By Robert Mullin

CAISO is nailing down its final preparations for the Aug. 21 solar eclipse, which is expected to take about 5,600 MW of utility-scale and rooftop solar generation off the California grid during morning hours when those resources would typically be ramping up output.

Still, the grid operator expressed confidence in its ability to avoid service outages stemming from the event, despite having to support an upward ramp of about 70 MW/minute heading into the eclipse and a downward ramp of 90 to 100 MW/minute coming out.

“We will ramp up generation to compensate for lost solar production, and there is plenty of capacity to meet need,” the ISO said in a FAQ published on its website. “It is not unusual for the ISO grid operators to manage ramps this large on certain days.”

CAISO currently has about 10,000 MW of utility-scale solar interconnected into its system, and its typical morning ramps average about 29 MW/minute.

The extra capacity will mostly come from traditional generating resources. (See CAISO Solar Eclipse Prep Relies on Conventional Mix.) With California’s water levels still relatively high after a wet winter, CAISO expects to have access to about 6,000 MW of flexible hydroelectric capacity in mid-August. The ISO has also been working with gas pipeline companies, utilities and generators to procure additional reserve and regulation capacity, both of which will be needed to grapple with the potential for oversupply and frequency regulation issues after the eclipse, as solar rapidly ramps up its output.

Tasks Completed

Begun last year, CAISO’s preparations for the eclipse have been extensive.

The ISO said it has consulted with the forecasting team that helped grid operators in Europe prepare for a 2015 eclipse, which especially affected Germany’s 40 GW of installed solar capacity. The ISO has developed its own event-day forecast using Aug. 22, 2016 — also a Monday — as the basis for projecting expected demand the morning of the eclipse. The ISO’s model assumes full sun, no “extraordinary” conservation measures and higher obscuration rates (representing the proportion of the sun obscured by the moon) in Northern California, along with a corresponding loss with rooftop solar output there.

The ISO has also completed a market simulation for the day of the eclipse and conducted “tabletop exercises” and training for real-time grid operators. It has also refined its renewable forecasts — in part by comparing them with third-party forecasts — and coordinated with natural gas companies to plan for increased output from gas-fired power plants.

The grid operator is also working with Western Energy Imbalance Market (EIM) participants to “incorporate eclipse impacts in their power schedules, maintain full operational energy transfers, and collaborate on forecasting.” CAISO expects the eclipse to have some impact on 1,700 to 2,000 MW of solar generation in neighboring EIM areas.

Still to Come

A week ahead of the eclipse, CAISO plans to “refine” its resource and load forecasts and update market participants about any changes to its reserve needs. Two days before the event, it will hold a conference call with market participants “to facilitate coordination and transparency,” the FAQ said.

Finally, on the morning of the eclipse, the ISO will ensure that its real-time forecasts are transferred into the ISO system in order to prepare generation and optimize the transmission network.

And while the ISO is not expecting the need for conservation measures, it did encourage electricity consumers to keep those measures in mind on the day of the eclipse.

“The ISO predicts the typical consumer will not notice the grid management challenges and balancing strategies,” CAISO said. “However, energy efficiency is always helpful to curb spikes in need for power and to lower consumer electricity bills during times of high demand.”