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The basics on the world’s fastest-growing source of renewable energy.
Solar power is already the backbone of the energy transition. But while the basic technology has been around for decades, in more recent years, installations have proceeded at a record pace. In the United States, solar capacity has grown at an average annual rate of 28% over the past decade. Over a longer timeline, the growth is even more extraordinary — from an stalled capacity base of under 1 gigawatt with virtually no utility-scale solar in 2010, to over 60 gigawatts of utility-scale solar in 2020, and almost 175 gigawatts today. Solar is the fastest-growing source of renewable energy in both the U.S. and the world.
There are some drawbacks to solar, of course. The sun, famously, does not always shine, nor does it illuminate all places on Earth to an equal extent. Placing solar where it’s sunniest can sometimes mean more expense and complexity to connect to the grid. But combined with batteries — especially as energy storage systems develop beyond the four hours of storage offered by existing lithium-ion technology — solar power could be the core of a decarbonized grid.
Solar power can be thought of as a kind of cousin of the semiconductors that power all digital technology. As Princeton energy systems professor and Heatmap contributor Jesse Jenkins has explained, certain materials allow for electrons to flow more easily between molecules, carrying an electrical charge. On one end of the spectrum are your classic conductors, like copper, which are used in transmission lines; on the other end are insulators, like rubber, which limit electrical charges.
In between on that spectrum are semiconductors, which require some amount of energy to be used as a conductor. In the computing context these are used to make transistors, and in the energy context they’re used to make — you guessed it — solar panels.
In a solar panel, the semiconductor material absorbs heat and light from the sun, allowing electrons to flow. The best materials for solar panels, explained Jenkins, have just the right properties so that when they absorb light, all of that energy is used to get the electrons flowing and not turned into wasteful heat. Silicon fits the bill.
When you layer silicon with other materials, you can force the electrons to flow in a single direction consistently; add on a conductive material to siphon off those subatomic particles, and voilà, you’ve got direct current. Combine a bunch of these layers, and you’ve got a photovoltaic panel.
Globally, solar generation capacity stood at over 2,100 terawatt-hours in 2024, according to Our World in Data and the Energy Institute, growing by more than a quarter from the previous year. A huge portion of that growth has been in China, which has almost half of the world’s total installed solar capacity. Installations there have grown at around 40% per year in the past decade.
Solar is still a relatively small share of total electricity generation, however, let alone all energy usage, which includes sectors like transportation and industry. Solar is the sixth largest producer of electricity in the world, behind coal, gas, hydropower, nuclear power, and wind. It’s the fourth largest non-carbon-emitting generation source and the third largest renewable power source, after wind and hydropower.
Solar has taken off in the United States, too, where utility-scale installations make up almost 4% of all electricity generated.
While that doesn’t seem like much, overall growth in generation has been tremendous. In 2024, solar hit just over 300 terawatt-hours of generation in the U.S., compared to about 240 terawatt-hours in 2023 and just under 30 in 2014.
Looking forward, there’s even more solar installation planned. Developers plan to add some 63 gigawatts of capacity to the grid this year, following an additional 30 gigawatts in 2024, making up just over half of the total planned capacity additions, according to Energy information Administration.
Solar is cheap compared to other energy sources, and especially other renewable sources. The world has a lot of practice dealing with silicon at industrial scale, and China especially has rapidly advanced manufacturing processes for photovoltaic cells. Once the solar panel is manufactured, it’s relatively simple to install compared to a wind turbine. And compared to a gas- or coal-fired power plant, the fuel is free.
From 1975 to 2022, solar module costs fell from over $100 per watt to below $0.50, according to Our World In Data. From 2012 to 2022 alone, costs fell by about 90%, and have fallen by “around 20% every time the global cumulative capacity doubles,” writes OWID analyst Hannah Ritchie. Much of the decline in cost has been attributed to “Wright’s Law,” which says that unit costs fall as production increases.
While construction costs have flat-lined or slightly increased recently due to supply chain issues and overall inflation, the overall trend is one of cost declines, with solar construction costs declining from around $3,700 per kilowatt-hour in 2013, to around $1,600 in 2023.
There are solar panels at extreme latitudes — Alaska, for instance, has seen solar growth in the past few years. But there are obvious challenges with the low amount of sunlight for large stretches of the year. At higher latitudes, irradiance, a measure of how much power is transmitted from the sun to a specific area, is lower (although that also varies based on climate and elevation). Then there are also more day-to-day issues, such as the effect of snow and ice on panels, which can cause issues in turning sunlight into power (they literally block the panel from the sun). High latitudes can see wild swings in solar generation: In Tromso, in northern Norway, solar generation in summer months can be three times as high as the annual average, with a stretch of literally zero production in December and January.
While many Nordic countries have been leaders in decarbonizing their electricity grids, they tend not to rely on solar in that project. In Sweden, nuclear and hydropower are its largest non-carbon-emitting fuel sources for electricity; in Norway, electricity comes almost exclusively from hydropower.
There has been some kind of policy support for solar power since 1978, when the Energy Tax Act provided tax credits for solar power investment. Since then, the investment tax credit has been the workhorse of American solar policy. The tax credit as it was first established was worth 10% of the system’s upfront cost “for business energy property and equipment using energy resources other than oil or natural gas,” according to the Congressional Research Service.
But above that baseline consistency has been a fair amount of higher-level turmoil, especially recently. The Energy Policy Act of 2005 kicked up the value of that credit to 30% through 2007; Congress kept extending that timeline, with the ITC eventually scheduled to come down to 10% for utility-scale and zero for residential projects by 2024.
Then came the 2022 Inflation Reduction Act, which re-instituted the 30% investment tax credit, with bonuses for domestic manufacturing and installing solar in designated “energy communities,” which were supposed to be areas traditionally economically dependent on fossil fuels. The tax then transitioned into a “technology neutral” investment tax credit that applied across non-carbon-emitting energy sources, including solar, beginning in 2024.
This year, Congress overhauled the tax incentives for solar (and wind) yet again. Under the One Big Beautiful Bill Act, signed in July, solar projects have to start construction by July 2026, or complete construction by the end of 2027 to qualify for the tax credit. The Internal Revenue Service later tightened up its definition of what it means for a project to start construction, emphasizing continuing actual physical construction activities as opposed to upfront expenditures, which could imperil future solar development.
At the same time, the Trump administration is applying a vise to renewables projects on public lands and for which the federal government plays a role in permitting. Renewable industry trade groups have said that the highest levels of the Department of Interior are obstructing permitting for solar projects on public lands, which are now subject to a much closer level of review than non-renewable energy projects.
Massachusetts Institute of Technology Researchers attributed the falling cost of solar this century to “scale economies.” Much of this scale has been achieved in China, which dominates the market for solar panel production, especially for export, even though much of the technology was developed in the United States.
At this point, however, the cost of an actual solar system is increasingly made up of “soft costs” like labor and permitting, at least in the United States. According to data from the National Renewables Energy Laboratory, a utility-scale system costs $1.20 per watt, of which soft costs make up a third, $0.40. Ten years ago, a utility-scale system cost $2.90 per watt, of which soft costs was $1.20, or less than half.
Beyond working to make existing technology even cheaper, there are other materials-based advances that promise higher efficiency for solar panels.
The most prominent is “perovskite,” the name for a group of compounds with similar structures that absorb certain frequencies of light particularly well and, when stacked with silicon, can enable more output for a given amount of solar radiation. Perovskite cells have seen measured efficiencies upwards of 34% when combined with silicon, whereas typical solar cells top out around 20%.
The issue with perovskite is that it’s not particularly durable, partially due to weaker chemical bonds within the layers of the cell. It’s also more expensive than existing solar, although much of that comes down inefficient manufacturing processes. If those problems can be solved, perovskite could promise more output for the same level of soft costs as silicon-based solar panels.
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Current conditions: In the Atlantic, the tropical storm that could, as it develops, take the name Jerry is making its way westward toward the U.S. • In the Pacific, Hurricane Priscilla strengthened into a Category 2 storm en route to Arizona and the Southwest • China broke an October temperature record with thermometers surging near 104 degrees Fahrenheit in the southeastern province of Fujian.
The Department of Energy appears poised to revoke awards to two major Direct Air Capture Hubs funded by the Infrastructure Investment and Jobs Act in Louisiana and Texas, Heatmap’s Emily Pontecorvo reported Tuesday. She got her hands on an internal agency project list that designated nearly $24 billion worth of grants as “terminated,” including Occidental Petroleum’s South Texas DAC Hub and Louisiana's Project Cypress, a joint venture between the DAC startups Heirloom and Climeworks. An Energy Department spokesperson told Emily that he was “unable to verify” the list of canceled grants and said that “no further determinations have been made at this time other than those previously announced,”referring to the canceled grants the department announced last week. Christoph Gebald, the CEO of Climeworks, acknowledged “market rumors” in an email, but said that the company is “prepared for all scenarios.” Heirloom’s head of policy, Vikrum Aiyer, said the company wasn’t aware of any decision the Energy Department had yet made.
While the list floated last week showed the Trump administration’s plans to cancel the two regional hydrogen hubs on the West Coast, the new list indicated that the Energy Department planned to rescind grants for all seven hubs, Emily reported. “If the program is dismantled, it could undermine the development of the domestic hydrogen industry,” Rachel Starr, the senior U.S. policy manager for hydrogen and transportation at Clean Air Task Force told her. “The U.S. will risk its leadership position on the global stage, both in terms of exporting a variety of transportation fuels that rely on hydrogen as a feedstock and in terms of technological development as other countries continue to fund and make progress on a variety of hydrogen production pathways and end uses.”
Remember the Tesla announcement I teased in yesterday’s newsletter? The predictions proved half right: The electric automaker did, indeed, release a cheaper version of its midsize SUV, the Model Y, with a starting price just $10 shy of $40,000. Rather than a new Roadster or potential vacuum cleaner, as the cryptic videos the company posted on CEO Elon Musk’s social media site hinted, the second announcement was a cheaper version of the Model 3, already the lower-end sedan offering. Starting at $36,990, InsideEVs called it “one of the most affordable cars Tesla has ever sold, and the cheapest in 2025.” But it’s still a far cry from Musk’s erstwhile promise to roll out a Tesla for less than $30,000.
That may be part of why the company is losing market share. As Heatmap’s Matthew Zeitlin reported, Tesla’s slice of the U.S. electric vehicle sales sank to its lowest-ever level in August despite Americans’ record scramble to use the federal tax credits before the September 30 deadline President Donald Trump’s new tax law set. General Motors, which sold more electric vehicles in the third quarter of this year than in all of 2024, offers the cheapest battery-powered passenger vehicle on the market today, the Chevrolet Equinox, which starts at $35,100.
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Trump’s pledge to revive the United States’ declining coal industry was always a gamble — even though, as Matthew reported in July, global coal demand is rising. Three separate stories published Tuesday show just how stacked the odds are against a major resurgence:
As you may recall from two consecutive newsletters last month, Secretary of Energy Chris Wright said “permitting reform” was “the biggest remaining thing” in the administration’s agenda. Yet Republican leaders in Congress expressed skepticism about tacking energy policy into the next reconciliation bill. This week, however, Utah Senator Mike Lee, the chairman of the Senate Committee on Energy and Natural Resources, called for a legislative overhaul of the National Environmental Policy Act. On Monday, the pro-development social media account Yimbyland — short for Yes In My Back Yard — posted on X: “Reminder that we built the Golden Gate Bridge in 4.5 years. Today, we wouldn’t even be able to finish the environmental review in 4.5 years.” In response, Lee said: “It’s time for NEPA reform. And permitting reform more broadly.”
Last month, a bipartisan permitting reform bill got a hearing in the House of Representatives. But that was before the government shutdown. And sources familiar with Democrats’ thinking have in recent months suggested to me that the administration’s gutting of so many clean energy policies has left Republicans with little to bargain with ahead of next year’s midterm elections.
Soon-to-be Japanese prime minister Sanae Takaichi.Yuichi Yamazaki - Pool/Getty Images
On Saturday, Japan’s long-ruling Liberal Democratic Party elected its former economic minister, Sanae Takaichi, as its new leader, putting her one step away from becoming the country’s first woman prime minister. Under previous administrations, Japan was already on track to restart the reactors idled after the 2011 Fukushima disaster. But Takaichi, a hardline conservative and nationalist who also vowed to re-militarize the nation, has pushed to speed up deployment of new reactors and technologies such as fusion in hopes of making the country 100% self-sufficient on energy.
“She wants energy security over climate ambition, nuclear over renewables, and national industry over global corporations,” Mika Ohbayashi, director at the pro-clean-energy Renewable Energy Institute, told Bloomberg. Shares of nuclear reactor operators surged by nearly 7% on Monday on the Tokyo Stock Exchange, while renewable energy developers’ stock prices dropped by as much as 15%
Researchers at the United Arab Emirates’ University of Sharjah just outlined a new method to transform spent coffee grounds and a commonly used type of plastic used in packaging into a form of activated carbon that can be used for chemical engineering, food processing, and water and air treatments. By repurposing the waste, it avoids carbon emitting from landfills into the atmosphere and reduces the need for new sources of carbon for industrial processes. “What begins with a Starbucks coffee cup and a discarded plastic water bottle can become a powerful tool in the fight against climate change through the production of activated carbon,” Dr. Haif Aljomard, lead inventor of the newly patented technology, said in a press release.
Last week’s Energy Department grant cancellations included funding for a backup energy system at Valley Children’s Hospital in Madera, California
When the Department of Energy canceled more than 321 grants in an act of apparent retribution against Democrats over the government shutdown, Russ Vought, President Trump’s budget czar, declared that the money represented “Green New Scam funding to fuel the Left's climate agenda.”
At least one of the grants zeroed out last week, however, was supposed to help keep the lights on at a children’s hospital.
The $29 million grant was intended to build a 3.3-megawatt long-duration energy storage system at Valley Children’s Hospital, a large pediatric hospital in Madera, California. The system would “power critical hospital operations during outage events,” such as when the California grid shuts down to avoid starting wildfires, according to project documents.
“The U.S. Department of Energy’s cancellation of funding for [the] long-duration energy storage demonstration grant is disappointing,” Zara Arboleda, a spokesperson for the hospital, told me.
Valley Children’s Hospital is a 358-bed hospital that says it serves more than 1.3 million children across California’s Central Valley. It has 28 neonatal intensive care unit beds and nationally ranked specialties in pediatric neurology, orthopedics, and lung surgery, among others.
Energy Secretary Chris Wright has characterized the more than $7.5 billion in grants canceled last week as part of an ongoing review of financial awards made by the Biden administration. But the timing of the cancellations — and Vought’s gleeful tweets about them — suggests a more vindictive purpose. Republican lawmakers and President Trump himself threatened to unleash Vought as a kind of rogue budget cutter before the federal government shut down last week.
“We don’t control what he’s going to do,” Senator John Thune told Politico last week. “I have a meeting today with Russ Vought, he of PROJECT 2025 Fame, to determine which of the many Democrat Agencies, most of which are a political SCAM, he recommends to be cut,” Trump posted on the same day.
Up until this year, canceling funding that is already under contract with a private party would have been thought to be straightforwardly illegal under federal law. But the Supreme Court’s conservative majority has allowed the Trump administration to act with previously unimaginable freedom while it considers ruling on similar cases.
Faraday Microgrids, the contractor that was due to receive the funding, is already building a microgrid for the hospital. The proposed backup power system — which the grant stipulated should be “non-lithium-ion” — was supposed to be funded by the Energy Department’s Office of Clean Energy Demonstrations, with the goal of finding new ways of storing electricity without using lithium-ion batteries, and was meant to work in concert with that new microgrid and snap on in times of high stress.
That microgrid project is still moving forward, Arboleda, the hospital’s spokesperson, told me. “Valley Children’s Hospital continues to build and soon will operate its microgrid announced in 2023 to ensure our facilities have access to reliable and sustainable energy every minute of every day for our patients and our care providers,” she added. That grid will contain some storage, but not the long-term storage system discussed in the official plan.
Faraday Microgrids, formerly known as Charge Bliss, didn’t respond to a request for comment, but its website touts its ability to secure grants and other government funding for energy projects.
In a statement, a spokesman for the Energy Department said that the grant was canceled because the project wasn’t feasible. “Following an in-depth review of the financial award, it was determined, among other reasons, that the viability of the project was not adequate to warrant further disbursements,” Ben Dietderich, a spokesman for the Energy Department, told me.
The children’s hospital, at least, is in good company. On Tuesday, a Trump administration document obtained by Heatmap News suggested the Energy Department is moving to kill bipartisan-backed funding for two direct air capture hubs in Texas and Louisiana. And although California has lost the most grants of any state, the Energy Department has also sought to terminate funding for new factories and industrial facilities across Republican-governed states.
Rob and Jesse break down China’s electricity generation with UC San Diego’s Michael Davidson.
China announced a new climate commitment under the Paris Agreement at last month’s United Nations General Assembly meeting, pledging to cut its emissions by 7% to 10% by 2035. Many observers were disappointed by the promise, which may not go far enough to forestall 2 degrees Celsius of warming. But the pledge’s conservatism reveals the delicate and shifting politics of China’s grid — and how the country’s central government and its provinces fight over keeping the lights on.
On this week’s episode of Shift Key, Rob and Jesse talk to Michael Davidson, an expert on Chinese electricity and climate policy. He is a professor at the University of California, San Diego, where he holds a joint faculty appointment at the School of Global Policy and Strategy and the Jacobs School of Engineering. He is also a senior associate at the Center for Strategic and International Studies, and he was previously the U.S.-China policy coordinator for the Natural Resources Defense Council.
Shift Key is hosted by Robinson Meyer, the founding executive editor of Heatmap, and Jesse Jenkins, a professor of energy systems engineering at Princeton University.
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Here is an excerpt from our conversation:
Robinson Meyer: Your research and other people’s research has revealed that basically, when China started making capacity payments to coal plants, in some cases, it didn’t have the effect on the bottom line of these plants that was hoped for, and also we didn’t really see coal generation go down or change in the year that it happened. It wasn’t like they were paying these plants to stick around and not run. They were basically paying these plants, it seems like, to do the exact same thing they did the year before, but now they also got paid. And maybe that was needed for their economics, we can talk about it.
Why did coal get those payments and not, say, batteries or other sources of spare capacity, like pumped hydro storage, like nuclear? Why did coal, specifically, get payments for capacity? And does it have to do with spinning reserve? Or does it have to do with the political economy of coal in China?
Michael Davidson: When it came out, we said exactly the same thing. We said, okay, this should be a technology neutral payment scheme, and it should be a market, not a payment, right? But China’s building these things up little by little. Over time we’ve seen, historically, actually, a number of systems internationally started with payments before they move to markets because they realize that you could get a lot more competitive pressure with markets.
The capacity payment scheme for coal is extremely simple, right? It says, okay, for each province, we’re going to say what percentage of our benchmark coal investment costs are we going to subsidize. It’s extremely simple. It does not account for how much you’re using it at a plant by plant level. It does not account for other factors, renewables, etc. It’s a very coarse metric. But I wouldn’t say that it had had some, you know, perverse negative effect on the outcome of what coal generation is. Probably more likely is that these payments were seen, for some, as extra support. But then for some that are really hurting, they’re saying, okay, well then we will maybe put up less obstacles to market reforms.
But then on top of that, you have to put in the hourly energy demand growth story and say, okay, well you have all these renewables, but you don’t have enough storage to shift to evening peaks. You are going to rely on coal to meet that given the current rigid dispatch system. And so you’re dispatching them kind of regardless of whether or not you have the payment schemes.
I will say that I was a skeptic, right? Because when people told me that China should put in place a capacity market, I said, China has overcapacity. So if you have an overcapacity situation, you put in place a market, the prices should be zero. So what’s the point? But actually, when you’re looking out ahead with all of this surplus coal capacity that you’re trying to push down, you’re trying to push those capacity factors of those coal plans from 50%, 60%, down to 20% or even lower, they need to have other revenue schemes if you’re not going to dramatically open up your spot markets, which China is very hesitant to do — very risk averse when it comes to the openness of spot markets, in terms of price gaps. So that’s a necessary part of this transition. But it can be done more efficiently, and it should done technology neutral.
And by the way that is happening in certain places. That’s a national scheme, but we actually see that the implementation — for example, Shaanxi province, we have a technology neutral scheme that would include other resources, not just coal.
Mentioned:
China’s new pledge to cut its emissions by 2035
What an ‘ambitious’ 2035 electricity target looks like for China
China’s Clean Energy Pledge is Clouded by Coal, The Wire China
Jesse’s upshift; Rob’s upshift.
This episode of Shift Key is sponsored by …
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A warmer world is here. Now what? Listen to Shocked, from the University of Chicago’s Institute for Climate and Sustainable Growth, and hear journalist Amy Harder and economist Michael Greenstone share new ways of thinking about climate change and cutting-edge solutions. Find it here.
Music for Shift Key is by Adam Kromelow.