Denham Capital invests in BioTherm Energy

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Denham Capital, a leading energy-focused global private equity firm, announced that it will invest equity of up to [US] $150 million, in BioTherm Energy, a South African developer, owner and operator of renewable and clean energy generation projects.

Commenting on Denham Capital's investment, Buyelwa Sonjica, South Africa Minister of Minerals and Energy said, "Having opened BioTherm's first plant just over a year ago, we are delighted with this substantial investment by Denham Capital, a major foreign investor, in a business that will generate more electricity in South Africa, contribute to the reduction of greenhouse gasses and create more jobs in the South African economy."

The Minister opened the 4.2 MW biogas to power plant, based at the PetroSA facility in Mossel Bay, east of Cape Town, in September 2007. At that time, it was the first private sector renewable power generation project in Southern Africa funded under the Clean Development Mechanism of the Kyoto Protocol, under which the project earns carbon credits because of its contribution to the reduction of greenhouse gasses. Under the European carbon-trading scheme these credits are in turn sold, primarily to European industries, which need to reduce the cost of their compliance liabilities.

The opportunity for small scale, on-site generation in South Africa has grown significantly and BioTherm Energy has secured, and is continuing to develop, a substantial pipeline in waste gas co-generation, biomass and combined heat and power projects, many of which qualify for carbon credits under the Kyoto Protocol. These projects can generate electricity much more rapidly than conventional large-scale power projects, thereby providing needed relief to the South African power system.

Dr. Louis van Pletsen, a Partner and Head of the London Office of Denham Capital, said, "Denham Capital will provide the necessary equity capital for BioTherm Energy to develop, invest or acquire projects totalling approximately 300 MW, equivalent to the electricity needed to supply about 500,000 households. Private sector investment from companies such as BioTherm Energy will be essential in addressing South Africa's energy deficit." He added, "Our investment in BioTherm reflects the range and geographic reach of Denham Capital's energy investment strategy."

Charles Liebenberg, co-founder and CEO of BioTherm Energy, said that a partnership with Denham Capital will allow BioTherm Energy to continue its aggressive expansion programme. He went further to say, "For years South Africa has had cheap energy and an unfortunate result of this is inefficient usage. BioTherm Energy's projects ensure that all forms of energy can be best harnessed to avoid waste, reduce carbon emissions and provide reliable power. The Power Conservation Programme, which will ration electricity supply to all consumers, reflects the severity of the power crisis in South Africa which BioTherm can help address."

BioTherm Energy is targeting energy intensive industries where industrial processes release significant amounts of waste energy both as heat and gasses. BioTherm Energy utilises this wasted energy to produce electricity and/or steam, which it sells to the host site or to third parties, including Eskom, the South African public electricity utility.

BioTherm Energy is also instituting multi-level sustainability in all of its projects through the participation of Black Economic Empowerment partners and community-based development programmes.

"Our investment in BioTherm reflects our strong belief in the potential for innovative solutions to the South African power crisis," said Scott Mackin, a Partner at Denham Capital. "We are delighted to be working to develop this exciting and valuable business, with a highly skilled and committed management team with a proven track record. We believe BioTherm Energy is well positioned to deliver much needed additional clean and reliable power to the Southern African economy."

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3 Reasons Why Cheap Abundant Electricity Is Getting Closer To Reality

Renewable Energy Breakthroughs drive quantum dots solar efficiency, Air-gen protein nanowires harvesting humidity, and cellulose membranes for flow batteries, enabling printable photovoltaics, 24/7 clean power, and low-cost grid storage at commercial scale.

 

Key Points

Advances like quantum dot solar, Air-gen, and cellulose flow battery membranes that improve clean power and storage.

✅ Quantum dots raise solar conversion efficiency, are printable

✅ Air-gen harvests electricity from humidity with protein nanowires

✅ Cellulose membranes cut flow battery costs, aid grid storage

 

Science never sleeps. The quest to find new and better ways to do things continues in thousands of laboratories around the world. Today, the global economy is based on the use of electricity, and one analysis shows wind and solar potential could meet 80% of US demand, underscoring what is possible. If there was a way to harness all the energy from the sun that falls on the Earth every day, there would be enough of electricity available to meet the needs of every man, woman, and child on the planet with plenty left over. That day is getting closer all the time. Here are three reasons why.

Quantum Dots Make Better Solar Panels
According to Science Daily, researchers at the University of Queensland have set a new world record for the conversion of solar energy to electricity using quantum dots — which pass electrons between one another and generate electrical current when exposed to solar energy in a solar cell device. The solar devices they developed have beaten the existing solar conversion record by 25%.

“Conventional solar technologies use rigid, expensive materials. The new class of quantum dots the university has developed are flexible and printable,” says professor Lianzhou Wang, who leads the research team. “This opens up a huge range of potential applications, including the possibility to use it as a transparent skin to power cars, planes, homes and wearable technology. Eventually it could play a major part in meeting the United Nations’ goal to increase the share of renewable energy in the global energy mix.”

“This new generation of quantum dots is compatible with more affordable and large-scale printable technologies,” he adds. “The near 25% improvement in efficiency we have achieved over the previous world record is important. It is effectively the difference between quantum dot solar cell technology being an exciting prospect and being commercially viable.” The research was published on January 20 in the journal Nature Energy.

Electricity From Thin Air
Science Daily also reports that researchers at UMass Amherst also have interesting news. They claim they created a device called an Air-gen, short for air powered generator. (Note: recently we reported on other research that makes electricity from rainwater.) The device uses protein nanowires created by a microbe called Geobacter. Those nanowires can generate electricity from thin air by tapping the water vapor present naturally in the atmosphere. “We are literally making electricity out of thin air. The Air-gen generates clean energy 24/7. It’s the most amazing and exciting application of protein nanowires yet,” researchers Jun Yao and Derek Lovely say. There work was published February 17 in the journal Nature.

The new technology developed in Yao’s lab is non-polluting, renewable, and low-cost. It can generate power even in areas with extremely low humidity such as the Sahara Desert. It has significant advantages over other forms of renewable energy including solar and wind, Lovley says, because unlike these other renewable energy sources, the Air-gen does not require sunlight or wind, and “it even works indoors,” a point underscored by ongoing grid challenges that slow full renewable adoption.

Yao says, “The ultimate goal is to make large-scale systems. For example, the technology might be incorporated into wall paint that could help power your home. Or, we may develop stand-alone air-powered generators that supply electricity off the grid, and in parallel others are advancing bio-inspired fuel cells that could complement such devices. Once we get to an industrial scale for wire production, I fully expect that we can make large systems that will make a major contribution to sustainable energy production. This is just the beginning of a new era of protein based electronic devices.”

Improved Membranes For Flow Batteries From Cellulose
Storing energy is almost as important to decarbonizing the environment as making it in the first place, with the rise of affordable solar batteries improving integration.  There are dozens if not hundreds of ways to store electricity and they all work to one degree or another. The difference between which ones are commercially viable and ones that are not often comes down to money.

Flow batteries — one approach among many, including fuel cells for renewable storage — use two liquid electrolytes — one positively charged and one negatively charged — separated by a membrane that allows electrons to pass back and forth between them. The problem is, the liquids are highly corrosive. The membranes used today are expensive — more than $1,300 per square meter.

Phys.org reports that Hongli Zhu, an assistant professor of mechanical and industrial engineering at Northeastern University, has successfully created a membrane for use in flow batteries that is made from cellulose and costs just $147.68 per square meter. Reducing the cost of something by 90% is the kind of news that gets people knocking on your door.

The membrane uses nanocrystals derived from cellulose in combination with a polymer known as polyvinylidene fluoride-hexafluoropropylene.  The naturally derived membrane is especially efficient because its cellular structure contains thousands of hydroxyl groups, which involve bonds of hydrogen and oxygen that make it easy for water to be transported in plants and trees.

In flow batteries, that molecular makeup speeds the transport of protons as they flow through the membrane. “For these materials, one of the challenges is that it is difficult to find a polymer that is proton conductive and that is also a material that is very stable in the flowing acid,” Zhu says.

Cellulose can be extracted from natural sources including algae, solid waste, and bacteria. “A lot of material in nature is a composite, and if we disintegrate its components, we can use it to extract cellulose,” Zhu says. “Like waste from our yard, and a lot of solid waste that we don’t always know what to do with.”

Flow batteries can store large amounts of electricity over long periods of time — provided the membrane between the storage tanks doesn’t break down. To store more electricity, simply make the tanks larger, which makes them ideal for grid storage applications where there is often plenty of room to install them. Slashing the cost of the membrane will make them much more attractive to renewable energy developers and help move the clean energy revolution forward.

The Takeaway
The fossil fuel crazies won’t give up easily. They have too much to lose and couldn’t care less if life on Earth ceases to exist for a few million years, just so long as they get to profit from their investments. But they are experiencing a death of a thousand cuts. None of the breakthroughs discussed above will end thermal power generation all by itself, but all of them, together with hundreds more just like them happening every day, every week, and every month, even as we confront clean energy's hidden costs across supply chains, are slowly writing the epitaph for fossil fuels.

And here’s a further note. A person of Chinese ancestry is the leader of all three research efforts reported on above. These are precisely the people being targeted by the United States government at the moment as it ratchets up its war on immigrants and anybody who cannot trace their ancestry to northern Europe. Imagine for a moment what will happen to America when researchers like them depart for countries where they are welcome instead of despised. 

 

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Calgary's electricity use soars in frigid February, Enmax says

Calgary Winter Energy Usage Surge highlights soaring electricity demand, added megawatt-hours, and grid reliability challenges driven by extreme cold, heating loads, and climate change, with summer air conditioning also shifting seasonal peaks.

 

Key Points

A spike in Calgary's power use from extreme cold, adding 22k MWh and testing reliability as heating demand rises.

✅ +22,000 MWh vs Feb 2018 amid fourth-coldest February

✅ Heating loads spike; summer A/C now drives peak demand

✅ Grid reliability monitored; more solar and green resources ahead

 

February was so cold in Calgary that the city used enough extra energy to power 3,400 homes for a whole year, echoing record-breaking demand in B.C. in 2021 during severe cold.

Enmax Power Corporation, the primary electricity utility in the city, says the city 's energy consumption was up 22,000 megawatt hours last month compared with Februray 2018.

"We've seen through this cold period our system has held up very well. It's been very reliable," Enmax vice-president Andre van Dijk told the Calgary Eyeopener on Friday. "You know, in the absence of a windstorm combined with cold temperatures and that sort of thing, the system has actually held up pretty well."

The past month was the fourth coldest in Calgary's history, and similar conditions have pushed all-time high demand in B.C. in recent years across the West. The average temperature for last month was –18.1 C. The long-term average for February is –5.4 C.

 

Watching use, predicting issues

The electricity company monitors demand and load on a daily basis, always trying to predict issues before they happen, van Dijk said, and utilities have introduced winter payment plans to help customers manage bills during prolonged cold.

One of the issues they're watching is climate change, and how extreme temperatures and weather affect both the grid's reliability, as seen when Quebec shattered consumption records during cold snaps, and the public's energy use.

The colder it gets, the higher you turn up the heat. The hotter it is, the more you use air conditioning.

He also noted that using fuels then contributes to climate change, creating a cycle.

​"We are seeing variations in temperature and we've seen large weather events across the continent, across the world, in fact, that impact electrical systems, whether that's flooding, as we've experienced here, or high winds, tornadoes," van Dijk said.

"Climate change and changing weather patterns have definitely had had an impact on us as an electrical industry."

In 2012, he said, Calgary switched from using the most power during winter to using the most during summer, in large part due to air conditioning, he said.

"Temperature is a strong influencer of energy consumption and of our demand," van Dijk said.

Christmas tree lights have also become primarily LED, van Dijk said, which cuts down on a big energy draw in the winter.

He said he expects more solar and other green resources will be added into the electrical system in the future to mitigate how much the increasingly levels of energy use impact climate change, and to help moderate electricity costs in Alberta over time.

 

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Demand for electricity in Yukon hits record high

Yukon Electricity Demand Record underscores peak load growth as winter cold snaps drive heating, lighting, and EV charging, blending hydro, LNG, and diesel with renewable energy and planned grid-scale battery storage in Whitehorse.

 

Key Points

It is the territory's new peak electricity load, reflecting winter demand, electric heating, EVs, and mixed generation.

✅ New peak: 104.42 MW, surpassing 2020 record of 103.84 MW

✅ Winter peaks met with hydro, LNG, diesel, and renewables mix

✅ Customers urged to shift use off peak hours and use timers

 

A new record for electricity demand has been set in Yukon. The territory recorded a peak of 104.42 megawatts, according to a news release from Yukon Energy.

The new record is about a half a megawatt higher than the previous record of 103.84 megawatts recorded on Jan. 14, 2020.

While in general, over 90 per cent of the electricity generated in Yukon comes from renewable resources each year, with initiatives such as new wind turbines expanding capacity, during periods of high electricity use each winter, Yukon Energy has to use its hydro, liquefied natural gas and diesel resources to generate the electricity, the release says.

But when it comes to setting records, Andrew Hall, CEO of Yukon Energy, says it's not that unusual.

"Typically, during the winter, when the weather is cold, demand for electricity in the Yukon reaches its maximum. And that's because folks use more electricity for heating their homes, for cooking meals, there's more lighting demand, because the days are shorter," he said.

"It usually happens either in December or sometimes in January, when we get a cold snap."

He said generally over the years, electricity demand has grown.

"We get new home construction, construction of new apartment buildings. And typically, those new homes are all heated by electricity, maybe not all of them but the majority," Hall said.

Vuntut Gwitchin First Nation's solar farm now generating electricity
In taking action on climate, this Arctic community wants to be a beacon to the world

Efforts to curb climate change add to electricity demand
There are also other reasons, ones that are "in the name of climate change," Hall added.

That includes people trying to limit fossil fuel heating by swapping to electric heating. And, he said some Yukoners are switching to electric vehicles as incentives expand across the North.

"Over time, those two new demands, in the name of climate change, will also contribute to growing demand for electricity," he said.

While Yukon did reach this new all time high, Hall said the territory still hadn't hit the maximum capacity for the week, which was 118 megawatts, and discussions about a potential connection to the B.C. grid are part of long-term planning.


Yukon Energy's hydroelectric dam in Whitehorse. Yukon Energy's CEO, Andrew Hall, said demand of 104 megawatts wasn't unexpected, nor was it an emergency. The corporation has the ability to generate 118 megawatts. (Paul Tukker/CBC)
Tips to curve demand
"When we plan our system, we actually plan for a scenario, guided by the view that sustainability is key to the grid's future, where we actually lose our largest hydro generating facility," Hall said.

"We had plenty of generation available so it wasn't an emergency situation, and, even as other provinces face electricity shortages, it was more just an observation that hey, our peaks are growing."

He also said it was an opportunity to reach out to customers on ways to curve their demand for electricity around peak times, drawing on energy efficiency insights from other provinces, which is typically between 7 a.m. and 9 a.m., and between 5 p.m. and 7 p.m., Monday to Friday.

For example, he said, people should consider running major appliances, like dishwashers, during non-peak hours, such as in the afternoon rather than in the morning or evening.

During winter peaks, people can also use a block heater timer on vehicles and turn down the thermostat by one or two degrees.

'We plan for each winter'
Hall said Yukon Energy is working to increase its peak output, including working on a large grid scale battery to be installed in Whitehorse, similar to Ontario's energy storage push now underway. 

When it comes to any added load from people working from home due to COVID-19, Hall said they haven't noticed any identifiable increase there.

"Presumably, if someone's working from home, you know, their computer is at home, and they're not using the computer at the office," he said.

Yukon Energy one step closer to having largest battery storage site in the North
He said there shouldn't be any concern for maxing out the capacity of electricity demand as Yukon moves into the colder winter months, since those days are forecast for.

"This number of 104 megawatts wasn't unexpected," he said, adding how much electricity is needed depends on the weather too.

"We plan for each winter."

 

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Competition in Electricity Has Been Good for Consumers and Good for the Environment

Electricity Market Competition drives lower wholesale prices, stable retail rates, better grid reliability, and faster emissions cuts as deregulation and renewables adoption pressure utilities, improve efficiency, and enhance consumer choice in power markets.

 

Key Points

Electricity market competition opens supply to rivals, lowering prices, improving reliability, and reducing emissions.

✅ Wholesale prices fell faster in competitive markets

✅ Retail rates rose less than in monopoly states

✅ Fewer outages, shorter durations, improved reliability

 

By Bernard L. Weinstein

Electricity used to be boring.  Public utilities that provided power to homes and businesses were regulated monopolies and, by law, guaranteed a fixed rate-of-return on their generation, transmission, and distribution assets. Prices per kilowatt-hour were set by utility commissions after lengthy testimony from power companies, wanting higher rates, and consumer groups, wanting lower rates.

About 25 years ago, the electricity landscape started to change as economists and others argued that competition could lead to lower prices and stronger grid reliability. Opponents of competition argued that consumers weren’t knowledgeable enough about power markets to make intelligent choices in a competitive pricing environment. Nonetheless, today 20 states have total or partial competition for electricity, allowing independent power generators to compete in wholesale markets and retail electric providers (REPs) to compete for end-use customers, a dynamic echoed by the Alberta electricity market across North America. (Transmission, in all states, remains a regulated natural monopoly).

A recent study by the non-partisan Pacific Research Institute (PRI) provides compelling evidence that competition in power markets has been a boon for consumers. Using data from the U.S. Energy Information Administration (EIA), PRI’s researchers found that wholesale electricity prices in competitive markets have been generally declining or flat, prompting discussions of free electricity business models, over the last five years. For example, compared to 2015, wholesale power prices in New England have dropped more than 44 percent, those in most Mid-Atlantic States have fallen nearly 42 percent, and in New York City they’ve declined by nearly 45 percent. Wholesale power costs have also declined in monopoly states, but at a considerably slower rate.

As for end-users, states that have competitive retail electricity markets have seen smaller price increases, as consumers can shop for electricity in Texas more cheaply than in monopoly states. Again, using EIA data, PRI found that in 14 competitive jurisdictions, retail prices essentially remained flat between 2008 and 2020. By contrast, retail prices jumped an average of 21 percent in monopoly states.  The ten states with the largest retail price increases were all monopoly-based frameworks. A 2017 report from the Retail Energy Supply Association found customers in states that still have monopoly utilities saw their average energy prices increase nearly 19 percent from 2008 to 2017 while prices fell 7 percent in competitive markets over the same period.

The PRI study also observed that competition has improved grid reliability, the recent power disruptions in California and Texas, alongside disruptions in coal and nuclear sectors across the U.S., notwithstanding. Looking at two common measures of grid resiliency, PRI’s analysis found that power interruptions were 10.4 percent lower in competitive states while the duration of outages was 6.5 percent lower.

Citing data from the EIA between 2008 and 2018, PRI reports that greenhouse gas emissions in competitive states declined on average 12.1 percent compared to 7.3 percent in monopoly states. This result is not surprising, and debates over whether Israeli power supply competition can bring cheaper electricity mirror these dynamics.  In a competitive wholesale market, independent power producers have an incentive to seek out lower-cost options, including subsidized renewables like wind and solar. By contrast, generators in monopoly markets have no such incentive as they can pass on higher costs to end-users. Perhaps the most telling case is in the monopoly state of Georgia where the cost to build nuclear Plant Vogtle has doubled from its original estimate of $14 billion 12 years ago. Overruns are estimated to cost Georgia ratepayers an average of $854, and there is no definite date for this facility to come on line. This type of mismanagement doesn’t occur in competitive markets.

Unfortunately, some critics are attempting to halt the momentum for electricity competition and have pointed to last winter’s “deep freeze” in Texas that left several million customers without power for up to a week. But this example is misplaced. Power outages in February were the result of unprecedented and severe weather conditions affecting electricity generation and fuel supply, and numerous proposals to improve Texas grid reliability have focused on weatherization and fuel resilience; the state simply did not have enough access to natural gas and wind generation to meet demand. Competitive power markets were not a factor.

The benefits of wholesale and retail competition in power markets are incontrovertible. Evidence shows that households and businesses in competitive states are paying less for electricity while grid reliability has improved. The facts also suggest that wholesale and retail competition can lead to faster reductions in greenhouse gas emissions. In short, competition in power markets is good for consumers and good for the environment.

Bernard L. Weinstein is emeritus professor of applied economics at the University of North Texas, former associate director of the Maguire Energy Institute at Southern Methodist University, and a fellow of Goodenough College, London. He wrote this for InsideSources.com.

 

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Solar changing shape of electricity prices in Northern Europe

EU Solar Impact on Electricity Prices highlights how rising solar PV penetration drives negative pricing, shifts peak hours, pressures wholesale markets, and challenges grid balancing, interconnection, and flexibility amid changing demand and renewables growth.

 

Key Points

Explains how rising solar PV cuts wholesale prices, shifts negative-price hours, and strains grid flexibility.

✅ Negative pricing events surge with higher solar penetration.

✅ Afternoon price dips replace night-time wind-led lows.

✅ Grid balancing, interconnectors, and flexibility become critical.

 

The latest EU electricity market report has confirmed the affect deeper penetration of solar is having on wholesale electricity prices more broadly.

The Quarterly Report on European Electricity Markets for the final three months of last year noted the number of periods of negative electricity pricing doubled from 2019, to almost 1,600 such events, as global renewables set new records in deployment across markets.

Having experienced just three negative price events in 2019, the Netherlands recorded almost 100 last year “amid a dramatic increase in solar PV capacity,” in the nation, according to the report.

Whilst stressing the exceptional nature of the Covid-19 pandemic on power consumption patterns, the quarterly update also noted a shift in the hours during which negative electric pricing occurred in renewables poster child Germany. Previously such events were most common at night, during periods of high wind speed and low demand, but 2020 saw a switch to afternoon negative pricing. “Thus,” stated the report, “solar PV became the main driver behind prices falling into negative territory in the German market in 2020, as Germany's solar boost accelerated, and also put afternoon prices under pressure generally.”

The report also highlighted two instances of scarce electricity–in mid September and on December 9–as evidence of the problems associated with accommodating a rising proportion of intermittent clean energy capacity into the grid, and called for more joined-up cross-border power networks, amid pushback from Russian oil and gas across the continent.

Rising solar generation–along with higher gas output, year on year–also helped the Netherlands generate a net surplus of electricity last year, after being a net importer “for many years.” The EU report also noted a beneficial effect of rising solar generation capacity on Hungary‘s national electricity account, and cited a solar “boom” in that country and Poland, mirroring rapid solar PV growth in China in recent years.

With Covid-19 falls in demand helping renewables generate more of Europe's electricity (39%) than fossil fuels (36%) for the first time, as renewables surpassed fossil fuels across Europe, the market report observed the 5% of the bloc's power produced from solar closed in on the 6% accounted for by hard coal. In the final three months of the year, European solar output rose 12%, year on year, to 18 TWh and “the increase was almost single-handedly driven by Spain,” the study added.

With coal and lignite-fired power plunging 22% last year across the bloc, it is estimated the European power sector reduced its carbon footprint 14% as part of Europe's green surge although the quarterly report warned cold weather, lower wind speeds and rising gas prices in the opening months of this year are likely to see carbon emissions rebound.

There was good news on the transport front, though, with the report stating the scale of the European “electrically-charged vehicle” fleet doubled in 2020, to 2 million, with almost half a million of the new registrations arriving in the final months of the year. That meant cars with plug sockets accounted for a remarkable 17% of new purchases in Q4, twice the proportion seen in China and a slice of the pie six times bigger than such products claimed in the U.S.

 

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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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