US Crosses the Electric-Car Tipping Point for Mass Adoption


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EV Tipping Point signals the S-curve shift to mainstream adoption as new car sales pass 5%, with the US joining Europe and China; charging infrastructure, costs, and supply align to accelerate electric car market penetration.

 

Key Points

The EV tipping point is when fully electric cars reach about 5% of new sales, triggering rapid S-curve adoption.

✅ 5% of new car sales marks start of mass adoption

✅ Follows S-curve seen in phones, LEDs, internet

✅ Barriers ease: charging, cost declines, model availability

 

Many people of a certain age can recall the first time they held a smartphone. The devices were weird and expensive and novel enough to draw a crowd at parties. Then, less than a decade later, it became unusual not to own one.

That same society-altering shift is happening now with electric vehicles, according to a Bloomberg analysis of adoption rates around the world. The US is the latest country to pass what’s become a critical EV tipping point: an EV inflection point when 5% of new car sales are powered only by electricity. This threshold signals the start of mass EV adoption, the period when technological preferences rapidly flip, according to the analysis.

For the past six months, the US joined Europe and China — collectively the three largest car markets — in moving beyond the 5% tipping point, as recent U.S. EV sales indicate. If the US follows the trend established by 18 countries that came before it, a quarter of new car sales could be electric by the end of 2025. That would be a year or two ahead of most major forecasts.

How Fast Is the Switch to Electric Cars?
19 countries have reached the 5% tipping point, and an earlier-than-expected shift is underway—then everything changes

Why is 5% so important? 
Most successful new technologies — electricity, televisions, mobile phones, the internet, even LED lightbulbs — follow an S-shaped adoption curve, with EVs going from zero to 2 million in five years according to market data. Sales move at a crawl in the early-adopter phase, then surprisingly quickly once things go mainstream. (The top of the S curve represents the last holdouts who refuse to give up their old flip phones.)

Electric cars inline tout
In the case of electric vehicles, 5% seems to be the point when early adopters are overtaken by mainstream demand. Before then, sales tend to be slow and unpredictable, and still behind gas cars in most markets. Afterward, rapidly accelerating demand ensues.

It makes sense that countries around the world would follow similar patterns of EV adoption. Most impediments are universal: there aren’t enough public chargers, grid capacity concerns linger, the cars are expensive and in limited supply, buyers don’t know much about them. Once the road has been paved for the first 5%, the masses soon follow.

Thus the adoption curve followed by South Korea starting in 2021 ends up looking a lot like the one taken by China in 2018, which is similar to Norway after its first 5% quarter in 2013. The next major car markets approaching the tipping point this year include Canada, Australia, and Spain, suggesting that within a decade many drivers could be in EVs worldwide. 

 

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US renewable energy hit record 28% in April.

U.S. Renewable Energy Record 28% signals a cleaner power grid as wind, solar, and hydroelectric output soar; EIA data shows cost-competitive clean energy reshaping the electricity mix and reducing carbon emissions across regions.

 

Key Points

EIA-reported April share of electricity from wind, solar, and hydro, reflecting cost-driven growth in U.S. clean power.

✅ Wind, solar additions dominated recent U.S. capacity buildouts

✅ Lower levelized costs make renewables most competitive

✅ Seasonal factors and outages lowered fossil and nuclear output

 

The amount of electricity generated by renewable resources hit a record 28% in April, a breakthrough number that shows how important renewable energy has become in U.S. energy markets as it surpassed coal in 2022 overall.

"It's a 'Wow' moment," said Peter Kelly-Detwiler, an energy analyst and author of "The Energy Switch," a recent book about the transition to a carbon-free energy economy.

The percentage of U.S. electricity produced by renewable energy from wind, solar and hydroelectric dams has been steadily rising, from 8.6% in April 2001 to this April's 28%. Those numbers were released this week by the U.S. Energy Information Administration, which tracks energy data for the nation.

What explains the surge?
There are several reasons. At the top is that wind and solar installations dominated U.S. energy buildouts.

"Basically, the only things we've added to the grid in the past decade are wind, solar and natural gas," said Harrison Fell, an economist and engineer at Columbia University, where he co-leads the Power Sector and Renewables Research Initiative.

That's happening for two reasons. The first is cost. Renewables are simply the most economically competitive power currently available, Kelly-Detwiler said.

In 2021, the cost of producing a megawatt-hour of electricity from a new wind turbine was $26 to $50. The same amount of electricity from the cheapest type of natural gas plant ranged from $45 to $74, according to Lazard, a financial advisory firm that publishes annual estimates of the cost of producing electricity. 

Federal and state mandates and incentives to increase the amount of clean energy used also help, Fell said, as renewables reached 25.5% of U.S. electricity recently. 

"When you do the math on what's the most profitable thing to add, it's often going to be wind and solar at this stage," he said.

Was weather a factor?
Yes. April tends to be a particularly windy month, and this spring was windier than most, Fell said.

There's also less power coming into the grid from fossil fuels and nuclear in the spring. That's because electricity demand is generally lower because of the mild weather and fossil fuel and nuclear power plants use the time for maintenance and refueling, which reduces their production, he said.

Another surprise was that in April, wind and solar power together produced more electricity than nuclear plants nationwide. 

Historically, nuclear power plants, which are carbon-neutral, have reliably produced about 20% of America's electricity. In April that number dropped to 18% while wind and solar combined stood at 19.6%.

The nuclear decrease is partly a result of the shutdown of two plants in the past year, Indian Point in New York state and Palisades in Michigan, as well as scheduled closures for maintenance.

Will the trend continue?
When all U.S. carbon-neutral energy sources are added together – nuclear, wind, hydroelectric and solar – almost 46% of U.S. electricity in April came from sources that don't contribute greenhouse gases to the environment, federal data shows.  

"It's a milestone," Kelly-Detwiler said. "But in a few years, we'll look back and say, 'This was a nice steppingstone to the next 'Wow!' moment."

 

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California allows electric school buses only from 2035

California Electric School Bus Mandate 2035 sets zero-emission requirements, outlines funding, state reimbursement, fleet electrification, infrastructure, and cost estimates, highlighting exemptions for frontier districts and alignment with clean transportation and climate policy goals.

 

Key Points

California's 2035 policy requires all new school buses be zero-emission, with funding and limited rural exemptions.

✅ Mandates zero-emission purchases for new school buses from 2035

✅ Estimates $5B transition cost with state reimbursement support

✅ Frontier districts may apply for 5-year extensions

 

California Governor Gavin Newsom has signed a new legislation requiring that from 2035, all newly ordered or contracted school buses must be zero-emission, a move aligned with California's push for expanded EV grid capacity statewide.

The state estimates that switching to electric school buses will cost around five billion dollars over the next decade, a projection reflecting electric bus challenges seen globally. That is because a diesel equivalent costs about 200,000 dollars less than a battery-electric version, as highlighted by critical analyses of California policy. And “the California Constitution requires the state to reimburse local agencies and school districts for certain costs mandated by the state.”

There are about 23,800 school buses on the road in California. About 500 are already electric, with conversion initiatives expected to expand the total, and 2,078 electric buses have been ordered.

There are – as always- exceptions to the rule. So-called “frontier districts,” which have less than 600 students or are in a county with a population density of less than ten persons per square mile, can file for a five-year extension, drawing on lessons from large electric bus fleets about route length and charging constraints. However, they must “reasonably demonstrate that a daily planned bus route for transporting pupils to and from school cannot be serviced through available zero-emission technology in 2035.”

Califonia is the fifth US state to mandate electric school buses, and jurisdictions like British Columbia are deploying electric school buses as well. Connecticut, Maryland, Maine, and New York implemented similar legislation, while California continues broader zero-emission freight adoption with Volvo VNR electric trucks entering service across the state.

 

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AZ goes EV: Rate of electric car ownership relatively high in Arizona

Arizona Electric Vehicle Ownership is surging, led by EV adoption, charging stations growth, state incentives, and local manufacturers; yet rural infrastructure gaps and limited fast-charging plugs remain key barriers to convenient, statewide electrification.

 

Key Points

Arizona Electric Vehicle Ownership shows rising EV adoption and incentives, but rural fast-charging access still lags.

✅ 28,770 EVs registered; sixth per 1,000 residents statewide

✅ 385 fast chargers; 1,448 Level 2 plugs; many not 24/7

✅ Incentives: lower registration, HOV access, utility rebates

 

For a mostly red state, Arizona has a lot of blue-state company when it comes to states ranked by electric vehicle ownership, according to recent government data.

Arizona had 28,770 registered electric vehicles as of June, according to the U.S. Department of Energy's Alternative Fuels Data Center, the seventh-highest number among states. When ownership is measured per 1,000 residents, Arizona inches up a notch to sixth place, with just over four electric vehicles per 1,000 people.

That rate put Arizona just behind Oregon and Colorado and just ahead of Nevada and Vermont. California was in the lead by far, with California's EV and charging lead reflected in 425,300 registered electric vehicles, or one for every 10.7 residents.

Arizona EV enthusiasts welcomed the ranking, which they said they have seen reflected in steady increases in group membership, but said the state can do better, even amid soaring U.S. EV sales this year.

"Arizona is growing by leaps and bounds in major areas, but still struggling out there in the hinterlands," said Jerry Asher, vice president of the Tucson Electric Vehicle Association.

He and others said the biggest challenge in Arizona, as in much of the country, is the lack of readily available charging stations for electric vehicles.

Currently, there are 385 public fast-charging plugs and 1,448 non-fast-charging plugs in the state, where charging networks compete to expand access, said Diane Brown, executive director with the Arizona Public Interest Research Group Education Fund. And many of those "are not available 24 hours a day, often making EV charging less convenient to the public," she said.

And in order for the state to hit 10% EV ownership by 2030, one scenario outlined by Arizona PIRG, the number of charging stations would need to grow significantly.

"According to the Arizona PIRG Education Fund, to support a future in which 10% of Arizona's vehicles are EVs – a conservative target for 2030 – Arizona will need more than 1,098 fast-charging plugs and 14,888 Level 2 plugs," Brown said.

This will require local, state and federal policies, as EVs challenge state power grids, to make "EV charging accessible, affordable, and easy," she said.

But advocates said there are several things working in their favor, even as an EV boom tests charging capacity across the country today. Jim Stack, president of the Phoenix Electric Auto Association, said many of the current plug-ins charging stations are at stores and libraries, places "where you would stop anyway."

"We have a good charging infrastructure and it keeps getting better," Stack said.

One way Asher said Arizona could be more EV-friendly would be to add charging stations at hotels, RV parks and shopping centers. In Tucson, he said, the Culinary Dropout and Jersey Mike's restaurants have already begun offering free electric vehicle charging to customers, Asher said.

While they push for more charging infrastructure, advocates said improving technology and lower vehicle expenses are on their side, as post-2021 electricity trends reshape costs, helping to sway more Arizonans to purchase an electric vehicle in recent years.

"The batteries are getting better and lower in cost as well as longer-lasting," Stack said. He said an EV uses about 50 cents of electricity to cover the same number of miles a gas-burning car gets from a gallon of gas – currently selling for $3.12 a gallon in Arizona, according to AAA.

In addition, the state is offering incentives to electric vehicle buyers.

"In AZ we get reduced registration on electric vehicles," Stack said. "It's about $15 a year compared to $300-700 a year for gas and diesel cars."

Electric vehicle owners also "get 24/7 access to HOV lanes, even with one person," he said. And utilities like Tucson Electric Power offer rebates and incentives for home charging stations, according to a report by the National Conference of State Legislatures, and neighboring New Mexico's EV benefits underscore potential economic gains for the region.

Stack also noted that Arizona is now home to three eclectic vehicle manufacturers: Lucid, which makes cars in Casa Grande, Nikola, which makes trucks in Phoenix and Coolidge, and Electra Meccanica, which plans to build the three-wheeled SOLO commuter in Mesa.

"We get clear skies. No oil changes, no muffler work, no transmission, faster acceleration. No smog or smog tests," Stack said. "It's priceless."

 

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The American EV boom is about to begin. Does the US have the power to charge it?

EV Charging Infrastructure accelerates with federal funding, NEVI corridors, and Level 2/3 DC fast charging to cut range anxiety, support apartment dwellers, and scale to 500,000 public chargers alongside tax credits and state mandates.

 

Key Points

The network of public and private hardware, software, and policies enabling reliable Level 2/3 EV charging at scale.

✅ $7,500/$4,000 tax credits spur adoption and charger demand

✅ NEVI funding builds 500,000 public, reliable DC fast chargers

✅ Equity focus: apartment, curbside, bidirectional and inductive tech

 

Speaking in front of a line of the latest electric vehicles (EVs) at this month’s North American International Auto Show, President Joe Biden declared: “The great American road trip is going to be fully electrified.”

Most vehicles on the road are still gas guzzlers, but Washington is betting big on change, with EV charging networks competing to expand as it hopes that major federal investment will help reach a target set by the White House for 50% of new cars to be electric by 2030. But there are roadblocks – specifically when it comes to charging them all. “Range anxiety,” or how far one can travel before needing to charge, is still cited as a major deterrent for potential EV buyers.

The auto industry recently passed the 5% mark of EV market share – a watershed moment, arriving ahead of schedule according to analysts, before rapid growth. New policies at the state and local level could very well spur that growth: the Inflation Reduction Act, which passed this summer, offers tax credits of $4,000 to purchase a used EV and up to $7,500 for certain new ones. In August, California, the nation’s largest state and economy, announced rules that would ban all new gas-powered cars by 2035, as part of broader grid stability efforts in the state. New York plans to follow.

So now, the race is on to provide chargers to power all those new EVs.

The administration’s target of 500,000 public charging units by 2030 is a far cry from the current count of nearly 50,000, according to the Department of Energy’s estimate. And those new chargers will have to be fast – what’s known as Level 2 or 3 charging – and functional in order to create a truly reliable system, even as state power grids face added demands across regions. Today, many are not.

Last week, the White House approved plans for all 50 states, along with Washington DC, and Puerto Rico, to set up chargers along highways, unlocking $1.5bn in federal funding to that end, as US automakers’ charger buildout to complement public funds. The money comes from the landmark infrastructure bill passed last year, which invests $7.5bn for EV charging in total.

But how much of that money is spent is largely going to be determined at the local level, amid control over charging debates among stakeholders. “It’s a difference between policy and practice,” said Drew Lipsher, the chief development officer at Volta, an EV charging provider. “Now that the federal government has these policies, the question becomes, OK, how does this actually get implemented?” The practice, he said, is up to states and municipalities.

As EV demand spikes, a growing number of cities are adopting policies for EV charging construction. In July, the city of Columbus passed an “EV readiness” ordinance, which will require new parking structures to host charging stations proportionate to the number of total parking spots, with at least one that is ADA-accessible. Honolulu and Atlanta have passed similar measures.

One major challenge is creating a distribution model that can meet a diversity of needs.

At the moment, most EV owners charge their cars at home with a built-in unit, which governments can help subsidize. But for apartment dwellers or those living in multi-family homes, that’s less feasible. “When we’re thinking about the largest pieces of the population, that’s where we need to really be focusing our attention. This is a major equity issue,” said Alexia Melendez Martineau, the policy manager at Plug-In America, an EV consumer advocacy group.

Bringing power to people is one such solution. In Hoboken, New Jersey, Volta is working with the city to create a streetside charging network. “The network will be within a five-minute walk of every resident,” said Lipsher. “Hopefully this is a way for us to really import it to cities who believe public EV charging infrastructure on the street is important.” Similarly, in parts of Los Angeles – as in Berlin and London – drivers can get a charge from a street lamp.

And there may be new technologies that could help, exciting experts and EV enthusiasts alike. That could include the roads themselves charging EVs through a magnetizable concrete technology being piloted in Indiana and Detroit. And bidirectional charging, where, similar to solar panels, drivers can put their electricity back into the grid – or perhaps even to another EV, through what’s known as electric vehicle supply equipment (EVSE). Nissan approved the technology for their Leaf model this month.

 

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What cities can learn from the biggest battery-powered electric bus fleet in North America

Canadian Electric Bus Fleet leads North America as Toronto's TTC deploys 59 battery-electric, zero-emission buses, advancing public transit decarbonization with charging infrastructure, federal funding, lower maintenance, and lifecycle cost savings for a low-carbon urban future.

 

Key Points

Canada's leading battery-electric transit push, led by Toronto's TTC, scaling zero-emission buses and charging.

✅ Largest battery-electric bus fleet in North America

✅ TTC trials BYD, New Flyer, Proterra for range and reliability

✅ Charging infrastructure, funding, and specs drive 2040 zero-emissions

 

The largest battery-powered electric bus fleet in North America is Canadian. Toronto's transit system is now running 59 electric buses from three suppliers, and Edmonton's first electric bus is now on the road as well. And Canadian pioneers such as Toronto offer lessons for other transit systems aiming to transition to greener fleets for the low-carbon economy of the future.

Diesel buses are some of the noisier, more polluting vehicles on urban roads. Going electric could have big benefits, even though 18% of Canada's 2019 electricity from fossil fuels remains a factor.

Emissions reductions are the main reason the federal government aims to add 5,000 electric buses to Canada's transit and school fleets by the end of 2024. New funding announced this week as part of the government's fall fiscal update could also give programs to electrify transit systems a boost.

"You are seeing huge movement towards all-electric," said Bem Case, the Toronto Transit Commission's head of vehicle programs. "I think all of the transit agencies are starting to see what we're seeing ... the broader benefits."

While Vancouver has been running electric trolley buses (more than 200, in fact), many cities (including Vancouver) are now switching their diesel buses to battery-electric buses in Metro Vancouver that don't require overhead wires and can run on regular bus routes.

The TTC got approval from its board to buy its first 30 battery-electric buses in November 2017. Its plan is to have a zero-emissions fleet by 2040.

That's a crucial part of Toronto's plan to meet its 2050 greenhouse gas targets, which requires 100 per cent of vehicles to transition to low-carbon energy by then.

But Case said the transition can't happen overnight. 


Finding the right bus
For one thing, just finding the right bus isn't easy.

"There's no bus, by any manufacturer, that's been in service for the entire life of a bus, which is 12 years," Case said.

"And so really, until then, we don't have enough experience, nor does anyone else in the industry, have enough experience to commit to an all-electric fleet immediately."

In fact, Case said, there are only three manufacturers that make suitable long-range buses — the kind needed in a city the size of Toronto.

Having never bought electric buses before, the city had no specifications for what it needed in an electric bus, so it decided to try all three suppliers: Winnipeg-based New Flyer; BYD, which is headquartered in Shenzhen, China, but built the TTC buses at its Newmarket, Ont. facility; and California-based Proterra.

They all had their strengths and weaknesses, based on their backgrounds as a traditional non-electric bus manufacturer, a battery maker and a vehicle technology and design startup, respectively.

"Each bus type has its own potential challenges." Case said all three manufacturers are working to resolve any adoption challenges as quickly as possible.

But the biggest challenge of all, Case said, is getting the infrastructure in place. 

"There's no playbook, really, for implementing charging infrastructure," he said.

Each bus type needed their own chargers, in some cases using different types of current. Each type has been installed in a different garage in partnership with local utility Toronto Hydro.

Buying and installing them represented about $70 million, or about half the cost of acquiring Toronto's first 60 electric buses. The $140 million project was funded by the federal Public Transit Infrastructure Fund.

Case said it takes about three hours to charge a battery that has been fully depleted. To maximize use of the bus, it's typically put on a long route in the morning, covering 200 to 250 kilometres. Then it's partially charged and put on a shorter run in the late afternoon.

"That way we get as much mileage on the buses as we can."


Cost and reliability?
Besides the infrastructure cost of chargers, each electric bus can cost $200,000 to $500,000 more per bus than an average $750,000 diesel bus. 

Case acknowledges that is "significantly" more expensive, but it is offset by fuel savings over time, as electricity costs are cheaper. Because the electric buses have fewer parts than diesel buses, maintenance costs are also about 25 per cent lower and the buses are expected to be more reliable.

As with many new technologies, the cost of electric buses is also falling over time.

Case expects they will eventually get to the point where the total life-cycle cost of an electric and a diesel bus are comparable, and the electric bus may even save money in the long run.

As of this fall, all but one of the 60 new electric buses have been put into service. The last one is expected to hit the road in early December.

Summer testing showed that air conditioning the buses reduced the battery capacity by about 15 per cent. 

But the TTC needs to see how much of the battery capacity is consumed by heating in winter, at least when the temperature is above 5 C. Below that, a diesel-powered heater kicks in.

Once testing is complete, the TTC plans to develop specifications for its electric bus fleet and order 300 more in 2023, for delivery between 2023 and 2025.


Potential benefits
Even with some diesel heating, the TTC estimates electric buses reduce fuel usage by 70 to 80 per cent. If its whole fleet were switched to electric buses, it could save $50 million to $70 million in fuel a year and 150 tonnes of greenhouse gases per bus per year, or 340,000 tonnes for the entire fleet.

Other than greenhouse gases, electric buses also generate fewer emissions of other pollutants. They're also quieter, creating a more comfortable urban environment for pedestrians and cyclists.

But the benefits could potentially go far beyond the local city.

"If the public agencies start electrifying their fleet and their service is very demanding, I think they'll demonstrate to the broader transportation industry that it is possible," Case said.

"And that's where you'll get the real gains for the environment."

Alex Milovanoff, a postdoctoral researcher in the University of Toronto's department of civil engineering, did a U of T EV study that suggested electrified transit has a crucial role to play in the low-carbon economy of the future.

His calculations show that 90 per cent of U.S. passenger vehicles — 300 million — would need to be electric by 2050 to reach targets under the global Paris Agreement to fight climate change.

And that would put a huge strain on resources, including both the mining of metals, such as lithium and cobalt, that are used in electric vehicle batteries and the electrical grid itself.

A better solution, he showed, was combining the transition to electric vehicles with a reduction in the number of private vehicles, and higher usage of transit, cycling and walking.

"Then that becomes a feasible picture," he said.

What's needed to make the transition
But in order to make that happen, governments need to make investments and navigate the 2035 EV mandate debate on timelines, he added.

That includes subsidies for buying electric buses and building charging stations so transit agencies don't need to make fares too high. But it also includes more general improvements to the range and reliability of transit infrastructure.

"Electrifying the bus fleet is only efficient if we have a large public transit fleet and if we have many buses on the road and if people take them," Milovanoff said.

In its fall economic update on Monday, the federal government announced $150 million over three years to speed up the installation of zero-emission vehicle infrastructure.

Josipa Petrunic, CEO of the Canadian Urban Transit Research and Innovation Consortium, a non-profit organization focused on zero-carbon mobility and transportation, said that in the past, similar funding has paid for high-powered charging systems for transit systems in B.C. and Ontario. But that's only a small part of what's needed, she said.

"Infrastructure Canada needs to come to the table with the cash for the buses and the whole rest of the system."

She said funding is needed for:

Feasibility studies to figure out how many and what kinds of buses are needed for different routes in different transit systems.

Targets and incentives to motivate transit systems to make the switch.

Incentives to encourage Canadian procurement to build the industry in Canada.

Technology to collect and share data on the performance of electric vehicles so transit systems can make the best-possible decisions to meet the needs of their riders.

Petrunic said that a positive side-effect of electrifying transit systems is that the infrastructure can support, in addition to buses, electric trucks for moving freight.

"It's not a lot given that we have 15,000 buses out there in the transit fleet," she said.

"But we should be able to get a lot further ahead if we match the city commitments to zero emissions with federal and provincial funding for jobs creating zero-emissions technologies."

 

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New Kind of 'Solar' Cell Shows We Can Generate Electricity Even at Night

Thermoradiative Diode Power leverages infrared radiation and night-sky cooling to harvest waste heat. Using MCT (mercury cadmium telluride) detectors with photovoltaics, it extends renewable energy generation after sunset, exploiting radiative cooling and low-power density.

 

Key Points

Technology using MCT infrared diodes to turn radiative Earth-to-space heat loss into electricity, aiding solar at night.

✅ MCT diodes radiate to cold sky, generating tiny current at 20 C

✅ Complements photovoltaics by harvesting post-sunset infrared flux

✅ Potential up to one-tenth solar output with further efficiency gains

 

Conventional solar technology soaks up rays of incoming sunlight to bump out a voltage. Strange as it seems, some materials are capable of running in reverse, producing power as they radiate heat back into the cold night sky environment.

A team of engineers in Australia has now demonstrated the theory in action, using the kind of technology commonly found in night-vision goggles to generate power, while other research explores electricity from thin air concepts under ambient humidity.

So far, the prototype only generates a small amount of power, and is probably unlikely to become a competitive source of renewable power on its own – but coupled with existing photovoltaics technology and thermal energy into electricity approaches, it could harness the small amount of energy provided by solar cells cooling after a long, hot day's work.

"Photovoltaics, the direct conversion of sunlight into electricity, is an artificial process that humans have developed in order to convert the solar energy into power," says Phoebe Pearce, a physicist from the University of New South Wales.

"In that sense, the thermoradiative process is similar; we are diverting energy flowing in the infrared from a warm Earth into the cold Universe."

By setting atoms in any material jiggling with heat, you're forcing their electrons to generate low-energy ripples of electromagnetic radiation in the form of infrared light, a principle also explored with carbon nanotube energy harvesters in ambient conditions.

As lackluster as this electron-shimmy might be, it still has the potential to kick off a slow current of electricity. All that's needed is a one-way electron traffic signal called a diode.

Made of the right combination of elements, a diode can shuffle electrons down the street as it slowly loses its heat to a cooler environment.

In this case, the diode is made of mercury cadmium telluride (MCT). Already used in devices that detect infrared light, MCT's ability to absorb mid-and long-range infrared light and turn it into a current is well understood.

What hasn't been entirely clear is how this particular trick might be used efficiently as an actual power source.

Warmed to around 20 degrees Celsius (nearly 70 degrees Fahrenheit), one of the tested MCT photovoltaic detectors generated a power density of 2.26 milliwatts per square meter.

Granted, it's not exactly enough to boil a jug of water for your morning coffee. You'd probably need enough MCT panels to cover a few city blocks for that small task.

But that's not really the point, either, given it's still very early days in the field, and there's potential for the technology to develop significantly further in the future.

"Right now, the demonstration we have with the thermoradiative diode is relatively very low power. One of the challenges was actually detecting it," says the study's lead researcher, Ned Ekins-Daukes.

"But the theory says it is possible for this technology to ultimately produce about 1/10th of the power of a solar cell."

At those kinds of efficiencies, it might be worth the effort weaving MCT diodes into more typical photovoltaic networks alongside thin-film waste heat solutions so that they continue to top up batteries long after the Sun sets.

To be clear, the idea of using the planet's cooling as a source of low-energy radiation is one engineers have been entertaining for a while now. Different methods have seen different results, all with their own costs and benefits, with low-cost heat-to-electricity materials also advancing in parallel.

Yet by testing the limits of each and fine-tuning their abilities to soak up more of the infrared bandwidth, we can come up with a suite of technologies and thermoelectric materials capable of wringing every drop of power out of just about any kind of waste heat.

"Down the line, this technology could potentially harvest that energy and remove the need for batteries in certain devices – or help to recharge them," says Ekins-Daukes.

"That isn't something where conventional solar power would necessarily be a viable option."

 

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