, states in the Southeast, such as Georgia and North Carolina, had substantially lower PV capacity factors than southwestern states at similar latitudes. States in the Northeast, such as New Jersey and Massachusetts, had even lower capacity factors.
Three main factors largely determine a solar PV power plantâ€™s capacity factor: resource quality, tracking capabilities, and inverter-sizing considerations.
Sunnier locations, such as in the southwestern United States,Â have more hours of direct, high-angle sunlight per year and, as a result, the solar PV modules can capture more sunlight, according to EIA.
TheÂ addition of equipment to track the sunâ€™s angle, either within a day (single-axis tracking) or across seasons (dual-axis tracking), further helps to maximize energy input into the PV system.
LargerÂ inverters, which convert the direct current produced by solar PV panels to grid-ready AC power, can also help to increase the total output of a system, according to EIA.