By - Jim Vess

Western utilities get ready for a solar power blackout during coming total eclipse

Energize Weekly, August 8, 2017

The total solar eclipse set to sweep across the sky on Aug. 21 is going to knock out power from photovoltaic solar panels, and nowhere will the darkness have more impact than in the West.

The eclipse will cast a 70-mile-wide shadow across the country affecting solar arrays from Oregon to South Carolina, briefly turning off more than 9,000 megawatts (MW) of generation—with nearly three-quarters of the losses coming in western states. It is the first nationwide total eclipse since 1918.

Facing the solar blackout, western utilities, wholesale power market managers and the regional reliability coordinator have been readying to meet the power loss.

“We had meetings with generators to be sure there are reserves,” said Brett Wangen, director of engineering at Peak Reliability, the regional reliability coordinator. “There has been a lot of coordination going on above what we normally do.”

The West is the most heavily solar-paneled section of the country with about 25,000 MW of arrays in 2016, according the Solar Energy Industries Association. Four of the top six states for solar—California, Arizona, Nevada and Utah—are in the region. The two other top states are North Carolina and New Jersey.

The planning has focused on the top four solar producers, Arizona Public Service Electric Co., PacifiCorp, the California Independent System Operator (CAISO), and the Los Angeles Department of Water and Power (LADWP), Wangen said.

The biggest impact is set to be felt in California, which on some days gets as much as 40 percent of its electricity from solar panels.

“We’ve been preparing for several months, and the best tool in our toolbox has been pre-planning, talking to all the market participants”—utilities, independent power producers, natural gas suppliers, said Steven Greenlee, a spokesman for CAISO, the wholesale power marketer serving 80 percent of the state.

CAISO is expecting the loss of 4,194 MW of utility-scale solar (there is a total of 10,000 MW of utility-scale facilities on the system) and the loss of 1,365 MW of rooftop solar. When some other elements are added in, the total generation gap from the eclipse will be 6,008 MW, Greenlee said.

The eclipse will affect operations from 9 a.m. to noon Pacific Time. The biggest gap will be between 9:30 a.m. and 11:30 a.m., Greenlee said.

LADWP is forecasting a loss of 466 MW of utility-scale solar in the Mojave Desert and 139 MW of rooftop solar between 9:05 a.m. and 11:50 a.m.

“At this time of day, solar is typically ramping up and has not yet reached full capacity,” the department said in a statement. “At about 10:25 a.m., solar production will begin ramping back up and by 11:50 a.m., solar is expected to reach its normal capacity of 941.5 MW. During a typical day in August, solar energy serves as much as 30 to 40 percent of LADWP’s customer load.

“LADWP routinely schedules power generation from a variety of energy resources to accommodate scheduled outages for maintenance, or adjust to fluctuations in solar and wind power,” the department said. “Just as we schedule power generation every day to meet our customers’ needs, LADWP power operators have planned for the dip in solar energy due to the forecasted solar eclipse.”

It isn’t just the loss of power, but the ramping down and ramping back up of the power that will be a challenge.

“CAISO is used to losing solar,” Greenlee said. “It’s now the monsoon season and we can see a drop of 800 MW to 1,200 MW within minutes. The difference with the eclipse is the magnitude.”

The ramp rate will drop off at 70 MW per minute and return at 90 MW per minute, Greenlee said. That compares with a normal ramp rate 29 MW per minute.

“Two weeks out, we will really look at the system,” Wangen said. “Then there is a day-ahead review.” This is done every day by Peak, although there will be added attention to the single, big event they will be facing. The system is ready to “mitigate potential problems real time,” Wangen said.

Peak’s tracking will start in San Francisco and move across Los Angeles, Phoenix and Salt Lake City. The western mountain states will see less impact, Wangen said.

Other regions will also be affected by the eclipse. The PJM Interconnection LLC, the transmission operator covering eastern mid-Atlantic and Midwestern states, estimates that the eclipse could hit 2,500 MW of solar between 1:30 p.m. and 3:40 p.m.  New Jersey and part of North Carolina are in the PJM.

“Certainly, this is an unusual solar event, but as far as potential impacts to the grid, PJM and its members are prepared,” PJM President and CEO Andrew L. Ott said in a statement. “While this is an anticipated event, we routinely plan and prepare for unpredictable events or things that can’t be forecast far in advance, such as severe storms and heat waves.”

The next total solar eclipse in the U.S. will be in April 2024.

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