New wind turbines, solar panels and batteries played a major role in propping up the grid on the hottest days, but natural gas and coal plants remained a bedrock. Grid operators and utilities say they’re better prepared than in past years for extreme weather. And a dash of luck played a role, suggesting that the responses to future hot summers may not necessarily be so successful.

“We’re seeing the grid operating at the outer limits of its capability,” said Mark Olson, manager of reliability assessments at the North American Electric Reliability Corp., a national grid watchdog.

This summer, he said, represented “uncharted territory” for the grid.

The calendar still has several weeks of summer left, and signs of strain have emerged — including in Florida, Georgia and the Carolinas, where more than 120,000 customers remained without power Friday after this week’s strike by Hurricane Idalia. That’s down from 500,000 customers at the storm’s peak.

The hurricane aside, parts of the Midwest and Southeast sweltered under a heat dome as August closed. The grid operator covering Texas asked residents to conserve electricity on six out of the last seven days of August, while the operator covering parts of 15 central states also signaled tight conditions. On Aug. 24, the organization overseeing electricity transmission in much of the Midwest announced an emergency requiring more generators to step in to meet demand, but stopped short of rolling blackouts.

With hotter summers predicted for the future, additional complications could further burden the electricity supply, such as climate conditions that hinder wind and solar output and spiking power demand from increased use of electric vehicles and electric appliances.

Here are four questions answered about the U.S. grid’s performance this summer:

Did green power save the day?

Not unilaterally, but it has played a major role.

At the beginning of August, the U.S. had about 237,000 megawatts of utility-scale solar, wind and battery storage online, up 12 percent from the same time last year, according to the American Clean Power Association. Of that, 10,000 megawatts were added in the first half of 2023. At the end of 2022, the entire U.S. grid had more than 1.1 million megawatts of capacity.

With that kind of volume, it’s not surprising that renewable energy is playing a bigger role than ever in keeping the lights on. But supporters say it’s also how green power sources are performing that matters.

“It’s become increasingly clear that renewables, along with enabling technologies like energy storage, are providing a more resilient source of power through the increasingly frequent weather extremes that we see with the changing climate,” said Gregory Wetstone, CEO of the American Council on Renewable Energy, a nonprofit representing the renewable energy sector.

Take Texas, which now hosts the most low-carbon energy capacity in the country. The Electric Reliability Council of Texas, which manages 90 percent of the state’s power load, said before the summer that the grid could plunge into chaos at peak demand if it saw outages totaling 11,000 megawatts from coal, gas and nuclear plants.

The state skirted that line with outages between 8,000 and 10,000 megawatts earlier this summer, then crossed it with more than 11,000 megawatts of outages this week. Demand has been even higher than forecast, with at least 10 days of record peaks. But wind and solar by and large held firm, on some days accounting for as much as a third of the grid’s needs.

One megawatt can power about 200 homes during periods of peak demand in ERCOT’s territory.

Crucially, wind and solar in Texas — and elsewhere — are working in tandem, said John Hensley, vice president of research and analytics for the American Clean Power Association, which represents renewable energy companies. Solar has been charging under the hot sun, and wind has stepped up in the evening hours when the sun has gone down and demand is still high. A surge of battery storage has also helped dispatch clean-generated power later into the evening.

According to Grid Status, a website that tracks power grids, all the country’s power grids have set solar generation records this summer. One week in late August, as a regional grid operator called the Southwest Power Pool set all-time maximum load records on three consecutive days amid a heat wave, renewables were contributing between 10 and 20 percent of generation at peak times, largely from wind.

Several grid operators — including those in California and another in the Central U.S. — also set records this spring for the percentage of renewables serving electricity load.

Hensley said renewables’ big role this summer should help address the “skepticism and concern” that more wind and solar means sacrificing reliability.

“We’re proving that narrative wrong,” said Hensley.

How much of this was luck?

It’s difficult to say, although grid operators benefited from seasonal conditions that they may not be able to count on in the future.

For example, a relatively temperate spring meant grid operators and asset owners could do routine maintenance on power plants and transmission infrastructure before demand peaked in the hot months. A wet winter meant ample hydropower production in the Northwest and Southwest, allowing California to be confident about adequate power supplies this summer.

The wind has also been especially strong in parts of the country, which is not always guaranteed during a heat wave and could become less likely as the Earth warms.

Some studies have shown that climate change could cause more times when the wind doesn’t blow. Other research has said climate change could bring more extreme gusts that could damage turbines, transmission lines and power poles.

Julie Lundquist, a professor of atmospheric and oceanic sciences at the University of Colorado at Boulder, said in an email that “no clear consensus” exists about what will happen to wind resources under climate change. However, she added, that doesn’t mean wind will simply lose its value.

“My personal perspective is that wind energy technology will be changing and evolving, so even if winds slow down slightly, the technology will improve so that we will still be able to rely on wind as part of our energy portfolio,” Lundquist said in an email.

To that end, NERC’s Olson said that grid operators who can be nimble in planning and technology upgrades will be better prepared to take advantage of the breaks that emerge. The summer, he said, was a reminder that “you make your own luck and reap the benefits.”

Clean energy groups say the need to adapt should come with new investments to support the grid. More energy storage can help avert dips in renewable production. Investments in transmission can help regions share resources, making individual parts of the country less dependent on weather without relying on fossil fuel plants.

“It’s hard to argue that at this point we need a 21st century grid to be able to withstand the reality of 21st century weather,” said Wetstone.

What about fossil fuels?

It’s not unusual for gas and coal plants running at full throttle in extreme heat to break down, and some buckled as expected as the heat dragged on this summer. But fossil fuels still accounted for a large share of the country’s power.

According to data from the U.S. Energy Information Administration, natural gas remained the top source of power generation across the country and accounted for a larger share of electricity than last summer. Research from data firm Refinitiv found that gas’ share of power from January through mid-August was 42.4 percent, compared with 38.9 percent in the same period of 2022.

Coal and nuclear were the two next most productive sources, although they swapped positions at times.

That means fossil fuels have shown their worth in balancing wind and solar at times when breezes don’t blow and the sun is not shining, said Scott Aaronson, vice president of security and preparedness for the Edison Electric Institute, which represents utilities.

“It sounds like a talking point when someone says ‘all of the above,’ but we genuinely benefit from an ‘all of the above’ strategy,” Aaronson said. “Each resource has its benefits and drawbacks … but taken holistically, they make for a much more resilient grid.”

As the grid transitions, some experts and power providers have said it’s important to keep quick-start fossil fuel power plants online to ensure reliability.

A June report from NERC warned that the grid can’t manage accelerated retirements of coal and gas plants at the same time, because wind and solar may not hold up in extreme weather.

The Texas Oil and Gas Association has pushed back on the notion that renewables were saving that state. In an August release, Dean Foreman, the group’s chief economist, wrote that the gas sector’s performance underscores why it “remains the backbone of the ERCOT power grid and is indispensable in powering modern life.”

What else can be done to prevent blackouts?

As 2023 smashes heat records, utilities say they’re planning for more summers like this one.

Rather than a day or two when customers crank their air conditioning and push the grid to its limits, operators are planning for those conditions for long stretches. They are leaning more on tools such as demand response programs, which encourage customers to turn down their power use during peak times.

For example, Arizona Public Service Co., the state’s largest utility, broke its demand record seven times during a period this summer when temperatures exceeded 110 degrees, said Justin Joiner, the utility’s vice president of resource management.

“What we’re seeing now is a trend, not an anomaly,” Joiner said. With that in mind, the utility is preparing for higher peak loads and finding ways to get extra power in case of outages or unexpected spikes in demand. That includes ramping up battery storage as well as demand response.

Some grids are also looking to virtual power plants, which allow customers to pool their small home batteries and electric vehicles to supply electricity to the grid.

A May report from the Pacific Northwest National Laboratory said that with climate change accelerating, “historical averages may no longer be sufficient for resource planning” and recommended that utilities consider “multiple scenarios … including those outside traditional history-based scenario analysis” to craft plans.

Operators may also need to think independently, since state-spanning heat waves can reduce the ability to import energy that has traditionally offered help.

With climate change expected to make heat waves more common, longer and more intense, grid operators will have to continue planning for more summers that look like this, said Michael Craig, an assistant professor in energy systems at the University of Michigan who studies the impact of climate change on energy systems.

“All these grid operators are making huge changes around decarbonization. Now climate change layers more complexity on top of it,” Craig said. “For example, you have to think about how to stress test systems not just for the peak temperatures we’ve seen historically, but what we could see in the next five or 10 years.”