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What happens to the grid when the sun goes away?

Early April is typically a kind of goldilocks moment for solar power. Days are getting longer but the weather is still mild, meaning that higher solar power generation isn’t entirely eaten up by increased demand due to air conditioning.
But that all depends on the sun actually shining.
Monday’s solar eclipse took a big chunk of power off the grid. Since 2017’s eclipse, solar power generation has increased substantially, both locally (think rooftops) and at utility scale (think massive fields of solar panels). In 2017, the U.S. had around 35 gigawatts of utility-scale solar capacity, a figure that had increased to an estimated 95 gigawatts by the end of 2023.
While total solar eclipses are rare (the next one to hit the lower 48 isn’t expected until 2044), the challenges they present to grid operators may be part of the new normal. With vastly expanded renewable energy generation comes a greater degree of unpredictability, as a growing a portion of the generation fleet can drop off the grid due to weather and climate conditions — like, say, clouds of smoke from a wildfire — that cannot be precisely predicted by 17th century science.
Grid operators were confident they’d be able to manage through the eclipse without any reliability issues, and what actually transpired mostly confirmed their forecasts. In Texas, solar power production shrunk from around 13.5 gigawatts at noon, making up 27% of the grid’s electricity supply, to a mere 0.8 gigawatts at 1:30 p.m. Things did not go as well for the Midcontinent Independent System Operator, however, which includes a swath of the middle of the country from Minnesota to Indiana to Louisiana. Solar output was estimated to drop from around 4 gigawatts at 1 p.m. Central time to 2 gigawatts an hour later, according to Grid Status. Instead, output dropped to around 300 megawatts, causing real-time prices for power on the grid to spike.

Overall, the U.S. Energy Information Administration estimated that some 6,500 megawatts of solar generation capacity would be fully obscured during the eclipse, which would “partially block sunlight to facilities with a combined 84.8 GW of capacity in an even larger swath of the United States around peak solar generating time.” Some 40 gigawatts may have come off the grid, enough power for about 28 million homes, according to a release from Solcast, a solar forecasting company.
By comparison, during the 2017 eclipse, solar power loss at its peak was between 4 and 6.5 gigawatts and the total loss of power was around 11 gigawatts, according to the National Renewable Energy Laboratory.
In states like Texas, the main effect was on utility-scale production of solar, but in the Northeast and parts of the mid-Atlantic and Midwest, there was also a related problem: Behind-the-meter solar fell off, too, thus requiring the homes and businesses that generate power for themselves in the middle of the day to get more power from the grid, increasing demand on the grid at a time of low supply.
New England has seen immense growth in rooftop solar, and solar production was expected to fall by “thousands” of megawatts, according to ISO New England, while the New York Independent System Operators expected to lose 700 megawatts of behind the meter solar.
During the 2017 eclipse, the National Renewable Energy Laboratory found that “the burden of compensating for the lost energy from solar generators fell to the thermal fleet,” i.e. natural gas, along with some increases in coal and hydropower production.
Since then, the coal fleet has shrunk, thus putting more of the burden of responding to Monday’s eclipse onto gas and hydro, but the basic logic still applies. “Grid operators are expected to rely on natural gas to ensure stability and meet the household demand spike across national grids, as was done during the previous eclipse in 2023 in California and Texas,” according to Solcast. As the sun was dimming in Texas, natural gas generation rose from 18.7 gigawatts to 27.5 gigawatts.
Something else that’s changed since 2017: batteries. By the end of 2023, Texas had installed 5.6 gigawatts of grid storage, most of it providing so-called “ancillary services,” power sources that can respond quickly to immediate needs. ERCOT, the electricity market that covers most of Texas, said in a presentation back in February that it would rely on these ancillary tools to get through the eclipse, and once again, it was right. Power from batteries on the grid got up 1.4 gigawatts during the eclipse.
Editor’s note: This story has been updated to reflect the actual effects of the eclipse on U.S. power generation.
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We got a much better sense of the Trump administration’s nuclear buildout plans today.
The Energy Department announced its long-awaited loan program that will aim to build a new fleet of nuclear reactors across the country. The department’s in-house bank will provide low-interest loans of up to $17.5 billion to help utilities and power developers buy up to 10 Westinghouse AP1000s, the third-generation nuclear reactor that is that company’s flagship product.
I can’t say this program was entirely a surprise: If you read Heatmap, you’ll remember we reported on the existence of this program — and the discussions between the government, utilities, power developers, and Westinghouse — back in February. Gregory Beard, who leads the Energy Department’s in-house bank, also teased the program at a Houston conference in April.
The program looks roughly as anticipated: It will aim to construct up to 10 new reactors, with two AP1000 Westinghouse reactors across five sites. That could add up to 11 gigawatts of nearly around the clock zero-carbon electricity to the power grid. What’s new is that Westinghouse and the utility will jointly own the power plants.
According to The Wall Street Journal, utilities and Westinghouse will each own part of the plants once they’re built. Five loans will become available; the department is already in talks with seven utilities.
At the high level, it’s a cool program — or at least I think so. Nuclear support has become surprisingly bipartisan, at least at the elite level, in recent years. In New York, Governor Kathy Hochul is trying to develop new nuclear plants. As we’ve noted before, the countries with some of the cleanest power grids in the world, such as France and Sweden, achieved their low carbon emissions in part by undertaking large, state-led nuclear energy buildouts. France, in particular, harmonized its nuclear power plants to a single reactor design and then built them to spec across the landscape. China is engaged in a similar buildout now with a variant of the AP1000. By getting behind the AP1000 in the United States, the Trump administration is following a global best practice.
The idea of a mass buildout makes sense for other reasons, too. Recent nuclear projects in the United States have often faced delays because construction and manufacturing timelines don’t line up. AP1000s are manufactured partly off-site in Westinghouse facilities and then shipped in; when a part arrives late, an expensive construction crew has to sit idle while they wait for it to arrive. (These timing misalignments drove part of the Vogtle plant’s runaway costs in Georgia.) By placing what is in essence a bulk order for AP1000 parts, the new program aims to bring down the cost of production and even allows project sites to swap identical parts as they come available — if one site isn’t ready to receive a pressure vessel, for instance, it can go somewhere else.
I hesitate to praise the project's climate bonafides at the risk of discouraging the Trump administration, but it is worth noting that if this project were to succeed, it would be one of the largest state-assisted build-outs of zero-carbon electricity in recent American history. But it would still take some time to arrive: These reactors aren’t forecast to come online til 2035.
Let me note one more irony. For a long time, the country’s policymakers and nuclear industry (to the extent the latter exists) have dreamt of small modular reactors: petite fission plants that can be manufactured in a factory and would produce a few hundred megawatts. The AP1000, in both its American and Chinese iterations, is a very large reactor — but it has become, in a sense, modular and manufacturable.
Cameco, which owns about half of Westinghouse, saw its stock rise 1.8% in the day’s trading. Brookfield Renewable Partners, which owns the other half, was flat. It was otherwise a choppy day in the markets, with the S&P 500 falling 1.4% and some tech and AI-exposed companies continuing their slide.
There will be much more to say about this program, and we look forward to covering it at Heatmap.
Hyperscalers might be paying billions to avoid blame for rising electricity prices.
Here is a mystery for you: On Wednesday, the House Energy and Commerce Committee will take up the Ratepayer Protection Act, a bipartisan bill sponsored by Colorado Republican Gabe Evans and Florida Democrat Kathy Castor that seeks to enshrine Trump’s similarly named pledge into law.
Among the bill’s supporters is Kentucky Representative Brett Guthrie, a Republican and the chair of the committee. Guthrie is no opponent of artificial intelligence, saying in a statement praising the bill that “Winning the race to AI dominance is essential to securing America’s future global leadership, and that means expeditiously building the power infrastructure needed to support new technologies, while doing so in a responsible way.” Guthrie did not respond to a request for comment.
Microsoft, one of seven large technology companies that agreed to cover any additional grid infrastructure costs stemming from their data centers under Trump’s original Ratepayer Protection Pledge, supports the bill, describing it as an “important step to help ensure American families are protected from rising electricity costs.” Google, another signatory, generally backs the idea of specialized large load tariffs that allocate network costs back to the hyperscalers.
But … why? After all, these companies are voluntarily putting themselves on the hook for what could be billions of dollars in costs that would typically be socialized to all the customers on the grid.
The Data Center Coalition, a trade group including several hyperscalers, has been more circumspect about the bill. Cy McNeill, the group’s senior director of federal affairs, told me in a statement that the group “is reviewing the details of the Ratepayer Protection Act with our members and looks forward to engaging with policymakers on this important topic.”
Evans, Castor, Guthrie, and and the rest appear to be acting not out of hostility towards the AI industry, but rather from a desire to protect it from public backlash fed by rising electricity prices. Earlier this month, Guthrie co-signed a letter to FBI Director Kash Patel, among others, raising concerns that China had “engaged in a coordinated effort to slow U.S. growth in AI development and the building of infrastructure supporting AI data centers” by fomenting domestic opposition — hardly the interpretation of someone working against the industry.
The explanation, perhaps, lies in the answers to two big questions about the Ratepayer Protection Act:
1. Are data centers responsible for higher electricity prices now, or will they be in the future?
2. And would the approach taken in the law actually work to protect ratepayers?
As to the first question, analysts have come up with a nuanced answer. The electricity cost increases we’ve seen in the last five or so years have been largely driven by expenses associated with the distribution grid, including the poles and wires themselves. In some states, like California, the costs come back to wildfires; in others, like Maine, to storm remediation. Looking backwards to 2019, researchers have not been able to find a regular relationship between load growth and price hikes.
In fact, several states “absorbed large industrial and data center load additions while reducing inflation-adjusted retail prices,” according to researchers at Columbia University’s Center on Global Energy Policy. By contrast, some states with little load growth from industry or data centers, such as Maine or California, have seen prices rise substantially.
Many analysts expect electricity prices to continue rising nationally, and data centers could be a driver going forward as demand hits a grid whose capacity to generate and transmit electricity is increasingly strained. This is likely already happening in the country’s largest electricity market, PJM Interconnection, where the system’s independent market monitor has claimed that current and forecasted data center demand has cost customers over $23 billion from recent capacity auctions.
To get prices to actually fall — or at least grow more slowly —it would require that “low-cost supply is available, existing infrastructure is more fully utilized, and cost allocation ensures that new demand contributes to system efficiency,” the Columbia researchers write. Under business as usual however, prices will likely continue to rise.
On the second question, there is much more cynicism.
Critics of the original Ratepayer Protection Pledge, including Harvard Law School’s Ari Peskoe, pointed out that the actual parties to ratemaking — utilities and state regulators — were not involved in the pledge at all. Already, there are accusations that projects developed by pledge signatories could lead to higher prices. Meta's sprawling planned data center project in Louisiana is responsible for the utility’s plans to buy a Texas natural gas-fired power plant, according to documents filed by regulators reviewed by the Times-Picayune. The $1.8 billion deal could lead to $8 a month in additional costs for typical Louisiana ratepayers.
The Ratepayer Protection Act would go a bit further than the pledge, amending the Public Utility Regulatory Policies Act to “establish a Federal standard relating to the recovery of the full, incremental costs of upgrades that serve large-load customers.” Peskoe, however, described this to me in an email as “largely symbolic” and noted that “Congress may not force state regulators to do anything” under current Supreme Court jurisprudence. “This section of PURPA is basically Congress asking state regulators to please take a look at the ratemaking standard.”
That being said, Peskoe noted that “many states and non-regulated utilities do tend to consider PURPA ratemaking standards,” but that there’s “no enforcement mechanism,” depriving the law of any teeth. “States can reject the ratemaking standards or adopt them in a way that deviates from what Congress may have intended.”
Still, it is likely in the political interest of state regulators to come up with something on large load tariffs, the Cato Institute’s Travis Fisher told me. He recommended that the National Association of Regulatory Utility Commissioners “spearhead an initiative to get every state regulator to sign a ratepayer protection pledge,” if only to insulate themselves from political backlash and maintain their power over retail ratemaking.
But even if states do adopt the cost allocation principle, determining exactly which infrastructure is being installed due to a data center and what serves all users can be tricky.
“Any real-world example of this is going to be quite complicated, and the devil’s always in the details,” Ben Schifman, a senior technology fellow at the Institute for Progress and a former attorney at the Department of the Interior and the Department of Justice, told me. While it might be possible to conclude that “a given substation is simply only needed for that data center,” he said, “as soon as you start zooming out into the larger, big-ticket investments, it’s quite complicated to attribute the cost to one user or one group of users.”
In summary, the Ratepayer Protection Act will ask state regulators to consider an approach to data center cost allocation that may not capture all of their costs and will likely do little to arrest the fundamental drivers of higher electricity costs. Viewed through this lens, the logic of the coalition supporting both the original Ratepayer Protection Pledge and the beefed-up Ratepayer Protection Act comes into focus.
Electricity prices are likely to continue to rise, and data center construction has powerful interests behind it. The public’s attitude towards data centers is rapidly souring, and no matter how many nuanced PDFs are published on the topic, people continue to blame data centers for higher electricity costs.
And if prices continue to rise, the big data center developers may be able to point to the Ratepayer Protection Act and say “well, it wasn’t me.”
On simplified oil and gas leases, lawsuits over plastic and coal, and a new climate research database
Current conditions: The U.K.’s Met Office issued its second-ever Red Extreme Heat Warning for Wednesday and Thursday • A wildfire near Eureka, Utah forced the town’s evacuation • Flash flood warnings are in effect today for Southern Massachusetts.
Lucid Motors is downsizing, again. The electric vehicle maker is laying off 18% of its staff just a few months after a 12% reduction in force in February, according to Electrek. The company also eliminated a second production shift at its factory in Casa Grande, Arizona. EV sales plummeted in the U.S. after the federal EV tax credit expired in September. While many automakers are canceling new electric vehicle lines in the U.S., Lucid hasn’t axed any plans yet, and will be releasing its first lower-cost EV, the Lucid Cosmos SUV, later this year with a price tag under $50,000. It’s also preparing to launch a robotaxi service later this year in partnership with Uber and the autonomous driving technology company Nuro. According to Lucid’s new CEO, Silvio Napoli, the staff cuts will help “simplify the company, sharpen execution, and position Lucid to become more competitive over time.”

Trump’s environmental deregulation crusade continues. The Interior Department proposed several changes to the rules governing oil and gas leasing on federal lands Monday that would limit public input and cut costs for companies. Under existing rules, which were updated during the Biden administration, companies must maintain a minimum bond of $500,000 for each state where they hold leases to cover the cost of capping oil and gas wells when they are done drilling. Trump’s proposal would reduce the requirement to $25,000, shifting the financial risk of remediation to state taxpayers. The new rules would also shorten public participation periods from 90 days to 10, and get rid of a requirement that companies include plans to minimize methane emissions when they apply for drilling permits.
Red states are going after California, this time for its nation-leading plastic regulations. In 2022, the Golden State passed a law setting plastic waste reduction targets and requiring companies to cover the cost of recycling of their own products. The state aims to cut single-use plastic packaging on products by 25% by 2032. Now, 17 attorneys general from red states have teamed up with the National Association of Wholesaler-Distributors, a trade group, to sue California, arguing that the rules represent an “unprecedented overreach” that will increase the cost of goods throughout the country.
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In the first case of its kind, 10 Australians are suing the government for violating their human rights by failing to limit fossil fuel production. The claimants, each of whom has been personally affected by climate change-fueled extreme weather, brought the case to the United Nations’ Human Rights Committee on Monday. Some of them have lost their homes to wildfires and floods, while others have experienced health impacts from heat waves. The case follows a 2025 ruling by the International Court of Justice that all governments have an obligation to protect people from climate change, citing support for fossil fuel production and consumption as a potential violation of this obligation. While that ruling didn’t have any enforcement power, it teed up the potential for country-level claims like this one in Australia. The country is the second largest exporter of coal in the world and the third largest exporter of liquified natural gas.
The rumors were true. The Trump administration has appointed Travis Kavulla, a former utility regulator and power company executive, to lead the Bonneville Power Administration, a federal agency that sells electricity from the government’s hydroelectric dams in the Pacific Northwest. Kavulla arrives as the agency prepares for a controversial exit from California’s real-time electricity trading market to join a new day-ahead market overseen by the Southwest Power Pool, a regional transmission organization. Environmental groups are urging Kavulla reconsider the decision, arguing that it risks raising energy costs for Northwest ratepayers.
The climate change research and news site Carbon Brief debuted Project Cosmos on Monday, the world’s largest database of research on the warming planet. It includes more than 1.8 million publications and “captures the vast body of human knowledge about climate change that has accumulated over more than a century of academic study.” The architects created a stunning “star” map that visualizes the collection by clustering of fields of study, such as medicine, chemistry, or agriculture. They also identified the 500 most-cited studies and scientists, with French carbon cycle modeler Philippe Ciais earning the top spot.