How The Solar Eclipse Will Impact California Utilities

California is home to 40% of the nation’s solar PV systems. Here’s how utilities there are preparing for the solar eclipse that will reduce output across the state by 6 gigawatts.

The Impact On California

According to the Energy Information Administration (EIA), California is home to about 40% of the nation’s utility-scale solar PV systems. As a result, it will be the state that is most impacted, by far, as a consequence of the eclipse. The state will have 8.8¬†gigawatts (GW) of affected utility-scale solar power. In comparison, North Carolina will be the second-most-affected state with an impact on only 2.8 GW of solar power.

The California ISO estimates that 4.2 GW of utility-scale solar PV will be lost during the eclipse, and an additional 1.4 GW will be lost from residential solar systems. An expected net load of 6.0 GW will need to be replaced during the eclipse.

Lessons From Germany

In preparation for the eclipse,¬†the California ISO studied the grid impacts of a total eclipse in Europe in 2015. Germany was in a similar situation to California in that it was home to half of Europe’s solar PV at the time of the eclipse.

One of the main conclusions was of the importance of excess available power supplies because the ramp will be much steeper than what is typically required. The California ISO notes:

“As the eclipse begins its path across the sun, the decrease in production will be about 70 megawatts (MW) a minute, and the ramp up is expected to be about 90 to 100 MW per minute as the sun begins to reappear. A typical average ramp-up rate is around 29 MW per minute during the 9 a.m. to noon time period.”

Germany successfully managed the eclipse by having excess dispatchable power — mostly from hydropower and natural gas — standing by during the event. These sources were rapidly ramped up and down as the eclipse began and after it ended.

How Much Residential Solar?

One of the biggest unknowns as California prepares for the eclipse is just how much residential solar PV is installed. There are estimates, but the eclipse will provide a data point as utilities are called upon to respond to the loss of power by these residential systems. This information will help utilities manage requirements under California’s Renewables Portfolio Standard (RPS), and it will help utilities and grid operators better model the impact of intermittency at varying solar PV penetration levels.

California will likely manage this event without any major issues. The event will probably be navigated as smoothly as the Y2K transition. But should the event be handled without a hitch, it is a testament to the planning the went into preparing for it.

Finally, utility-scale storage solutions such as batteries may eventually render such intermittent events a concern of the past, but at least today it’s a reminder of the need to maintain sufficient backup power supplies — even in the case of a perhaps once-in-a-lifetime event.

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