California’s heatwave is a big moment for batteries

During a late Summer heat wave in California, golden hour turns into danger hour. The offices of the California Independent System Operator, which manages the state’s power grid, are getting crowded. Your mission is to get the electrons where they need to go – otherwise millions of electricity blackouts are at risk.

This risk arises from a brief but important mismatch between supply and demand. A growing proportion of the state’s energy comes from solar panels, which accounted for about a fifth of supplies last year. But when the sun goes down and these panels stop receiving photons, the demand for electricity continues to rise. People come home from work, plug in their electric vehicles, and then turn on the air conditioning to eliminate afternoon drowsiness. Maybe they’ll make dinner and run the dishwasher. Meanwhile, back at work, the lights in the office are probably still humming.

Such were concerns during this week’s heat emergency, as dozens of cities smashed all-time temperature records and energy demands soared. But this time, California’s ISO had a little more juice to work with: a relatively new fleet of grid-scale batteries. They’re designed to last about four hours – just long enough to bridge the gap in the evening. According to an analysis by BloombergNEF, at peak power, about 6 percent of energy supply comes from these depleting batteries, up from 0.1 percent in 2017. Capacity has nearly doubled over the past year. Just after 6 p.m. Tuesday, batteries surpassed the output of the state’s last remaining nuclear plant, peaking at just under 3,000 megawatts.


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There was also a second push, this time on the demand side. At around 5:45 p.m., the phones of millions of Californians were buzzing when a massive block of text arrived, imploring them to postpone all those evening rituals to conserve energy. Apparently they did. In the next 20 minutes, more than 2,000 megawatts of demand disappeared from the grid, according to Anne Gonzales, a California ISO spokeswoman. It happened so quickly that many energy experts were stunned. “I was pleasantly surprised to see how everyone came together,” says Ryan Hanna, an energy researcher at the University of California, San Diego.

Overall, Hanna says, both battery drain and text alerts are relatively “marginal” inputs to balancing supply and demand given this week’s record-breaking peak demand: 52,000 megawatts. In the evening hours, the state still relies on natural gas to round off the power supply and on imports from other states. (By comparison, gas peaked at nearly 27,000 megawatts.) But in a crisis like this, “margins are everything,” he adds. While utility companies in some Bay Area communities staged rotating outages Tuesday that affected about 50,000 customers — the result of what the California ISO later called miscommunication — that was far fewer than expected. Power outages were again avoided on Wednesday and Thursday, despite approaching Tuesday’s demand record.

It was a relatively slow ramp-up for large-scale battery deployment. Efforts to overhaul the grid and create more storage began a decade ago, but have lagged behind renewable energy generation like wind and solar farms in terms of actual installations. That’s partly because batteries are a regulatory conundrum. Finding the right incentives for a power source that stores energy instead of producing it requires some tricky math. And while solar panels and wind turbines are now ubiquitous, grid operators have less experience deploying batteries at scale, so technical uncertainties remain. The state’s largest battery, a 1,600 MW-hour facility housed in a natural gas facility at Moss Landing, was mostly offline for almost a year due to problems controlling the temperature of the giant stacks of lithium-ion batteries.

There are other kinks that need to be worked out. Earlier this week, some batteries began draining earlier than expected when the price battery operators were paying for their energy exceeded a government-mandated cap. (These operators may include local utilities or independent companies.) Because there was no benefit in holding their electrons longer, the batteries began draining their loads well before the grid went on alert. Analysis of whether that was the right move “is pending,” says Dan Kammen, an energy expert at the University of California, Berkeley. But it will likely spark discussions about the right way to encourage battery operation — and potentially redesigning the software that controls its operation to be more flexible in extreme situations.


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Over the past two years, the difference in battery usage in the early evening hours has been striking – an increase of more than 10 times at peak usage in 2022 compared to 2020. Government plans call for an increase to 41 gigawatts of energy storage by 2045. from today about 3 gigawatts.

And that’s a good thing, Kammen points out, because in a way, California was lucky for most of this heat wave. Although it was brutally hot, it wasn’t stormy. High winds risk power line problems that can start fires, so utility companies can preemptively turn off power to avoid problems. Worse, when fires spark, they can force other parts of the system to shut down or create smoke that blocks the sun and reduces solar output. (That came at the end of Thursday night’s heat wave from fires in Southern California, forcing officials to start earlier in the day with calls for demand cuts.) Mostly calm conditions this week meant network operators had the luxury most of it to use the tools at their disposal. And it meant hundreds of thousands of homes and businesses were providing their own electricity thanks to rooftop solar panels, relieving strain on the power grid. Solar on the roof delivered up to 8,000 megawatts during Tuesday’s peak period.

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