New downtown HQ dims lights overnight

By Knight Ridder Tribune


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Manpower is tweaking candlepower as it seeks the sweet spot in the automated lighting systems for its new downtown Milwaukee headquarters.

Late-night observers who noticed the building fully lighted along the Milwaukee River earlier this month should start getting a dimmer view. The 5,100 or so lights inside the four-story building were set to go off from 7:30 p.m. to 5:30 a.m. Most of the lights at Manpower's riverside plaza fade out at 10 p.m.

The light show reflects how the global employment services company is balancing aesthetics and efficiency. Manpower is seeking "green" certification of its building under the Leadership in Energy and Environmental Design rating system. But it also wants to keep a spotlight on its $78 million headquarters, what Mayor Tom Barrett has hailed as "front and center" in Milwaukee's renaissance.

"We do want to be energy efficient, of course," said Jennifer Dettman, director of strategic sourcing and corporate real estate for Manpower. "But we also want to make sure that we stay in tune with the look and the feel of downtown and how it is lit up at night." Manpower will continue working with contractors to fine tune the lighting system, Dettman said.

She expects strategic exterior lights to stay on, including those on the flags - which represent a fraction of the 73 countries where Manpower has offices - and the water wall. All of those fixtures are energy efficient and shine downward, minimizing light pollution, Dettman said.

The 280,000-square-foot building is positioned to use daylight to illuminate more than 90% of the work spaces for the headquarters' 900 employees. Interior lights by the windows can automatically dim by 50% when the sun shines. Other lights use occupancy sensors to shut off when no one is around. Overall, the lighting remains a work in progress, Dettman said.

"We will probably continue to look at even further tuning down some of the lights as we take a look at it in the evenings," Dettman said.

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Wartsila to Power USA’s First Battery-Electric High-Speed Ferries

San Francisco Battery-Electric Ferries will deliver zero-emission, high-speed passenger service powered by Wartsila electric propulsion, EPMS, IAS, batteries, and shore power, advancing maritime decarbonization under the REEF program and USCG Subchapter T standards.

 

Key Points

They are the first US zero-emission high-speed passenger ferries using integrated electric propulsion and shore power

✅ Dual 625 kW motors enable up to 24-knot service speeds

✅ EPMS, IAS, DC hub, and shore power streamline operations

✅ Built to USCG Subchapter T for safety and compliance

 

Wartsila, a global leader in sustainable marine technology, has been selected to supply the electric propulsion system for the United States' first fully battery-electric, zero-emission high-speed passenger ferries. This significant development marks a pivotal step in the decarbonization of maritime transport, aligning with California's ambitious environmental goals, including recent clean-transport investments across ports and corridors.

A Leap Toward Sustainable Maritime Transport

The project, commissioned by All American Marine (AAM) on behalf of San Francisco Bay Ferry, involves the construction of three 150-passenger ferries, reflecting broader U.S. advances like the Washington State Ferries hybrid upgrade now underway. These vessels will operate on new routes connecting the rapidly developing neighborhoods of Treasure Island and Mission Bay to downtown San Francisco. The ferries are part of the Rapid Electric Emission Free (REEF) Ferry Program, a comprehensive initiative by San Francisco Bay Ferry to transition its fleet to zero-emission propulsion technology. The first vessel is expected to join the fleet in early 2027.

Wärtsilä’s Role in the Project

Wärtsilä's involvement encompasses the supply of a comprehensive electric propulsion system, including the Energy and Power Management System (EPMS), integrated automation system (IAS), batteries, DC hub, transformers, electric motors, and shore power supply. This extensive scope underscores Wärtsilä’s expertise in providing integrated solutions for emission-free marine transportation. The company's extensive global experience in developing and supplying integrated systems and solutions for zero-emission high-speed vessels, as seen with electric ships on the B.C. coast operating today, was a key consideration in the selection process.

Technical Specifications of the Ferries

The ferries will be 100 feet (approximately 30 meters) in length, with a beam of 26 feet and a draft of 5.9 feet. Each vessel will be powered by dual 625-kilowatt electric motors, enabling them to achieve speeds of up to 24 knots. The vessels will be built to U.S. Coast Guard Subchapter T standards, ensuring compliance with stringent safety regulations.

Environmental and Operational Benefits

The transition to battery-electric propulsion offers numerous environmental and operational advantages. Electric ferries produce zero emissions during operation, as demonstrated by Berlin's electric ferry deployments, significantly reducing the carbon footprint of maritime transport. Additionally, electric propulsion systems are generally more efficient and require less maintenance compared to traditional diesel engines, leading to lower operational costs over the vessel's lifespan.

Broader Implications for Maritime Decarbonization

This project is part of a broader movement toward sustainable maritime transport in the United States. San Francisco Bay Ferry has also approved the purchase of two larger 400-passenger battery-electric ferries for transbay routes, further expanding its commitment to zero-emission operations. The agency has secured approximately $200 million in funding from local, state, and federal sources, echoing infrastructure bank support seen in B.C., to support these initiatives, including vessel construction and terminal electrification.

Wartsila’s involvement in this project highlights the company's leadership in the maritime industry's transition to sustainable energy solutions, including hybrid-electric pathways like BC Ferries' new hybrids now in service. With a proven track record in supplying integrated systems for zero-emission vessels, Wärtsilä is well-positioned to support the global shift toward decarbonized maritime transport.

As the first fully battery-electric high-speed passenger ferries in the United States, these vessels represent a significant milestone in the journey toward sustainable and environmentally responsible maritime transportation, paralleling regional advances such as the Kootenay Lake electric-ready ferry entering service. The collaboration between Wärtsilä, All American Marine, and San Francisco Bay Ferry exemplifies the collective effort required to realize a zero-emission future for the maritime industry.

The deployment of these battery-electric ferries in San Francisco Bay not only advances the city's environmental objectives but also sets a precedent for other regions to follow. With continued innovation and collaboration, the maritime industry can look forward to a future where sustainable practices are the standard, not the exception.

 

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Class-action lawsuit: Hydro-Québec overcharged customers up to $1.2B

Hydro-QuE9bec Class-Action Lawsuit alleges overbilling and monopoly abuse, citing RE9gie de l'E9nergie rate increases, Quebec Superior Court filings, and calls for refunds on 2008-2013 electricity bills to residential and business customers.

 

Key Points

Quebec class action alleging Hydro-QuE9bec overbilled customers in 2008-2013, seeking court-ordered refunds.

✅ Filed in Quebec Superior Court; certification pending.

✅ Alleges up to $1.2B in overcharges from 2008-2013.

✅ Questions RE9gie de l'E9nergie rate approvals and data.

 

A group representing Hydro-Québec customers has filed a motion for a class-action lawsuit against the public utility, alleging it overcharged customers over a five-year period.

Freddy Molima, one of the representatives of the Coalition Peuple allumé, accuses Hydro-Québec of "abusing its monopoly."

The motion, which was filed in Quebec Superior Court, claims Hydro-Québec customers paid more than they should have for electricity between 2008 and 2013, to the tune of nearly $1.2 billion, even as Hydro-Québec later refunded $535 million to customers in a separate case. 

The coalition has so far recruited nearly 40,000 participants online as part of its plan to sue the public utility.

A lawyer representing the group said Quebec's energy board, the Régie de l'énergie, also recently approved Hydro-Québec rate increases for residential and business customers without knowing all the facts, even as Manitoba Hydro hikes face opposition in regulatory hearings.

"There's certain information provided to the Régie that isn't true," said Bryan Furlong. "Hydro-Québec has not been providing the Régie the proper numbers."

In its motion, the group asks that overcharged clients be retroactively reimbursed.

Hydro-Québec denies allegations

Hydro-Québec, for its part, denies it ever overbilled any of its clients, while other utilities such as Hydro One plan to redesign bills to improve clarity.

"All our efficiencies have been returned to the government through our profits, and to Quebecers we have billed exactly what we agreed to bill," said spokesperson Serge Abergel, adding that the utility won't seek a rate hike next year according to its current plans.

Quebec Energy Minister Pierre Moreau also came to the public utility's defence, saying it has no choice but to comply with the  energy board's regulations, while customer protections are in focus as Hydro One moves to reconnect 1,400 customers in Ontario.

The group says the public utility has overbilled clients by up to $1.2 billion. (Radio-Canada)

It would be "shocking" if customers were charged too much money, he added.

"I know for a fact that Hydro-Québec is respecting the decision of this body," he said.

While the motion has been filed, the group cannot say how much each customer would receive if the class-action lawsuit goes ahead because it all depends on how much electricity was consumed by each client over that five-year period.

The coalition plans to present its motion to a judge next February.

 

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Nova Scotia Power delays start of controversial new charge for solar customers

Nova Scotia Power solar charge proposes an $8/kW monthly system access fee on net metering customers, citing grid costs. UARB review, carbon credits, rate hikes, and solar industry impacts fuel political and consumer backlash.

 

Key Points

A proposed $8/kW monthly grid access fee on net metered solar customers, delayed to Feb 1, 2023, pending UARB review.

✅ $8/kW monthly system access fee on net metering

✅ Delay to Feb 1, 2023 after industry and political pushback

✅ UARB review; debate over grid costs and carbon credits

 

Nova Scotia Power has pushed back by a year the start date of a proposed new charge for customers who generate electricity and sell it back to the grid, following days of concern from the solar industry and politicians worried that it will damage the sector.

The company applied to the Nova Scotia Utility and Review Board (UARB) last week for various changes, including a "system access charge" of $8 per kilowatt monthly on net metered installations, and the province cannot order the utility to lower rates under current law. The vast majority of the province's 4,100 net metering customers are residential customers with solar power, according to the application. 

The proposed charge would have come into effect Tuesday if approved, but Nova Scotia Power said in a news release Tuesday it will change the date in its filing from Feb. 1, 2022, to Feb. 1, 2023.

"We understand that the solar industry was taken off guard," utility CEO Peter Gregg said in an interview.

"There could have been an opportunity to have more conversations in advance."

Gregg said the utility will meet with members of the solar industry over the next year to work on finding solutions that support the sector's growth, while addressing what NSP sees as an inequity in the net metering system.

NSP recognized that customers who choose solar invest a significant amount and pay for the electricity they use, but they don't pay for costs associated with accessing the electrical grid when they need energy, such as on cold winter evenings when the sun is not shining.

"I know that's hit a nerve, but it doesn't take away the fact that it is an issue," Gregg said.

He said this is an issue utilities are navigating around North America, where seasonal rate designs have sparked consumer backlash in New Brunswick, and NSP is open to hearing ideas for other models of charges or fees.

The utility's suggested system access charge closely resembles one proposed in California, which has also raised major concerns from the solar industry and been criticized by the likes of Elon Musk, and has parallels to Massachusetts solar demand charges as well.

Although the "solar profile" of Nova Scotia and California is very different, with far more solar customers in that state, and in other provinces such as Saskatchewan, NDP criticism of 8% hikes has intensified affordability debates, Gregg said the fundamental issues are the same.

For those with a typical 10-kilowatt solar system, which generates around $1,800 of electricity a year, the new charge would mean those customers would be required to pay $960 back to NSP. That would roughly double the length of time it takes for those customers to pay off their investment for the panels.

David Brushett, chair of Solar Nova Scotia, said he relayed concerns from solar installers and others in the industry to Gregg on Monday. 

Brushett said the year delay is a positive first step, but he is still calling on the province to take a strong stance against the application, which has led to customers cancelling their panel installations and companies considering layoffs.

"There's still an urgency to this situation that hasn't been addressed, and we need to kind of protect the industry," he said Tuesday.

NSP's original application proposed exempting net metering customers who enrolled before Feb. 1, 2022, from the charge for 25 years after they sign up. But any benefit would be lost if those customers sold their home, and the exemption wouldn't extend to the new buyers, said Brushett.


Carbon offsets missing from equation: industry
Brushett said NSP "completely ignored" the fact that it's getting free carbon offset credits from homeowners who use solar energy under the provincial cap and trade program.

If the net metering system continues as is, NSP has said non-solar customers would pay about $55 million between now and 2030. That number assumes about 2,000 people sign up for net metering each year over the next nine years.

When asked whether those carbon emission credits were factored into the calculations for the proposed charge, Gregg said, "I don't believe in the current structure it is, but it's something that certainly we'd be open to hearing about."

Brushett said his group is finalizing a legal response to NSP's proposal and has already filed an official complaint against the company with the UARB.


Base charge on actual electrical output: customer
At least one shareholder in NSP parent company Emera is considering selling his shares in response to the application.

Joe Hood, a shareholder from Middle Sackville, said the proposed charge won't apply to his existing 11.16-kilowatt solar system, but if it did, it would cost him $1,071 a year.

"I am offended that a company I would invest in would do this to the solar industry in Nova Scotia," he said.

According to his meter, Hood said he pushed 9,600 kilowatt hours of solar electricity to the grid last year— some only for a brief period, and all of which was used by his home by the end of the year.

Under the proposed charge, someone with one solar panel who goes away on vacation in the summer would push all their electricity to the grid, and be charged far less than someone with 10 panels who has used all their own power and hasn't pushed anything.

"Nova Scotia Power's argument is that it's an issue with the grid. Well, then it should be based on what touches the grid," Hood said.

Far from actually making the system fair for everyone, Hood said this charge places solar only in the hands of the super-rich or NSP, with projects like its community solar gardens in Amherst, N.S.


Green Party suggests legislation update
Nova Scotia's Green Party also said Tuesday that Gregg's arguments of fairness are misleading, echoing earlier premier opposition to a 14% hike on rates.

The party is calling for an update to the Electricity Act that would "prevent penalizing any activity that helps Nova Scotia reach its emissions target," aligning with calls to make the electricity system more accountable to residents.

In its application, NSP has also asked to increase electricity rates for residential customers by at least 10 per cent over the next three years, amid debate that culminated in a 14% rate hike approval by regulators. 

The company wants to maintain its nine per cent rate of return.

NSP expects to earn $153 million this year, $192 million in 2023, and $213 million in 2024 from its rate of return. 

 

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The biggest problem facing the U.S. electric grid isn't demand. It's climate change

US power grid modernization addresses aging infrastructure, climate resilience, extreme weather, EV demand, and clean energy integration, using AI, transmission upgrades, and resilient substations to improve reliability, reduce outages, and enable rapid recovery.

 

Key Points

US power grid modernization strengthens infrastructure for resilience, reliability, and clean energy under rising demand.

✅ Hardening substations, lines, and transformers against extreme weather

✅ Integrating EV load, DERs, and renewables into transmission and distribution

✅ Using AI, sensors, and automation to cut outages and speed restoration

 

The power grid in the U.S. is aging and already struggling to meet current demand, with dangerous vulnerabilities documented across the system today. It faces a future with more people — people who drive more electric cars and heat homes with more electric furnaces.

Alice Hill says that's not even the biggest problem the country's electricity infrastructure faces.

"Everything that we've built, including the electric grid, assumed a stable climate," she says. "It looked to the extremes of the past — how high the seas got, how high the winds got, the heat."

Hill is an energy and environment expert at the Council on Foreign Relations. She served on the National Security Council staff during the Obama administration, where she led the effort to develop climate resilience. She says past weather extremes can no longer safely guide future electricity planning.

"It's a little like we're building the plane as we're flying because the climate is changing right now, and it's picking up speed as it changes," Hill says.

The newly passed infrastructure package dedicates billions of dollars to updating the energy grid with smarter electricity infrastructure programs that aim to modernize operations. Hill says utility companies and public planners around the country are already having to adapt. She points to the storm surge of Hurricane Sandy in 2012.

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"They thought the maximum would be 12 feet," she says. "That storm surge came in close to 14 feet. It overcame the barriers at the tip of Manhattan, and then the electric grid — a substation blew out. The city that never sleeps [was] plunged into darkness."

Hill noted that Con Edison, the utility company providing New York City with energy, responded with upgrades to its grid: It buried power lines, introduced artificial intelligence, upgraded software to detect failures. But upgrading the way humans assess risk, she says, is harder.

"What happens is that some people tend to think, well, that last storm that we just had, that'll be the worst, right?" Hill says. "No, there is a worse storm ahead. And then, probably, that will be exceeded."

In 2021, the U.S. saw electricity outages for millions of people as a result of historic winter storms in Texas, a heatwave in the Pacific Northwest and Hurricane Ida along the Gulf Coast. Climate change will only make extreme weather more likely and more intense, driving longer, more frequent outages for utilities and customers.

In the West, California's grid reliability remains under scrutiny as the state navigates an ambitious clean energy shift.

And that has forced utility companies and other entities to grapple with the question: How can we prepare for blackouts and broader system stress we've never experienced before?

A modern power station in Maryland is built for the future
In the town of Edgemere, Md., the Fitzell substation of Baltimore Gas and Electric delivers electricity to homes and businesses. The facility is only a year or so old, and Laura Wright, the director of transmission and substation engineering, says it's been built with the future in mind.

She says the four transformers on site are plenty for now. And to counter the anticipated demand of population growth and a future reliance on electric cars, she says the substation has been designed for an easy upgrade.

"They're not projecting to need that additional capacity for a while, but we designed this station to be able to take that transformer out and put in a larger one," Wright says.

Slopes were designed to insulate the substation from sea level rise. And should the substation experience something like a catastrophic flooding event or deadly tornado, there's a plan for that too.

"If we were to have a failure of a transformer," Wright says, "we can bring one of those mobile transformers into the substation, park it in the substation, connect it up in place of that transformer. And we can do that in two to three days."

The Fitzell substation is a new, modern complex. Older sites can be knocked down for weeks.

That raises the question: Can the amount of money dedicated to the power grid in the new infrastructure legislation actually make meaningful changes to the energy system across the country, where studies find more blackouts than other developed nations persist?

"The infrastructure bill, unfortunately, only scratches the surface," says Daniel Cohan, an associate professor in civil and environmental engineering at Rice University.

Though the White House says $65 billion of the infrastructure legislation is dedicated to power infrastructure, a World Resources Institute analysis noted that only $27 billion would go to the electric grid — a figure that Cohan also used.

"If you drill down into how much is there for the power grid, it's only about $27 billion or so, and mainly for research and demonstration projects and some ways to get started," he says.

Cohan, who is also author of the forthcoming book Confronting Climate Gridlock, says federal taxpayer dollars can be significant but that most of the needed investment will eventually come from the private sector — from utility companies and other businesses spending "many hundreds of billions of dollars per decade," even as grid modernization affordability remains a concern. He also says the infrastructure package "misses some opportunities" to initiate that private-sector action through mandates.

"It's better than nothing, but, you know, with such momentous challenges that we face, this isn't really up to the magnitude of that challenge," Cohan says.

Cohan argues that thinking big, and not incrementally, can pay off. He believes a complete transition from fossil fuels to clean energy by 2035 is realistic and attainable — a goal the Biden administration holds — and could lead to more than just environmental benefit.

"It also can lead to more affordable electricity, more reliable electricity, a power supply that bounces back more quickly when these extreme events come through," he says. "So we're not just doing it to be green or to protect our air and climate, but we can actually have a much better, more reliable energy supply in the future."

 

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US Approves Rule to Boost Renewable Transmission

FERC Transmission Rule accelerates grid modernization and interregional high-voltage lines, enabling renewable energy integration, load balancing, and reliability to advance net-zero goals while strengthening resilience, capacity expansion, and decarbonization across U.S. regional transmission organizations.

 

Key Points

A federal policy mandating interregional grid planning and cost sharing to expand high-voltage lines for renewables.

✅ Expands interregional high-voltage transmission capacity

✅ Improves reliability, resilience, and load balancing

✅ Aligns cost allocation and long-term planning for renewables

 

On May 13th, 2024, the US took a monumental step towards its clean energy goals. The Federal Energy Regulatory Commission (FERC) approved a long-awaited rule designed to significantly expand the transmission of renewable energy across the nation's power grid, a US grid overhaul that many advocates say was overdue. This decision aligns with President Biden's ambitious plan to achieve net-zero carbon emissions by 2050, with renewable energy playing a central role.

The new rule tackles a critical bottleneck hindering the widespread adoption of renewables – transmission infrastructure. Unlike traditional power plants like coal or natural gas that run constantly, solar and wind power generation fluctuates with weather conditions. This variability poses a challenge for the existing grid, which is not designed to efficiently handle large-scale integration of these intermittent sources, helping explain why the grid isn't 100% renewable today.

The FERC rule aims to address this by promoting the construction of new, high-voltage transmission lines, particularly those connecting different regions, where grid limitations in the Pacific Northwest have highlighted the need for better interregional transfers. This improved connectivity would allow for a more strategic distribution of renewable energy. Imagine solar energy harnessed in the sun-drenched Southwest being transmitted eastward to meet peak demand during hot summer days on the Atlantic Coast.

The benefits of this expanded transmission network are multifaceted. First, it unlocks the full potential of renewable resources by allowing for their efficient utilization across the country, a trend consistent with wind and solar surpassing coal in U.S. generation. Abundant wind power in the Midwest could be utilized on the West Coast, while surplus solar energy from the South could supplement demand in the Northeast.

Second, a more robust grid with a higher capacity for renewables reduces reliance on fossil fuel-based power plants and complements other ways to meet decarbonization goals across sectors. This translates to cleaner air and a significant reduction in greenhouse gas emissions, contributing to the fight against climate change.

Third, a modernized grid with improved long-distance transmission bolsters the nation's energy security. Extreme weather events, a growing concern due to climate change, can disrupt energy production in specific regions. This interconnected grid would provide a buffer, ensuring a more reliable and resilient power supply and helping put regions on the road to 100% renewables even during adverse weather conditions.

The FERC's decision is a win for environmental groups and the renewable energy industry. They see it as a critical step towards a cleaner energy future and a significant driver of job creation in the construction and maintenance of new transmission lines. However, concerns have been raised by some stakeholders, particularly investor-owned utilities. They worry about the potential cost burden associated with building these expansive new lines, and recent reports of stalled grid spending underscore those concerns and the need for efficient cost allocation mechanisms. Striking a balance between efficiency, affordability, and environmental responsibility will be crucial for the successful implementation of this policy.

 

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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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