The PJM Interconnection recorded a drop of approximately 520 megawatts of wholesale solar generation from before the Aug. 21 eclipse until the peak of the eclipse, the mid-Atlantic grid operator recently reported.
In addition, PJM also estimated that electricity from behind-the-meter solar generation -- mostly rooftop solar panels that offset load -- decreased by approximately 1,700 MW, it said in an Aug. 22 post on its website.
PJM said that it expected a reduction in power from rooftop panels to result in an increase in electric demand on the grid. “However, because of a variety of potential factors, including reduced air conditioning, increased cloud cover and changes in human behavior related to the event, PJM recorded a net decrease in demand for electricity of about 5,000 MW throughout the eclipse,” the grid operator reported.
The PJM footprint experienced an average temperature decrease of about 2 degrees Fahrenheit through the duration of the eclipse. The Chicago area also experienced storms after the eclipse’s onset, the grid operator noted.
PJM said it will continue to study the impact of the solar eclipse on its system. It intends to integrate lessons learned from the Aug. 21 event into preparing for the next solar eclipse, predicted to occur in 2024, when the PJM grid is expected to have more solar generation. Solar generation currently comprises less than 1 percent of PJM’s 185,000 MW of generation capacity.
PJM said it will present a more detailed analysis of the Aug. 21 solar eclipse at its next operating committee meeting Sept. 12.
PJM’s operating committee reviews system operations from season to season, identifying emerging demand, supply and operating issues.
EIA report on CAISO and eclipse
Meanwhile, the Energy Information Administration on Aug. 24 released a “Today in Energy” report that said that during the solar eclipse that passed across the continental U.S. on Aug. 21, solar output on the California Independent System Operator electric system dropped while the sun was partially obscured.
“Much of the decrease in solar output was made up by increased electricity imports and increased generation from thermal units, most of which is fueled by natural gas,” the EIA noted.
The EIA said that although California was not in the path of totality during the eclipse, meaning the sun was not completely obscured, California contains 43% of the national total for utility-scale solar and 40% of small-scale solar (as of May, 2017). “Much of the state’s solar capacity is located in areas where sunlight was obscured by as much as 60%–70% during the eclipse,” the federal agency said.
Based on an average of the previous five weekdays, CAISO’s solar power output typically increases to about 9.1 gigawatts between 10:00 a.m. and 11:00 a.m. Pacific Time, or to roughly 31% of total load. On August 21, as the moon partially obscured sunlight, CAISO’s solar power output fell to a low of 3.6 GW for that hour, about 60% lower than normal, according to the EIA.
CAISO worked with EIM participants, gas generators
The EIA said that CAISO worked with other participants in the Western Energy Imbalance Market to include the impact of the eclipse in their forecasts so that planning accurately reflected available electricity supply. Several public power utilities have agreed to join the EIM.
“The EIM allowed for balancing across much of the Western Interconnect as the eclipse moved across the region and affected solar output in different places at different times,” the EIA said.
CAISO also worked with natural gas generators in California to ensure sufficient fuel supplies ahead of the eclipse, it noted.
According to the report, CAISO planned for the rapid reduction and resumption of net load caused by the loss of solar during the eclipse by procuring an additional 100 MW to 150 MW of regulation capacity for the eclipse period.
Regulation capacity is a market-based ancillary service that is used to cover short-term gaps between demand and supply.
Public power entities provided power
The EIA also reported that imports of electricity increased by 2.2 GW during the hour of the eclipse as CAISO drew power from the Los Angeles Department of Water and Power, the Salt River Project Agricultural Improvement and Power District in Arizona, and the Bonneville Power Administration in the Pacific Northwest, among others. LADWP, SRP and BPA are all public power entities.
The full EIA report is available here.
