Most sun-tracking solar arrays are west of Mississippi River

More than 50% of U.S. solar plants use technology that tracks the path of the sun, and the majority of plants with these systems are in the Southwest, according to the U.S. Energy Information Administration.

Solar plants with these systems track the sun along one or two axis points. In states west of the Mississippi River, 56% of total solar capacity comprised of plants with a single-axis system. Plants with fixed-tilt arrays, which don’t track the sun, accounted for 37%, or 3,904 megawatts, of solar capacity in the western United States.

But in the eastern United States, plants with fixed-tilt arrays accounted for 80% or 2,468 megawatts of solar capacity. “Because of the cost of solar-tracking units and the differences in weather and (exposure to the sun) across the United States, solar-tracking units may not be the most economic choice for producers in some regions,” according to the EIA.

States east of the Mississippi River have more average cloud cover annually than the western United States. “As a result, the east receives higher proportions of diffuse radiation, reducing the benefits of tracking technologies and leading to a higher percentage of fixed-tilt solar panels,” according to the EIA. But the west receives more direct sunlight, allowing for arrays with the tracking technology to capture more direct radiation than a fixed-tilt array.

In Los Angeles, “a single-axis tracking system will produce 21% more electricity than a system titled at a fixed 20 degrees,” according to the PVWatts calculator developed by the National Renewable Energy Laboratory. “A dual-axis tracking system in the same location would produce 31% more than the fixed-tilt system.”

Between the end of 2015 and January 2017, 6.5 gigawatts of solar capacity has been added in the United States.