Solar and batteries are helping Texas weather heat waves. Here’s how.

The Texas power grid has broken new records throughout this summer — for how much electricity it has had to deliver as residents cranked up their air conditioners and for how much it has used solar power and batteries to keep grid emergencies at bay.

Take last week, when temperatures soared into the triple digits across most of the state, causing demand to surge on the grid operated by the Electric Reliability Council of Texas, or ERCOT.

Last Tuesday, August 20, ERCOT set a new record for peak demand on its state-spanning power grid — 85,931 megawatts, edging out the 85,612 MW record set 10 days prior, according to data from Grid Status, a startup that collects and shares grid data from across the country.

Luckily for the 22 million power customers reliant on ERCOT’s grid, solar power generation also hit a near-record level of 20,799 MW on August 20, just below the 20,832 MW record set two days before. That flood of solar power kept supply matched to demand throughout the midday hours — and because solar is the cheapest source of electricity on the grid today, wholesale electricity prices remained low. 

Then the sun started to go down and solar began to fade away — but because temperatures were still high, air-conditioner use didn’t wane. At 7:50 p.m. last Tuesday, ERCOT hit another record: 70,900 MW of ​“net load,” a measurement of the moment in the day when available generation capacity, minus solar and wind power, is furthest out of alignment with electricity demand, forcing the grid to dispatch the highest-cost ​“marginal” resources available.

Those marginal resources include fossil-gas-fired peaker plants contracted expressly for the purpose, as well as data centers, factories, and other big customers being paid to limit their energy use to reduce demand. As ERCOT dispatched and depleted those resources, energy prices quickly spiked to reach their cap of $5,000 per megawatt-hour, as shown by the turquoise lines on the charts above and below. 

“The key risks shift from peak load to net load,” said Connor Waldoch, co-founder and head of strategy at Grid Status. ​“You end up with a situation where ERCOT can beat its load record and prices are pretty low — and an hour or two later is when you see your price spike, and you see the deployment of ancillary services and all the things that ERCOT has designed specifically to deal with this.”

But just as they had during similar heat-driven grid peaks over the spring and summer, the batteries that had been storing up solar power throughout the day came to the rescue — and presumably earned a healthy profit for it. Energy storage discharged to the grid hit its own record of 3,927 MW at 7:35 p.m. on August 20, well above the prior record of 3,283 MW just the day before. 

The end result? ERCOT was able to avoid resorting to options like sending out emergency power conservation alerts to customers — or the measure of last resort, requiring utilities to institute ​“rolling outages,” or turning off entire sections of the grid one after another to force demand downward.

Throughout this year, the Texas grid faced several days that looked similar to August 20, starting as far back as late April and early May, when unseasonably warm spring weather pushed the system to the brink.

All in all, ​“things have worked pretty well the way they are supposed to,” said Doug Lewin, president of the Texas-based energy consultancy Stoic Energy. ​“It’s not overstating it at all to say that solar and storage has been determinative” in keeping the ERCOT grid steady through trying heat waves this year.

In fact, Lewin wrote in his Texas Energy and Power Newsletter last week, it’s likely ERCOT would have had to institute emergency measures absent the state’s staggering increase in battery capacity. Last week, ERCOT’s physical responsive capability, which is the capacity for power plants to spin up and customers to shut down at a moment’s notice, had been approaching the threshold that could require ERCOT to consider implementing rolling outages — but instead, batteries swooped in and restored stability. 

The Texas model for a solar- and battery-backed grid 

What makes this transformation more noteworthy is that Texas has become the leading state for wind, solar, and now battery deployments without any state-level clean-energy mandates driving that deployment.

California also saw enormous growth in solar power and batteries ease the heat-wave-driven grid stresses that had led to rolling outages in August 2020 and emergency conservation measures in September 2022. But that growth has been driven by decades of state clean-energy policy.

In Texas, by contrast, ERCOT’s highly competitive power-market structure and permissive grid interconnection rules have allowed clean resources to outcompete their fossil-fueled rivals. Texas topped the country for wind power in 2020, beat out California as the top state for utility-scale solar in 2023, and may out-deploy California on utility-scale battery systems this year.

All told, zero-carbon power from wind, solar, and nuclear made up 47 percent of the power delivered on ERCOT’s grid in the first quarter of 2024, up from 40 percent throughout 2023 — a shift driven almost entirely by utility-scale solar and batteries economically outcompeting fossil-fueled power plants.

Solar and batteries have continued to expand even as Texas lawmakers last year pushed through a series of policies in support of fossil-fueled power plants. Those policies include a $5 billion low-interest loan program, which recently drew 72 applications seeking $24 billion to build as much as 38 gigawatts of new fossil-gas-fired power plants. They also include a plan to create a ​“performance credit mechanism” that would pay gas-fired generators more money for being available during grid emergencies.

But gas-fired power plants aren’t always able to be available during such emergencies. Solar and batteries filled in gaps in gas-fired generation last spring, when a heat wave coincided with many power plants being offline for annual maintenance. And sometimes fossil-fueled power plants fail to come online or are forced to reduce their power output, particularly at times of extreme heat and extreme cold, which can cause operational problems.

Lewin noted that ​“thermal outages” — when coal, gas, and nuclear power plants are unavailable or underperform — were 20 percent higher than ERCOT’s forecasts during last week’s heat wave, and 30 percent higher on August 20.

“Giving credit where it’s due, thermal power plant outages were generally lower than last summer,” he added — although that’s ​“kind of damning with faint praise because they were too high last summer.”

But the biggest change from last summer to this summer is that Texas has increased its solar production from 13 GW to 21 GW and has roughly doubled its battery capacity over the past 12 months. Last year, the grid operators issued 11 such calls for conservation, ​“compared to none this year,” Lewin said.

“The biggest difference is a whole lot more solar and a whole lot more storage.”

Gas-fired power plants remain the largest generation resource on the ERCOT grid, and their backers say Texas needs even more of them to be available to turn on when the wind isn’t blowing and the sun isn’t shining. But for the state’s hottest summer afternoons and evenings, the combination of solar and batteries has proved to be a reliable, cheaper — and cleaner — alternative.