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EIA: Aug. 21 eclipse expected to affect solar units, but not reliability

From the August 8, 2017 issue of Public Power Daily

Originally published August 7, 2017

By Jeannine Anderson
News Editor

On Aug. 21, a solar eclipse will block the sunlight needed to generate electricity at about 1,900 utility-scale solar photovoltaic power plants in the United States, but the North American Electric Reliability Corporation, or NERC, does not expect the rare event to create reliability issues for the bulk power system, the Energy Information Administration said Aug. 7. Separately, one of the nation’s largest electricity generators — the Tennessee Valley Authority — said it is ready for the Aug. 21 eclipse. The California Independent System Operator also said it is prepared for the eclipse.

According to NASA, this is the first time since 1918 that a total solar eclipse will traverse the whole country, from coast to coast.

Relatively little solar PV capacity lies in the “path of totality” — where the sun will be completely obscured by the moon, the EIA said in its Aug. 7 Today in Energy report.

“Solar-powered generators centered in the path of totality will be affected the most, as the moon will block all direct sunlight for up to three minutes,” said the EIA, which is part of the Department of Energy. “These generators will also be affected to a lesser extent throughout the entire eclipse event, which will last for up to three hours, measured from the onset to the ending of any blockage of direct sunlight.”

Generators outside of the path of totality will be affected to a lesser extent, depending on how much sunlight is cut off by the moon. The path of totality will span the United States, starting in Oregon and moving eastward to South Carolina over the course of approximately 90 minutes.

The path of totality will affect only 17 utility-scale solar PV generators, mostly in eastern Oregon, the EIA said. Hundreds of plants totaling about 4.0 gigawatts of capacity — mostly in North Carolina and Georgia — “will be at least 90 percent obscured,” the EIA said. “Another 2.2 GW and 3.9 GW of capacity are in areas that will be at least 80 percent and at least 70 percent obscured, respectively.”

The EIA’s analysis reflects utility-scale generators of at least one megawatt of capacity and does not include small-scale solar PV systems or utility-scale solar thermal generators. Last year, those smaller generators provided 0.5 percent and 0.1 percent of total U.S. electricity generation, respectively, compared with utility-scale solar PV, which provided 0.8 percent, the agency noted.

During the eclipse, “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,” the EIA explained.

The report added that NERC’s recent 2017 Summer Reliability Assessment does not anticipate any impacts on the reliability of North America’s bulk power system attributable to the eclipse, based on an analysis published in April.

California has 8.8 GW of utility-scale solar

California is not in the path of totality, but the state’s 8.8 GW of utility-scale solar PV make up 40 percent of the country’s total capacity as of May 2017, the EIA pointed out.

Based on the amount of sunlight that will be obscured for each of the state’s generators, the California Independent System Operator estimates that California will experience a reduction in solar generating capacity of almost 4.2 GW during the eclipse. The Aug. 21 event is projected to partially darken the state from 9:02 a.m. to 11:54 a.m. local time.

To ensure electricity demand is met during those hours, “CAISO plans to replace solar generation with electricity from natural gas and hydropower plants, the latter of which are generating at higher levels than previous years,” the EIA said.

North Carolina has 2.8 GW utility-scale PV

North Carolina has the greatest amount of installed photovoltaic capacity in the band that will be at least 90 percent obscured, the EIA said. As of May, the state had a total of 2.8 GW of utility-scale PV installations, or about 13 percent of the national total.

Duke Energy, one of North Carolina’s largest utilities, has estimated that solar energy output across its system “will drop from about 2.5 GW to 0.2 GW at the height of the eclipse,” the EIA said in its Aug. 7 report. However, solar power “makes up a much smaller portion of North Carolina’s generation compared with California,” the agency said.

In August 2016, utility-scale PV, utility-scale solar thermal, and distributed PV supplied 3.1 percent of North Carolina’s electricity generation, compared with 14 percent in California.

TVA says it is ready for this unusual event

Meanwhile, one of the nation’s largest electricity generators — the Tennessee Valley Authority — said it has been preparing for the eclipse.

“With the Great American Eclipse ready to darken the sky on Aug. 21, the 9 million people of the Tennessee Valley are wondering: ‘Is TVA ready?’” TVA said in an Aug. 1 update on its website. The answer is yes, the utility said.

Patrick Walshe, TVA operations and analysis manager, said the utility has been getting ready for this event for months. “We are absolutely ready because we’ve been preparing for this eclipse like a major storm or temperature event that could affect our ability to keep electricity flowing to our consumers,” he said.

For those in TVA’s large service territory, electricity shouldn’t be a concern, Walshe said, because TVA has conducted proactive maintenance, reviewed processes and procedures with employees, and closely coordinated with other nearby utilities to mitigate any negative impacts the eclipse may have on the power grid.

Walshe encouraged residents of the Tennessee Valley to take advantage of this rare opportunity — the first solar eclipse to cross the U.S. coast to coast in nearly a century. Nashville is the largest city in the Valley to lie wholly within the path of totality, and numerous others are within a short drive, TVA said.

TVA added that it monitors the power grid 24/7 from its command center in Chattanooga, Tenn., and will have extra staff on hand during the eclipse. 

The total solar eclipse “begins near Lincoln City, Oregon, at 10:15 a.m. PDT (1:15 p.m. EDT),” NASA said on its website.

“Totality ends at 2:48 p.m. EDT near Charleston, South Carolina. The partial eclipse will start earlier and end later, but the total eclipse itself will take about one hour and 40 minutes to cross the country.”

California ISO expects network to be reliable during eclipse

The California Independent System Operator — one of the nation’s most solar-connected electrical grids — said Aug. 7 that it is prepared for the Aug. 21 eclipse. The ISO expects sufficient energy supplies and network reliability during the event.

California has among the most ambitious renewable energy goals in the nation, including reaching 33 percent renewable energy by 2020, and 50 percent by 2030. Currently, the CAISO’s solar generation capacity is nearly 10,000 MW, and can serve up to 40 percent of load some days, the ISO said in an Aug. 7 news release.

“I am confident in the technology of our market and grid,” said ISO President and CEO Steve Berberich. “Our team is committed to keeping the power flowing for Californians, as we navigate the unusual circumstances presented by the eclipse.”

Nancy Traweek, the CAISO’s executive director of system operations, said the ISO will use lessons learned from this eclipse to prepare for the next North American solar eclipse, which will occur in 2024.

The eclipse will affect the ISO’s balancing area and energy imbalance market (EIM) participants from about 9 a.m. to noon, reducing solar output from both utility-scale generation connected to the grid, and from rooftop solar installations that serve homes and businesses, the ISO said. As solar power production declines that morning, the ISO forecasts it will need to dispatch about 6,000 megawatts of power from alternative sources.

The ISO said that it, along with state energy leaders, the California Public Utilities Commission and California utilities, have been planning for the loss of solar generation during the eclipse for more than a year. Preparation has centered on analyzing the likely loss of solar energy and arranging procurement of additional reserves and system resources, primarily from flexible ramping sources such as hydropower and natural gas-fired power plants.

The CAISO has created a new webpage dedicated to the eclipse and said that viewers will be able to use it to track the ramp down and ramp up of solar production, along with the current and net energy demand in real time.



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