California’s Solar Power Peak: The Real Story

The California Independent System Operator, which runs the state’s grid, has released a revised graphic for the day the state reached a milestone 1 gigawatt in utility solar power production that clears up confusion about when solar’s contribution to the grid peaked that day.

An earlier graphic had left many media with the impression that solar peaked between 5 and 6 p.m. on Aug. 14, just as millions of Golden State residents were arriving home from work and firing up their air conditioners, popping frozen delectables into the microwave and tuning in Two and a Half Men reruns.

california peak solar

Revised Aug. 14 graphic from California’s grid managers (image via California ISO)

But as EarthTechling had reported, solar power production actually peaked at 1,003 megawatts around 1 p.m. that day – 12:59 p.m., to be precise, a California ISO representative confirmed to us in an interview this week.

This isn’t surprising: As a National Renewable Energy Laboratory fact sheet [PDF] states, “PV provides the most electricity during midday on sunny days, but none during the evenings or at night.”

california solar 1 gigawatt record

Earlier graphic for Aug. 14, since replaced (image via California ISO)

Whether solar provides “none” during evenings could be a bit of a question of semantics – when exactly does “evening” start? Here’s what we know: during hot summer days, solar continues to contribute significant if declining energy to the grid up to the 5 p.m. hour. On Aug. 14, 5 p.m. output was 700 MW – 30 percent less than at the 1 p.m. peak, but still pretty hefty. An hour later, at 6 p.m., it was down to 495 MW and by 7 p.m. it was at 321 MW.

That suggests that solar isn’t quite the contributor to peak demand that it is made out to be when California ISO says, as Communications Director Stephanie McCorkle did to the Desert Sun recently, “The beauty of solar power is it comes when you need it the most. Right at that air-conditioning rush hour, typically we see the peak of solar.”

The ISO’s own graphic shows that wasn’t the case on Aug. 14 (and patterns are pretty consistent on hot summer days). But that doesn’t mean solar wasn’t helping take a bite out of peak demand, which inched to around 45 gigawatts at 3 p.m. and more or less stayed at that level until about 5:30. As we said, solar was still at 90 percent of its peak production at 3 p.m., and even at 5 p.m. was at around 70 percent.

So the takeaway here is that solar is a contributor to meeting peak demand, as California ISO says, but it’s not as perfectly aligned to demand as we all might wish. Which is why combining solar with energy storage is gaining favor – but that’s another story.

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.


  • Reply September 13, 2012


    Try the IDbox system The best monitoring tool. All the nuclear plants in Spain, uses it. Comparation, statistical, trending, historical, … Analysis in just ONE system.

  • Reply September 14, 2012


    Alignment to peak demand is not important. It PV’s contribution to the base-load during hours where residence turn on their AC’s that is benefiting the grid infrastructure. Distributed generation concepts increase the longevity of the current grid infrastructure.

    Look at all that wind power too!! Awesome! Electricity is the future of energy, lets generate it as cleanly as possible.

    • Reply September 14, 2012

      Pete Danko

      Agreed, PV’s contribution (and wind’s) is always important! But just to be clear, PV’s contribution is *fading* as the ACs go on. Thus, it could be good to have more concentrating solar in the mix, since it can extend into the evening.
      Thanks for reading and commenting,
      Pete Danko

      • Reply September 14, 2012


        Nice! Concentrating solar is sweeter in that aspect. Too bad we can’t strap a concentrating solar system to our houses, but then again maybe that could be dangerous.

        PV, concentrating solar, wind, it’s all good as far as I’m concerned. Renewables rock.

Leave a Reply