Sales team suspended for dodgy practices

By The Worcester News


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A Worcester-based utility firm has suspended 17 members of staff following allegations they used dodgy sales tactics to con householders into signing up as new customers.

An internal investigation is underway at npower after it closed down a sales team in London, following allegations in a national newspaper.

Other members of staff have now been given a reminder about how they should go about their jobs, while calls have been made to put a stop to cold-calling customers on their doorsteps.

A spokesman for npower, which has its head office at Oak House, Bridgwater Road, Warndon, said the investigation was being carried out by employees not connected to the sales department but said she did not know how long it would take.

Mid-Worcestershire MP Peter Luff, who is chairman of the Commons business and enterprise committee, said he was "shocked" about the claims and added he is worried about whether there is a wider problem not only in npower but the industry.

"The question in my mind is how could the Sunday Times journalist get placed with the only team in npower not doing their job properly?

"Are there other people who are working in the same way?"

Mr Luff said npower had taken all of the right steps in response to the allegations but urged the company to look at its working practices across the country.

He said energy regulator Ofgem as well as his own committee would now look at the case.

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Carbon capture: How can we remove CO2 from the atmosphere?

CO2 Removal Technologies address climate change via negative emissions, including carbon capture, reforestation, soil carbon, biochar, BECCS, DAC, and mineralization, helping meet Paris Agreement targets while managing costs, land use, and infrastructure demands.

 

Key Points

Methods to extract or sequester atmospheric CO2, combining natural and engineered approaches to limit warming.

✅ Includes reforestation, soil carbon, biochar, BECCS, DAC, mineralization

✅ Balances climate goals with costs, land, energy, and infrastructure

✅ Key to Paris Agreement targets under 1.5-2.0 °C warming

 

The world is, on average, 1.1 degrees Celsius warmer today than it was in 1850. If this trend continues, our planet will be 2 – 3 degrees hotter by the end of this century, according to the Intergovernmental Panel on Climate Change (IPCC).

The main reason for this temperature rise is higher levels of atmospheric carbon dioxide, which cause the atmosphere to trap heat radiating from the Earth into space. Since 1850, the proportion of CO2 in the air has increased, with record greenhouse gas concentrations documented, from 0.029% to 0.041% (288 ppm to 414 ppm).

This is directly related to the burning of coal, oil and gas, which were created from forests, plankton and plants over millions of years. Back then, they stored CO2 and kept it out of the atmosphere, but as fossil fuels are burned, that CO2 is released. Other contributing factors include industrialized agriculture and slash-and-burn land clearing techniques, and emissions from SF6 in electrical equipment are also concerning today.

Over the past 50 years, more than 1200 billion tons of CO2 have been emitted into the planet's atmosphere — 36.6 billion tons in 2018 alone, though global emissions flatlined in 2019 before rising again. As a result, the global average temperature has risen by 0.8 degrees in just half a century.


Atmospheric CO2 should remain at a minimum
In 2015, the world came together to sign the Paris Climate Agreement which set the goal of limiting global temperature rise to well below 2 degrees — 1.5 degrees, if possible.

The agreement limits the amount of CO2 that can be released into the atmosphere, providing a benchmark for the global energy transition now underway. According to the IPCC, if a maximum of around 300 billion tons were emitted, there would be a 50% chance of limiting global temperature rise to 1.5 degrees. If CO2 emissions remain the same, however, the CO2 'budget' would be used up in just seven years.

According to the IPCC's report on the 1.5 degree target, negative emissions are also necessary to achieve the climate targets.


Using reforestation to remove CO2
One planned measure to stop too much CO2 from being released into the atmosphere is reforestation. According to studies, 3.6 billion tons of CO2 — around 10% of current CO2 emissions — could be saved every year during the growth phase. However, a study by researchers at the Swiss Federal Institute of Technology, ETH Zurich, stresses that achieving this would require the use of land areas equivalent in size to the entire US.

Young trees at a reforestation project in Africa (picture-alliance/OKAPIA KG, Germany)
Reforestation has potential to tackle the climate crisis by capturing CO2. But it would require a large amount of space


More humus in the soil
Humus in the soil stores a lot of carbon. But this is being released through the industrialization of agriculture. The amount of humus in the soil can be increased by using catch crops and plants with deep roots as well as by working harvest remnants back into the ground and avoiding deep plowing. According to a study by the German Institute for International and Security Affairs (SWP) on using targeted CO2 extraction as a part of EU climate policy, between two and five billion tons of CO2 could be saved with a global build-up of humus reserves.


Biochar shows promise
Some scientists see biochar as a promising technology for keeping CO2 out of the atmosphere. Biochar is created when organic material is heated and pressurized in a zero or very low-oxygen environment. In powdered form, the biochar is then spread on arable land where it acts as a fertilizer. This also increases the amount of carbon content in the soil. According to the same study from the SWP, global application of this technology could save between 0.5 and two billion tons of CO2 every year.


Storing CO2 in the ground
Storing CO2 deep in the Earth is already well-known and practiced on Norway's oil fields, for example. However, the process is still controversial, as storing CO2 underground can lead to earthquakes and leakage in the long-term. A different method is currently being practiced in Iceland, in which CO2 is sequestered into porous basalt rock to be mineralized into stone. Both methods still require more research, however, with new DOE funding supporting carbon capture, utilization, and storage.

Capturing CO2 to be held underground is done by using chemical processes which effectively extract the gas from the ambient air, and some researchers are exploring CO2-to-electricity concepts for utilization. This method is known as direct air capture (DAC) and is already practiced in other parts of Europe.  As there is no limit to the amount of CO2 that can be captured, it is considered to have great potential. However, the main disadvantage is the cost — currently around €550 ($650) per ton. Some scientists believe that mass production of DAC systems could bring prices down to €50 per ton by 2050. It is already considered a key technology for future climate protection.

The inside of a carbon capture facility in the Netherlands (RWE AG)
Carbon capture facilities are still very expensive and take up a huge amount of space

Another way of extracting CO2 from the air is via biomass. Plants grow and are burned in a power plant to produce electricity. CO2 is then extracted from the exhaust gas of the power plant and stored deep in the Earth, with new U.S. power plant rules poised to test such carbon capture approaches.

The big problem with this technology, known as bio-energy carbon capture and storage (BECCS) is the huge amount of space required. According to Felix Creutzig from the Mercator Institute on Global Commons and Climate Change (MCC) in Berlin, it will therefore only play "a minor role" in CO2 removal technologies.


CO2 bound by rock minerals
In this process, carbonate and silicate rocks are mined, ground and scattered on agricultural land or on the surface water of the ocean, where they collect CO2 over a period of years. According to researchers, by the middle of this century it would be possible to capture two to four billion tons of CO2 every year using this technique. The main challenges are primarily the quantities of stone required, and building the necessary infrastructure. Concrete plans have not yet been researched.


Not an option: Fertilizing the sea with iron
The idea is use iron to fertilize the ocean, thereby increasing its nuturient content, which would allow plankton to grow stronger and capture more CO2. However, both the process and possible side effects are very controversial. "This is rarely treated as a serious option in research," concludes SWP study authors Oliver Geden and Felix Schenuit.

 

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Is a Resurgence of Nuclear Energy Possible in Germany?

Germany Nuclear Phase-Out reflects a decisive energy policy shift, retiring reactors as firms shun new builds amid high costs, radioactive waste challenges, climate goals, insurance gaps, and debate over small modular reactors and subsidies.

 

Key Points

Germany's policy to end nuclear plants and block new builds, emphasizing safety, waste, climate goals, and viability.

✅ Driven by safety risks, waste storage limits, and insurance gaps

✅ High capital costs and subsidies make new reactors uneconomic

✅ Political debate persists; SMRs raise cost and proliferation concerns

 

A year has passed since Germany deactivated its last three nuclear power plants, marking a significant shift in its energy policy.

Nuclear fission once heralded as the future of energy in Germany during the 1960s, was initially embraced with minimal concern for the potential risks of nuclear accidents. As Heinz Smital from Greenpeace recalls, the early optimism was partly driven by national interest in nuclear weapon technology rather than energy companies' initiatives.

Jochen Flasbarth, State Secretary in the Ministry of Development, reflects on that era, noting Germany's strong, almost naive, belief in technology. Germany, particularly the Ruhr region, grappled with smog-filled skies at that time due to heavy industrialization and coal-fired power plants. Nuclear energy presented a "clean" alternative at the time.

This sentiment was also prevalent in East Germany, where the first commercial nuclear power plant came online in 1961. In total, 37 nuclear reactors were activated across Germany, reflecting a widespread confidence in nuclear technology.

However, the 1970s saw a shift in attitudes. Environmental activists protested the construction of new power plants, symbolizing a generational rift. The 1979 Three Mile Island incident in the US, followed by the catastrophic Chornobyl disaster in 1986, further eroded public trust in nuclear energy.

The Chornobyl accident, in particular, significantly dampened Germany's nuclear ambitions, according to Smital. Post-Chernobyl, plans for additional nuclear power plants in Germany, once numbering 60, drastically declined.

The emergence of the Green Party in 1980, rooted in anti-nuclear sentiment, and its subsequent rise to political prominence further influenced Germany's energy policy. The Greens, joining forces with the Social Democrats in 1998, initiated a move away from nuclear energy, facing opposition from the Christian Democrats (CDU) and Christian Social Union (CSU).

However, the Fukushima disaster in 2011 prompted a policy reversal from CDU and CSU under Chancellor Angela Merkel, leading to Germany's eventual nuclear phase-out in March 2023, after briefly extending nuclear power amid the energy crisis.

Recently, the CDU and CSU have revised their stance once more, signaling a potential U-turn on the nuclear phaseout, advocating for new nuclear reactors and the reactivation of the last shut-down plants, citing climate protection and rising fossil fuel costs. CDU leader Friedrich Merz has lamented the shutdown as a "black day for Germany." However, these suggestions have garnered little enthusiasm from German energy companies.

Steffi Lemke, the Federal Environment Minister, isn't surprised by the companies' reluctance, noting their longstanding opposition to nuclear power, which she argues would do little to solve the gas issue in Germany, due to its high-risk nature and the long-term challenge of radioactive waste management.

Globally, 412 reactors are operational across 32 countries, even as Europe is losing nuclear power during an energy crunch, with the total number remaining relatively stable over the years. While countries like China, France, and the UK plan new constructions, there's a growing interest in small, modern reactors, which Smital of Greenpeace views with skepticism, noting their potential military applications.

In Germany, the unresolved issue of nuclear waste storage looms large. With temporary storage facilities near power plants proving inadequate for long-term needs, the search for permanent sites faces resistance from local communities and poses financial and logistical challenges.

Environment Minister Lemke underscores the economic impracticality of nuclear energy in Germany, citing prohibitive costs and the necessity of substantial subsidies and insurance exemptions.

As things stand, the resurgence of nuclear power in Germany appears unlikely, with economic factors playing a decisive role in its future.

 

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EPA, New Taipei spar over power plant

Shenao Power Plant Controversy intensifies as the EPA, Taipower, and New Taipei officials clash over EIA findings, a marine conservation area, fisheries, public health risks, and protests against a coal-fired plant in Rueifang.

 

Key Points

Dispute over coal plant EIA, marine overlap, and health risks, pitting EPA and Taipower against New Taipei and residents.

✅ EPA approved EIA changes; city cites marine conservation conflict

✅ Rueifang residents protest; 400+ signatures, wardens oppose

✅ Debate centers on fisheries, public health, and coal plant impacts

 

The controversy over the Shenao Power Plant heated up yesterday as Environmental Protection Administration (EPA) and New Taipei City Government officials quibbled over the project’s potential impact on a fisheries conservation area and other issues, mirroring New Hampshire hydropower clashes seen elsewhere.

State-run Taiwan Power Co (Taipower) wants to build a coal-fired plant on the site of the old Shenao plant, which was near Rueifang District’s (瑞芳) Shenao Harbor.

The company’s original plan to build a new plant on the site passed an environmental impact assessment (EIA) in 2006, similar to how NEPA rules function in the US, and the EPA on March 14 approved the firm’s environmental impact difference analysis report covering proposed changes to the project.

#google#

That decision triggered widespread controversy and protests by local residents, environmental groups and lawmakers, echoing enforcement disputes such as renewable energy pollution cases reported in Maryland.

The controversy reached a new peak after New Taipei City Mayor Eric Chu on Tuesday last week posted on Facebook that construction of wave breakers for the project would overlap with a marine conservation area that was established in November 2014.

The EPA and Taipower chose to ignore the demarcation lines of the conservation area, Chu wrote.

Dozens of residents from Rueifang and other New Taipei City districts yesterday launched a protest at 9am in front of the Legislative Yuan in Taipei, amid debates similar to the Maine power line proposal in the US, where the Health, Environment and Labor Committee was scheduled to review government reports on the project.

More than 400 Rueifang residents have signed a petition against the project, including 17 of the district’s 34 borough wardens, Anti-Shenao Plant Self-Help Group director Chen Chih-chiang said.

Ruifang residents have limited access to information, and many only became aware of the construction project after the EPA’s March 14 decision attracted widespread media coverage, Chen said,

Most residents do not support the project, despite Taipower’s claims to the contrary, Chen said.

New Power Party Executive Chairman Huang Kuo-chang, who represents Rueifang and adjacent districts, said the EPA has shown an “arrogance of power” by neglecting the potential impact on public health and the local ecology of a new coal-fired power plant, even as it moves to revise coal wastewater limits elsewhere.

Huang urged residents in Taipei, Keelung, Taoyaun and Yilan County to reject the project.

If the New Taipei City Government was really concerned about the marine conservation area, it should have spoken up at earlier EIA meetings, rather than criticizing the EIA decision after it was passed, Environmental Protection Administration Deputy Minister Chan Shun-kuei told lawmakers at yesterday’s meeting.

Chan said he wondered if Chu was using the Shenao project for political gain.

However, New Taipei City Environmental Protection Department specialist Sun Chung-wei  told lawmakers that the Fisheries Agency and other experts voiced concerns about the conservation area during the first EIA committee meeting on the proposed changes to the Shenao project on June 15 last year.

Sun was invited to speak to the legislative committee by Chinese Nationalist Party (KMT) Legislator Arthur Chen.

While the New Taipei City Fisheries and Fishing Port Affairs Management Office did not present a “new” opinion during later EIA committee meetings, that did not mean it agreed to the project, Sun said.

However, Chan said that Sun was using a fallacious argument and trying to evade responsibility, as the conservation area had been demarcated by the city government.

 

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Scientists Built a Genius Device That Generates Electricity 'Out of Thin Air'

Air-gen Protein Nanowire Generator delivers clean energy by harvesting ambient humidity via Geobacter-derived conductive nanowires, generating continuous hydrovoltaic electricity through moisture gradients, electrodes, and proton diffusion for sustainable, low-waste power in diverse climates.

 

Key Points

A device using Geobacter protein nanowires to harvest humidity, producing continuous DC power via proton diffusion.

✅ 7 micrometer film between electrodes adsorbs water vapor.

✅ Output: ~0.5 V, 17 uA/cm2; stack units to scale power.

✅ Geobacter optimized via engineered E. coli for mass nanowires.

 

They found it buried in the muddy shores of the Potomac River more than three decades ago: a strange "sediment organism" that could do things nobody had ever seen before in bacteria.

This unusual microbe, belonging to the Geobacter genus, was first noted for its ability to produce magnetite in the absence of oxygen, but with time scientists found it could make other things too, like bacterial nanowires that conduct electricity.

For years, researchers have been trying to figure out ways to usefully exploit that natural gift, and they might have just hit pay-dirt with a device they're calling the Air-gen. According to the team, their device can create electricity out of… well, almost nothing, similar to power from falling snow reported elsewhere.

"We are literally making electricity out of thin air," says electrical engineer Jun Yao from the University of Massachusetts Amherst. "The Air-gen generates clean energy 24/7."

The claim may sound like an overstatement, but a new study by Yao and his team describes how the air-powered generator can indeed create electricity with nothing but the presence of air around it. It's all thanks to the electrically conductive protein nanowires produced by Geobacter (G. sulfurreducens, in this instance).

The Air-gen consists of a thin film of the protein nanowires measuring just 7 micrometres thick, positioned between two electrodes, referencing advances in near light-speed conduction in materials science, but also exposed to the air.

Because of that exposure, the nanowire film is able to adsorb water vapour that exists in the atmosphere, offering a contrast to legacy hydropower models, enabling the device to generate a continuous electrical current conducted between the two electrodes.

The team says the charge is likely created by a moisture gradient that creates a diffusion of protons in the nanowire material.

"This charge diffusion is expected to induce a counterbalancing electrical field or potential analogous to the resting membrane potential in biological systems," the authors explain in their study.

"A maintained moisture gradient, which is fundamentally different to anything seen in previous systems, explains the continuous voltage output from our nanowire device."

The discovery was made almost by accident, when Yao noticed devices he was experimenting with were conducting electricity seemingly all by themselves.

"I saw that when the nanowires were contacted with electrodes in a specific way the devices generated a current," Yao says.

"I found that exposure to atmospheric humidity was essential and that protein nanowires adsorbed water, producing a voltage gradient across the device."

Previous research has demonstrated hydrovoltaic power generation using other kinds of nanomaterials – such as graphene-based systems now under study – but those attempts have largely produced only short bursts of electricity, lasting perhaps only seconds.

By contrast, the Air-gen produces a sustained voltage of around 0.5 volts, with a current density of about 17 microamperes per square centimetre, and complementary fuel cell solutions can help keep batteries energized, with a current density of about 17 microamperes per square centimetre. That's not much energy, but the team says that connecting multiple devices could generate enough power to charge small devices like smartphones and other personal electronics – concepts akin to virtual power plants that aggregate distributed resources – all with no waste, and using nothing but ambient humidity (even in regions as dry as the Sahara Desert).

"The ultimate goal is to make large-scale systems," Yao says, explaining that future efforts could use the technology to power homes via nanowire incorporated into wall paint, supported by energy storage for microgrids to balance supply and demand.

"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."

If there is a hold-up to realising this seemingly incredible potential, it's the limited amount of nanowire G. sulfurreducens produces.

Related research by one of the team – microbiologist Derek Lovley, who first identified Geobacter microbes back in the 1980s – could have a fix for that: genetically engineering other bugs, like E. coli, to perform the same trick in massive supplies.

"We turned E. coli into a protein nanowire factory," Lovley says.

"With this new scalable process, protein nanowire supply will no longer be a bottleneck to developing these applications."

 

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When paying $1 for a coal power plant is still paying too much

San Juan Generating Station eyed for $1 coal-plant sale, as Farmington and Acme propose CCS retrofit, meeting emissions caps and renewable mandates by selling captured CO2 for enhanced oil recovery via a nearby pipeline.

 

Key Points

A New Mexico coal plant eyed for $1 and a CCS retrofit to cut emissions and sell CO2 for enhanced oil recovery.

✅ $400M-$800M CCS retrofit; 90% CO2 capture target

✅ CO2 sales for enhanced oil recovery; 20-mile pipeline gap

✅ PNM projects shutdown savings; renewable and emissions mandates

 

One dollar. That’s how much an aging New Mexico coal plant is worth. And by some estimates, even that may be too much.

Acme Equities LLC, a New York-based holding company, is in talks to buy the 847-megawatt San Juan Generating Station for $1, after four of its five owners decided to shut it down. The fifth owner, the nearby city of Farmington, says it’s pursuing the bargain-basement deal with Acme to avoid losing about 1,600 direct and indirect jobs in the area amid a broader just transition debate for energy workers.

 

We respectfully disagree with the notion that the plant is not economical

Acme’s interest comes as others are looking to exit a coal industry that’s been plagued by costly anti-pollution regulations. Acme’s plan: Buy the plant "at a very low cost," invest in carbon capture technology that will lower emissions, and then sell the captured CO2 to oil companies, said Larry Heller, a principal at the holding group.

By doing this, Acme “believes we can generate an acceptable rate of return,” Heller said in an email.

Meanwhile, San Juan’s majority owner, PNM Resources Inc., offers a distinctly different view, echoing declining coal returns reported by other utilities. A 2022 shutdown will push ratepayers to other energy alternatives now being planned, saving them about $3 to $4 a month on average, PNM has said.

“We could not identify a solution that would make running San Juan Generating Station economical,” said Tom Fallgren, a PNM vice president, in an email.

The potential sale comes as a new clean-energy bill, supported by Governor Lujan Grisham, is working its way through the state legislature. It would require the state to get half of its power from renewable sources by 2030, and 100 percent by 2045, even as other jurisdictions explore small modular reactor strategies to meet future demand. At the same time, the legislation imposes an emissions cap that’s about 60 percent lower than San Juan’s current levels.

In response, Acme is planning to spend $400 million to $800 million to retrofit the facility with carbon capture and sequestration technology that would collect carbon dioxide before it’s released into the atmosphere, Heller said. That would put the facility into compliance with the pending legislation and, at the same time, help generate revenue for the plant.

The company estimates the system would cut emissions by as much as 90 percent, and the captured gas could be sold to oil companies, which uses it to enhance well recovery. The bottom line, according to Heller: “A winning financial formula.”

It’s a tricky formula at best. Carbon-capture technology has been controversial, even as new coal plant openings remain rare, expensive to install and unproven at scale. Additionally, to make it work at the San Juan plant, the company would need to figure out how to deliver the CO2 to customers since the nearest pipeline is about 20 miles (32 kilometers) away.

 

Reducing costs

Acme is also evaluating ways to reduce costs at San Juan, Heller said, including approaches seen at operators extending the life of coal plants under regulatory scrutiny, such as negotiating a cheaper coal-supply contract and qualifying for subsidies.

Farmington’s stake in the plant is less than 10 percent. But under terms of the partnership, the city — population 45,000 — can assume full control of San Juan should the other partners decide to pull out, mirroring policy debates over saving struggling nuclear plants in other regions. That’s given Farmington the legal authority to pursue the plant’s sale to Acme.

 

At the end of the day, nobody wants the energy

“We respectfully disagree with the notion that the plant is not economical,” Farmington Mayor Nate Duckett said by email. Ducket said he’s in better position than the other owners to assess San Juan’s importance “because we sit at Ground Zero.”

The city’s economy would benefit from keeping open both the plant and a nearby coal mine that feeds it, according to Duckett, with operations that contribute about $170 million annually to the local area.

While the loss of those jobs would be painful to some, Camilla Feibelman, a Sierra Club chapter director, is hard pressed to see a business case for keeping San Juan open, pointing to sector closures such as the Three Mile Island shutdown as evidence of shifting economics. The plant isn’t economical now, and would almost certainly be less so after investing the capital to add carbon-capture systems.

 

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Turning thermal energy into electricity

Near-Field Thermophotovoltaics captures radiated energy across a nanoscale gap, using thin-film photovoltaic cells and indium gallium arsenide to boost power density and efficiency, enabling compact Army portable power from emitters via radiative heat transfer.

 

Key Points

A nanoscale TPV method capturing near-field photons for higher power density at lower emitter temperatures.

✅ Nanoscale gap boosts radiative transfer and usable photon flux

✅ Thin-film InGaAs cells recycle sub-band-gap photons via reflector

✅ Achieved ~5 kW/m2 power density with higher efficiency

 

With the addition of sensors and enhanced communication tools, providing lightweight, portable power has become even more challenging, with concepts such as power from falling snow illustrating how diverse new energy-harvesting approaches are. Army-funded research demonstrated a new approach to turning thermal energy into electricity that could provide compact and efficient power for Soldiers on future battlefields.

Hot objects radiate light in the form of photons into their surroundings. The emitted photons can be captured by a photovoltaic cell and converted to useful electric energy. This approach to energy conversion is called far-field thermophotovoltaics, or FF-TPVs, and has been under development for many years; however, it suffers from low power density and therefore requires high operating temperatures of the emitter.

The research, conducted at the University of Michigan and published in Nature Communications, demonstrates a new approach, where the separation between the emitter and the photovoltaic cell is reduced to the nanoscale, enabling much greater power output than what is possible with FF-TPVs for the same emitter temperature.

This approach, which enables capture of energy that is otherwise trapped in the near-field of the emitter is called near-field thermophotovoltaics or NF-TPV and uses custom-built photovoltaic cells and emitter designs ideal for near-field operating conditions, alongside emerging smart solar inverters that help manage conversion and delivery.

This technique exhibited a power density almost an order of magnitude higher than that for the best-reported near-field-TPV systems, while also operating at six-times higher efficiency, paving the way for future near-field-TPV applications, including remote microgrid deployments in extreme environments, according to Dr. Edgar Meyhofer, professor of mechanical engineering, University of Michigan.

"The Army uses large amounts of power during deployments and battlefield operations and must be carried by the Soldier or a weight constrained system," said Dr. Mike Waits, U.S. Army Combat Capabilities Development Command's Army Research Laboratory. "If successful, in the future near-field-TPVs could serve as more compact and higher efficiency power sources for Soldiers as these devices can function at lower operating temperatures than conventional TPVs."

The efficiency of a TPV device is characterized by how much of the total energy transfer between the emitter and the photovoltaic cell is used to excite the electron-hole pairs in the photovoltaic cell, where insights from near-light-speed conduction research help contextualize performance limits in semiconductors. While increasing the temperature of the emitter increases the number of photons above the band-gap of the cell, the number of sub band-gap photons that can heat up the photovoltaic cell need to be minimized.

"This was achieved by fabricating thin-film TPV cells with ultra-flat surfaces, and with a metal back reflector," said Dr. Stephen Forrest, professor of electrical and computer engineering, University of Michigan. "The photons above the band-gap of the cell are efficiently absorbed in the micron-thick semiconductor, while those below the band-gap are reflected back to the silicon emitter and recycled."

The team grew thin-film indium gallium arsenide photovoltaic cells on thick semiconductor substrates, and then peeled off the very thin semiconductor active region of the cell and transferred it to a silicon substrate, informing potential interfaces with home battery systems for distributed use.

All these innovations in device design and experimental approach resulted in a novel near-field TPV system that could complement distributed resources in virtual power plants for resilient operations.

"The team has achieved a record ~5 kW/m2 power output, which is an order of magnitude larger than systems previously reported in the literature," said Dr. Pramod Reddy, professor of mechanical engineering, University of Michigan.

Researchers also performed state-of-the-art theoretical calculations to estimate the performance of the photovoltaic cell at each temperature and gap size, informing hybrid designs with backup fuel cell solutions that extend battery life, and showed good agreement between the experiments and computational predictions.

"This current demonstration meets theoretical predictions of radiative heat transfer at the nanoscale, and directly shows the potential for developing future near-field TPV devices for Army applications in power and energy, communication and sensors," said Dr. Pani Varanasi, program manager, DEVCOM ARL that funded this work.

 

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