By - Jim Vess

NREL study finds western grid held up as it lost 5.5 gigawatts of generation during solar eclipse

Energize Weekly, June 13, 2018

The western grid solar energy output dropped by nearly 5.5 gigawatts (GW) during last August’s solar eclipse, but the loss did not have a great impact on grid operations or costs, according to an analysis by the National Renewable Energy Laboratory (NREL).

“The 2017 total solar eclipse came and went without causing any issues to the operation of the North American electric power system,” the NREL report, Evaluating the Impact and Developing Mitigation Measures for the 2017 Solar Eclipse on Peak Reliability Operations, concluded.

On Aug. 21, 2017, an eclipse totally blocked the sun from Oregon to South Carolina along a 70-mile-wide path, while the rest of the continent experienced reduced sunlight. Even though the eclipse’s peak lasted only a few minutes, along the path, the penumbra lasted a few hours.

The federal Energy Information Administration estimated that more than 21 GW of installed photovoltaic (PV) systems would be affected nationwide.

The estimated installed capacity utility-scale PV in the western region is 15,800 megawatts (MW), and distributed PV, such as rooftop solar, is 9,200 MW.

NREL researchers analyzed data from the Western Interconnection, which serve nine western states, from the days immediately preceding and following the eclipse, focusing on load and generation statistics.

The peak loss of the event was estimated at about 5.5 GW, with utility-scale system losing about 4 GW and distributed systems accounting for the rest.

The California Independent System Operator (CAISO) had predicted that it would be affected by a partial eclipse between 9:02 a.m. and 11:54 p.m. Pacific Daylight Time, obscuring 62 percent to 76 percent of the sun from Southern California to Northern California, respectively.

Initial estimates showed that at the peak of the eclipse, utility-scale solar production within CAISO would be reduced from an estimated 8,754 MW to 3,143 MW before returning to 9,046 MW.

The NREL analysis found that “the loss of PV generation can be easily compensated by the existing generation fleet, with the natural gas fleet picking up the majority of the slack because of its flexibility. The change in production costs were minimal.”

The third part of the analysis consisted simulations to assess the stability and reliability of grid operations. The analysis identified no reliability concerns, even for large system disturbance events.

“The focus of this study is to develop the framework and the tools for understanding the impact of a wide-area phenomena like a storm, or even another eclipse, on PV output and grid reliability,” Santosh Veda, a research engineer at NREL and co-author of the report, said in a statement. “These tools will become increasingly important as the PV penetration continues to grow so we can plan to reduce the effects of these events on the grid.”

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