California ISO preps solar-heavy grid for total eclipse this summer

Dive Brief:

The California ISO is marshaling its resources in preparation for a solar eclipse on Aug. 21, 2017.
By the date of the eclipse, the ISO expects to have nearly 10,000 MW of grid-connected solar capacity on its system. The operator estimates that at the peak of the eclipse projected output of 8,754 MW will be reduced to 3,134 MW and then return to 9,046 MW when the eclipse passes.
With the mitigation measures, such as increased procurement of regulation service, both up and down, CAISO expects no interruption to reliability service, despite the burden the eclipse will put on dispatchable resources.

Dive Insight:

California’s infamous duck curve will go into overdrive in August when a solar eclipse casts a shadow over the Pacific Northwest.

The partial eclipse will occur between 9:02 am and 11:54 am and will obscure the sun by 76% in Northern California and by 62% in Southern California.

The amount of solar power on California’s grid has grown so large that the eclipse will interrupt the normal morning power ramp up at the start of the eclipse and be followed by a greatly accentuated ramp up from 10:22 a.m. to noon as the moon moves past the sun.

Overall, CAISO expects to see a 4,194 MW reduction in solar generation during the 82 minute duration of the eclipse, which is a ramp down rate of 70 MW/minute. As the eclipse wanes the ramp up will be 98 MW/min. The estimated ramp rate for a clear day at that time of year would be 12.6 MW/min.

Assuming the sky is clear, CAISO expects to see a 1,365 MW increase in load as a result of obscured residential solar panels. The operator estimates there will be about 5,800 MW of rooftop solar installed by the mid-August. 35% percent of the rooftop solar is C&I installations.

The ISO expects to buy more regulation service and more flexible ramp services during the eclipse. And, among other measures, is asking that gas-fired generators ensure that they contract for sufficient fuel supplies in advance of the eclipse.

While CAISO says the eclipse will be a first for it, the agency noted that the European grid experienced its first near total eclipse in March 2015 when it had nearly 90 GW of solar power on its system, and was able to maintain reliability throughout the duration of the three-hour eclipse.