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Five findings from an extremely thorough study by the National Renewable Energy Lab.
Some Americans install heat pumps because they care about climate change. But most people aren’t going to make the switch until it makes sense economically. Pinpointing where and for whom heat pumps are a good investment is surprisingly tricky because U.S. housing is so diverse, with a wide range of building sizes and ages, situated in different local climates with different utility rates.
But for the first time, researchers at the National Renewable Energy Lab have sorted through much of this complexity to get deeper to the truth about the costs, benefits, and challenges of deploying heat pumps in the U.S.
Ultimately, they found that heat pumps are a cost-effective choice in roughly 65 million U.S. homes, or about 60% of the country — and that’s before taking into account available subsidies. But there are substantial economic barriers to widespread adoption.
It’s hard to overstate how detailed the study is. The authors started with a model of 550,000 statistically representative households — basically housing archetypes that typify different combinations of building size, age, occupancy level, local climate, heating usage patterns, and existing heating systems. Each one represents about 242 real-world households. Then the authors looked at how switching to a heat pump would affect greenhouse gas emissions and energy bills across all of these different homes in a wide range of scenarios. They considered heat pumps with lower and higher efficiency ratings, and whether or not the building owner pursued insulation upgrades. They looked at different scenarios for how quickly the grid would decarbonize, how sensitive the results were to energy prices, and how subsidies from the Inflation Reduction Act affect the economics.
The paper has many interesting findings beyond the top-line result. Here are five things that stood out.
Eric Wilson, a senior research engineer at NREL and the study’s lead author, told me one of his motivations was to try to settle the question of whether heat pumps reduce emissions.
“I see a lot of people saying, well, the grid is still dirty in this state, and maybe it makes sense to wait five years to put in a heat pump because it could increase emissions,” he said.
But he found that in each of the 48 contiguous U.S. states, switching to a heat pump reduces emissions today, even if that heat pump is one of the cheaper, less-efficient models. Heat pumps are just so much more efficient than other options that they still reduce emissions despite today’s relatively dirty grid.
On average, each home could cut between 2.5 to 4.4 tons of carbon over the approximately 16 years the equipment lasts, meaning widespread adoption could result in a 5% to 9% drop in national economy-wide emissions. The effect is much more pronounced in some states, like those in the Northeast, where a lot of homes currently use fossil fuels for heating. A household in Maine that installs a high efficiency model, combined with completing insulation upgrades, would reduce emissions by an average of 11 tons per year — or about the equivalent of taking two cars off the road for a year.
The study breaks down the costs of switching to a heat pump in a few different ways.
First, there’s the up-front costs of upgrading to a heat pump, which are relatively high. A lower-rated, less efficient heat pump system may be a cheaper option than a new furnace or boiler for about 43% of households. But a higher-performing heat pump is almost always more expensive, costing an extra $8,000 to $13,000 before government subsidies (more on them later). That alone might keep heat pumps out of reach for many households.
Next, there's the potential for bill savings — which is significant. Using state average electricity and gas rates in the winter of 2021 to 2022, the study found that 86% of households can save money on their utility bills by switching to a medium-efficiency heat pump, and a whopping 95% of households will see their bills go down if they install the highest efficiency system.
So in theory, if homeowners do have the extra cash to put down, there’s a chance they could make up for high up-front costs in bill savings over time. But how good a chance?
Putting this all together, the authors looked at what percentage of households that upgraded to heat pumps would see a positive cash flow, calculated as the “net present value,” from the initial investment. Here, the results were less rosy. In many cases, high up-front costs cancel out potential savings. For example, despite the near-certain bill savings from buying one of the most efficient heat pump models, only 21% of households would see an overall economic benefit from the switch.
Still, more than half of all homes would see a positive cash flow by switching to a cheaper, minimum-efficiency heat pump.
Distribution of energy bill savings, upgrade costs, and unsubsidized net present value, relative to a reference equipment replacement scenario, using energy prices from winter 2021 to 2022 Courtesy NREL / Wilson et al., Heat pumps for all? Distributions of the costs and benefits of residential air-source heat pumps in the United States, Joule (2024), https://doi.org/10.1016/j.joule.2024.01.022
These findings underscore the importance of bringing down the cost of more efficient heat pump models, which are out of reach for many Americans but can provide significant energy bill savings. The authors suggest that policymakers can help by deploying incentives more strategically and pursuing research on “lower-cost, higher performance, and easier to install equipment.” There also may be opportunities for bulk purchasing and aggregating installations across an apartment building or neighborhood.
When it comes to bill savings, the study found that those who have systems that run on propane, fuel oil, or electric resistance heaters will pretty much always lower their bills by switching to a heat pump, no matter how efficient it is. But those who use natural gas are far more likely to lower their bills if they can afford to switch to one of the pricier, better-performing heat pumps — which cuts into the value proposition.
The following maps show the percentage of homes in each state that would see a positive cash flow from switching to a heat pump, looking at those switching from natural gas, electric resistance, or fuel oil and propane, illustrating how the value proposition is most challenging for those using natural gas.
Percentage of homes that currently have air conditioning that will see a positive cash flow from switching to a heat pump from natural gas, electricity, and fuel oil and propane. Courtesy NREL / Wilson et al. 2024
The authors also note that fixed charges on natural gas bills can play a significant role in the economics of switching to a heat pump. Most natural gas utilities charge customers a fixed amount each month, regardless of how much gas they use. If a homeowner switches to heat pumps but continues using gas for cooking, they’ll still have to pay the full fee, which can be as high as $34 a month, whereas homes that fully electrify can avoid these fees.
The results I described in the previous two sections include homes both with and without existing air conditioning systems of some kind. (With the exception of the maps, which only consider homes that have air conditioning already.)
But since heat pumps provide both heating and cooling, the economics are actually quite different for those households who already have air conditioners versus those who don't. If a household already has A/C, heat pumps appear more favorable, because a family would be able to replace two systems — an air conditioner and a furnace — with just one. If there is no pre-existing air conditioner, the heat pump will not only have higher up-front costs, but it’s more likely to increase energy bills, since the family might start using the heat pump for cooling in addition to heating.
Here are the same maps included in the previous section, but looking just at homes that do not have air conditioning.
Percentage of homes that do not have air conditioning that will see a positive cash flow from switching to a heat pump. The first column is homes that currently use natural gas, the second column is those that us electricity, and the third is those that use fuel oil and propane. Courtesy NREL / Wilson et al. 2024
There are basically zero cases where a house with natural gas heating, and no A/C, will save by switching to a heat pump. However, that result doesn’t take into account the benefits of getting air conditioning for the first time.
“They didn't include the new value that someone has, especially in a warming world and a world with more heat waves, of now having an air conditioner in your home,” Kevin Kircher, an assistant professor of mechanical engineering at Purdue University, told me. “So if you add that in, I think the economics look better.”
None of the results in the previous sections take into account the various subsidies that states and the federal government offer for heat pumps. For example, the Inflation Reduction Act included a $2,000 tax credit for heat pumps and an additional $11,500 in rebates for low- and moderate-income households. Both will increase the percentage of households for whom the investment will pencil out.
The study also doesn’t take into account the potential for homes to use smart controls that optimize their systems, or the opportunity for households to participate in demand response programs which will pay them to turn down their thermostats by a few degrees when the grid is taxed. Kircher, the Purdue professor, recently published a study of a real-world house in a cold climate where smart controls reduced heating energy costs by 23-34%.
Finally, one big takeaway from the study was that the results are very sensitive to the price ratio between natural gas rates and electricity rates, and there are reasons to believe that may become more favorable. For example, as more renewable energy is deployed, electricity could become more affordable. Meanwhile, if the U.S. increases exports of liquified natural gas, the cost of domestic natural gas could go up. The study cites a 2022 survey of oil and gas executives which found that 69% expect ‘‘the age of inexpensive U.S. natural gas to end by year-end 2025.”
“Big modeling like this entails a lot of assumptions about the future that are really hard to pin down with any real precision,” said Kircher. “But I think there's cause for optimism there.”
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Instead of rocket fuel, they’re burning biomass.
Arbor Energy might have the flashiest origin story in cleantech.
After the company’s CEO, Brad Hartwig, left SpaceX in 2018, he attempted to craft the ideal resume for a future astronaut, his dream career. He joined the California Air National Guard, worked as a test pilot at the now-defunct electric aviation startup Kitty Hawk, and participated in volunteer search and rescue missions in the Bay Area, which gave him a front row seat to the devastating effects of wildfires in Northern California.
That experience changed everything. “I decided I actually really like planet Earth,” Hartwig told me, “and I wanted to focus my career instead on preserving it, rather than trying to leave it.” So he rallied a bunch of his former rocket engineer colleagues to repurpose technology they pioneered at SpaceX to build a biomass-fueled, carbon negative power source that’s supposedly about ten times smaller, twice as efficient, and eventually, one-third the cost of the industry standard for this type of plant.
Take that, all you founders humble-bragging about starting in a dingy garage.
“It’s not new science, per se,” Hartwig told me. The goal of this type of tech, called bioenergy with carbon capture and storage, is to combine biomass-based energy generation with carbon dioxide removal to achieve net negative emissions. Sounds like a dream, but actually producing power or heat from this process has so far proven too expensive to really make sense. There are only a few so-called BECCS facilities operating in the U.S. today, and they’re all just ethanol fuel refineries with carbon capture and storage technology tacked on.
But the advances in 3D printing and computer modeling that allowed the SpaceX team to build an increasingly simple and cheap rocket engine have allowed Arbor to move quickly into this new market, Hartwig explained. “A lot of the technology that we had really pioneered over the last decade — in reactor design, combustion devices, turbo machinery, all for rocket propulsion — all that technology has really quite immediate application in this space of biomass conversion and power generation.”
Arbor’s method is poised to be a whole lot sleeker and cheaper than the BECCS plants of today, enabling both more carbon sequestration and actual electricity production, all by utilizing what Hartwig fondly refers to as a “vegetarian rocket engine.” Because there’s no air in space, astronauts have to bring pure oxygen onboard, which the rocket engines use to burn fuel and propel themselves into the stratosphere and beyond. Arbor simply subs out the rocket fuel for biomass. When that biomass is combusted with pure oxygen, the resulting exhaust consists of just CO2 and water. As the exhaust cools, the water condenses out, and what’s left is a stream of pure carbon dioxide that’s ready to be injected deep underground for permanent storage. All of the energy required to operate Arbor’s system is generated by the biomass combustion itself.
“Arbor is the first to bring forward a technology that can provide clean baseload energy in a very compact form,” Clea Kolster, a partner and Head of Science at Lowercarbon Capital told me. Lowercarbon is an investor in Arbor, alongside other climate tech-focused venture capital firms including Gigascale Capital and Voyager Ventures, but the company has not yet disclosed how much it’s raised.
Last month, Arbor signed a deal with Microsoft to deliver 25,000 tons of permanent carbon dioxide removal to the tech giant starting in 2027, when the startup’s first commercial project is expected to come online. As a part of the deal, Arbor will also generate 5 megawatts of clean electricity per year, enough to power about 4,000 U.S. homes. And just a few days ago, the Department of Energy announced that Arbor is one of 11 projects to receive a combined total of $58.5 million to help develop the domestic carbon removal industry.
Arbor’s current plan is to source biomass from forestry waste, much of which is generated by forest thinning operations intended to prevent destructive wildfires. Hartwig told me that for every ton of organic waste, Arbor can produce about one megawatt hour of electricity, which is in line with current efficiency standards, plus about 1.8 tons of carbon removal. “We look at being as efficient, if not a little more efficient than a traditional bioenergy power plant that does not have carbon capture on it,” he explained.
The company’s carbon removal price targets are also extremely competitive — in the $50 to $100 per ton range, Hartwig said. Compare that to something like direct air capture, which today exceeds $600 per ton, or enhanced rock weathering, which is usually upwards of $300 per ton. “The power and carbon removal they can offer comes at prices that meet nearly unlimited demand,”Mike Schroepfer, the founder of Gigascale Capital and former CTO of Meta, told me via email. Arbor benefits from the fact that the electricity it produces and sells can help offset the cost of the carbon removal, and vice versa. So if the company succeeds in hitting its cost and efficiency targets, Hartwig said, this “quickly becomes a case for, why wouldn’t you just deploy these everywhere?”
Initial customers will likely be (no surprise here) the Microsofts, Googles and Metas of the world — hyperscalers with growing data center needs and ambitious emissions targets. “What Arbor unlocks is basically the ability for hyperscalers to stop needing to sacrifice their net zero goals for AI,” Kolster told me. And instead of languishing in the interminable grid interconnection queue, Hartwig said that providing power directly to customers could ensure rapid, early deployment. “We see it as being quicker to power behind-the-meter applications, because you don’t have to go through the process of connecting to the grid,” he told me. Long-term though, he said grid connection will be vital, since Arbor can provide baseload power whereas intermittent renewables cannot.
All of this could serve as a much cheaper alternative, to say, re-opening shuttered nuclear facilities, as Microsoft also recently committed to doing at Three Mile Island. “It’s great, we should be doing that,” Kolster said of this nuclear deal, “but there’s actually a limited pool of options to do that, and unfortunately, there is still community pushback.”
Currently, Arbor is working to build out its pilot plant in San Bernardino, California, which Hartwig told me will turn on this December. And by 2030, the company plans to have its first commercial plant operating at scale, generating 100 megawatts of electricity while removing nearly 2 megatons of CO2 every year. “To put it in perspective: In 2023, the U.S. added roughly 9 gigawatts of gas power to the grid, which generates 18 to 23 megatons of CO2 a year,” Schroepfer wrote to me. So having just one Arbor facility removing 2 megatons would make a real dent. The first plant will be located in Louisiana, where Arbor will also be working with an as-yet-unnamed partner to do the carbon storage.
The company’s carbon credits will be verified with the credit certification platform Isometric, which is also backed by Lowercarbon and thought to have the most stringent standards in the industry. Hartwig told me that Arbor worked hand-in-hand with Isometric to develop the protocol for “biogenic carbon capture and storage,” as the company is the first Isometric-approved supplier to use this standard.
But Hartwig also said that government support hasn’t yet caught up to the tech’s potential. While the Inflation Reduction Act provides direct air capture companies with $180 per ton of carbon dioxide removed, technology such as Arbor’s only qualifies for $85 per ton. It’s not nothing — more than the zero dollars enhanced rock weathering companies such as Lithos or bio-oil sequestration companies such as Charm are getting. “But at the same time, we’re treated the same as if we’re sequestering CO2 emissions from a natural gas plant or a coal plant,” Hartwig told me, as opposed to getting paid for actual CO2 removal.
“I think we are definitely going to need government procurement or involvement to actually hit one, five, 10 gigatons per year of carbon removal,” Hartwig said. Globally, scientists estimate that we’ll need up to 10 gigatons of annual CO2 removal by 2050 in order to limit global warming to 1.5 degrees Celsius. “Even at $100 per ton, 10 gigatons of carbon removal is still a pretty hefty price tag,” Hartwig told me. A $1 trillion price tag, to be exact. “We definitely need more players than just Microsoft.”
New research out today shows a 10-fold increase in smoke mortality related to climate change from the 1960s to the 2010.
If you are one of the more than 2 billion people on Earth who have inhaled wildfire smoke, then you know firsthand that it is nasty stuff. It makes your eyes sting and your throat sore and raw; breathe in smoke for long enough, and you might get a headache or start to wheeze. Maybe you’ll have an asthma attack and end up in the emergency room. Or maybe, in the days or weeks afterward, you’ll suffer from a stroke or heart attack that you wouldn’t have had otherwise.
Researchers are increasingly convinced that the tiny, inhalable particulate matter in wildfire smoke, known as PM2.5, contributes to thousands of excess deaths annually in the United States alone. But is it fair to link those deaths directly to climate change?
A new study published Monday in Nature Climate Change suggests that for a growing number of cases, the answer should be yes. Chae Yeon Park, a climate risk modeling researcher at Japan’s National Institute for Environmental Studies, looked with her colleagues at three fire-vegetation models to understand how hazardous emissions changed from 1960 to 2019, compared to a hypothetical control model that excluded historical climate change data. They found that while fewer than 669 deaths in the 1960s could be attributed to climate change globally, that number ballooned to 12,566 in the 2010s — roughly a 20-fold increase. The proportion of all global PM2.5 deaths attributable to climate change jumped 10-fold over the same period, from 1.2% in the 1960s to 12.8% in the 2010s.
“It’s a timely and meaningful study that informs the public and the government about the dangers of wildfire smoke and how climate change is contributing to that,” Yiqun Ma, who researches the intersection of climate change, air pollution, and human health at the Yale School of Medicine, and who was not involved in the Nature study, told me.
The study found the highest climate change-attributable fire mortality values in South America, Australia, and Europe, where increases in heat and decreases in humidity were also the greatest. In the southern hemisphere of South America, for example, the authors wrote that fire mortalities attributable to climate change increased from a model average of 35% to 71% between the 1960s and 2010s, “coinciding with decreased relative humidity,” which dries out fire fuels. For the same reason, an increase in relative humidity lowered fire mortality in other regions, such as South Asia. North America exhibited a less dramatic leap in climate-related smoke mortalities, with climate change’s contribution around 3.6% in the 1960s, “with a notable rise in the 2010s” to 18.8%, Park told me in an email.
While that’s alarming all on its own, Ma told me there was a possibility that Park’s findings might actually be too conservative. “They assume PM2.5 from wildfire sources and from other sources” — like from cars or power plants — “have the same toxicity,” she explained. “But in fact, in recent studies, people have found PM2.5 from fire sources can be more toxic than those from an urban background.” Another reason Ma suspected the study’s numbers might be an underestimate was because the researchers focused on only six diseases that have known links to PM2.5 exposure: chronic obstructive pulmonary disease, lung cancer, coronary heart disease, type 2 diabetes, stroke, and lower respiratory infection. “According to our previous findings [at the Yale School of Medicine], other diseases can also be influenced by wildfire smoke, such as mental disorders, depression, and anxiety, and they did not consider that part,” she told me.
Minghao Qiu, an assistant professor at Stony Brook University and one of the country’s leading researchers on wildfire smoke exposure and climate change, generally agreed with Park’s findings, but cautioned that there is “a lot of uncertainty in the underlying numbers” in part because, intrinsically, wildfire smoke exposure is such a complicated thing to try to put firm numbers to. “It’s so difficult to model how climate influences wildfire because wildfire is such an idiosyncratic process and it’s so random, ” he told me, adding, “In general, models are not great in terms of capturing wildfire.”
Despite their few reservations, both Qiu and Ma emphasized the importance of studies like Park’s. “There are no really good solutions” to reduce wildfire PM2.5 exposure. You can’t just “put a filter on a stack” as you (sort of) can with power plant emissions, Qiu pointed out.
Even prescribed fires, often touted as an important wildfire mitigation technique, still produce smoke. Park’s team acknowledged that a whole suite of options would be needed to minimize future wildfire deaths, ranging from fire-resilient forest and urban planning to PM2.5 treatment advances in hospitals. And, of course, there is addressing the root cause of the increased mortality to begin with: our warming climate.
“To respond to these long-term changes,” Park told me, “it is crucial to gradually modify our system.”
On the COP16 biodiversity summit, Big Oil’s big plan, and sea level rise
Current conditions: Record rainfall triggered flooding in Roswell, New Mexico, that killed at least two people • Storm Ashley unleashed 80 mph winds across parts of the U.K. • A wildfire that broke out near Oakland, California, on Friday is now 85% contained.
Forecasters hadn’t expected Hurricane Oscar to develop into a hurricane at all, let alone in just 12 hours. But it did. The Category 1 storm made landfall in Cuba on Sunday, hours after passing over the Bahamas, bringing intense rain and strong winds. Up to a foot of rainfall was expected. Oscar struck while Cuba was struggling to recover from a large blackout that has left millions without power for four days. A second system, Tropical Storm Nadine, made landfall in Belize on Saturday with 60 mph winds and then quickly weakened. Both Oscar and Nadine developed in the Atlantic on the same day.
Hurricane OscarAccuWeather
The COP16 biodiversity summit starts today in Cali, Colombia. Diplomats from 190 countries will try to come up with a plan to halt global biodiversity loss, aiming to protect 30% of land and sea areas and restore 30% of degraded ecosystems by 2030. Discussions will revolve around how to monitor nature degradation, hold countries accountable for their protection pledges, and pay for biodiversity efforts. There will also be a big push to get many more countries to publish national biodiversity strategies. “This COP is a test of how serious countries are about upholding their international commitments to stop the rapid loss of biodiversity,” said Crystal Davis, Global Director of Food, Land, and Water at the World Resources Institute. “The world has no shot at doing so without richer countries providing more financial support to developing countries — which contain most of the world’s biodiversity.”
A prominent group of oil and gas producers has developed a plan to roll back environmental rules put in place by President Biden, The Washington Post reported. The paper got its hands on confidential documents from the American Exploration and Production Council (AXPC), which represents some 30 producers. The documents include draft executive orders promoting fossil fuel production for a newly-elected President Trump to sign if he takes the White House in November, as well as a roadmap for dismantling many policies aimed at getting oil and gas producers to disclose and curb emissions. AXPC’s members, including ExxonMobil, ConocoPhillips, and Hess, account for about half of the oil and gas produced in the U.S., the Post reported.
A new report from the energy think tank Ember looks at how the uptake of electric vehicles and heat pumps in the U.K. is affecting oil and gas consumption. It found that last year the country had 1.5 million EVs on the road, and 430,000 residential heat pumps in homes, and the reduction in fossil fuel use due to the growth of these technologies was equivalent to 14 million barrels of oil, or about what the U.K. imports over a two-week span. This reduction effect will be even stronger as more and more EVs and heat pumps are powered by clean energy. The report also found that even though power demand is expected to rise, efficiency gains from electrification and decarbonization will make up for this, leading to an overall decline in energy use and fossil fuel consumption.
Ember
The world’s sea levels are projected to rise by more than 6 inches on average over the next 30 years if current trends continue, according to a new study published in the journal Nature. “Such rates would represent an evolving challenge for adaptation efforts,” the authors wrote. By examining satellite data, the researchers found that sea levels have risen by about .4 inches since 1993, and that they’re rising faster now than they were then. In 1993 the seas were rising by about .08 inches per year, and last year they were rising at .17 inches per year. These are averages, of course, and some areas are seeing much more extreme changes. For example, areas around Miami, Florida, have already seen sea levels rise by 6 inches over the last 31 years.
“As the climate crisis grows more urgent, restoring faith in government will be more important than ever.” –Paul Waldman writing for Heatmap about the profound implications of America becoming a low-trust society.