Solar projects hinge on DOE loan guarantees

By Reuters


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The success of SolarReserve's first two U.S. solar power projects hinges on the survival of the U.S. Department of Energy loan guarantee program, the company's chief executive said.

Santa Monica, California-based SolarReserve is awaiting approval of federal loan guarantees that will enable it to start building two solar thermal power plants with a combined price tag of about $1.5 billion.

Chief Executive Kevin Smith said privately held SolarReserve is weeks away from getting conditional approval for its first project, the 110-megawatt Crescent Dunes plant in Nevada. Meanwhile, a Republican budget bill would cut the DOE's loan guarantee program for renewable energy companies significantly.

SolarReserve argues that any serious curtailment of the loan guarantee program would not just endanger solar plants, but also jeopardize much-needed jobs and economic activity.

"If they shut it down tomorrow we're in big trouble," Smith said in an interview at SolarReserve's headquarters. "We're looking at least a 12-month delay in the project, if not termination of the project."

Crescent Dunes will create about 600 jobs once it goes into construction, Smith said. Not only that, he added, the government stands to make money on the loan guarantee program.

"That money has to be repaid... and the federal government earns interest on it," he said.

SolarReserve's 150-MW Rice project in California is also going through the DOE loan guarantee process.

The company is developing large solar thermal power plants using molten salt energy storage technology licensed from Pratt & Whitney Rocketdyne, a unit of United Technologies Corp.

Founded in 2007, SolarReserve's investors include US Renewables Group, Good Energies, Citigroup Inc, PCG Clean Energy & Technology Fund LLC, Nazarian Enterprises, CalPERs, Argonaut Private Equity and Credit Suisse.

The company's technology has yet to be employed in a large-scale power plant, and traditional project financiers since the financial crisis have shied away from taking those kinds of technology risks.

"Pre-financial meltdown we felt there was a pretty good chance that we could have gotten financing through the normal commercial lenders," Smith said. "In this market, no. For our initial projects, it's the Department of Energy Loan Guarantee Program that is instrumental in getting these kinds of technologies kicked off."

Once it has two projects under construction, Smith believes SolarReserve in 2012 "will be more favorably received by the commercial lending market."

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Barakah Unit 1 reaches 100% power as it steps closer to commercial operations, due to begin early 2021

Barakah Unit 1 100 Percent Power signals the APR-1400 reactor delivering 1400MW of clean baseload electricity to the UAE grid, advancing decarbonisation, reliability, and Power Ascension Testing milestones ahead of commercial operations in early 2021.

 

Key Points

The milestone where Unit 1 reaches full 1400MW output to the UAE grid, providing clean, reliable baseload electricity.

✅ Delivers 1400MW from a single generator to the UAE grid

✅ Enables clean, reliable baseload power with zero operational emissions

✅ Completes key Power Ascension Testing before commercial operations

 

The Emirates Nuclear Energy Corporation, ENEC, has announced that its operating and maintenance subsidiary, Nawah Energy Company, Nawah, has successfully achieved 100% of the rated reactor power capacity for Unit 1 of the Barakah Nuclear Energy Plant. This major milestone, seen as a crucial step in Abu Dhabi towards completion, brings the Barakah plant one step closer to commencing commercial operations, scheduled in early 2021.

100% power means that Unit 1 is generating 1400MW of electricity from a single generator connected to the UAE grid for distribution. This milestone makes the Unit 1 generator the largest single source of electricity in the UAE.

The Barakah Nuclear Energy Plant is the largest source of clean baseload electricity in the country, capable of providing constant and reliable power in a sustainable manner around the clock. This significant achievement accelerates the decarbonisation of the UAE power sector, while also supporting the diversification of the Nation’s energy portfolio as it transitions to cleaner electricity sources, similar to the steady development in China of nuclear energy programs now underway.

The accomplishment follows shortly after the UAE’s celebration of its 49th National Day, providing a strong example of the country’s progress as it continues to advance towards a sustainable, clean, secure and prosperous future, having made the UAE the first Arab nation to open a nuclear plant as it charts this path. As the Nation looks towards the next 50 years of achievements, the Barakah plant will generate up to 25 percent of the country’s electricity, while also acting as a catalyst of the clean carbon future of the Nation.

Mohamed Ibrahim Al Hammadi, Chief Executive Officer of ENEC said: "We are proud to deliver on our commitment to power the growth of the UAE with safe, clean and abundant electricity. Unit 1 marks a new era for the power sector and the future of the clean carbon economy of the Nation, with the largest source of electricity now being generated without any emissions. I am proud of our talented UAE Nationals, working alongside international experts who are working to deliver this clean electricity to the Nation, in line with the highest standards of safety, security and quality." Nawah is responsible for operating Unit 1 and has been responsible for safely and steadily raising the power levels since it commenced the start-up process in July, and connection to the grid in August.

Achieving 100% power is one of the final steps of the Power Ascension Testing (PAT) phase of the start-up process for Unit 1. Nawah’s highly skilled and certified nuclear operators will carry out a series of tests before the reactor is safely shut down in preparation for the Check Outage. During this period, the Unit 1 systems will be carefully examined, and any planned or corrective maintenance will be performed to maintain its safety, reliability and efficiency prior to the commencement of commercial operations.

Ali Al Hammadi, Chief Executive Officer of Nawah, said: "This is a key achievement for the UAE, as we safely work through the start-up process for Unit 1 of the Barakah plant. Successfully reaching 100% of the rated power capacity in a safe and controlled manner, undertaken by our highly trained and certified nuclear operators, demonstrates our commitment to safe, secure and sustainable operations as we now advance towards our final maintenance activities and prepare for commercial operations in 2021." The Power Ascension Testing of Unit 1 is overseen by the independent national regulator – the Federal Authority for Nuclear Regulation (FANR), which has conducted 287 inspections since the start of Barakah’s development. These independent reviews have been conducted alongside more than 40 assessments and peer reviews by the International Atomic Energy Agency, IAEA, and World Association of Nuclear Operators, WANO, reflecting milestones at nuclear projects worldwide that benchmark safety and performance.

This is an important milestone for the commercial performance of the Barakah plant. Barakah One Company, ENEC’s subsidiary in charge of the financial and commercial activities of the Barakah project signed a Power Purchase Agreement, PPA, with the Emirates Water and Electricity Company, EWEC, in 2016 to purchase all of the electricity generated at the plant for the next 60 years. Electricity produced at Barakah feeds into the national grid in the same manner as other power plants, flowing to homes and business across the country.

This milestone has been safely achieved despite the challenges of COVID-19. Since the beginning of the global pandemic, ENEC, and subsidiaries Nawah and Barakah One Company, along with companies that form Team Korea, including Korea Hydro & Nuclear Power, with KHNP’s work in Bulgaria illustrating its global role, have worked closely together, in line with all national and local health authority guidelines, to ensure the highest standards for health and safety are maintained for those working on the project. ENEC and Nawah’s robust business continuity plans were activated, alongside comprehensive COVID-19 prevention and management measures, including access control, rigorous testing, and waste water sampling, to support health and wellbeing.

The Barakah Nuclear Energy Plant, located in the Al Dhafra region of the Emirate of Abu Dhabi, is one of the largest nuclear energy new build projects in the world, with four APR-1400 units. Construction of the plant began in 2012 and has progressed steadily ever since. Construction of Units 3 and 4 are in the final stages with 93 percent and 87 percent complete respectively, benefitting from the experience and lessons learned during the construction of Units 1 and 2, while the construction of the Barakah Plant as a whole is now more than 95 percent complete.

Once the four reactors are online, Barakah Plant will deliver clean, efficient and reliable electricity to the UAE grid for decades to come, providing around 25 percent of the country’s electricity and, as other nations like Bangladesh expand with IAEA assistance, reinforcing global decarbonisation efforts, preventing the release of up to 21 million tons of carbon emissions annually – the equivalent of removing 3.2 million cars off the roads each year.

 

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Ukraine Helps Spain Amid Blackouts

Ukraine-Spain Power Aid highlights swift international solidarity as Kyiv offers grid restoration expertise to Spain after unprecedented blackouts, aiding energy infrastructure recovery, interconnectors, and emergency response while operators restore power across Spain and Portugal.

 

Key Points

Ukraine sends grid experts to help Spain recover from blackouts, restore power, and reinforce energy infrastructure.

✅ Ukraine offers grid restoration expertise and emergency support.

✅ Partial power restored; cause of blackouts under investigation.

✅ EU funding and Ukrenergo bolster infrastructure resilience.

 

In a remarkable display of international solidarity, Ukraine has extended assistance to Spain as the country grapples with widespread power outages. On April 28, 2025, Spain and neighboring Portugal experienced unprecedented blackouts that disrupted daily life, including internet connectivity and subway operations. The two nations declared a state of emergency as they worked to restore power.

Ukraine's Offer of Assistance

In response to the crisis, Ukrainian President Volodymyr Zelensky reached out to Spanish Prime Minister Pedro Sánchez, offering support to help restore Spain's power grid. Zelensky emphasized Ukraine's extensive experience in managing energy challenges, particularly in fighting to keep the lights on during sustained Russian attacks on its energy infrastructure. He instructed Ukraine’s Energy Minister, Herman Haluschchenko, to mobilize technical experts to assist Spain swiftly. As of April 29, grid operators in both Spain and Portugal reported partial restoration of power, with recovery efforts ongoing. Authorities continue to investigate the cause of the outages. 

Ukraine's Energy Crisis: A Background

Ukraine's offer of assistance is particularly poignant given its own recent struggles with energy security. Throughout 2024, Russia launched numerous aerial strikes targeting Ukraine's energy infrastructure, including strikes on western Ukraine that severely damaged power generation facilities and transmission networks. These attacks led to significant challenges during the winter season, including widespread blackouts and difficulties in heating households, prompting efforts to keep the lights on this winter across the country. Despite these adversities, Ukraine managed to navigate the winter without major power shortages, thanks to rapid repairs and the resilience of its energy sector. 

International Support for Ukraine

The international community has played a crucial role in supporting Ukraine's energy sector, even as U.S. support for grid restoration has shifted, with continued aid from European partners. In July 2024, the European Union allocated nearly $110 million through the KfW Development Bank to modernize high-voltage substations and develop interconnectors with continental Europe's power system. This funding has been instrumental in repairing and restoring equipment damaged by Russian attacks and enhancing the protection of Ukraine's substations. Since the onset of the conflict, Ukraine's energy grid operator, Ukrenergo, has received international assistance totaling approximately €1.5 billion. 

A Gesture of Solidarity

Ukraine's offer to assist Spain underscores the deepening ties between the two nations and reflects a broader spirit of international cooperation. While Spain continues its recovery efforts, the support from Ukraine serves as a reminder of the importance of solidarity, and of Ukraine's electricity reserves that help prevent further outages in times of crisis. As both countries work towards restoring and securing their energy infrastructures, their collaboration highlights the shared challenges and mutual support that define the European community.

Ukraine's proactive stance in offering assistance to Spain amidst the recent blackouts exemplifies the strength of international partnerships and the shared commitment to new energy solutions that overcome energy challenges. As the situation develops, the continued cooperation between nations will be pivotal in ensuring energy security and resilience as winter looms over Ukraine once more.

 

 

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America’s Electricity is Safe From the Coronavirus—for Now

US Grid Pandemic Response coordinates control rooms, grid operators, and critical infrastructure, leveraging hydroelectric plants, backup control centers, mutual assistance networks, and deep cleaning protocols to maintain reliability amid reduced demand and COVID-19 risks.

 

Key Points

US Grid Pandemic Response encompasses measures by utilities and operators to safeguard power reliability during COVID-19

✅ Control rooms staffed on-site; operators split across backup centers

✅ Health screenings, deep cleaning, and isolation protocols mitigate contagion

✅ Reduced demand and mutual assistance improve grid resilience

 

Control rooms are the brains of NYPA’s power plants, which are mostly hydroelectric and supply about a quarter of all the electricity in New York state. They’re also a bit like human petri dishes. The control rooms are small, covered with frequently touched switches and surfaces, and occupied for hours on end by a half-dozen employees. Since social distancing and telecommuting isn’t an option in this context, NYPA has instituted regular health screenings and deep cleanings to keep the coronavirus out.

The problem is that each power plant relies on only a handful of control room operators. Since they have a specialized skill set, they can’t be easily replaced if they get sick. “They are very, very critical,” says Gil Quiniones, NYPA president and CEO. If the pandemic worsens, Quiniones says that NYPA may require control room operators to live on-site at power plants to reduce the chance of the virus making it in from the outside world. It sounds drastic, but Quiniones says NYPA has done it before during emergencies—once during the massive 2003 blackout, and again during Hurricane Sandy.

Meanwhile, PJM is one of North America’s nine regional grid operators and manages the transmission lines that move electricity from power plants to millions of customers in 13 states on the Eastern seaboard, including Washington, DC. PJM has had a pandemic response plan on the books for 15 years, but Mike Bryson, senior vice president of operations, says that this is the first time it’s gone into full effect. As of last week, about 80 percent of PJM’s 750 full-time employees have been working from home. But PJM also requires a skeleton crew of essential workers to be on-site at all times in its control centers. As part of its emergency planning, PJM built a backup control center years ago, and now it is splitting control center operators between the two to limit contact.

Past experience with large-scale disasters has helped the energy sector keep the lights on and ventilators running during the pandemic. Energy is one of 16 sectors that the US government has designated as “critical infrastructure,” which also includes the communications industry, transportation sector, and food and water systems. Each is seen as vital to the country and therefore has a duty to maintain operations during national emergencies.

“We need to be treated as first responders,” says Scott Aaronson, the vice president of security and preparedness at the Edison Electric Institute, a trade group representing private utilities. “Everybody's goal right now is to keep the public healthy, and to keep society functioning as best we can. A lack of electricity will certainly create a challenge for those goals.”

America’s electricity grid is a patchwork of regional grid operators connecting private and state-owned utilities. This means simply figuring out who’s in charge and coordinating among the various organizations is one of the biggest challenges to keeping the electricity flowing during a national emergency, according to Aaronson.

Generally, a lot of this responsibility falls on formal energy organizations like the nonprofit North American Electric Reliability Corporation and the Federal Energy Regulatory Commission. But during the coronavirus outbreak, an obscure organization run by the CEOs of electric utilities called the Electricity Subsector Coordinating Council has also served as a primary liaison between the federal government and the thousands of utility companies around the US. Aaronson says the organization has been meeting twice a week for the past three weeks to ensure that utilities are implementing best practices in their response to the coronavirus, as well as to inform the government of material needs to keep the energy sector running smoothly.

This tight-knit coordination will be especially important if the pandemic gets worse, as many forecasts suggest it will. Most utilities belong to at least one mutual assistance group, an informal network of electricity suppliers that help each other out during a catastrophe. These mutual assistance networks are usually called upon following major storms that threaten prolonged outages. But they could, in principle, be used to help during the coronavirus pandemic too. For example, if a utility finds itself without enough operators to manage a power plant, it could conceivably borrow trained operators from another company to make sure the power plant stays online.

So far, utilities and grid operators have managed to make it work on their own. There have been a handful of coronavirus cases reported at power plants, but they haven’t yet affected these plants’ ability to deliver energy. The challenges of running a power plant with a skeleton crew is partially offset by the reduced power demand as businesses shut down and more people work from home, says Robert Hebner, the director of the Center for Electromechanics at the University of Texas. “The reduced demand for power gives utilities a little breathing room,” says Hebner.

A recent study by the University of Chicago’s Energy Policy Institute found that electricity demand in Italy has plunged by 18 percent following the severe increase in coronavirus cases in the country. Energy demand in China also plummeted as a result of the pandemic. Bryson, at PJM, says the grid operator has seen about a 6 percent decrease in electricity demand in recent weeks, but expects an even greater drop if the pandemic gets worse.

Generally speaking, problems delivering electricity in the US occur when the grid is overloaded or physically damaged, such as during California wildfires or a hurricane.

An open question among coronavirus researchers is whether there will be a second wave of the pandemic later this year. During the Spanish flu pandemic in the early 20th century, the second wave turned out to be deadlier than the first. If the coronavirus remerges later this year, it could be a serious threat to reliable electricity in the US, says John MacWilliams, a former associate deputy secretary of the Department of Energy and a senior fellow at Columbia University’s Center on Global Energy Policy.

“If this crisis extends into the fall, we're going to hit hurricane season along the coasts,” MacWilliams says. “Utilities are doing a very good job right now, but if we get unlucky and have an active hurricane season, they're going to get very stressed because the number of workers that are available to repair damage and restore power will become more limited.”

This was a sentiment echoed by Bryson at PJM. “Any one disaster is manageable, but when you start layering them on top of each other, it gets much more challenging,” he adds. The US electricity grid struggles to handle major storms as it is, and these challenges will be heightened if too many workers are home sick. In this sense, the energy sector’s ability to deliver the electricity needed to keep manufacturing medical supplies or keep ventilators running depends to a large extent on our ability to flatten the curve today. The coronavirus is bad enough without having to worry about the lights going out.

 

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Amazon Announces Three New Renewable Energy Projects to Support AWS Global Infrastructure

AWS Renewable Energy Projects deliver new wind power for AWS data centers in Ireland, Sweden, and the US, adding 229 MW and 670,000 MWh annually, supporting 100% renewable targets and global cloud sustainability.

 

Key Points

AWS projects add wind power in Ireland, Sweden, and the US to supply clean energy for AWS data centers.

✅ 229 MW new wind capacity; 670,000 MWh annual generation

✅ Sites: Donegal (IE), Backhammar (SE), Tehachapi (US)

✅ Advances 100% renewable goal for global AWS infrastructure

 

 Amazon has announced three new clean energy projects as part of its long-term goal to power all Amazon Web Services (AWS) global infrastructure with renewable energy. These projects – one in Ireland, one in Sweden, and one in the United States – will deliver wind-generated energy that will total over 229 megawatts (MW) of power, with expected generation of over 670,000 megawatt hours (MWh) of renewable energy annually. The new projects are part of AWS’s long-term commitment to achieve 100 percent renewable energy for its global infrastructure. In 2018, AWS exceeded 50 percent renewable energy for its global infrastructure.

Once complete, these projects, combined with AWS’s previous nine renewable energy projects, reflect how renewable power developers benefit from diversified sources and are expected to generate more than 2,700,000 MWh of renewable energy annually – equivalent to the annual electricity consumption of over 262,000 US homes, which is approximately the size of the city of Nashville, Tennessee.

“Each of these projects brings us closer to our long-term commitment to use 100 percent renewable energy to power our global AWS infrastructure,” said Peter DeSantis, Vice President of Global Infrastructure and Customer Support, Amazon Web Services. “These projects are well-positioned to serve AWS data centers in Ireland, Sweden, and the US. We expect more projects in 2019 as we continue toward our goal of powering all AWS global infrastructure with renewable energy.”

Amazon has committed to buying the energy from a new wind project in Ireland, a 91.2 MW wind farm in Donegal. The Donegal wind farm project is expected to deliver clean energy no later than the end of 2021.

“AWS’s investment in renewable projects in Ireland illustrates their continued commitment to adding clean energy to the grid and it will make a positive contribution to Ireland’s renewable energy goals,” said Leo Varadkar, An Taoiseach of Ireland. “As a significant employer in Ireland, it is very encouraging to see Amazon taking a lead on this issue. We look forward to continuing to work with Amazon as we strive to make Ireland a leader on renewable energy.”

Amazon will also purchase 91 MW of power from a new wind farm in Bäckhammar, Sweden, which is expected to deliver renewable energy by the end of 2020.

“Sweden has long been known for ambitious renewable energy goals, and this new wind farm showcases both our country’s leadership and AWS’s commitment to renewable energy,” said Anders Ygeman, Sweden’s Minister for Energy and Digital Development. “This is a significant step in Sweden’s renewable energy production as we work toward our target of 100 percent renewable energy by 2040.”

California leads the United States in renewable electricity generation from non-hydroelectric sources, as US solar and wind growth accelerates, and the state’s Tehachapi Mountains, where AWS’s wind farm will be located, contain some of the largest wind farms in the country. The wind farm project in Tehachapi is expected to bring up to 47 MW of new renewable energy capacity by the end of 2020.

“This announcement from AWS is great news, not just for California, but for the entire country, as it reaffirms our role as a leader in renewable energy and allows us to take an important step forward on deploying the clean energy we need to respond to climate change,” said California State Senator Jerry Hill, San Mateo and Santa Clara Counties, a member of the Senate Standing Committee on Energy, Utilities and Communications.

Beyond the sustainability initiatives focused on powering the AWS global infrastructure, Amazon recently announced Shipment Zero, which is Amazon’s vision to make all Amazon shipments net zero carbon, with 50 percent of all shipments net zero by 2030. Additional sustainability programs across the company include Amazon Wind Farm Texas, which adds more than 1 million MWh of clean energy each year, alongside Amazon Wind Farm US East that is now fully operational, demonstrating scale. In total, Amazon has enabled 53 wind and solar projects worldwide, which produce more than 1,016 MW and are expected to deliver over 3,075,636 million MWh of energy annually, while peers like Arvato's solar power plant underscore broader momentum across the industry. These projects support hundreds of jobs, while providing tens of millions of dollars of investment in local communities, with Iowa wind power offering a strong example. Amazon has also set a goal to host solar energy systems at 50 fulfillment centers by 2020. This deployment of rooftop solar systems, aided by cheap batteries that enhance storage, is part of a long-term initiative that will start in North America and spread across the globe. Amazon also implemented the District Energy Project that uses recycled energy for heating Amazon offices in Seattle. For more information on Amazon’s sustainability initiatives, visit www.amazon.com/sustainability.

 

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Battery-electric buses hit the roads in Metro Vancouver

TransLink Electric Bus Pilot launches zero-emission service in Metro Vancouver, cutting greenhouse gas emissions with fast-charging stations on Route 100, supporting renewable energy goals alongside trolley buses, CNG, and hybrid fleets.

 

Key Points

TransLink's Metro Vancouver program deploying charging, zero-emission buses on Route 100 to cut emissions and fuel costs.

✅ Cuts ~100 tonnes GHG and saves $40k per bus annually

✅ Five-minute on-route charging at terminals on Route 100

✅ Pilot data to guide zero-emission fleet transition by 2050

 

TransLink's first battery-electric buses are taking to the roads in Metro Vancouver as part of a pilot project to reduce emissions, joining other initiatives like electric school buses in B.C. that aim to cut pollution in transportation.

The first four zero-emission buses picked up commuters in Vancouver, Burnaby and  New Westminster on Wednesday. Six more are expected to be brought in, and similar launches like Edmonton's first electric bus are underway across Canada.

"With so many people taking transit in Vancouver today, electric buses will make a real difference," said Merran Smith, executive director of Clean Energy Canada, a think tank at Simon Fraser University, in a release.

According to TransLink, each bus is expected to reduce 100 tonnes of greenhouse gas emissions and save $40,000 in fuel costs per year compared to a conventional diesel bus.

"Buses already help tackle climate change by getting people out of cars, and Vancouver is ahead of the game with its electric trolleys," Smith said.

She added there is still more work to be done to get every bus off diesel, as seen with the TTC's battery-electric buses rollout in Toronto.

The buses will run along the No. 100 route connecting Vancouver and New Westminster. They recharge — it takes about five minutes — at new charging stations installed at both ends of the route while passengers load and unload or while the driver has a short break. 

Right now, more than half of TransLink's fleet currently operates with clean technology, offering insights alongside Toronto's large battery-electric fleet for other cities. 

In addition to the four new battery-electric buses, the fleet also includes hundreds of zero-emission electric trolley buses, compressed natural gas buses and hybrid diesel-electric buses, while cities like Montreal's first STM electric buses continue to expand adoption.

"Our iconic trolley buses have been running on electricity since 1948 and we're proud to integrate the first battery-electric buses to our fleet," said TransLink CEO Kevin Desmond in a press release.

TransLink has made it a goal to operate its fleet with 100 per cent renewable energy in all operations by 2050. Desmond says, the new buses are one step closer to meeting that goal.

The new battery-electric buses are part of a two-and-a-half year pilot project that looks at the performance, maintenance, and customer experience of making the switch to electric, complementing BC Hydro's vehicle-to-grid pilot initiative underway in the province.

 

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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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