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Why California's Solar Power Could Soon Be Curtailed

Inside the California Independent System Operator, a high-security complex where a handful of operators are working to find ways to secure the state's electrical grid before it's too late.
(Photo: California Independent System Operator)

(Photo: California Independent System Operator)

The headquarters of the California Independent System Operator, where the bulk of California’s electricity system is managed, has the feel of a high-security prison. The steel-and-glass building in Folsom, just outside Sacramento, squats behind guarded electric gates. Visits must be cleared through the Department of Homeland Security. Getting past the electric gates requires a passport.

Cal-ISO, as it’s called, beefed up security in 2007 after Lonnie Denison, a fired employee with an axe to grind, tried to sabotage the computer systems by breaking a glass panel and hitting the emergency “off” switch. He served five years in prison and was fined $34,000.

But lately, the biggest risks to the state’s electricity grid come not from vandalism, but from trying to comply with California law. The state has mandated that utilities get a third of their electricity from renewable sources by 2020; legislators are currently working on a bill that could raise that to 50 percent by 2030.

Cal-ISO ran a simulation about what might happen when renewable energy is producing more than 33 percent of the states’ power, a moment that is projected to happen in 2024. In that case, the state will be overproducing electricity about 822 hours in a year, or about 10 percent of the time. That substantially increases the risk of frying portions of the electricity grid. If California is going to meet its renewables goals, Cal-ISO needs to be prepared to stave off a disaster.

As the 6 p.m. shift starts, and the sun dips toward the Pacific, the daily scramble begins for the technicians inside Cal-ISO’s cavernous control room. California’s supply of solar-generated electricity is about to plunge, and they have to quickly route power in from other sources in order to keep the lights on. A slip-up, though rare, could interrupt the flow of electricity and disrupt the entire California economy.

By many measures, California’s rush toward renewable energy has been a success. The state currently receives around 23 percent of its power from clean sources. In the past decade, wind farms have multiplied throughout California’s mountains, and solar panels blanket its rooftops. Tax breaks—both federal and state—have made solar panels in particular cheaper than ever before.

Though these new sources of power don’t add carbon to the atmosphere, they don’t add much stability to state’s electricity grid either. A cloudy day can turn the flow of solar power into a trickle. A placid afternoon can slow a wind turbine’s rotors. It’s the job of the Cal-ISO controllers to anticipate even a small change in renewable electricity supply and immediately find power elsewhere.

“Our number one golden rule is that supply must balance demand,” says Steven Greenlee, the Cal-ISO public information officer. Not enough energy, and people’s lights go out. Too much, and the grid could sustain damage.

The bulk of California’s energy is tied up in contracts that are automatically delivered, essentially standing orders. But this doesn’t account for sudden changes in the supply of solar or wind energy.

These workers have to secure the last few percent of market demand, which varies from day to day. If there looks to be a shortfall on the grid, they have to talk to the energy providers to make sure that the grid is topped up. That can mean routing in power from several states away (27 percent of California's power comes from outside the state).

The further away the energy source is, though, the larger the chances are that power could be lost along the way. The Cal-ISO operators work like railway switch operators, opening and closing the breakers to direct the electricity to the right points.

From a skybox overlooking the windowless control room, I watch as weather maps, flashing diagrams, and live graphs flicker on an 80-foot screen. Nine men and one woman below cluster around various desktop computers. They are the Cal-ISO operators. They look calm, but that’s because they’re working 24 hours ahead, looking at potential developments in tomorrow’s energy market.

(Photo: California Independent System Operator)

(Photo: California Independent System Operator)

Off to the side, in a small room with tinted windows, things are more tense. There, two men sit still, transfixed by their screens. There’s no collegial joshing. They are the “hour-ahead team,” overseeing real-time energy market trading. This team deals with the grid demands of the coming hour in 15-minute slots, breaking each slot into five-minute increments.

Cal-ISO’s hour-ahead team contacts the power generators at any of California’s dozens of natural gas power plants and asks them to increase production. It’s not like flicking a switch, though. Most of the state’s gas-fired power plants need to warm up for a day or so before they can produce power. As such, the plants operate at minimum loads, their pilot lights contributing even when not needed.

Ten years ago, when the Energy Commission began examining a 33 percent renewable target, the majority of California’s electricity was generated by natural gas, nuclear, and imports. Those sources were not renewable, but they were reliable.

Now, though, a growing proportion of the system's power input spikes and dips at different times of the day. Solar energy is at its most productive in the middle of the day when demand is relatively low. The sun sets, and solar production drops rapidly, but demand can shoot up at the same moment as people return home and flip on air conditioners. This forms the neck of what energy companies are calling the “duck curve.”

Named for its resemblance to the bird, the duck curve shows the amount of energy on the grid at a given time with solar and wind power taken away. It shows how many megawatts of traditional energy would be needed to plug a gap in the event of a cloudy or still day.

“The main message of the duck curve,” says Robert Strauss of the California Public Utilities Commission, “is that when the solar goes off, you have to have something take its place.”

Increasingly, that slack is being picked up by natural gas.

“About half of the state’s electricity comes from natural gas power. It is currently the backbone of reliability in the state’s electrical generation,” says Robert Freehling, the Sierra Club’s consultant on renewable energies and the grid.

As the state’s renewable energy requirements rise, the problem of solar overloading the system with unwanted power is only going to get worse.

“It’s not a question of likely or not. We will shut down plants,” Greenlee says. The growing number of solar plants will put unsustainable stress on the system without alternative renewables to pick up the slack when night comes.

Aside from examining better storage solutions and sliding pricing incentives, energy companies are trying to improve exchanges with out-of-state generators. Neighboring states like Oregon have an abundance of wind power, which could plug California’s early evening gap in return for California’s excess solar power. Better exchanges would allow the Pacific states to send and receive power as needed with greater ease.

The problems are already beginning, though. Cal-ISO saw four days of over-generation last year.

“We were surprised to see it,” Greenlee says, “and there are some indications that there may be even more over-generation concern, greater than what the duck chart shows, because it seems like it's accelerating.”

The Cal-ISO operators are going to have their work cut out for them.


This story is part of our week-long special report on energy issues in California produced in collaboration with the University of Southern California's Annenberg School for Communication and Journalism. For more, visit the project's landing page.