Should coal be considered a clean fuel?

U.S. Grid Modernization is critical for renewable energy integration, EV adoption, climate resilience, and reliability, requiring transmission upgrades, inter-regional links, hardened substations, and smart grid investments to handle extreme weather and decarbonization targets.

Key Points

U.S. Grid Modernization upgrades power networks to improve reliability, integrate renewables, and support EV demand.

✅ $2T+ investment needed for transmission upgrades

✅ Extreme weather doubling outages since 2017

✅ Regulatory fragmentation slows inter-regional lines

After decades of struggle, the U.S. clean-energy business is booming, with soaring electric-car sales and fast growth in wind and solar power. That’s raising hopes for the fight against climate change.

All this progress, however, could be derailed, as the green revolution stalls without a massive overhaul of America’s antiquated electric infrastructure – a task some industry experts say requires more than $2 trillion. The current network of transmission wires, substations and transformers is decaying with age and underinvestment, a condition highlighted by catastrophic failures during increasingly frequent and severe weather events.

Power outages over the last six years have more than doubled in number compared to the previous six years, according to a Reuters examination of federal data. In the past two years, power systems have collapsed in Gulf Coast hurricanes, West Coast wildfires, Midwest heat waves and a Texas deep freeze and recurring Texas grid crisis risks, causing long and sometimes deadly outages.

Compounding the problem, the seven regional grid operators in the United States are underestimating the growing threat of severe weather caused by climate change, Reuters found in a review of more than 10,000 pages of regulatory documents and operators’ public disclosures. Their risk models, used to guide transmission-network investments, consider historical weather patterns extending as far back as the 1970s. None account for scientific research documenting today’s more extreme weather and how it can disrupt grid generation, transmission and fuel supplies simultaneously.

The decrepit power infrastructure of the world’s largest economy is among the biggest obstacles to expanding clean energy and combating climate change on the ambitious schedule laid out by U.S. President Joe Biden. His administration promises to eliminate or offset carbon emissions from the power sector by 2035 and from the entire U.S. economy by 2050. Such rapid clean-energy growth would pressure the nation’s grid in two ways: Widespread EV adoption will spark a huge surge in power demand; and increasing dependence on renewable power creates reliability problems on days with less sun or wind, as seen in Texas, where experts have outlined reliability improvements that address these challenges.

The U.S. transmission network has seen outages double in recent years amid more frequent and severe weather events, driven by climate change and a utility supply-chain crunch that slows critical repairs. The system needs a massive upgrade to handle expected growth in clean energy and electric cars. 

“Competition from renewables is being strangled without adequate and necessary upgrades to the transmission network,” said Simon Mahan, executive director of the Southern Renewable Energy Association, which represents solar and wind companies.

The federal government, however, lacks the authority to push through the massive grid expansion and modernization needed to withstand wilder weather and accommodate EVs and renewable power. Under the current regulatory regime, and amid contentious electricity pricing proposals in recent years, the needed infrastructure investments are instead controlled by a Byzantine web of local, state and regional regulators who have strong political incentives to hold down spending, according to Reuters interviews with grid operators, federal and state regulators, and executives from utilities and construction firms.

“Competition from renewables is being strangled without adequate and necessary upgrades to the transmission network.”

Paying for major grid upgrades would require these regulators to sign off on rate increases likely to spark strong opposition from consumers and local and state politicians, who are keen to keep utility bills low. In addition, utility companies often fight investments in transmission-network improvements because they can result in new connections to other regional grids that could allow rival companies to compete on their turf, even as coal and nuclear disruptions raise brownout risks in some regions. With the advance of green energy, those inter-regional connections will become ever more essential to move power from far-flung solar and wind installations to population centers.

The power-sharing among states and regions with often conflicting interests makes it extremely challenging to coordinate any national strategy to modernize the grid, said Alison Silverstein, an independent industry consultant and former senior adviser to the U.S. Federal Energy Regulatory Commission (FERC).

“The politics are a freakin’ nightmare,” she said.

The FERC declined to comment for this story. FERC Commissioner Mark Christie, a Republican, acknowledged the limitations of the agency’s power over the U.S. grid in an April 21 agency meeting involving transmission planning and costs.

“We can’t force states to do anything,” Christie said.

The White House and Energy Department did not comment in response to detailed questions from Reuters on the Biden administration’s plans to tackle U.S. grid problems and their impact on green-energy expansion.

The administration said in an April news release that it plans to offer $2.5 billion in grants for grid-modernization projects as part of Biden’s $1 trillion infrastructure package, complementing a proposed clean electricity standard to accelerate decarbonization over the next decade. A modernized grid, the release said, is the “linchpin” of Biden’s clean-energy agenda.

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Eastern Kings Wind Farm Expansion advances P.E.I. renewable energy with seven new wind turbines, environmental assessment, wildlife monitoring of birds and bats, and community consultation to double output to 30 MW for domestic consumption.

Key Points

A P.E.I. project adding seven turbines for 30 MW, under 17 conditions, with wildlife monitoring and community oversight.

✅ Seven new turbines, larger than existing units

✅ 17 conditions, monthly compliance reporting

✅ Two-year wildlife study for birds and bats

A proposal to expand an existing wind farm in eastern P.E.I. has been given the go-ahead, according to P.E.I.’s Department of Environment, Water and Climate Change, as related grid work like a new transmission line progresses in the region.

Minister Natalie Jameson approved the P.E.I. Energy Corporation’s Eastern Kings Wind Farm expansion project, the province announced in a release Wednesday afternoon, as Atlantic Canada advances other renewable initiatives like tidal power to diversify supply.

The project will be subject to 17 conditions, which were drawn from a review of the 80 responses the province received from the public on the proposed Eastern Kings Wind Farm expansion.

The corporation must provide a summary on the status of each condition to the department on a monthly basis.

“This decision balances the needs of people, communities, wellness and the environment,” Jameson said in the release.

“It allows this renewable energy project to proceed and reduce greenhouse [gas] emissions that cause climate change while mitigating the project’s impact to the Island’s ecosystem.”

The P.E.I. Energy Corporation wants to double the output of its Eastern Kings Wind Farm with the installation of seven wind turbines between the communities of Elmira and East Point to develop 30 megawatts of wind power for domestic consumption, according to the minister’s impact assessment, aligning with regional moves to expand wind and solar projects across Atlantic Canada.

The new turbines are expected to be larger than the existing 10 at the site, even as regional utilities study major grid changes to integrate more renewables.

Project must comply with conditions

In February, the province said it would identify any specific questions or concerns it felt needed to be addressed in the submissions, according to Greg Wilson, manager of environmental land management for the province, while some advocate for independent electricity planning to guide such decisions.

Public feedback closed in January, after an earlier extension to wait for a supplemental report on birds and bats.

The corporation needs to comply with all conditions – such as monitoring environmental impact, setting up an environmental management plan and creating a committee to address concerns – listed in the release on Wednesday, amid calls from environmental advocates to reduce biomass use in electricity generation.

A condition in the release suggests representatives from L’nuey, the Souris and Area Wildlife Branch, the Rural Municipality of Eastern Kings and local residents to make up the committee.

The corporation will also need to conduct a study over two years after construction to look at the impact on bats and birds, and implement a protocol to report deaths of birds to federal and provincial authorities.

According to Canada Energy Regulator, roughly 98 per cent of power generated on P.E.I. comes from wind farms. It also said there were 203 megawatts installed on P.E.I. as of 2018, and the majority of energy consumed on the Island comes from New Brunswick from a mix of nuclear, fossil fuels and hydroelectricity, while in Nova Scotia, the utility has increased biomass generation as part of its supply mix.

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Manitoba NDP Geothermal Conversion Program offers full-cost heat pump installation for 5,000 homes, lowering electricity bills, funding contractor training and rebates, and cutting greenhouse gas emissions via geothermal energy administered by Efficiency Manitoba.

Key Points

A plan funding 5,000 home heat pump conversions to cut electricity bills, reduce emissions, and expand installer capacity.

✅ Covers equipment and installation for 5,000 homes

✅ Cuts electricity bills up to 50% vs electric heat

✅ Administered by Efficiency Manitoba; trains contractors

An NDP government would cover the entire cost for 5,000 families to switch their homes to geothermal energy, New Democrats have promised.

If elected on Oct. 3, the NDP will pay for the equipment and installation of new geothermal systems at 5,000 homes, St. James candidate Adrien Sala announced outside a St. Boniface home that previously made the switch. 

The homes that switch to geothermal energy could save as much as 50 per cent on their electricity bills, Sala said.

"It will save you money, it will grow our economy and it will reduce greenhouse gas emissions. And I think we can safely call that a win, win, win," Sala said.

Geothermal energy is derived from heat that is generated within the Earth.

The NDP said each conversion to geothermal heating and cooling would cost an estimated $26,000, and comes as new turbine investments advance in Manitoba, and it would take four years to complete all 5,000 conversions.

The program would be administered through Efficiency Manitoba, the Crown corporation responsible for conserving energy, as Manitoba Hydro's new president navigates changes at the utility. The NDP estimates it will cost $32.5 million annually over the four years, at a time of red ink at Manitoba Hydro as new power generation needs loom. Some of that money would support the training of more contractors who could install geothermal systems.

Subsidies get low pickup: NDP
Sala wouldn't say Wednesday which homeowners or types of homes would be eligible.

He said the NDP's plan would be a first in Canada, even as Ontario's energy plan seeks to address growing demand elsewhere.

"What we've seen elsewhere is where other jurisdictions have used a strict subsidy model, where they try to reduce the cost of geothermal, and while Ontario reviews a halt to natural gas generation to cut emissions, approaches differ across provinces. We really haven't seen a lot of uptake in those other jurisdictions," Sala said.

"This is an attempt at dealing with one of those key barriers for homeowners."

Efficiency Manitoba runs a subsidy program for geothermal energy through ground source heat pumps, supporting using more electricity for heat across the province, valued at up to $2.50 per square foot. It is estimated a 1,600 sq. ft. home switching from an electric furnace to geothermal will receive a rebate of around $4,000 and save around $900 annually on their electricity bills, the Crown corporation said.anitoba homeProgressive Conservative spokesperson Shannon Martin questioned how NDP Leader Wab Kinew can afford his party's numerous election promises.

"He will have no choice but to raise taxes, and history shows the NDP will raise them all," said Martin, the McPhillips MLA who isn't seeking re-election.

Wednesday's announcement was the first for the NDP in which Kinew wasn't present. The party has criticized the Progressive Conservatives for leader Heather Stefanson showing up for only a few announcements a week.

Sala said Kinew was busy preparing for the debate later in the day.

"This stuff is near and dear to Wab's heart, and frankly, I think he's probably hurting that he's not here with us right now."

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Duke Energy Clean Energy Strategy advances renewables, battery storage, grid modernization, and energy efficiency to cut carbon, retire coal, and target net-zero by 2050 across the Carolinas with robust IRPs and capital investments.

Key Points

Plan to expand renewables, storage, and grid upgrades to cut carbon and reach net-zero electricity by 2050.

✅ 56B investment in renewables, storage, and grid modernization

✅ Targets 50% carbon reduction by 2030 and net-zero by 2050

✅ Retires coal units; expands energy efficiency and IRPs

Duke Energy says that the company will continue advancing its ambitious clean energy goals without the Atlantic Coast Pipeline (ACP) by investing in renewables, battery storage, energy efficiency programs and grid projects that support U.S. electrification efforts.

Duke Energy, the nation's largest electric utility, unveils its new logo. (PRNewsFoto/Duke Energy) (PRNewsfoto/Duke Energy)

Duke Energy's $56 billion capital investment plan will deliver significant customer benefits and create jobs at a time when policymakers at all levels are looking for ways to rebuild the economy in 2020 and beyond. These investments will deliver cleaner energy for customers and communities while enhancing the energy grid to provide greater reliability and resiliency.

"Sustainability and the reduction of carbon emissions are closely tied to our region's success," said Lynn Good, Duke Energy Chair, President and CEO. "In our recent Climate Report, we shared a vision of a cleaner electricity future with an increasing focus on renewables and battery storage in addition to a diverse mix of zero-carbon nuclear, natural gas, hydro and energy efficiency programs.

"Achieving this clean energy vision will require all of us working together to develop a plan that is smart, equitable and ensures the reliability and affordability that will spur economic growth in the region. While we're disappointed that we're not able to move forward with ACP, we will continue exploring ways to help our customers and communities, particularly in eastern North Carolina where the need is great," said Good.

Already a clean-energy leader, Duke Energy has reduced its carbon emissions by 39% from 2005 and remains on track to cut its carbon emissions by at least 50% by 2030, as peers like Alliant's carbon-neutral plan demonstrate broader industry momentum toward decarbonization. The company also has an ambitious clean energy goal of reaching net-zero emissions from electricity generation by 2050. 

In September 2020, Duke Energy plans to file its Integrated Resource Plans (IRP) for the Carolinas after an extensive process of working with the state's leaders, policymakers, customers and other stakeholders. The IRPs will include multiple scenarios to support a path to a cleaner energy future in the Carolinas, reflecting key utility trends shaping resource planning.

Since 2010, Duke Energy has retired 51 coal units totaling more than 6,500 megawatts (MW) and plans to retire at least an additional 900 MW by the end of 2024. In 2019, the company proposed to shorten the book lives of another approximately 7,700 MW of coal capacity in North Carolina and Indiana.

Duke Energy will host an analyst call in early August 2020 to discuss second quarter 2020 financial results and other business and financial updates. The company will also host its inaugural Environmental, Social and Governance (ESG) investor day in October 2020.

Duke Energy

Duke Energy is transforming its customers' experience, modernizing the energy grid, generating cleaner energy and expanding natural gas infrastructure to create a smarter energy future for the people and communities it serves. The Electric Utilities and Infrastructure unit's regulated utilities serve 7.8 million retail electric customers in six states: North Carolina, South Carolina, Florida, Indiana, Ohio and Kentucky. The Gas Utilities and Infrastructure unit distributes natural gas to 1.6 million customers in five states: North Carolina, South Carolina, Tennessee, Ohio and Kentucky. The Duke Energy Renewables unit operates wind and solar generation facilities across the U.S., as well as energy storage and microgrid projects.

Duke Energy was named to Fortune's 2020 "World's Most Admired Companies" list and Forbes' "America's Best Employers" list. More information about the company is available at duke-energy.com. The Duke Energy News Center contains news releases, fact sheets, photos, videos and other materials. Duke Energy's illumination features stories about people, innovations, community topics and environmental issues. Follow Duke Energy on Twitter, LinkedIn, Instagram and Facebook.

Forward-Looking Information

This document includes forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Forward-looking statements are based on management's beliefs and assumptions and can often be identified by terms and phrases that include "anticipate," "believe," "intend," "estimate," "expect," "continue," "should," "could," "may," "plan," "project," "predict," "will," "potential," "forecast," "target," "guidance," "outlook" or other similar terminology. Various factors may cause actual results to be materially different than the suggested outcomes within forward-looking statements; accordingly, there is no assurance that such results will be realized. These factors include, but are not limited to:

• The impact of the COVID-19 electricity demand shift on operations and revenues;
• State, federal and foreign legislative and regulatory initiatives, including costs of compliance with existing and future environmental requirements, including those related to climate change, as well as rulings that affect cost and investment recovery or have an impact on rate structures or market prices;
• The extent and timing of costs and liabilities to comply with federal and state laws, regulations and legal requirements related to coal ash remediation, including amounts for required closure of certain ash impoundments, are uncertain and difficult to estimate;
• The ability to recover eligible costs, including amounts associated with coal ash impoundment retirement obligations and costs related to significant weather events, and to earn an adequate return on investment through rate case proceedings and the regulatory process;
• The costs of decommissioning nuclear facilities could prove to be more extensive than amounts estimated and all costs may not be fully recoverable through the regulatory process;
• Costs and effects of legal and administrative proceedings, settlements, investigations and claims;
• Industrial, commercial and residential growth or decline in service territories or customer bases resulting from sustained downturns of the economy and the economic health of our service territories or variations in customer usage patterns, including energy efficiency and demand response efforts and use of alternative energy sources, such as self-generation and distributed generation technologies;
• Federal and state regulations, laws and other efforts designed to promote and expand the use of energy efficiency measures and distributed generation technologies, such as private solar and battery storage, in Duke Energy service territories could result in customers leaving the electric distribution system, excess generation resources as well as stranded costs;
• Advancements in technology;
• Additional competition in electric and natural gas markets and continued industry consolidation;
• The influence of weather and other natural phenomena on operations, including the economic, operational and other effects of severe storms, hurricanes, droughts, earthquakes and tornadoes, including extreme weather associated with climate change;
• The ability to successfully operate electric generating facilities and deliver electricity to customers including direct or indirect effects to the company resulting from an incident that affects the U.S. electric grid or generating resources;
• The ability to obtain the necessary permits and approvals and to complete necessary or desirable pipeline expansion or infrastructure projects in our natural gas business;
• Operational interruptions to our natural gas distribution and transmission activities;
• The availability of adequate interstate pipeline transportation capacity and natural gas supply;
• The impact on facilities and business from a terrorist attack, cybersecurity threats, data security breaches, operational accidents, information technology failures or other catastrophic events, such as fires, explosions, pandemic health events or other similar occurrences;
• The inherent risks associated with the operation of nuclear facilities, including environmental, health, safety, regulatory and financial risks, including the financial stability of third-party service providers;
• The timing and extent of changes in commodity prices and interest rates and the ability to recover such costs through the regulatory process, where appropriate, and their impact on liquidity positions and the value of underlying assets;
• The results of financing efforts, including the ability to obtain financing on favorable terms, which can be affected by various factors, including credit ratings, interest rate fluctuations, compliance with debt covenants and conditions and general market and economic conditions;
• Credit ratings of the Duke Energy Registrants may be different from what is expected;
• Declines in the market prices of equity and fixed-income securities and resultant cash funding requirements for defined benefit pension plans, other post-retirement benefit plans and nuclear decommissioning trust funds;
• Construction and development risks associated with the completion of the Duke Energy Registrants' capital investment projects, including risks related to financing, obtaining and complying with terms of permits, meeting construction budgets and schedules and satisfying operating and environmental performance standards, as well as the ability to recover costs from customers in a timely manner, or at all;
• Changes in rules for regional transmission organizations, including FERC debates on coal and nuclear subsidies and new and evolving capacity markets, and risks related to obligations created by the default of other participants;
• The ability to control operation and maintenance costs;
• The level of creditworthiness of counterparties to transactions;
• The ability to obtain adequate insurance at acceptable costs;
• Employee workforce factors, including the potential inability to attract and retain key personnel;
• The ability of subsidiaries to pay dividends or distributions to Duke Energy Corporation holding company (the Parent);
• The performance of projects undertaken by our nonregulated businesses and the success of efforts to invest in and develop new opportunities;
• The effect of accounting pronouncements issued periodically by accounting standard-setting bodies;
• The impact of U.S. tax legislation to our financial condition, results of operations or cash flows and our credit ratings;
• The impacts from potential impairments of goodwill or equity method investment carrying values; and
• The ability to implement our business strategy, including enhancing existing technology systems.
• Additional risks and uncertainties are identified and discussed in the Duke Energy Registrants' reports filed with the SEC and available at the SEC's website at sec.gov. In light of these risks, uncertainties and assumptions, the events described in the forward-looking statements might not occur or might occur to a different extent or at a different time than described. Forward-looking statements speak only as of the date they are made and the Duke Energy Registrants expressly disclaim an obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

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EU Renewable Energy Transition is accelerating under REPowerEU, as wind and solar generation hit records, improving energy security, efficiency, and decarbonization while reducing reliance on Russian fossil fuels across the EU grid.

Key Points

EU shift to wind and solar under REPowerEU to cut fossil fuels, boost efficiency, and secure energy supply.

✅ Wind and solar set record 22% of EU electricity in 2022

✅ REPowerEU targets over 40% renewables and 15% lower demand by 2030

✅ Diversifies away from Russian fuels; partners with US and Norway

Europe is producing all-time highs of wind and solar energy as the 27-country group works to reduce its reliance on fossil fuels from Russia, a shift underscored by Europe's green surge across the bloc.

Four months after Vladimir Putin’s full-scale invasion of Ukraine in February 2022, the European Commission launched REPowerEU. This campaign aims to:

• Boost the use of renewable energy.
• Reduce overall energy consumption.
• Diversify energy sources.

EU countries were already moving toward renewable energy, but Russia’s war against Ukraine accelerated that trend. In 2022, for the first time, renewables surpassed fossil fuels and wind and solar power surpassed gas as a source of electricity. Wind and solar provided a record-breaking 22% of EU countries’ electrical supply, according to London-based energy think tank Ember.

“We have to double down on investments in home-grown renewables,” European Commission President Ursula von der Leyen said in October 2022. “Not only for the climate but also because the transition to the clean energy is the best way to gain independence and to have security of energy supply.”

Across the continent, growth in solar generation rose by 25% in 2022, according to Ember, as solar reshapes electricity prices in Northern Europe. Twenty EU countries produced their highest share of solar power in 2022. In October, Greece ran entirely on renewables for several hours and is seven years ahead of schedule for its 2030 solar capacity target.

Meanwhile, Ireland's green electricity target aims to make more than a third of its power supply renewable within four years.

By 2030, RePowerEU aims to provide more than 40% of the EU’s total power from renewables, aligning with global renewable records being shattered worldwide.

To meet the European Commission’s goal to cut EU energy usage by 15%, people and governments changed their habits and became more energy-efficient, while Germany's solar power boost helped bolster supply. Among their actions:

• Germany turned down the heat in public buildings and lowered the cost of train tickets to reduce car usage, as clean energy hit 50% in Germany during this period.
• Spain ordered stores and public buildings to turn off their lights at night.
• France dimmed the Eiffel Tower and reduced city speed limits.

For the oil and gas that the EU still needed to import, countries turned to partners such as Norway and the United States.

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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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