July | August 2017







Solar Eclipse Puts a Spotlight on Solar’s Increasing Role in Energy Production

By Devashree Saha, CSG director of energy and environmental policy
The Aug. 21 solar eclipse, during which the moon will pass between the earth and the sun, will throw a wide swath of the United States into darkness. While the moon will at least partially block the sun for the entire nation, a path of totality or complete obscuration, will touch 14 states from Oregon to South Carolina.
The solar eclipse is expected to cause numerous disruptions, with heavy traffic delays and strained cellphone networks. However, there is another disruption that will be brought on by the eclipse: power.
Since the last total eclipse in mainland United States on Feb. 26, 1979, the country has grown more dependent on solar for energy generation. Even though solar accounts for less than 1 percent of the nation’s net electricity generation, it has witnessed tremendous growth, albeit from a small base. According to the Solar Energy Industries Association, solar has experienced an average annual growth rate of 68 percent in the last decade and about 260,000 Americans are employed in the industry. In 2016, for the first time ever, solar ranked as the No. 1 source of new electric generating capacity additions on an annual basis. These numbers attest to solar’s ever-increasing role in U.S. energy production as well as economic development.
Among states, nearly 10 percent of California’s generation comes from solar, representing 50 percent of solar production nationwide. Other states where solar is becoming increasingly important include Nevada (6 percent share of state’s net electricity generation in 2016), Vermont (4 percent), Arizona (3.5 percent) and North Carolina (3 percent). In addition, the amount of solar used can vary significantly by time of year. For three hours on March 11 this year, solar accounted for 50 percent of electricity used in California.
As state policymakers, utilities and the solar industry continue to figure out how to mesh solar resources, which are variable throughout the day, with an electric grid that wasn’t designed with solar in mind, the eclipse will be a test case to see how grid operators responsible for keeping electricity supply and demand in balance handle the change in resources.
The total eclipse will first be visible in Oregon and then travel on a diagonal path toward South Carolina in the course of about 90 minutes. According to the U.S. Energy Information Administration, approximately 1,900 utility-scale solar photovoltaic, or PV, power plants in the country, generating more than 20,000 megawatts of energy at peak generation, are likely to lose some of their sunlight for several hours through the course of the day. However, relatively little solar PV capacity lies in the path of totality.
Totality will affect 17 utility-scale solar PV generators in Oregon. Hundreds of plants totaling about 4 gigawatts, or GW, of capacity, mostly in North Carolina and Georgia, will be at least 90 percent obscured. Another 2.2 GW and 3.9 GW of capacity will be affected in areas to be at least 80 percent and 70 percent obscured respectively. Electricity generators in the areas affected by the eclipse will have to increase output from other sources of electricity generation to supplement the decrease in solar power.
Grid operators have been preparing for this event for months. The North American Electric Reliability Corporation, or NERC, anticipates no threats to grid reliability through the course of the eclipse. Still, the eclipse will test the reliability of solar generation on a national scale.
California, whose 8.8 GW of utility-scale solar PV accounts for 40 percent of the country’s total capacity, could perhaps face the greatest challenge. The California Independent System Operator, or CAISO, which manages 80 percent of California’s electric flow, estimates that the state will experience a reduction in solar generating capacity of almost 4.2 GW during the eclipse. From about 9 a.m. to noon Pacific time, CAISO is prepared to call on hydropower and natural gas plants to fill the demand gap.  CAISO has also reached out to German grid operators to learn any lessons they may have picked up from their experience with a 2015 European eclipse when 80 percent of Germany’s sunlight was cut off. Germany, whose electricity is 40 percent powered by solar, stabilized its grid by dialing up its fossil fuel, nuclear and hydro power.
“The eclipse presents some grid management challenges for California and the West,” Nancy Traweek, CAISO’s executive director of systems operations, said in a statement. “However, with detailed planning and engagement among all parties we are expecting no shortage of electricity or reliability incidents related to the eclipse.”
The eclipse will have a major impact on solar electricity production in North Carolina too. Duke Energy, one of the largest utilities in North Carolina, estimates that solar energy output across their system will drop from about 2.5 GW to 0.2 GW at the height of the eclipse. In a blog post, Duke Energy said that “operators will have natural gas plants ready to step in during the eclipse. In addition to replacing the lost energy with a flexible fuel source, operators can gradually decrease solar production before the sky darkens depending on weather conditions.”
The next solar eclipse in North America will occur in 2024. By that time, there is likely to be lot more solar on the grid. In that sense, the Aug. 21 solar eclipse is going to provide a better understanding of how the grid has to change to accommodate the variability and intermittencies of solar power.