San Antonio Spurs' arena to be powered by wind

By Associated Press


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The arena where the San Antonio Spurs play will be powered solely by wind-generated electricity for the next two years.

Spurs owner Peter Holt said that the energy switch is part of an initiative to make the AT&T Center the greenest arena in the U.S.

"We are exploring recycling and water conservation ideas as well," Holt said in a press release. "We really want to be a model for arenas across the country regarding sensitivity to the environment."

The arena has been powered with "Windtricity" from CPS Energy since June 1.

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UK must start construction of large-scale storage or fail to meet net zero targets.

UK Hydrogen Storage Caverns enable long-duration, low-carbon electricity balancing, storing surplus wind and solar power as green hydrogen in salt formations to enhance grid reliability, energy security, and net zero resilience by 2035 and 2050.

 

Key Points

They are salt caverns storing green hydrogen to balance wind and solar, stabilizing a low-carbon UK grid.

✅ Stores surplus wind and solar as green hydrogen in salt caverns

✅ Enables long-duration, low-carbon grid balancing and security

✅ Complements wind and solar; reduces dependence on flexible CCS

 

The U.K. government must kick-start the construction of large-scale hydrogen storage facilities if it is to meet its pledge that all electricity will come from low-carbon electricity sources by 2035 and reach legally binding net zero targets by 2050, according to a report by the Royal Society.

The report, "Large-scale electricity storage," published Sep. 8, examines a wide variety of ways to store surplus wind and solar generated electricity—including green hydrogen, advanced compressed air energy storage (ACAES), ammonia, and heat—which will be needed when Great Britain's electricity generation is dominated by volatile wind and solar power.

It concludes that large scale electricity storage is essential to mitigate variations in wind and sunshine, particularly long-term variations in the wind, and to keep the nation's lights on. Storing most of the surplus as hydrogen, in salt caverns, would be the cheapest way of doing this.

The report, based on 37 years of weather data, finds that in 2050 up to 100 Terawatt-hours (TWh) of storage will be needed, which would have to be capable of meeting around a quarter of the U.K.'s current annual electricity demand. This would be equivalent to more than 5,000 Dinorwig pumped hydroelectric dams. Storage on this scale, which would require up to 90 clusters of 10 caverns, is not possible with batteries or pumped hydro.

Storage requirements on this scale are not currently foreseen by the government, and the U.K.'s energy transition faces supply delays. Work on constructing these caverns should begin immediately if the government is to have any chance of meeting its net zero targets, the report states.

Sir Chris Llewellyn Smith FRS, lead author of the report, said, "The need for long-term storage has been seriously underestimated. Demand for electricity is expected to double by 2050 with the electrification of heat, transport, and industrial processing, as well as increases in the use of air conditioning, economic growth, and changes in population.

"It will mainly be met by wind and solar generation. They are the cheapest forms of low-carbon electricity generation, but are volatile—wind varies on a decadal timescale, so will have to be complemented by large scale supply from energy storage or other sources."

The only other large-scale low-carbon sources are nuclear power, gas with carbon capture and storage (CCS), and bioenergy without or with CCS (BECCS). While nuclear and gas with CCS are expected to play a role, they are expensive, especially if operated flexibly.

Sir Peter Bruce, vice president of the Royal Society, said, "Ensuring our future electricity supply remains reliable and resilient will be crucial for our future prosperity and well-being. An electricity system with significant wind and solar generation is likely to offer the lowest cost electricity but it is essential to have large-scale energy stores that can be accessed quickly to ensure Great Britain's energy security and sovereignty."

Combining hydrogen with ACAES, or other forms of storage that are more efficient than hydrogen, could lower the average cost of electricity overall, and would lower the required level of wind power and solar supply.

There are currently three hydrogen storage caverns in the U.K., which have been in use since 1972, and the British Geological Survey has identified the geology for ample storage capacity in Cheshire, Wessex and East Yorkshire. Appropriate, novel business models and market structures will be needed to encourage construction of the large number of additional caverns that will be needed, the report says.

Sir Chris observes that, although nuclear, hydro and other sources are likely to play a role, Britain could in principle be powered solely by wind power and solar, supported by hydrogen, and some small-scale storage provided, for example, by batteries, that can respond rapidly and to stabilize the grid. While the cost of electricity would be higher than in the last decade, we anticipate it would be much lower than in 2022, he adds.

 

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NB Power launches public charging network for EVs

NB Power eCharge Network expands EV charging in New Brunswick with fast chargers, level 2 stations, Trans-Canada Highway coverage, and green infrastructure, enabling worry-free electric vehicle travel and lower emissions across the province.

 

Key Points

NB Power eCharge Network is a provincewide EV charging system with fast and level 2 stations for reliable travel.

✅ 15 fast-charging sites on Trans-Canada and northern New Brunswick

✅ Level 2 stations at highways, municipalities, and businesses

✅ 20-30 minute DC fast charging; cut emissions ~80% and fuel ~75%

 

NB Power announced Friday the eCharge Network, the province’s first electric vehicle charging network aimed at giving drivers worry-free travel everywhere in the province.

The network includes 15 locations along the province’s busiest highways where both fast-chargers and level-2 chargers will be available. In addition, nine level-2 chargers are already located at participating municipalities and businesses throughout the province. The new locations will be installed by the end of 2017.

NB Power is working with public and private partners to add to the network to enable electric vehicle owners to drive with confidence and to encourage others to make the switch from gas to electric vehicles, supported by a provincial rebate program now available.

“We are incredibly proud to offer our customers and visitors to New Brunswick convenient charging with the launch of our eCharge Network,” said Gaëtan Thomas, president and CEO of NB Power. “Our goal is to make it easy for owners of electric vehicles to drive wherever they choose in New Brunswick, and to encourage more drivers to consider an electric vehicle for their next purchase.”

An electric vehicle owner in New Brunswick can shrink their vehicle carbon footprint by about 80 per cent while reducing their fuel-related costs by about 75 per cent, according to NB Power, and broader grid benefits are being explored through Nova Scotia's vehicle-to-grid pilot across the region.

In addition to the network of standard charging stations, the eCharge network will also include 400 volt fast-charging stations along the Trans-Canada Highway and in the northern parts of New Brunswick. The first of their kind in New Brunswick, these 15 fast-charging stations, similar to Newfoundland and Labrador's newly completed fast-charging network connecting communities, will enable all-electric vehicles to recharge in as little as 20 to 30 minutes. Fast-charge sites will include standard level-2 stations for both battery electric vehicles and plug-in hybrids.

NB Power will install fast-charge and level-2 sites at five locations throughout northern New Brunswick, addressing northern coverage challenges seen elsewhere, such as Labrador's infrastructure gaps today, which will be cost-shared with government. Locations include the areas of Saint-Quentin/Kedgwick, Campbellton, Bathurst, Tracadie, and Miramichi.

“Our government understands that embracing the green economy and reducing our carbon footprint is a priority for New Brunswickers,” said Environment and Local Government Minister Serge Rousselle. “Our climate change action plan calls for a collaborative approach to creating the strategic infrastructure to support electric vehicles throughout all regions in the province, and we are pleased to see this important step underway. New Brunswickers will now have the necessary network to adopt new methods of transportation and contribute to our provincial plan to increase the number of electric vehicles on the road and will help meet emission reduction targets as we work to combat climate change.”

An investment of $500,000 from Natural Resources Canada will go towards purchasing and installing the charging stations for the 10 fast-charging stations along the Trans-Canada Highway.

“The eCharge Network will make it easier for Canadians to choose cleaner options and helps put New Brunswick’s transportation system on a path to a lower-carbon future,” said Moncton-Riverview-Dieppe MP Ginette Petitpas Taylor. “The Government of Canada continues to support green infrastructure in the transportation sector that will advance Canada’s efforts to build a clean economy, create well-paying jobs, and achieve our climate change goals.”

Petitpas Taylor attended for federal Natural Resources Minister Jim Carr.

Fast chargers are being installed at the following locations along the Trans-Canada Highway across New Brunswick:

– Irving Big Stop, Aulac

– Edmundston Truck Stop

– Irving Big Stop, Saint-André

– Johnson Guardian, Perth-Andover

– Murray’s Irving, Woodstock

– Petro-Canada / Acorn Restaurant, Prince William

– Irving Big Stop, Waasis

 

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Covid-19: Secrets of lockdown lifestyle laid bare in electricity data

Lockdown Electricity Demand Trends reveal later mornings, weaker afternoons, and delayed peaks as WFH, streaming, and video conferencing reshape energy demand curves, grid forecasting, and residential electricity usage across Europe, New York, Tokyo, and Singapore.

 

Key Points

Shifts in power use during lockdowns: later ramps, weaker afternoons, and higher, delayed evening peaks.

✅ Morning ramp starts later; midday demand dips

✅ Evening peak shifts 1-2 hours; higher late-night usage

✅ WFH and streaming raise residential load; industrial demand falls

 

Life in lockdown means getting up late, staying up till midnight and slacking off in the afternoons.

That’s what power market data in Europe show in the places where restrictions on activity have led to a widespread shift in daily routines of hundreds of millions of people.

It’s a similar story wherever lockdowns bite. In New York City electricity use has fallen as much as 18% from normal times at 8am. Tokyo and three nearby prefectures had a 5% drop in power use during weekdays after Japan declared a state of emergency on April 7, according to Tesla Asia Pacific, an energy forecaster.

Italy’s experience shows the trend most clearly since the curbs started there on March 5, before any other European country. Data from the grid operator Terna SpA gives a taste of what other places are also now starting to report, with global daily demand dips observed in many markets as well.


1. People are sleeping later

With no commute to the office people can sleep longer. Normally, electricity demand began to pick up between 6 a.m. and 8 a.m. Now in Germany, it’s clear coffee machines don’t go on until between 8 a.m. and 9 a.m., said Simon Rathjen, founder of the trading company MFT Energy A/S.

Germany, France and Italy -- which between them make up almost two thirds of the euro-zone economy -- all have furlough measures that allow workers to receive a salary while temporarily suspended from their jobs. The U.K. also has a support package. Many of these workers will be getting up later.

"Now I have quite a relaxed start to the morning,” said David Freeman, an analyst in financial services from London. "I don’t get up until about half an hour before I need to start work.”

2. Less productive afternoons

There is a deeper dip in electricity use in the afternoons. Previously, power use rose between 2pm and 5pm. Now it dips as people head out for a walk or some air, according to UK demand data from National Grid Plc

It’s "as though we are living through a month of Sundays”, said Iain Staffell, senior lecturer in sustainable energy at Imperial College London.

3. Evenings in

From 6pm electricity use begins to rise steeply as people finish work and start chores. Restrictions like work and home schooling that prevent much daytime TV watching lifts in the early evening. This following chart for Germany shows the evening peak for power use coming during later hours.

The evening is when electricity use is highest, with most people confined to their homes. Netflix Inc reported a record 15.8 million paid subscribers – almost double the figure forecast by Wall Street analysts. Video-streaming services like Netflix and YouTube have found a captive audience. The new Disney+ service surpassed 50 million subscribers in just five months, a faster pace than predicted.

Internet traffic is skyrocketing, with a surge in bandwidth-intensive applications like streaming services and Zoom. This may mean that monthly broadband consumption of as much as 600 gigabytes, about 35% higher than before, according to Bloomberg Intelligence.

In Singapore, electricity use has dropped off significantly since the country’s "circuit-breaker” efforts to keep people at home began April 7. Electricity use has fallen and stayed low during the day. But late at night is a different story, as power demand fell sharply immediately after the lockdown began, it has steadily crept back in the past two weeks, perhaps a sign that Tiger King and The Last Dance have been finding late-night fans in the city state.

In Ottawa, COVID-19 closures made it seem as if the city had fallen off the electricity grid, according to local reports.

4. Staying up late

We’re going to bed later too. Demand doesn’t start to drop off until 10pm to 12am, at least an hour later than before.

"My children are definitely going to bed later,” said Liz Stevens, a teaching assistant from London. "Our whole routine is out the window.”

It’s challenging for those that need to predict behaviour – power grids and electricity traders. Forecasting is based on historical data, and there isn’t anything to go into the models gauging use now.

The closest we can get is looking at big events like football World Championships when people are all sitting down at the same time, according to Rathjen at MFT.

"Forecasting demand right now is very tricky,” said Chris Kimmett, director of power grids at Reactive Technologies Ltd. "A global pandemic is uncharted territory."

What normal looks like when the crisis passes is also an open question. Different countries are set to unravel their measures in their own ways, and global power demand has already surged above pre-pandemic levels in some analyses, with Germany and Austria loosening restrictions first and Italy remaining under tight control. Some changes may be permanent, with both workers and employers becoming more comfortable with working from home.

5. Different sectors consume more

In China, which is further along recovering from the pandemic than Europe or the US, the sharp contraction in overall power output masks a shift in daily routines.

Eating habits have changed. Restaurants are expanding delivery and even offering grocery services as the preference for dining at home persists. Household electricity consumption in China probably increased from activities such as cooking and heating, according to IHS Markit, which said that residential demand rose by 2.4% in the first two months as people stayed in.

The increase in technology use also drove China’s power demand from the telecom and web-service sectors to rise by 27%, the consultancy said.

Overall, China power demand in the first quarter of the year fell 6.5% from the same period in 2019 to 1.57 trillion kilowatt-hours, China’s National Energy Administration said last week. Industry uses about 70% of the country’s electricity, while the commercial sector and households account for 14% each. – Bloomberg

 

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Smart grid and system improvements help avoid more than 500,000 outages over the summer

ComEd Smart Grid Reliability drives outage reduction across Illinois, leveraging smart switches, grid modernization, and peak demand programs to keep customers powered, improve power quality, and enhance energy savings during extreme weather and severe storms.

 

Key Points

ComEd's smart grid performance, cutting outages and improving power quality to enhance reliability and customer savings.

✅ Smart switches reroute power to avoid customer interruptions

✅ Fewer outages during extreme weather across northern Illinois

✅ Peak Time Savings rewards for reduced peak demand usage

 

While the summer of 2019 set records for heat and brought severe storms, ComEd customers stayed cool thanks to record-setting reliability during the season. These smart grid investments over the last seven years helped to set records in key reliability measurements, including frequency of outages metrics, and through smart switches that reroute power around potential problem areas, avoided more than 538,000 customer interruptions from June to August.

"In a summer where we were challenged by extreme weather, we saw our smart grid investments and our people continue to deliver the highest levels of reliability, backed by extensive disaster planning across utilities, for the families and businesses we serve," said Joe Dominguez, CEO of ComEd. "We're proud to deliver the most affordable, cleanest and, as we demonstrated this summer, most reliable energy to our customers. I want to thank our 6,000 employees who work around the clock in often challenging conditions to power our communities."

ComEd has avoided more than 13 million customer interruptions since 2012, due in part to smart grid and system improvements. The avoided outages have resulted in $2.4 billion in estimated savings to society. In addition to keeping energy flowing for residents, strong power reliability continues to help persuade industrial and commercial companies to expand in northern Illinois and Chicago. The GridWise Alliance recently recognized Illinois as the No. 2 state in the nation for its smart grid implementation.

"Our smart grid investments has vastly improved the infrastructure of our system," said Terry Donnelly, ComEd president and chief operating officer. "We review the system and our operations continually to make sure we're investing in areas that benefit the greatest number of customers, and to prepare for public-health emergencies as well. On a daily basis and during storms or to reduce wildfire risk when necessary, our customers are seeing fewer and fewer interruptions to their lives and businesses."

ComEd customers also set records for energy savings this summer. Through its Peak Time Savings program and other energy-efficiency programs offered by utilities, ComEd empowered nearly 300,000 families and individuals to lower their bills by a total of more than $4 million this summer for voluntarily reducing their energy use during times of peak demand. Since the Peak Time Savings program launched in 2015, participating customers have earned a total of more than $10 million in bill credits.

 

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What to know about the big climate change meeting in Katowice, Poland

COP24 Climate Talks in Poland gather nearly 200 nations to finalize the Paris Agreement rulebook, advance the Talanoa Dialogue, strengthen emissions reporting and transparency, and align finance, technology transfer, and IPCC science for urgent mitigation.

 

Key Points

UNFCCC summit in Katowice to finalize Paris rules, enhance transparency, and drive stronger emissions cuts.

✅ Paris rulebook on reporting, transparency, markets, and timelines

✅ Talanoa Dialogue to assess gaps and raise ambition by 2020

✅ Finance and tech transfer for developing countries under UNFCCC

 

Delegates from nearly 200 countries have assembled this month in Katowice, Poland — the heart of coal country — to try to move the ball forward on battling climate change.

It’s now the 24th annual meeting, or “COP” — conference of the parties — under the landmark U.N. Framework Convention on Climate Change, which the United States signed under then-President George H.W. Bush in 1992. More significantly, it’s the third such meeting since nations adopted the Paris climate agreement in 2015, widely seen at the time as a landmark moment in which, at last, developed and developing countries would share a path toward cutting greenhouse gas emissions, as Obama's clean energy push sought to lock in momentum.

But the surge of optimism that came with Paris has faded lately. The United States, the second largest greenhouse gas emitter, said it would withdraw from the agreement, though it has not formally done so yet. Many other countries are off target when it comes to meeting their initial round of Paris promises — promises that are widely acknowledged to be too weak to begin with. And emissions have begun to rise after a brief hiatus that had lent some hope of progress.

The latest science, meanwhile, is pointing toward increasingly dire outcomes. The amount of global warming that the world already has seen — 1 degree Celsius, 1.8 degrees Fahrenheit — has upended the Arctic, is killing coral reefs and may have begun to destabilize a massive part of Antarctica. A new report from the U.N.'s Intergovernmental Panel on Climate Change (IPCC), requested by the countries that assembled in Paris to be timed for this year’s meeting, finds a variety of increasingly severe effects as soon as a rise of 1.5 degrees Celsius arrives — an outcome that can’t be avoided without emissions cuts so steep that they would require societal transformations without any known historical parallel, the panel found.

It’s in this context that countries are meeting in Poland, with expectations and stakes high.

So what’s on the agenda in Poland?

The answer starts with the Paris agreement, which was negotiated three years ago, has been signed by 197 countries and is a mere 27 pages long. It covers a lot, laying out a huge new regime not only for the world as a whole to cut its greenhouse gas emissions, but for each individual country to regularly make new emissions-cutting pledges, strengthen them over time, report emissions to the rest of the world and much more. It also addresses financial obligations that developed countries have to developing countries, including how to achieve clean and universal electricity at scale, and how technologies will be transferred to help that.

But those 27 pages leave open to interpretation many fine points for how it will all work. So in Poland, countries are performing a detailed annotation of the Paris agreement, drafting a “rule book” that will span hundreds of pages.

That may sound bureaucratic, but it’s key to addressing many of the flash points. For instance, it will be hard for countries to trust that their fellow nations are cutting emissions without clear standards for reporting and vetting. Not everybody is ready to accept a process like the one followed in the United States, which not only publishes its emissions totals but also has an independent review of the findings.

“A number of the developing countries are resisting that kind of model for themselves. They see it as an intrusion on their sovereignty,” said Alden Meyer, director of strategy and policy at the Union of Concerned Scientists and one of the many participants in Poland this week. “That’s going to be a pretty tough issue at the end of the day.”

It’s hardly the only one. Also unclear is what countries will do after the time frames on their current emissions-cutting promises are up, which for many is 2025 or 2030. Will all countries then start reporting newer and more ambitious promises every five years? Every 10 years?

That really matters when five years of greenhouse gas emissions — currently about 40 billion tons of carbon dioxide annually — are capable of directly affecting the planet’s temperature.

What can we expect each day?

The conference is in its second week, when higher-level players — basically, the equivalent of cabinet-level leaders in the United States — are in Katowice to advance the negotiations.

As this happens, several big events are on the agenda. On Tuesday and Wednesday is the “Talanoa Dialogue,” which will bring together world leaders in a series of group meetings to discuss these key questions: “Where are we? Where do we want to go? How do we get there?”

Friday is the last day of the conference, but pros know these events tend to run long. On Friday — or after — we will be waiting for an overall statement or decision from the meeting which may signal how much has been achieved.

What is the “Talanoa Dialogue”?

“Talanoa” is a word used in Fiji and in many other Pacific islands to refer to “the sharing of ideas, skills and experience through storytelling.” This is the process that organizers settled on to fulfill a plan formed in Paris in 2015.

That year, along with signing the Paris agreement, nations released a decision that in 2018 there should be a “facilitative dialogue" among the countries “to take stock” of where their efforts stood to reduce greenhouse gas emissions. This was important because going into that Paris meeting, it was already clear that countries' promises were not strong enough to hold global warming below a rise of 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial temperatures.

This dialogue, in the Talanoa process, was meant to prompt reflection and maybe even soul searching about what more would have to be done. Throughout the year, “inputs” to the Talanoa dialogue — most prominently, the recent report by the United Nations' Intergovernmental Panel on Climate Change on the meaning and consequences of 1.5 degrees Celsius of warming —have been compiled and synthesized. Now, over two days in Poland, countries' ministers will assemble to share stories in small groups about what is working and what is not and to assess where the world as a whole is on achieving the required greenhouse gas emissions reductions.

What remains to be seen is whether this process will culminate in any kind of product or statement that calls clearly for immediate, strong ramping up of climate change promises across the world.

With the clock ticking, will countries do anything to increase their ambition at this meeting?

If negotiating the Paris rule book sounds disappointingly technical, well, you’re not the only one feeling that way. Pressure is mounting for countries to accomplish something more than that in Poland — to at minimum give a strong signal that they understand that the science is looking worse and worse, and the world’s progress on the global energy transition isn’t matching that outlook.

“The bigger issue is how we’re going to get to an outcome on greater ambition,” said Lou Leonard, senior vice president for climate and energy at the World Wildlife Fund, who is in Poland observing the talks. “And I think the first week was not kind on moving that part of the agenda forward.”

Most countries are not likely to make new emissions-cutting promises this week. But there are two ways that the meeting could give a strong statement that countries should — or will — come up with new promises at least by 2020. That’s when extremely dramatic emissions cuts would have to start, including progress toward net-zero electricity by mid-century, according to the recent report on 1.5 degrees Celsius of warming.

The first is the aforementioned “Talanoa dialogue” (see above). It’s possible that the outcome of the dialogue could be a statement acknowledging that the world isn’t nearly far enough along and calling for much stronger steps.

There will also be a decision text released for the meeting as a whole, which could potentially send a signal. Leonard said he hopes that would include details for the next steps that will put the world on a better course.

“We have to create milestones, and the politics around it that will pressure countries to do something that quite frankly they don’t want to do,” he said. “It’s not going to be easy. That’s why we need a process that will help make it happen. And make the most of the IPCC report that was designed to come out right now so it could do this for us. That’s why we have it, and it needs to serve that role.”

The United States says it will withdraw from the agreement, so what role is it playing in Poland?

Despite President Trump’s pledge to withdraw, the United States remains in the Paris agreement (for now) and has sent a delegation of 44 people to Poland, largely from the State Department but also from the Environmental Protection Agency, Energy Department and even the White House, while domestically a historic U.S. climate law has recently passed to accelerate clean energy. Many of these career government officials remain deeply engaged in hashing out details of the agreement.

Still, the country as a whole is being cast in an antagonistic role in the talks.

 

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Cheap material converts heat to electricity

Polycrystalline Tin Selenide Thermoelectrics enable waste heat recovery with ZT 3.1, matching single crystals while cutting costs, powering greener car engines, industrial furnaces, and thermoelectric generators via p-type and emerging n-type designs.

 

Key Points

Low-cost tin selenide devices that turn waste heat into power, achieving ZT 3.1 and enabling p-type and n-type modules.

✅ Oxygen removal prevents heat-leaking tin oxide grain skins.

✅ Polycrystalline ingots match single-crystal ZT 3.1 at lower cost.

✅ N-type tin selenide in development to pair with p-type.

 

So-called thermoelectric generators turn waste heat into electricity without producing greenhouse gas emissions, providing what seems like a free lunch. But despite helping power the Mars rovers, the high cost of these devices has prevented their widespread use. Now, researchers have found a way to make cheap thermoelectrics that work just as well as the pricey kind. The work could pave the way for a new generation of greener car engines, industrial furnaces, and other energy-generating devices.

“This looks like a very smart way to realize high performance,” says Li-Dong Zhao, a materials scientist at Beihang University who was not involved with the work. He notes there are still a few more steps to take before these materials can become high-performing thermoelectric generators. However, he says, “I think this will be used in the not too far future.”

Thermoelectrics are semiconductor devices placed on a hot surface, like a gas-powered car engine or on heat-generating electronics using thin-film converters to capture waste heat. That gives them a hot side and a cool side, away from the hot surface. They work by using the heat to push electrical charges from one to the other, a process of turning thermal energy into electricity that depends on the temperature gradient. If a device allows the hot side to warm up the cool side, the electricity stops flowing. A device’s success at preventing this, as well as its ability to conduct electrons, feeds into a score known as the figure of merit, or ZT.

 Over the past 2 decades, researchers have produced thermoelectric materials with increasing ZTs, while related advances such as nighttime solar cells have broadened thermal-to-electric concepts. The record came in 2014 when Mercouri Kanatzidis, a materials scientist at Northwestern University, and his colleagues came up with a single crystal of tin selenide with a ZT of 3.1. Yet the material was difficult to make and too fragile to work with. “For practical applications, it’s a non-starter,” Kanatzidis says.

So, his team decided to make its thermoelectrics from readily available tin and selenium powders, an approach that, once processed, makes grains of polycrystalline tin selenide instead of the single crystals. The polycrystalline grains are cheap and can be heated and compressed into ingots that are 3 to 5 centimeters long, which can be made into devices. The polycrystalline ingots are also more robust, and Kanatzidis expected the boundaries between the individual grains to slow the passage of heat. But when his team tested the polycrystalline materials, the thermal conductivity shot up, dropping their ZT scores as low as 1.2.

In 2016, the Northwestern team discovered the source of the problem: an ultrathin skin of tin oxide was forming around individual grains of polycrystalline tin selenide before they were pressed into ingots. And that skin acted as an express lane for the heat to travel from grain to grain through the material. So, in their current study, Kanatzidis and his colleagues came up with a way to use heat to drive any oxygen away from the powdery precursors, leaving pristine polycrystalline tin selenide, whereas other devices can generate electricity from thin air using ambient moisture.

The result, which they report today in Nature Materials, was not only a thermal conductivity below that of single-crystal tin selenide but also a ZT of 3.1, a development that echoes nighttime renewable devices showing electricity from cold conditions. “This opens the door for new devices to be built from polycrystalline tin selenide pellets and their applications to be explored,” Kanatzidis says.

Getting through that door will still take some time. The polycrystalline tin selenide the team makes is spiked with sodium atoms, creating what is known as a “p-type” material that conducts positive charges. To make working devices, researchers also need an “n-type” version to conduct negative charges.

Zhao’s team recently reported making an n-type single-crystal tin selenide by spiking it with bromine atoms. And Kanatzidis says his team is now working on making an n-type polycrystalline version. Once n-type and p-type tin selenide devices are paired, researchers should have a clear path to making a new generation of ultra-efficient thermoelectric generators. Those could be installed everywhere from automobile exhaust pipes to water heaters and industrial furnaces to scavenge energy from some of the 65% of fossil fuel energy that winds up as waste heat. 

 

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