EPA to set power plant emission limits

By St. Petersburg Times


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The Environmental Protection Agency said it would set standards for greenhouse gas emissions from the country's two biggest sources: coal-fired power plants and refineries.

Gina McCarthy, the assistant administrator for the EPA's Office of Air and Radiation, said it would be possible to hold down costs, add jobs and reduce overall emissions even as the plants continue to burn fossil fuels. She said it wasn't possible to estimate yet how much emissions would be reduced.

Scientists globally agree that heat-trapping gases are accumulating in the atmosphere mainly because of fossil-fuel use and that sharp cuts in emissions will be needed in the next few decades.

The EPA's new regulations are likely to have only a modest impact despite consensus that dramatic cuts are needed to lower the risks of dangerous climate shifts. A plan to impose mandatory reductions on emissions died in Congress last summer.

The EPA rule would set standards only for new plants and those that make major modifications.

Under a provision of the Clear Air Act, existing plants — about 500 coal-fired power plants and 150 refineries — would operate as usual until states impose their own regulations based on EPA guidelines. McCarthy said state regulations aren't expected until 2015 or 2016.

Jeff Holmstead, a former EPA air administrator in the Bush administration who's a lobbyist for the electric industry at Bracewell & Giuliani, predicts the standards will be delayed past the 2012 elections.

"They're out trying to reassure everybody this is going to be reasonable and no big deal," he said. "If that's what they do, then they're not going to be any reduction of emissions and they're going to make the environmental community upset."

Any meaningful restrictions on emissions would make energy costs rise, he said.

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Ottawa hands N.L. $5.2 billion for troubled Muskrat Falls hydro project

Muskrat Falls funding deal delivers federal relief to Newfoundland and Labrador: Justin Trudeau outlines loan guarantees, transmission investment, Hibernia royalties, and $10-a-day child care to stabilize hydroelectric costs and curb electricity rate hikes.

 

Key Points

A $5.2b federal plan aiding NL hydro via loan guarantees, transmission funds, and Hibernia royalties to curb power rates.

✅ $1b for transmission and $1b in federal loan guarantees

✅ $3.2b via Hibernia royalty transfers through 2047

✅ Limits power rate hikes; adds $10-a-day child care in NL

 

Prime Minister Justin Trudeau was in Newfoundland and Labrador Wednesday to announce a $5.2-billion ratepayer protection plan to help the province cover the costs of a troubled hydroelectric project ahead of an expected federal election call.

Trudeau's visit to St. John's, N.L., wrapped up a two-day tour of Atlantic Canada that featured several major funding commitments, and he concluded his day in Newfoundland and Labrador by announcing the province will become the fourth to strike a deal with Ottawa for a $10-a-day child-care program.

As he addressed reporters, the prime minister was flanked by the six Liberal members of Parliament from the province. He alluded to the mismanagement that led the over-budget Muskrat Falls hydroelectric project to become what Liberal Premier Andrew Furey has called an "anchor around the collective souls" of the province.

"The pressures and challenges faced by Newfoundlanders and Labradorians for mistakes made in the past is something that Canadians all needed to step up on, and that's exactly what we did," Trudeau said.

Furey, who joined Trudeau for the two announcements and was effusive in his praise for the federal government, said the federal funding will help Newfoundland and Labrador avoid a spike in electricity rates as customers start paying for Muskrat Falls ahead of when the project begins generating power this November.

"Muskrat Falls has been the No. 1 issue facing Newfoundlanders and Labradorians now for well over a decade," Furey said, adding that he is regularly asked by people whether their electricity rates are going to double, a concern other provinces address through rate legislation in Ontario as well.

"We landed on a deal today that I think -- I know -- is a big deal for Newfoundland and Labrador and will finally get the muskrat off our back," he said.

The agreement-in-principle between the two governments includes a $1-billion investment from Ottawa in a transmission through Quebec portion of the project, as well as $1 billion in loan guarantees. The rest will come from annual transfers from Ottawa equivalent to its annual royalty gains from its share in the Hibernia offshore oilfield, which sits off the coast of St. John's. Those transfers are expected to add up to about $3.2 billion between now and 2047, when the oilfield is expected to run dry.

The money will help cover costs set to come due when the Labrador project comes online, preventing rate increases that would have been needed to pay the bills, and officials have discussed a lump-sum bill credit to help households. Though electricity rates in the province will still rise, to 14.7 cents per kilowatt hour from the current 12.5 cents, that's well below the projected 23 cents that officials had said would be needed to cover the project's costs.

Muskrat Falls was commissioned in 2012 at a cost of $7.4 billion, but its price tag has since ballooned to $13.1 billion. Ottawa previously backed the project with billions of dollars in loan guarantees, and in December, Trudeau announced he had appointed Serge Dupont, former deputy clerk of the Privy Council, to oversee rate mitigation talks with the province about financially restructuring the project.

Its looming impact on the provincial budget is set against an already grim financial situation: the province projected an $826-million deficit in its latest budget, and a recent financial update from the provincial energy corporation reflected pandemic impacts, coupled with $17.2 billion in net debt.

After visiting with children from a daycare centre in the College of the North Atlantic, Trudeau and Furey announced that in 2023, the average cost of regulated child care in the province for children under six would be cut to $10 a day from $25 a day. Trudeau said that within five years, almost 6,000 new daycare spaces would be created in the province.

"As part of the agreement, a new full-day, year-round pre-kindergarten program for four-year-olds will also start rolling out in 2023," the prime minister told reporters. "For parents, this agreement is huge."

Newfoundland and Labrador is the fourth province, after Prince Edward Island, Nova Scotia and British Columbia, to sign on to the federal government's child-care program.

 

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ACCIONA Energía Launches 280 MW Wind Farm in Alberta

Forty Mile Wind Farm delivers 280 MW of renewable wind power in Alberta, with 49 Nordex turbines by ACCIONA Energía, supplying clean electricity to the grid, lowering carbon emissions, and enabling future 120 MW expansion.

 

Key Points

A 280 MW ACCIONA Energía wind farm in Alberta with 49 Nordex turbines, delivering clean power and cutting carbon.

✅ 280 MW via 49 Nordex N155 turbines on 108 m towers

✅ Supplies clean power to 85,000+ homes, reducing emissions

✅ Phase II could add 120 MW, reaching 400 MW capacity

 

ACCIONA Energía, a global leader in renewable energy, has successfully launched its Forty Mile Wind Farm in southern Alberta, Canada, amid momentum from a new $200 million wind project announced elsewhere in the province. This 280-megawatt (MW) project, powered by 49 Nordex turbines, is now supplying clean electricity to the provincial grid and stands as one of Canada's ten largest wind farms. It also marks the company's largest wind installation in North America to date. 

Strategic Location and Technological Specifications

Situated approximately 50 kilometers southwest of Medicine Hat, the Forty Mile Wind Farm is strategically located in the County of Forty Mile No. 8. Each of the 49 Nordex N155 turbines boasts a 5.7 MW capacity and stands 108 meters tall. The project's design allows for future expansion, with a potential Phase II that could add an additional 120 MW, bringing the total capacity to 400 MW, a scale comparable to Enel's 450 MW U.S. wind farm now in operation. 

Economic and Community Impact

The Forty Mile Wind Farm has significantly contributed to the local economy. During its peak construction phase, the project created approximately 250 jobs, with 25 permanent positions anticipated upon full operation. These outcomes align with an Alberta renewable energy surge projected to power thousands of jobs across the province. Additionally, the project has injected new tax revenues into the local economy and provided direct financial support to local non-profit organizations, including the Forty Mile Family & Community Support Services, the Medicine Hat Women’s Shelter Society, and the Root Cellar Food & Wellness Hub. 

Environmental Benefits

Once fully operational, the Forty Mile Wind Farm is expected to generate enough clean energy to power more than 85,000 homes, supporting wind power's competitiveness in electricity markets today. This substantial contribution to Alberta's energy mix aligns with ACCIONA Energía's commitment to sustainability and its goal of reducing carbon emissions. The project is part of the company's broader strategy to expand its renewable energy footprint in North America and support the transition to a low-carbon economy. 

Future Prospects

Looking ahead, ACCIONA Energía plans to continue its expansion in the renewable energy sector, as peers like TransAlta add 119 MW in the U.S. to their portfolios. The success of the Forty Mile Wind Farm serves as a model for future projects and underscores the company's dedication to delivering sustainable energy solutions, even as Alberta's energy future presents periodic headwinds. With ongoing developments and a focus on innovation, ACCIONA Energía is poised to play a pivotal role in shaping the future of renewable energy in North America.

The Forty Mile Wind Farm exemplifies ACCIONA Energía's commitment to advancing renewable energy, supporting local communities, and contributing to environmental sustainability, and it benefits from evolving demand signals, including a federal green electricity contract initiative in Canada that encourages clean supply. As the project continues to operate and expand, it stands as a testament to the potential of wind energy in Canada's clean energy landscape.

 

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Flowing with current, Frisco, Colorado wants 100% clean electricity

Frisco 100% Renewable Electricity Goal outlines decarbonization via Xcel Energy, wind, solar, and battery storage, enabling beneficial electrification and a smarter grid for 100% municipal power by 2025 and community-wide clean electricity by 2035.

 

Key Points

Frisco targets 100% renewable electricity: municipal by 2025, community by 2035, via Xcel decarbonization.

✅ Municipal operations to reach 100% renewable electricity by 2025

✅ Community-wide electricity to be 100% carbon-free by 2035

✅ Partnerships: Xcel Energy, wind, solar, storage, grid markets

 

Frisco has now set a goal of 100-per-cent renewable energy, joining communities on the road to 100% renewables across the country. But unlike some other resolutions adopted in the last decade, this one isn't purely aspirational. It's swimming with a strong current.

With the resolution adopted last week by the town council, Frisco joins 10 other Colorado towns and cities, plus Pueblo and Summit counties, a trend reflected in tracking progress on clean energy targets reports nationwide, in adopting 100-per-cent goals.

The goal is to get the municipality's electricity to 100-per-cent by 2025 and the community altogether by 2035, a timeline aligned with scenarios showing zero-emissions electricity by 2035 is possible in North America.

Decarbonizing electricity will be far easier than transportation, and transportation far easier than buildings. Many see carbon-free electricity as being crucial to both, a concept called "beneficial electrification," and point to ways to meet decarbonization goals that leverage electrified end uses.

Electricity for Frisco comes from Xcel Energy, an investor-owned utility that is making giant steps toward decarbonizing its power supply.

Xcel first announced plans to close its work-horse power plants early to take advantage of now-cheap wind and solar resources plus what will be the largest battery storage project east of the Rocky Mountains. All this will be accomplished by 2026 and will put Xcel at 55 per cent renewable generation in Colorado.

In December, a week after Frisco launched the process that produced the resolution, Xcel announced further steps, an 80 percent reduction in carbon dioxide emissions by 2030 as compared to 2050 levels. By 2050, the company vows to be 100 per cent "carbon-free" energy by 2050.

Frisco's non-binding goals were triggered by Fran Long, who is retired and living in Frisco. For eight years, though, he worked for Xcel in helping shape its response to the declining prices of renewables. In his retirement, he has also helped put together the aspirational goal adopted by Breckenridge for 100-per-cent renewables.

A task force that Long led identified a three-pronged approach. First, the city government must lead by example. The resolution calls for the town to spend $25,000 to $50,000 annually during the next several years to improve energy efficiency in its municipal facilities. Then, through an Xcel program called Renewable Connect, it can pay an added cost to allow it to say it uses 100-per-cent electricity from renewable sources.

Beyond that, Frisco wants to work with high-end businesses to encourage buying output from solar gardens or other devices that will allow them to proclaim 100-per-cent renewable energy. The task force also recommends a marketing program directed to homes and smaller businesses.

Goals of 100-per-cent renewable electricity are problematic, given why the grid isn't 100% renewable today for technical and economic reasons. Aspen Electric, which provides electricity for about two-thirds of the town, by 2015 had secured enough wind and hydro, mostly from distant locations, to allow it to proclaim 100 per cent renewables.

In fact, some of those electrons in Aspen almost certainly originate in coal or gas plants. That doesn't make Aspen's claim wrong. But the fact remains that nobody has figured out how, at least at affordable cost, to deliver 100-per-cent clean energy on a broad basis.

Xcel Energy, which supplies more than 60 per cent of electricity in Colorado, one of six states in which it operates, has a taller challenge. But it is a very different utility than it was in 2004, when it spent heavily in advertising to oppose a mandate that it would have to achieve 10 per cent of its electricity from renewable sources by 2020.

Once it lost the election, though, Xcel set out to comply. Integrating renewables proved far more easily than was feared. It has more than doubled the original mandate for 2020. Wind delivers 82 per cent of that generation, with another 18 per cent coming from community, rooftop, and utility-scale solar.

The company has become steadily more proficient at juggling different intermittent power supplies while ensuring lights and computers remain on. This is partly the result of practice but also of relatively minor technological wrinkles, such as improved weather forecasting, according to an Energy News Network story published in March.

For example, a Boulder company, Global Weather corporation, projects wind—and hence electrical production—from turbines for 10 days ahead. It updates its forecasts every 15 minutes.

Forecasts have become so good, said John T. Welch, director of power operations for Xcel in Colorado, that the utility uses 95 per cent to 98 per cent of the electricity generated by turbines. This has allowed the company to use its coal and natural gas plants less.M

Moreover, prices of wind and then solar declined slowly at first and then dramatically.

Xcel is now comfortable that existing technology will allow it to push from 55 per cent renewables in 2026 to an 80 per cent carbon reduction goal by 2030.

But when announcing their goal of emissions-free energy by mid-century in December, the company's Minneapolis-based chief executive, Ben Fowke, and Alice Jackson, the chief executive of the company's Colorado subsidiary, freely admitted they had no idea how they will achieve it. "I have a lot of confidence they will be developed," Fowke said of new technologies.

Everything is on the table, they said, including nuclear. But also including fossil fuels, if the carbon dioxide can be sequestered. So far, such technology has proven prohibitively expensive despite billions of dollars in federal support for research and deployment. They suggested it might involve new technology.

Xcel's Welch told Energy News Network that he believes solar must play a larger role, and he believes solar forecasting must improve.

Storage technology must also improve as batteries are transforming solar economics across markets. Batteries, such as produced by Tesla at its Gigafactory near Reno, can store electricity for hours, maybe even a few days. But batteries that can store large amounts of electricity for months will be needed in Colorado. Wind is plentiful in spring but not so much in summer, when air conditioners crank up.

Increased sharing of cheap renewable generation among utilities will also allow deeper penetration of carbon-free energy, a dynamic consistent with studies finding wind and solar could meet 80% of demand with improved transmission. Western US states and Canadian provinces are all on one grid, but the different parts are Balkanized. In other words, California is largely its own energy balancing authority, ensuring electricity supplies match electricity demands. Ditto for Colorado. The Pacific Northwest has its own balancing authority.

If they were all orchestrated as one in an expanded energy market across the West, however, electricity supplies and demands could more easily be matched. California's surplus of solar on summer afternoons, for example, might be moved to Colorado.

Colorado legislators in early May adopted a bill that requires the state's Public Utilities Commission to begin study by late this year of an energy imbalance market or regional transmission organization.

 

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Germany considers U-turn on nuclear phaseout

Germany Nuclear Power Extension debated as Olaf Scholz weighs energy crisis, gas shortages from Russia, slow grid expansion in Bavaria, and renewables delays; stress test results may guide policy alongside coal plant reactivations.

 

Key Points

A proposal to delay Germany's nuclear phaseout to stabilize power supply amid gas cuts and slow grid upgrades.

✅ Driven by Russia gas cuts and Nord Stream 1 curtailment

✅ Targets Bavaria grid bottlenecks; renewables deployment delays

✅ Decision awaits grid stress test; coalition parties remain split

 

The German chancellor on Wednesday said it might make sense to extend the lifetime of Germany's three remaining nuclear power plants.

Germany famously decided to stop using atomic energy in 2011, and the last remaining plants were set to close at the end of this year.

However, an increasing number of politicians have been arguing for the postponement of the closures amid energy concerns arising from Russia's invasion of Ukraine. The issue divides members of Scholz's ruling traffic-light coalition.

What did the chancellor say?
Visiting a factory in western Germany, where a vital gas turbine is being stored, Chancellor Olaf Scholz was responding to a question about extending the lifetime of the power stations.

He said the nuclear power plants in question were only relevant for a small proportion of electricity production. "Nevertheless, that can make sense," he said.

The German government has previously said that renewable energy alternatives are the key to solving the country's energy problems.

However, Scholz said this was not happening quickly enough in some parts of Germany, such as Bavaria.

"The expansion of power line capacities, of the transmission grid in the south, has not progressed as quickly as was planned," the chancellor said.

"We will act for the whole of Germany, we will support all regions of Germany in the best possible way so that the energy supply for all citizens and all companies can be guaranteed as best as possible."

The phaseout has been planned for a long time. Germany's Social Democrat government, under Merkel's predecessor Gerhard Schröder, had announced that Germany would stop using nuclear power by 2022 as planned.

Schröder's successor Angela Merkel — herself a former physicist — had initially sought to extend to life of existing nuclear plants to as late as 2037. She viewed nuclear power as a bridging technology to sustain the country until new alternatives could be found.

However, Merkel decided to ditch atomic energy in 2011, after the Fukushima nuclear disaster in Japan, setting Germany on a path to become the first major economy to phase out coal and nuclear in tandem.

Nuclear power accounted for 13.3% of German electricity supply in 2021. This was generated by six power plants, of which three were switched off at the end of 2021. The remaining three — Emsland, Isar and Neckarwestheim — were due to shut down at the end of 2022. 

Germany's energy mix 1st half of 2022
The need to fill an energy gap has emerged after Russia dramatically reduced gas deliveries to Germany through the Nord Stream 1 pipeline, though nuclear power would do little to solve the gas issue according to some officials. Officials in Berlin say the Kremlin is seeking to punish the country — which is heavily reliant on Moscow's gas — for its support of Ukraine and sanctions on Russia.

Germany has already said it will temporarily fire up mothballed coal and oil power plants in a bid to solve the looming power crisis.

Social Democrat Scholz and Germany's energy minister, Robert Habeck, from the Green Party, a junior partner in the three-way coalition government, had previously ruled out any postponement of the nuclear phasout, despite debate over a possible resurgence of nuclear energy among some lawmakers. The third member of Scholz's coalition, the neoliberal Free Democrats, has voiced support for the extension, as has the opposition conservative CDU-CSU bloc.

Berlin has said it will await the outcome of a new "stress test" of Germany's electric grid before deciding on the phaseout.

 

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Charting a path to net zero electricity emissions by the middle of the century

Clean Energy Standard charts a federal path to decarbonize the power sector, scaling renewables, wind, solar, nuclear, and carbon capture to slash emissions, create green jobs, and reach net-zero targets amid the climate crisis.

 

Key Points

A federal policy to expand clean power and cut emissions with renewables, nuclear, and carbon capture toward net-zero.

✅ Mandates annual increases in clean electricity supply

✅ Includes renewables, nuclear, hydro, and carbon capture

✅ Targets rapid emissions cuts and net-zero by mid-century

 

The world has been put on notice. Last year, both the UN Intergovernmental Panel on Climate Change and the U.S. National Climate Assessment warned that we need to slash greenhouse gas emissions to avoid disastrous impacts of global warming. Their direct language forecasting devastating effects on our health, economics, environment, and ways of life has made even more urgent the responsibility we all have to act boldly to combat the climate crisis.

This week, we’re adding one important tool for addressing the climate crisis to the national conversation.

Together, we’re taking that bold action. The Climate reports made clear that to limit the global temperature rise and stave off devastating impacts to our climate—human-caused CO2 emissions must fall rapidly by 2030 and that we, as a global community, underscored at the Katowice climate talks, must reach net-zero emissions by the middle of the century. The Clean Energy Standard is federal legislation that offers a pathway toward decarbonizing our power sector and helping our nation accomplish a goal of net-zero emissions by the 2050s.

Under this plan, any company selling retail electricity will have a mandate to increase the amount of clean energy provided to its customers. It will incentivize clean electricity investment to put the U.S. on a sustainable path.

To deal most effectively with a crisis, all tools must be on the table. Our plan focuses solely on emissions, and there is a place for all technologies that can put us on the path to net zero. That will mean drastic increases in wind and solar energy for sure, as states like California pursue a 100% carbon-free electricity mandate to accelerate deployment, but nuclear power, hydro power, and fossil fuels with carbon capture and storage all have important roles to play.

We’re doing this because the science is clear – tackling our climate crisis requires serious and rapid action to control greenhouse gas emissions, and the push for decarbonization is irreversible according to many. Inaction on the climate crisis puts our families at risk, and we’re not wasting any time. This is also an opportunity to create good-paying green jobs that can last generations and uplift the middle class.

We are doing this for the environment, but also for jobs and economic competitiveness. The green economy is the future and we’re ready to see it grow, with states like New York advancing a Green New Deal that drives innovation. The United States can lead, or we can follow, and we want our nation to lead.

And, because as a New Mexican and a Minnesotan, we know that the impacts of climate change go far beyond the headlines and political discourse. It means devastation within tamarack forests and an increase in deadly fires. It means hotter summers and shorter winters with extreme temperature swings throughout the year. It means devastating flash floods with increasingly intense rain. It’s impacting our pocketbooks when farmers and small businesses who work the land in rural communities are unable to make ends meet.

States across the country are already acting to combat the climate crisis – including Minnesota's 2050 carbon-free electricity plan and New Mexico. But in order to truly address climate change, we have to be in this together as Americans. If the problem is far-reaching, our solutions must be equally as holistic.

It's why we've worked with green groups and activists, unions, and communities across the country - from urban to rural - to create a solution that understands the different starting points communities face in reaching net zero emissions, but doesn't shrink from the absolute need to reach that standard.

There is not one solution to climate change – it will take a collective group of individuals prepared to boldly act. And we are ready to take on that fight.

In Congress, we have formed the House Select Committee on the Climate Crisis and the Senate Democrats’ Special Committee on the Climate Crisis to hear from everyday Americans how climate change is affecting them – and how we can come together to find solutions that build on the historic climate deal passed this year. We have heard the stories of young people worried about their futures. And we realize there is a sense of urgency to act.

Over the coming weeks and months, we will be building support from communities across the country to make this plan a reality. We will continue working with stakeholders to ensure every voice is heard. Most importantly, we will continue listening to you and your communities.

 

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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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