Southwestern U.S. solar resource leads to top performance for PV solar installations

Energize Weekly, June 19, 2019

Some of the most robust state solar energy plans are in states such as Massachusetts and New Jersey, but the most robust solar resource is, perhaps not surprisingly, the Southwest based on performance analysis by the federal Energy Information Administration (EIA).

In the analysis of photovoltaic (PV) solar generating capacity factors – the percentage of nameplate capacity actually used – Western states posted the highest values. Because of the intermittency of wind and solar, only a fraction of the nameplate capacity gets used.

The capacity factor for wind generation varies by season, but on average, it was around 40 percent in 2018, according to the EIA.

The average annual capacity factor for PV power plants in the U.S. was about 25 percent from 2014 through 2017. It was calculated based on summer performance for plants with a full year of operation. New Jersey had a 16.8 percent capacity factor, and Massachusetts had a 16.5 percent capacity factor.

The Western states, however, outperformed the national average by far. Arizona, which had 1.7 gigawatts (GW) of solar PV by 2017, equal to 7 percent of the U.S. total capacity, was the top performing state with an average capacity factor of 29.1 percent.

Utah, with 900 megawatts of installed solar, was second with a capacity factor of 29 percent.

California – the largest market for solar PV in the country with 9.4 GW installed by 2017, about 37 percent of the U.S. total – had a capacity factor of 28.4 percent for the 2014-2017 period, putting it in third place.

Nevada with 1.7 GW of installed solar capacity and a capacity factor of 27.8 percent was fourth.

By way of comparison, Southeast states such North Carolina, with 3.4 GW of solar installations and Georgia with 1 GW of PV capacity were below the national average. North Carolina’s capacity was 21 percent and Georgia’s 23.3 percent.

Texas, which had 1.7 GW of capacity in 2017 and is also moving to add more solar capacity, had a capacity factor of 24.6 percent.

“Three main factors largely determine a solar PV power plant’s capacity factor: resource quality, tracking capabilities, and inverter-sizing considerations,” the EIA said. “Sunnier locations, such as in the southwestern United States has more hours of direct, high-angle sunlight per year and, as a result, the solar PV modules can capture more sunlight.”

The agency said that larger 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.

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