Eliminating carbon pollution from aviation is one of the most challenging parts of the climate puzzle, simply because large commercial airlines are too heavy and need too much power during takeoff for today’s batteries to do the job. 

But one way that companies and governments are striving to make some progress is through the use of various types of sustainable aviation fuels (SAFs), which are derived from non-petroleum sources and promise to be less polluting than standard jet fuel.

This week, the US announced a push to help its biggest commercial crop, corn, become a major feedstock for SAFs. 

Federal guidelines announced on April 30 provide a pathway for ethanol producers to earn SAF tax credits within the Inflation Reduction Act, President Biden’s signature climate law, when the fuel is produced from corn or soy grown on farms that adopt certain sustainable agricultural practices.

It’s a limited pilot program, since the subsidy itself expires at the end of this year. But it could set the template for programs in the future that may help ethanol producers generate more and more SAFs, as the nation strives to produce billions of gallons of those fuels per year by 2030. 

Consequently, the so-called Climate Smart Agricultural program has already sounded alarm bells among some observers, who fear that the federal government is both overestimating the emissions benefits of ethanol and assigning too much credit to the agricultural practices in question. Those include cover crops, no-till techniques that minimize soil disturbances, and use of “enhanced-efficiency fertilizers,” which are designed to increase uptake by plants and thus reduce runoff into the environment.

The IRA offers a tax credit of $1.25 per gallon for SAFs that are 50% lower in emissions than standard jet fuel, and as much as 50 cents per gallon more for sustainable fuels that are cleaner still. The new program can help corn- or soy-based ethanol meet that threshold when the source crops are produced using some or all of those agricultural practices.

Since the vast majority of US ethanol is produced from corn, let’s focus on the issues around that crop. To get technical, the program allows ethanol producers to subtract 10 grams of carbon dioxide per megajoule of energy, a measure of carbon intensity, from the life-cycle emissions of the fuel when it’s generated from corn produced with all three of the practices mentioned. That’s about an eighth to a tenth of the carbon intensity of gasoline.

Ethanol’s questionable climate footprint

Today, US-generated ethanol is mainly mixed with gasoline. But ethanol producers are eager to develop new markets for the product as electric vehicles make up a larger share of the cars and trucks on the road. Not surprisingly, then, industry trade groups applauded the announcement this week.

The first concern with the new program, however, is that the emissions benefits of corn-based ethanol have been hotly debated for decades.

Corn, like any plant that uses photosynthesis to produce food, sucks up carbon dioxide from the air. But using corn for fuel rather than food also creates pressure to clear more land for farming, a process that releases carbon dioxide from plants and soil. In addition, planting, fertilizing, and harvesting corn produce climate pollution as well, and the same is true of refining, distributing, and burning ethanol. 

For its analyses under the new program, the Treasury Department intends to use an updated version of the so-called GREET model to evaluate the life-cycle emissions of SAFs, which was developed by the Department of Energy’s Argonne National Lab. A 2021 study from the lab, relying on that model, concluded that US corn ethanol produced as much as 52% less greenhouse gas than gasoline. 

But some researchers and nonprofits have criticized the tool for accepting low estimates of the emissions impacts of land-use changes, among other issues. Other assessments of ethanol emissions have been far more damning.

A 2022 EPA analysis surveyed the findings from a variety of models that estimate the life-cycle emissions of corn-based ethanol and found that in seven out of 20 cases, they exceeded 80% of the climate pollution from gasoline and diesel.

Moreover, the three most recent estimates from those models found ethanol emissions surpassed even the higher-end estimates for gasoline or diesel, Alison Cullen, chair of the EPA’s science advisory board, noted in a 2023 letter to the administrator of the agency.

“Thus, corn starch ethanol may not meet the definition of a renewable fuel” under the federal law that mandates the use of biofuels in the market, she wrote. If so, it’s then well short of the 50% threshold required by the IRA, and some say it’s not clear that the farming practices laid out this week could close the gap.

Agricultural practices

Nikita Pavlenko, who leads the fuels team at the International Council on Clean Transportation, a nonprofit research group, asserted in an email that the climate-smart agricultural provisions “are extremely sloppy” and “are not substantiated.” 

He said the Department of Energy and Department of Agriculture especially “put their thumbs on the scale” on the question of land-use changes, using estimates of soy and corn emissions that were 33% to 55% lower than those produced for a program associated with the UN’s International Civil Aviation Organization.

He finds that ethanol sourced from farms using these agriculture practices will still come up short of the IRA’s 50% threshold, and that producers may have to take additional steps to curtail emissions, potentially including adding carbon capture and storage to ethanol facilities or running operations on renewables like wind or solar.

Freya Chay, a program lead at CarbonPlan, which evaluates the scientific integrity of carbon removal methods and other climate actions, says that these sorts of agricultural practices can provide important benefits, including improving soil health, reducing erosion, and lowering the cost of farming. But she and others have stressed that confidently determining when certain practices actually and durably increase carbon in soil is “exceedingly complex” and varies widely depending on soil type, local climate conditions, past practices, and other variables.

One recent study of no-till practices found that the carbon benefits quickly fade away over time and reach nearly zero in 14 years. If so, this technique would do little to help counter carbon emissions from fuel combustion, which can persist in the atmosphere for centuries or more.

“US policy has a long history of asking how to continue justifying investment in ethanol rather than taking a clear-eyed approach to evaluating whether or not ethanol helps us reach our climate goals,” Chay wrote in an email. “In this case, I think scrutiny is warranted around the choice to lean on agricultural practices with uncertain and variable benefits in a way that could unlock the next tranche of public funding for corn ethanol.”

There are many other paths for producing SAFs that are or could be less polluting than ethanol. For example, they can be made from animal fats, agriculture waste, forest trimmings, or non-food plants that grow on land unsuitable for commercial crops. Other companies are developing various types of synthetic fuels, including electrofuels produced by capturing carbon from plants or the air and then combining it with cleanly sourced hydrogen. 

But all these methods are much more expensive than extracting and refining fossil fuels, and most of the alternative fuels will still produce more emissions when they’re used than the amount that was pulled out of the atmosphere by the plants or processes in the first place. 

The best way to think of these fuels is arguably as a stopgap, a possible way to make some climate progress while smart people strive to develop and build fully emissions-free ways of quickly, safely, and reliably moving things and people around the globe.

Whenever you see a solar panel, most parts of it probably come from China. The US invented the technology and once dominated its production, but over the past two decades, government subsidies and low costs in China have led most of the solar manufacturing supply chain to be concentrated there. The country will soon be responsible for over 80% of solar manufacturing capacity around the world.

But the US government is trying to change that. Through high tariffs on imports and hefty domestic tax credits, it is trying to make the cost of manufacturing solar panels in the US competitive enough for companies to want to come back and set up factories. The International Energy Agency has forecast that by 2027, solar-generated energy will be the largest source of power capacity in the world, exceeding both natural gas and coal—making it a market that already attracts over $300 billion in investment every year.

To understand the chances that the US will succeed, MIT Technology Review spoke to Shawn Qu. As the founder and chairman of Canadian Solar, one of the largest and longest-standing solar manufacturing companies in the world, Qu has observed cycle after cycle of changing demand for solar panels over the last 28 years. 

After decades of mostly manufacturing in Asia, Canadian Solar is pivoting back to the US because it sees a real chance for a solar industry revival, mostly thanks to the Inflation Reduction Act (IRA) passed in 2022. The incentives provided in the bill are just enough to offset the higher manufacturing costs in the US, Qu says. He believes that US solar manufacturing capacity could grow significantly in two to three years, if the industrial policy turns out to be stable enough to keep bringing companies in. 

How tariffs forced manufacturing capacity to move out of China

There are a few important steps to making a solar panel. First silicon is purified; then the resulting polysilicon is shaped and sliced into wafers. Wafers are treated with techniques like etching and coating to become solar cells, and eventually those cells are connected and assembled into solar modules.

For the past decade, China has dominated almost all of these steps, for a few reasons: low labor costs, ample supply of proficient workers, and easy access to the necessary raw materials. All these factors make made-in-China solar modules extremely price-competitive. By the end of 2024, a US-made solar panel will still cost almost three times as much as one produced in China, according to researchers at BloombergNEF. 

The question for the US, then, is how to compete. One tool the government has used since 2012 is tariffs. If a solar module containing cells made in China is imported to the US, it’s subject to as much as a 250% tariff. To avoid those tariffs, many companies, including Canadian Solar, have moved solar cell manufacturing and the downstream supply chain to Southeast Asia. Labor costs and the availability of labor forces are “the number one reason” for that move, Qu says.

When Canadian Solar was founded in 2001, it made all its solar products in China. By early 2023, the company had factories in four countries: China, Thailand, Vietnam, and Canada. (Qu says it used to manufacture in Brazil and Taiwan too, but later scaled back production in response to contracting local demand.)

But that equilibrium is changing again as further tariffs imposed by the US government aim to force supply chains to move out of China. Starting in June 2024, companies importing silicon wafers from China to make cells outside the country will also be subject to tariffs. The most likely solution for solar companies would be to “set up wafer capacity or set up partnerships with wafer makers in Southeast Asia,” says Jenny Chase, the lead solar analyst at BloombergNEF.

Qu says he’s confident the company will meet the new requirements for tariff exemption after June. “They gave the industry about two years to adapt, so I believe most of the companies, at least the tier-one companies, will be able to adapt,” he says.

The IRA, and moving the factories to the US

While US policies have succeeded in turning Southeast Asia into a solar manufacturing hot spot, not much of the supply chain has actually come back to the US. But that’s slowly changing thanks to the IRA, introduced in 2022. The law will hand out tax credits for companies producing solar modules in the US, as well as those installing the panels. 

The credits, Qu says, are enough to make Canadian Solar move some production from Southeast Asia to the US. “According to our modeling, the incentives provided just offset the cost differences—labor and supply chain—between Southeast Asia and the US,” he says.

Jesse Jenkins, an assistant professor in energy and engineering at Princeton University, has come to the same conclusion through his research. He says that the IRA subsidies and tax credits should offset higher costs of manufacturing in the US. “That should drive a significant increase in demand for made-In-America solar modules and subcomponents,” Jenkins says. And the early signs point that way too: since the introduction of the IRA, solar companies have announced plans to build over 40 factories in the US.

In 2023, Canadian Solar announced it would build its first solar module plant in Mesquite, Texas, and a solar cell plant in Jeffersonville, Indiana. The Texas factory started operating in late 2023, while the Indiana one is still in the works. 

The remaining challenges

While the IRA has brought new hope to American solar manufacturing, there are still a few obstacles ahead.

Qu says one big challenge to getting his Texas factory up and running is the lack of experienced workers. “Let’s face the reality: there was almost no silicon-based solar manufacturing in the US, so it takes time to train people,” he says. That’s a process that he expects to take at least six months. 

Another challenge to reshoring solar manufacturing is the uncertainty about whether the US will keep heavily subsidizing the clean energy industry, especially if the White House changes hands after the election this year. “The key is stability,” Qu says, “Sometimes politicians are swayed by special-interest groups.”

“Obviously, if you build a factory, then you do want to know that the incentives to support that factory will be there for a while,” says Chase. There are some indications that support for the IRA won’t necessarily be swayed by the elections. For example, jobs created in the solar industry would be concentrated in red states, so even a Republican administration would be motivated to maintain them. But there’s no guarantee that US policies won’t change course.

This article is from The Spark, MIT Technology Review’s weekly climate newsletter. To receive it in your inbox every Wednesday, sign up here.

Usually when we talk about climate change, the focus is squarely on the role that greenhouse-gas emissions play in driving up global temperatures, and rightly so. But another important, less-known phenomenon is also heating up the planet: reductions in other types of pollution.

In particular, the world’s power plants, factories, and ships are pumping much less sulfur dioxide into the air, thanks to an increasingly strict set of global pollution regulations. Sulfur dioxide creates aerosol particles in the atmosphere that can directly reflect sunlight back into space or act as the “condensation nuclei” around which cloud droplets form. More or thicker clouds, in turn, also cast away more sunlight. So when we clean up pollution, we also ease this cooling effect. 

Before we go any further, let me stress: cutting air pollution is smart public policy that has unequivocally saved lives and prevented terrible suffering. 

The fine particulate matter produced by burning coal, gas, wood, and other biomatter is responsible for millions of premature deaths every year through cardiovascular disease, respiratory illnesses, and various forms of cancer, studies consistently show. Sulfur dioxide causes asthma and other respiratory problems, contributes to acid rain, and depletes the protective ozone layer. 

Air pollution is killing millions of people per year.

It would be a vastly better outcome for humanity if we could cut it rapidly, despite the resulting warming impact on the climate. https://t.co/JYWAWwVtiG

— Zeke Hausfather (@hausfath) April 8, 2024

But as the world rapidly warms, it’s critical to understand the impact of pollution-fighting regulations on the global thermostat as well. Scientists have baked the drop-off of this cooling effect into net warming projections for the coming decades, but they’re also striving to obtain a clearer picture of just how big a role declining pollution will play.

A new study found that reductions in emissions of sulfur dioxide and other pollutants are responsible for about 38%, as a middle estimate, of the increased “radiative forcing” observed on the planet between 2001 and 2019. 

An increase in radiative forcing means that more energy is entering the atmosphere than leaving it, as Kerry Emanuel, a professor of atmospheric science at MIT, lays out in a handy explainer here. As that balance has shifted in recent decades, the difference has been absorbed by the oceans and atmosphere, which is what is warming up the planet. 

The remainder of the increase is “mainly” attributable to continued rising emissions of heat-trapping greenhouse gases, says Øivind Hodnebrog, a researcher at the Center for International Climate and Environment Research in Norway and lead author of the paper, which relied on climate models, sea-surface temperature readings, and satellite observations.

The study underscores the fact that as carbon dioxide, methane, and other gases continue to drive up temperature​​s, parallel reductions in air pollution are revealing more of that additional warming, says Zeke Hausfather, a scientist at the independent research organization Berkeley Earth. And it’s happening at a point when, by most accounts, global warming is about to begin accelerating or has already started to do so. (There’s ongoing debate over whether researchers can yet detect that acceleration and whether the world is now warming faster than researchers had expected.)

Because of the cutoff date, the study did not capture a more recent contributor to these trends. Starting in 2020, under new regulations from the International Maritime Organization, commercial shipping vessels have also had to steeply reduce the sulfur content in fuels. Studies have already detected a decrease in the formation of “ship tracks,” or the lines of clouds that often form above busy shipping routes. 

Again, this is a good thing in the most important way: maritime pollution alone is responsible for tens of thousands of early deaths every year. But even so, I have seen and heard of suggestions that perhaps we should slow down or alter the implementation of some of these pollution policies, given the declining cooling effect.

A 2013 study explored one way to potentially balance the harms and benefits. The researchers simulated a scenario in which the maritime industry would be required to use very low-sulfur fuels around coastlines, where the pollution has the biggest effect on mortality and health. But then the vessels would double the fuel’s sulfur content when crossing the open ocean. 

In that hypothetical world, the cooling effect was a bit stronger and premature deaths declined by 69% with respect to figures at the time, delivering a considerable public health improvement. But notably, under a scenario in which low-sulfur fuels were required across the board, mortality declined by 96%, a difference of more than 13,000 preventable deaths every year.

Now that the rules are in place and the industry is running on low-sulfur fuels, intentionally reintroducing pollution over the oceans would be a far more controversial matter.

While society basically accepted for well over a century that ships were inadvertently emitting sulfur dioxide into the air, flipping those emissions back on for the purpose of easing global warming would amount to a form of solar geoengineering, a deliberate effort to tweak the climate system.

Many think such planetary interventions are far too powerful and unpredictable for us to muck around with. And to be sure, this particular approach would be one of the more ineffective, dangerous, and expensive ways to carry out solar geoengineering, if the world ever decided it should be done at all. The far more commonly studied concept is emitting sulfur dioxide high in the stratosphere, where it would persist for longer and, as a bonus, not be inhaled by humans. 

On an episode of the Energy vs. Climate podcast last fall, David Keith, a professor at the University of Chicago who has closely studied the topic, said that it may be possible to slowly implement solar geoengineering in the stratosphere as a means of balancing out the reduced cooling occurring from sulfur dioxide emissions in the troposphere.

“The kind of solar geoengineering ideas that people are talking about seriously would be a thin wedge that would, for example, start replacing what was happening with the added warming we have from unmasking the aerosol cooling from shipping,” he said. 

Positioning the use of solar geoengineering as a means of merely replacing a cruder form that the world was shutting down offers a somewhat different mental framing for the concept—though certainly not one that would address all the deep concerns and fierce criticisms.

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Read more from MIT Technology Review’s archive: 

Back in 2018, I wrote a piece about the maritime rules that were then in the works and the likelihood that they would fuel additional global warming, noting that we were “about to kill a massive, unintentional” experiment in solar geoengineering.

Another thing

Speaking of the concerns about solar geoengineering, late last week I published a deep dive into Harvard’s unsuccessful, decade-long effort to launch a high-altitude balloon to conduct a tiny experiment in the stratosphere. I asked a handful of people who were involved in the project or followed it closely for their insights into what unfolded, the lessons that can be drawn from the episode—and their thoughts on what it means for geoengineering research moving forward.

Keeping up with Climate 

Yup, as the industry predicted (and common sense would suggest), this week’s solar eclipse dramatically cut solar power production across North America. But for the most part, grid operators were able to manage their systems smoothly, minus a few price spikes, thanks in part to a steady buildout of battery banks and the availability of other sources like natural gas and hydropower. (Heatmap)

There’s been a pile-up of bad news for Tesla in recent days. First, the company badly missed analyst expectations for vehicle deliveries during the first quarter. Then, Reuters reported that the EV giant has canceled plans for a low-cost, mass-market car. That may have something to do with the move to “prioritize the development of a robotaxi,” which the Wall Street Journal then wrote about. Over on X, Elon Musk denied the Reuters story, sort of—posting that “Reuters is lying (again).” But there’s a growing sense that his transformation into a “far-right activist” is exacting an increasingly high cost on his personal and business brands. (Wall Street Journal)

In a landmark ruling this week, the European Court of Human Rights determined that by not taking adequate steps to address the dangers of climate change, including increasingly severe heat waves that put the elderly at particular risk, Switzerland had violated the human rights of a group of older Swiss women who had brought a case against the country. Legal experts say the ruling creates a precedent that could unleash many similar cases across Europe. (The Guardian)

A shut-down nuclear power plant in Michigan could get a second life thanks to a $1.52 billion loan from the US Department of Energy. If successful, it will be the first time a shuttered nuclear power plant reopens in the US.  

Palisades Power Plant shut down on May 20, 2022, after 50 years of generating low-carbon electricity. But the plant’s new owner thinks economic conditions have improved in the past few years and plans to reopen by the end of 2025.

A successful restart would be a major milestone for the US nuclear fleet, and the reactor’s 800 megawatts of capacity could help inch the country closer to climate goals. But reopening isn’t as simple as flipping on a light switch—there are technical, administrative, and regulatory hurdles ahead before Palisades can start operating again. Here’s what it takes to reopen a nuclear power plant.

Step 1: Stay ready

One of the major reasons Palisades has any shot of restarting is that the site’s new owner has been planning on this for years. “Technically, the stars had all aligned for the plant to stay operating,” says Patrick White, research director at the Nuclear Innovation Alliance, a nonprofit think tank.

Holtec International supplies equipment for nuclear reactors and waste and provides services like decommissioning nuclear plants. Holtec originally purchased Palisades with the intention of shutting it down, taking apart the facilities, and cleaning up the site. The company has decommissioned other recently shuttered nuclear plants, including Indian Point Energy Center in New York. 

Changing economic conditions have made continued operation too expensive to justify for many nuclear power plants, especially smaller ones. Those with a single, relatively small reactor, like Palisades, have been the most vulnerable.  

Once a nuclear power plant shuts down, it can quickly become difficult to start it back up. As with a car left out in the yard, White says, “you expect some degradation.” Maintenance and testing of critical support systems might slow down or stop. Backup diesel generators, for example, would need to be checked and tested regularly while a reactor is online, but they likely wouldn’t be treated the same way after a plant’s shutdown, White says.

Holtec took possession of Palisades in 2022 after the reactor shut down and the fuel was removed. Even then, there were already calls to keep the plant’s low-carbon power on the grid, says Nick Culp, senior manager for government affairs and communications at Holtec.

The company quickly pivoted and decided to try to keep the plant open, so records and maintenance work largely continued. “It looks like it shut down yesterday,” Culp says.

Because of the continued investment of time and resources, starting the plant back up will be more akin to restarting after a regular refueling or maintenance outage than starting a fully defunct plant. After maintenance is finished and fresh fuel loaded in, the Palisades reactor could restart and provide enough electricity for roughly 800,000 homes.

Step 2: Line up money and permission

Support has poured in for Palisades, with the state of Michigan setting aside $300 million in funding for the plant’s restart in the last two years. And now, the Department of Energy has issued a conditional loan commitment for $1.52 billion.

Holtec will need to meet certain technical and legal conditions to get the loan money, which will eventually be repaid with interest. (Holtec and the DOE Loan Programs Office declined to give more information about the loan’s conditions or timeline.)

The state funding and federal loan will help support the fixes and upgrades needed for the plant’s equipment and continue paying the approximately 200 workers who have stayed on since its shutdown. The plant employed about 700 people while it was operating, and the company is now working on rehiring additional workers to help with the restart, Culp says.  

One of the major remaining steps in a possible Palisades restart is getting authorization from regulators, as no plant in the US has restarted operations after shutting down. “We’re breaking new ground here,” says Jacopo Buongiorno, a professor of nuclear engineering at MIT. 

The Nuclear Regulatory Commission oversees nuclear power plants in the US, but the agency doesn’t have a specific regulatory framework for restarting operations at a nuclear power plant that has shut down and entered decommissioning, White says. The NRC created a panel that will oversee reopening efforts.

Palisades effectively gave up the legal right to operate when it shut down and took the fuel out of the reactor. Holtec will need to submit detailed plans to the NRC with information about how it plans to reopen and operate the plant safely. Holtec formally began the process of reauthorizing operations with the NRC in October 2023 and plans to submit the rest of its materials this year.

Step 3: Profit?

If regulators sign off, the plan is to have Palisades up and running again by the end of 2025. The fuel supply is already lined up, and the company has long-term buyers committed for the plant’s full power output, Culp says.

If all goes well, the plant could be generating power until at least 2051, 80 years after it originally began operations.

Expanded support for low-carbon electricity sources, and nuclear in particular, have helped make it possible to extend the life of older plants across the US. “This restart of a nuclear plant represents a sea change in support for clean firm power,” says Julie Kozeracki, a senior advisor for the US Department of Energy’s Loan Programs Office.

As of last year, a majority of Americans (57%) support more nuclear power in the country, up from 43% in 2016, according to a poll from the Pew Research Center. There’s growing funding available for the technology as well, including billions of dollars in tax credits for nuclear and other low-carbon energy included in the Inflation Reduction Act. 

Growing support and funding, alongside rising electricity prices, contribute to making existing nuclear plants much more valuable than they were just a few years ago, says MIT’s Buongiorno. “Everything has changed,” he adds.   

But even a successful Palisades restart wouldn’t mean that we’ll see a wave of other shuttered nuclear plants reopening around the US. “This is a really rare case where you had someone doing a lot of forward thinking,” White says. For other plants that are nearing decommissioning, it would be cheaper, simpler, and more efficient to extend their operations rather than allowing them to shut down in the first place. 

Update: This story has been updated with additional details regarding how the NRC may reauthorize Palisades Nuclear Plant.

Plug-in hybrids are supposed to be the best of both worlds—the convenience of a gas-powered car with the climate benefits of a battery electric vehicle. But new data suggests that some official figures severely underestimate the emissions they produce. 

According to new real-world driving data from the European Commission, plug-in hybrids produce roughly 3.5 times the emissions official estimates suggest. The difference is largely linked to driver habits: people tend to charge plug-in hybrids and drive them in electric mode less than expected.

“The environmental impact of these vehicles is much, much worse than what the official numbers would indicate,” says Jan Dornoff, a research lead at the International Council on Clean Transportation.

While conventional hybrid vehicles contain only a small battery to slightly improve fuel economy, plug-in hybrids allow fully electric driving for short distances. These plug-in vehicles typically have a range of roughly 30 to 50 miles (50 to 80 kilometers) in electric driving mode, with a longer additional range when using the secondary fuel, like gasoline or diesel. But drivers appear to be using much more fuel than was estimated.

According to the new European Commission report, drivers in plug-in hybrid vehicles produce about 139.4 grams of carbon dioxide for every kilometer driven, based on measurements of how much fuel vehicles use over time. On the other hand, official estimates from manufacturers, which are determined using laboratory tests, put emissions at 39.6 grams per kilometer driven.

Some of this gap can be explained by differences between the controlled conditions in a lab and real-world driving. Even conventional combustion-engine vehicles tend to have higher real-world emissions than official estimates suggest, though the gap is roughly 20%, not 200% or more as it is for plug-in hybrids.

The major difference comes down to how drivers tend to use plug-in hybrids. Researchers have noticed the problem in previous studies, some of them using crowdsourced data. 

In one study from the ICCT published in 2022, researchers examined real-world driving habits of people in plug-in hybrids. While the method used to determine official emissions values estimated that drivers use electricity to power vehicles 70% to 85% of the time, the real-world driving data suggested that vehicle owners actually used electric mode for 45% to 49% of their driving. And if vehicles were company-provided cars, the average was only 11% to 15%.

The difference between reality and estimates can be a problem for drivers, who may buy plug-in hybrids expecting climate benefits and gas savings. But if drivers are charging less than expected, the benefits might not be as drastic as promised. Trips taken in a plug-in hybrid cut emissions by only 23% relative to trips in a conventional vehicle, rather than the nearly three-quarters reduction predicted by official estimates, according to the new analysis.

“People need to be realistic about what they face,” Dornoff says. Driving the vehicles in electric mode as much as possible can help maximize the financial and environmental benefits, he adds.

It’s important to close the gap between expectations and reality not only for individuals’ sake, but also to ensure that policies aimed at cutting emissions have the intended effects. 

The European Union passed a law last year that will end sales of gas-powered cars in 2035. This is aimed at cutting emissions from transportation, a sector that makes up around one-fifth of global emissions. In the EU, manufacturers are required to have a certain average emissions value for all their vehicles sold. If plug-in hybrids are performing much worse in the real world than expected, it could mean the transportation sector is actually making less progress toward climate goals than it’s getting credit for.

Plug-in hybrids’ failure to meet expectations is also a problem in the US, says Aaron Isenstadt, a senior researcher at the ICCT based in San Francisco. Real-world fuel consumption was about 50% higher than EPA estimates in one ICCT study, for example. The gap between expectations and reality is smaller in the US partly because official emissions estimates are calculated differently, and partly because US drivers have different driving habits and may have better access to charging at home, Isenstadt says.

The Biden administration recently finalized new tailpipe emissions rules, which set guidelines for manufacturers about the emissions their vehicles can produce. The rules aim at ramping down emissions from new vehicles sold, so by 2032, roughly half of new cars sold in the US will need to produce zero emissions in order to meet the standards.

Both the EU and the US have plans to update estimates about how drivers are using plug-in hybrids, which should help policies in both markets better reflect reality. The EU will make an adjustment to estimates about driver behavior beginning in 2025, while the US will do so later, in 2027.

Walk just a few blocks in New York City and you’ll likely spot an electric bike zipping by.

The vehicles have become increasingly popular in recent years, especially among delivery drivers, tens of thousands of whom weave through New York streets. But the e-bike influx has caused a wave of fires sparked by their batteries, some of them deadly.

Now, the city wants to fight those fires with battery swapping. A pilot program will provide a small number of delivery drivers with alternative options to power up their e-bikes, including swapping stations that supply fully charged batteries on demand. 

Proponents say the program could lay the groundwork for a new mode of powering small electric vehicles in the city, one that’s convenient and could reduce the risk of fires. But the road to fire safety will likely be long and winding given the sheer number of batteries we’re integrating into our daily lives, in e-bikes and beyond.

A swapping solution

The number of fires caused by batteries in New York City increased nearly ninefold between 2019 and 2023, according to reporting from The City. Concern over fires has been steadily growing, and in March 2023 Mayor Eric Adams announced a plan to address the problem that included regulations for e-bikes and their batteries, crackdowns on unsafe charging practices, and outreach for delivery drivers.

While batteries can catch fire for a variety of reasons, many incidents appear to have been caused by e-bike drivers charging their batteries in apartment buildings, including a February blaze that killed one person and injured 22.

The city’s most recent effort, designed to address charging, is a pilot program for delivery drivers who use e-bikes. For six months, 100 drivers will be matched with one of three startups that will provide a charging solution that doesn’t involve plugging in batteries in apartment buildings.

One of the startups, Swiftmile, is building fast charging stations that look like bike racks and can charge an e-bike battery within two hours. The other two participating companies, Popwheels and Swobbee, are proposing a different, even quicker solution: battery swapping. Instead of plugging in a battery and waiting for it to power up, a rider can swap out a dead battery for a fresh one.

Battery swapping is already being used for some electric vehicles, largely across Asia. Chinese automaker Nio operates a network of battery swapping stations that can equip a car with a fresh battery in just under three minutes. Gogoro, one of MIT Technology Review’s 2023 Climate Tech Companies to Watch, has a network of battery swapping stations for electric scooters that can accommodate more than 400,000 swaps each day.

The concept will need to be adjusted for New York and for delivery drivers, says Baruch Herzfeld, co-founder and CEO of Popwheels. “But if we get it right,” he says, “we think everybody in New York will be able to use light electric vehicles.”

Existing battery swap networks like Nio’s have mostly included a single company’s equipment, giving the manufacturer control over the vehicle, battery, and swapping equipment. That’s because one of the keys to making battery swapping work is fleet commonality—a base of many vehicles that can all use the same system.

Fortunately, delivery drivers have formed something of a de facto fleet in New York City, says David Hammer, co-founder and president of Popwheels. Roughly half of the city’s 60,000-plus delivery workers rely on e-bikes, according to city estimates. Many of them use bikes from a brand called Arrow, which include removable batteries.

Convenience is key for delivery drivers working on tight schedules. “For a lot of people, battery charging, battery swapping, it’s just technology. But for [delivery workers], it’s their livelihood,” says Irene Figueroa-Ortiz, a policy advisor at the NYC Department of Transportation.

For the New York pilot, Popwheels is building battery cabinets in several locations throughout the city that will include 16 charging slots for e-bike batteries. Riders will open a cabinet door using a smartphone app, plug in the used battery and take a fresh one from another slot. Based on the company’s modeling, each cabinet should be able to support constant use by 40 to 50 riders, Hammer says.

“Maybe it leads to an even larger vision of battery swapping as a part of an urban future,” Hammer says. “But for now, it’s solving a very real and immediate problem that delivery workers have around how they can work a full day, and earn a reasonable living, and do it without having to put their lives at risk for battery fires.”

A growing problem

Lithium-ion batteries power products from laptops and cellphones to electric vehicles, including cars, trucks, and e-bikes. A major benefit of the battery chemistry is its energy density, or ability to pack a lot of energy into a small container. But all that stored energy can also be dangerous.

Batteries can catch fire during charging or use, and even while being stored. Generally, fires happen when temperatures around the battery rise to unsafe levels or if a physical problem in a battery causes a short circuit, allowing current to flow unchecked. These factors can set in motion a dangerous process called thermal runaway.

Most batteries include a battery management system to control charging, which prevents temperatures from spiking and sparking a fire. But if this system malfunctions or if a battery doesn’t include one, charging can lead to fires, says Ben Hoff, who leads fire safety engineering and hardware design at Popwheels.

Some of the delivery drivers who attended a sign-up event for New York’s charging pilot program in late February cited safety as a reason they were looking for alternative solutions for their batteries. “Of course, I worry about that,” Jose Sarmiento, a longtime delivery worker, said at the event. “Even when I’m sleeping, I’m thinking about the battery.”  

Battery swapping could also be a key to safer electric transit, Popwheels’ Hammer says. The company has tight control over the batteries it provides drivers, and its monitoring systems include temperature sensors installed in the charging cabinets. Charging can be shut down immediately if a battery starts to overheat, and an aerosol fire suppression system can slow a fire if one does happen to start inside a cabinet.

The batteries Popwheels provides are also UL-certified, meaning they’re required to pass third-party safety tests. New York City banned the sale of uncertified batteries and e-bikes last year, but many drivers still use them, Hammer says.

Low-quality batteries are more likely to cause fires, a problem that can often be traced to the manufacturing process, says Michael Pecht, a professor at the University of Maryland who studies the reliability and safety of electronic devices.

Battery manufacturing facilities should be as clean as a medical operating room or a semiconductor facility, Pecht explains. Contamination from dust and dirt that wind up in batteries can create problems over time as charging and discharging a battery causes small physical changes. After enough charging cycles, even a tiny dust particle can lead to a short circuit that sparks a fire.

Low-quality manufacturing makes battery fires more likely, but it’s a daunting task to keep tight control over the huge number of cells being made each year. Large manufacturers can produce billions of batteries annually, making the solution to battery fires a complex one, Pecht says: “I think there’s a group who want an easy answer. To me, the answer is not that easy.”

New programs that provide well-manufactured batteries and tightly control charging could make a dent in safety concerns. But real progress will require quick and dramatic scale-up, alongside regulations and continual outreach to communities. 

Popwheels would need to install hundreds of its battery swapping cabinets to support a significant fraction of the city’s delivery drivers. The pilot will help determine whether riders are willing to use new methods of powering their livelihood. As Hammer says, “If they don’t use it, it doesn’t matter.”