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Sweltering heat and earlier sunsets are a big problem for solar power.
The biggest problem in renewable energy goes by a few names.
Classically, it’s called the “duck curve,” which shows the relationship between solar generation and how much power the rest of the grid uses during the day. At the bottom of the curve, typically around midday, solar can sometimes generate 100% of the power demanded from the grid. But as the sun traces its arc towards the horizon, solar power generation falls and then quickly goes to zero as the sun sets. Often, temperatures and electricity use remains high, especially as people come home from work and start using home appliances, meaning non-solar sources of power must quickly come on line to fill in the gap.
It’s not a coincidence that utilities and grid operators tend to ask consumers to conserve in the later afternoon or evening. The phenomenon is classically associated with solar-heavy California, but it has come to Texas as well, where it goes by the name of the “Armadillo Curve” or the “Dead Armadillo Curve.”
But the relation between the sun and the Earth doesn’t just create darkness and light on daily scales but on annual ones as well. Yes, I know this isn’t breaking news, but it’s important, especially as the power system and climate are changing.
Right now we might be in the neck of the annual duck curve.
In case you haven’t noticed, the sun is setting earlier and it’s still really hot out. Kids are going back to school while much of the country is still facing summer temperatures.
In New York City this week, high temperatures are forecast to get into the 90s, while the sun will set before 7:30; in Washington, D.C., forecast highs are over 100 later this week with a sunset just past 7:30; in Houston, daytime highs to get over 100 later this week, with the sun setting before 7:40; and in Los Angeles , sunsets are at around 7:15 with expected daytime highs in the 90s this weekend.
And Septembers are only getting hotter. Septembers 2021 and 2022 were tied for the fifth hottest on record for the last 143 years, according to the National Oceanic and Atmospheric Administration; 10 of the hottest Septembers have occurred since 2012. The warmest was in 2020.
These higher temperatures mean prolonged periods of high electricity usage, even as one resource — solar — becomes less potent. This matters because, at least in the United States, we tend to organize our lives — and our electricity usage — around the clock, not the sun.
As the sun is setting earlier, our high electricity usage stretches longer compared to the length of the solar day, exacerbating the duck curve dynamics inherent to solar power. A dishwasher that runs when the sun’s still up in July is pulling the same power from the grid as one that runs during fall’s early twilight. The saving grace of shorter days in a grid that uses solar power is supposed to be that air conditioning usage goes down, but that doesn’t happen when summer temperatures persist past Labor Day.
If hot Septembers and even Octobers become the norm, grid conditions could tighten up both during and across the days, with higher cost, less reliable power or increased usage of fossil fuels to fill in the gap.
These longer, hotter summers can make operating electric grids more difficult. ERCOT, the electricity market that covers the vast majority of Texas, restricts power plants from having planned outages between May 15 and September 15 for maintenance. While still in the summer restriction window, ERCOT on Tuesday issued an alert for later this week, warning of “forecasted higher temperatures, higher electrical demand, and the potential for lower reserves.” If ERCOT extends its restrictions on outages for maintenance, there should be more unplanned outages, making power scarcer, meaning higher prices and a greater possibility of blackouts.
Not every country sees peak electricity usage in late summer. In New England, peak electricity demand tends to hit in July. In the sprawling PJM Interconnection last year, the electricity market that spans from the Chicago area to Virginia, demand peaks tended to be in June or August. In New York, peak demand is often in July.
But summer peaks are later in the year in two the country's largest electricity markets: California and Texas.
The Texas energy market had hit its peak day in July in 2022, but it moved out to August this year. And Texas is already bursting through its September demand records. It reached over 78,000 megawatts in just the first week of this month, well over its previous record of 72,370 megawatts, which it set in 2021.
And California hit its power demand record last September amidst a heat wave that covered much of the western United States.
It’s not just there being literally fewer hours of sunlight that drags down solar production later in the year, but also the lower angle of the sun. “As the sun gets lower in the sky we see solar production numbers will drop,” Joshua Rhodes, a senior research scientist at the University of Texas, told me.
“As the sun is lower in the sky it’s up fewer hours ... the photons are coming in at a steeper angle, the panels are not going to get as much light. Even when the sun is at the highest point of the day, the panels are not getting the same level of irradiance as when the sun is at the highest point of the day [at other times of year].”
The best angle for solar panels can change around 15 degrees a year, depending on the year and solar panels are more efficient when they can track the sun during the day. Most homeowners who install solar panels won’t have tracking technology, while utility-scale solar developers are more likely to. This means that a state like Texas, whose renewable mix is more focused on large solar arrays, could see less dramatic drop-offs in solar power throughout the day or throughout the year than a state like California, which has more residential solar.
A roof-mounted four kilowatt-hour solar PV system with standard specs where I grew up in Northern California would get 7.45 kilowatts-hours per meter squared per day in July, generating 689 kilowatt-hours of power, according to National Renewable Energy Laboratory PVWatts tool; in September, solar radiation would drop down to 6.6 kilowatt-hours per meter squared per day and 587 kilowatt-hours per month.
This admittedly basic math suggests it's possible California could struggle this month — and in future Septembers — with meeting electricity demand.
In the past 10 years, California’s annual load peak has occurred in September five times, with the peak loads in 2022 and 2021 occurring on September 6 and 8 respectively.
This year has been, so far, not particularly stressful for the Golden State’s grid thanks to some good luck — no region-wide, prolonged heat waves that max out California’s grid and make imports scarce, mild temperatures on the coasts where the state’s population is concentrated, no major wildfires, and plentiful hydro power thanks to massive snowfall this past winter — as well as massive deployment of batteries across the grid. The batteries especially can help alleviate these duck curve dynamics, as they essentially redistribute power from the sunniest part of the day to the evenings.
While Texas set several new records this year in electricity usage, California has stayed well short of its 52,000 megawatt record last September. California set records for solar power in June and July, with almost 16,000 megawatts, while total demand over 40,000 megawatts.
“While we haven’t seen substantial stress on the grid this summer, we haven’t been fully tested. If we got the kind of west-wide heat we experienced in September 2022, we could need to tap into the state’s emergency or strategic reserves again,” Anne Gonzales, a spokesperson for the California Independent System Operator, told me in an email.
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While you were watching Florida and Wisconsin, voters in Naperville, Illinois were showing up to fight coal.
It’s probably fair to say that not that many people paid close attention to last night’s city council election in Naperville, Illinois. A far western suburb of Chicago, the city is known for its good schools, small-town charm, and lovely brick-paved path along the DuPage River. Its residents tend to vote for Democrats. It’s not what you would consider a national bellwether.
Instead, much of the nation’s attention on Tuesday night focused on the outcomes of races in Wisconsin and Florida — considered the first electoral tests of President Donald Trump and Elon Musk’s popularity. Outside of the 80,000 or so voters who cast ballots in Naperville, there weren’t likely many outsiders watching the suburb’s returns.
But for clean energy and environmental advocates, the Naperville city council results represent an encouraging, if overlooked, victory. On Tuesday, voters in the suburb elected four candidates — incumbents Benjamin White and Ian Holzhauer, and newcomers Mary Gibson and Ashfaq Syed — all of whom oppose the city signing a new contract with the Prairie State Generating Station, the state’s largest and youngest coal-fired plant and the seventh-dirtiest electricity provider in the country.
Naperville is one of 30 municipal investors in the Prairie State plant whose contract with the Illinois Municipal Electric Agency, a public power agency and one of the nine partial owners of Prairie State, has it locked into coal through 2035. Recently, IMEA approached the municipal investors with the promise of favorable terms on a new contract if the cities and towns were willing to re-sign a decade early — by April 30 — and commit to another 20 years of coal power. Most municipalities took the deal, which will run through 2055; Naperville, along with the towns of St. Charles and Winnetka, are still debating the decision, with the deadline looming.
“IMEA’s proposition for communities is, ‘Hey, instead of paying Wall Street and shareholder dividends, we don’t have any of that because we’re a nonprofit, so you get lower energy costs,’” Fernando Arriola, the community relations chair for Naperville Environment and Sustainability Task Force, which opposes the deal with IMEA, told me. “But the way I look at it is, it’s a deal with the devil because you’re locked in for 30 years. And it’s like Hotel California — you can check in anytime you like, but you can never leave.”
In a statement to Heatmap, Staci Wilson, the vice president of government affairs and member services at IMEA, told me that the contract it offered to Naperville is “designed to help … secure more future green resources to serve our member communities for the long term. IMEA is the only power supplier to allow the city to have a direct voice in procuring their wholesale power supply and make reliable, economical, and sustainable resource decisions for the future.”
While it’s true that IMEA allows its municipal members a voice in its future planning, those in Naperville who oppose the new contract point out that the community has just one vote in the process despite making up 35% of the utility’s market.
The pending contract decision became one of the major themes of the city council race in Naperville — attention that caused some locals to grumble about the injection of partisan politics and outside interest in the campaigns. But Syed, a newly elected city council member and a recent immigrant from Dubai, told me that learning that his city relied on coal for 80% of its energy needs was what ultimately galvanized him into running. “Naperville has been a leader in many things, but in this area, we were not doing good,” he said. “So I stepped up.”
Illinois has one of the nation’s most aggressive decarbonization timelines, requiring coal and gas plants to close by 2030. But there is a carve-out for plants owned by public entities like municipal utilities or rural electric cooperatives, and Prairie State fits that bill. Instead, the power plant has to reduce emissions by 45% by 2038, a goal IMEA says it can reach by installing multi-billion dollar carbon capture and storage technologies. Energy experts have been widely skeptical of the proposal. “The people I’ve talked to say that’s unproven and it doesn’t necessarily work, and it’s a high price,” Arriola said.
Still, cost concerns related to transitioning away from coal had “definitely been a conversation in town” leading up to Tuesday’s election, Arriola told me. “A lot of people are seriously concerned about pricing, and there are also concerns about the reliability.” Syed told me that was one of the objections he heard the most when talking to constituents during his campaign. “Some of the Republicans who were against [exporing alternative energy options] were trying to influence people, saying we need to think about the cost,” he said. “My standard answer to these people was that I am not going to compromise clean energy just for the cost purpose.”
Perhaps most interestingly, unlike many communities that oppose power plants, Naperville is located almost 300 miles north of the Prairie State Generating Station and is unaffected by its immediate pollution. Naperville voters who opposed renewing the contract did so on the merits of finding cleaner energy sources and on the objection to dirty electricity that is otherwise out of sight and out of mind. As Amanda Pankau, the director of energy and community resiliency at the Prairie Rivers Network, an environmental nonprofit in the state, told me, “From a climate perspective, we should all care about the Prairie State coal plant.” She noted that the emissions from the plant — around 12.4 million tons of carbon dioxide a year — are “impacting every single Illinoisan and every single person that lives on planet Earth.”
Despite those existential stakes, it could be tempting to wave away the results in Naperville as being on trend for a relatively affluent and liberal-leaning town. Compared to the Wisconsin supreme court election, where the Democrat-backed candidate overcame enormous spending margins to trounce her Republican-backed opponent, it does not necessarily indicate the same momentum for the party heading into 2026’s midterms. (Nor does it even have the biggest climate-related election headline of the night: Tesla is suing Wisconsin for a law preventing car manufacturers from owning car dealerships, which the state’s high court will likely decide.)
But at a time of little good news in the climate sphere, the Naperville election is an encouraging and invigorating reminder that there are candidates who believe in cleaner technologies, and that the battles can still — or especially — be won at the local level. “Twenty-five or 30 years ago, the IMEA contract we signed for that time was okay,” Syed said. “But it’s not okay today. We cannot have this $2 billion contract until 2055 because the next generation will ask us this question: ‘What have you people done for us this time?’”
The Department of Energy has put together a list of sites and is requesting proposals from developers, Heatmap has learned.
The Department of Energy is moving ahead with plans to allow companies to build AI data centers and new power plants on federal land — and it has put together a list of more than a dozen sites nationwide that could receive the industrial-scale facilities, according to an internal memo obtained by Heatmap News.
The memo lists sites in Texas, Illinois, New Jersey, Colorado, and other locations. The government could even allow new power plants — including nuclear reactors and carbon-capture operations — to be built on the same sites to generate enough electricity to power the data centers, the memo says.
Trump officials hope to start construction on the new data centers by the end of this year and switch them on by the end of 2027, according to the memo.
The agency will request formal feedback from artificial intelligence companies and developers about how best to proceed with its proposal as soon as Thursday, according to an individual who wasn’t authorized to speak about the matter publicly.
The effort, aimed at maintaining America’s “global AI dominance,” represents one of the few points of agreement between the Trump and Biden administrations. In the final days of his term, President Biden ordered the government to identify federal properties where new data centers could be built.
Scarcely a week later, President Trump issued an executive order lifting all Biden-era limits on AI development — but keeping the mandate to move quickly to maintain America’s alleged edge in the new technology. “It is the policy of the United States to sustain and enhance America’s global AI dominance,” the Trump order said.
The new memo proposes a list of 16 federal sites that could host AI data centers, new power plants, and other “AI infrastructure.” They include several sites where nuclear weapon components are made, including the Pantex site near Amarillo, Texas, and the Kansas City National Security Campus, which is operated by Honeywell International. The other candidate sites are:
Other sites could still be considered, the memo says, and the current list has no particular ranking or order.
The offer may not be enough to convince developers to work with the federal government, one energy expert told me.
“I think it’s important that the government is thinking about how to help the industry, but you also have to think about it from the perspective of the industry a little bit. Why is doing this on a DOE site better than doing this as a project in Texas?” said Peter Freed, a founding partner at the Near Horizon Group and the former director of energy strategy at Meta.
“Historically, the perspective is that anything involving government land just adds complexity,” Freed told me. “I love Idaho National Lab. It’s a national treasure. But if you want a data center there by the end of 2027 — where is the power going to come from?”
Only if the government were able to guarantee fast-track access to certain kinds of equipment — such as transformers or circuit breakers, which are in a severe shortage — would it make sense for most developers to work with them, he said.
The new memo raises the idea that “innovative energy technologies” including “nuclear reactors, enhanced geothermal systems, fuel cells, carbon capture, energy storage systems, and portfolios of on-site technologies” could be considered to power the new data centers.
The memo asks potential developers, “What information would you need to determine the suitability of various energy storage systems (e.g., subsurface thermal energy storage, flow battery, metal anode battery) as a means for supporting data center cooling or other operations?” It also asks what companies would need to know about a site’s suitability for carbon capture and storage operations. It asks, too, what information might be needed about a site’s topography, physical security, and earthquake risk to build a new nuclear power plant.
The memo doesn’t mention wind turbines or new solar farms, although they could fall under some of the terms it sets out. It also asks companies what information they might need about nearby nuclear power plants or the local power grid — and it inquires whether some data center operations could be turned on and off depending on local power availability.
Although the government could allow new data centers to be built, it won’t accept all liability for them. The memo adds that companies might need to “agree to bear all responsibility for costs and liabilities related to construction and operation of the Al data centers as well as other infrastructure upgrades necessary to support those data centers.”
The Trump administration seems intent on moving quickly on the proposal. Once it publishes the request, companies will have 30 days to respond.
Current conditions: A rare wildfire alert has been issued for London this week due to strong winds and unseasonably high temperatures • Schools are closed on the Greek islands of Mykonos and Paros after a storm caused intense flooding • Nearly 50 million people in the central U.S. are at risk of tornadoes, hail, and historic levels of rain today as a severe weather system barrels across the country.
President Trump today will outline sweeping new tariffs on foreign imports during a “Liberation Day” speech in the White House Rose Garden scheduled for 4 p.m. EST. Details on the levies remain scarce. Trump has floated the idea that they will be “reciprocal” against countries that impose fees on U.S. goods, though the predominant rumor is that he could impose an across-the-board 20% tariff. The tariffs will be in addition to those already announced on Chinese goods, steel and aluminum, energy imports from Canada, and a 25% fee on imported vehicles, the latter of which comes into effect Thursday. “The tariffs are expected to disrupt the global trade in clean technologies, from electric cars to the materials used to build wind turbines,” explained Josh Gabbatiss at Carbon Brief. “And as clean technology becomes more expensive to manufacture in the U.S., other nations – particularly China – are likely to step up to fill in any gaps.” The trade turbulence will also disrupt the U.S. natural gas market, with domestic supply expected to tighten, and utility prices to rise. This could “accelerate the uptake of coal instead of gas, and result in a swell in U.S. power emissions that could accelerate climate change,” Reutersreported.
Republican candidates won in two House races in Florida on Tuesday, one of which was looking surprisingly tight going into the special elections. The victories by Jimmy Patronis in Florida’s First District and Randy Fine in the Sixth District bolster the party’s slim House majority and could spell trouble for the Inflation Reduction Act as the House Ways and Means Committee mulls which programs to cut to pay for tax cuts. But the result in Wisconsin’s Supreme Court election was less rosy for Republicans. Liberal Judge Susan Crawford defeated conservative Brad Schimel despite Schimel’s huge financial backing from Tesla CEO and Trump adviser Elon Musk, who poured some $15 million into the competition. The outcome “could tarnish the billionaire’s political clout and trigger worry for some Republicans about how voters are processing the opening months of Trump’s new administration,” as The Wall Street Journalexplained.
The Trump administration announced mass layoffs across the Department of Health and Human Services on Wednesday, part of a larger effort to reduce the agency’s workforce by 25%. The cuts included key staffers with the Low Income Home Energy Assistance Program, which has existed since 1981 and helps some 6.7 million low-income households pay their energy bills. A 2022 white paper calls LIHEAP “one of the most critical components of the social safety net.” The move comes at a time when many U.S. utilities are preparing to raise their energy prices to account for higher costs for materials, labor, and grid upgrades. In a scathing letter to HHS Secretary Robert F. Kennedy. Jr., Senate Energy and Commerce Democrats call the workforce cuts “reckless” and demand detailed explanations for why roles have been eliminated.
Energy storage startup Energy Vault on Wednesday announced it had closed $28 million in project financing for a hybrid green hydrogen microgrid energy storage facility in California. The firm says its Calistoga Resiliency Center, deployed in partnership with utility company Pacific Gas & Electric, is “specifically designed to address power resiliency given the growing challenges of wildfire risk in California.” The zero-emission system will feature advanced hydrogen fuel cells that are integrated with lithium-ion batteries, which can provide about 48 hours of back-up power via a microgrid to the city of Calistoga during wildfire-related power shutoffs. The site is expected to be commercially operational in the second quarter of 2025.
“The CRC serves as a model for Energy Vault’s future utility-scale hybrid microgrid storage system deployments as the only existing zero-emission solution to address [power shutoff] events that is scalable and ready to be deployed across California and other regions prone to wildfires,” the company said in a press release. As Heatmap’s Katie Brigham wrote last fall, PG&E has become an important partner for climate and energy tech companies with the potential to reduce risk and improve service on the grid.
China will finalize its first-ever sale of a green sovereign bond Wednesday. The country is expected to issue the bond on the London Stock Exchange and has reportedly received more than $5 billion in bids. “It’s no coincidence that China has chosen to list its debut green bond in London, given European investors’ continued strong demand for environmental products,” Bloombergnoted. Green bonds are investment vehicles that raise money exclusively for projects that benefit the climate or environment. China’s finance ministry wants the bond to “attract international funds to support domestic green and low-carbon development,” and specifically climate change mitigation and adaptation, nature conservation and biodiversity, and pollution prevention and control. Some of the money raised might also go toward China’s EV charging infrastructure, according toReuters.
GE Vernova has now produced more than half of the turbines needed for the SunZia Wind project in New Mexico. When completed in 2026, the 2.4 gigawatt project will be the largest onshore wind farm in the Western Hemisphere.