Finding new power for old tractors

By Associated Press


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At Blue Fox Farm, the tractor is old but the fuel is new.

Like a small but growing number of organic farmers around the country, Chris Jagger has converted an old Allis-Chalmers Model G tractor built in the 1940s to run on electricity at his farm in southwest Oregon.

They like the small tractor's nimble ways around row crops. And with an electric motor instead of a gasoline engine bolted on the back, it runs cleanly, quietly and slowly with no belches of exhaust, few breakdowns and no direct consumption of fossil fuel.

Jagger still plugs into the grid back at the barn, but some farmers are setting up photovoltaic panels in the fields or on the tractors to draw power from the same source that grows their vegetables: the rays of the sun.

"As long as I'm alive, I am probably always going to be dependent on petroleum myself," said Jagger, who has a conventional tractor for heavier work at his farm outside Applegate. "But I think it's important to be always making a step in the direction of looking for alternatives."

The founding father of the idea, organic farmer Ron Khosla in New Paltz, N.Y., is embarrassed to admit that when he built his first one in the winter of 2001-2002, he was not interested in saving the Earth so much as finding a less smelly and more reliable alternative to his Model G's balky gasoline engine.

"There was no idealism in my conversion," he wrote in an e-mail to The Associated Press. "I thought electric motors would be no maintenance."

He said the torque curves are flatter than with gas or diesel engines, and it was easy to double the power. Plus, the machines can be driven extremely slowly.

"We have two of them now, and they're terrific," he added. "Absolutely no trouble with the motors. I have had connections to the batteries loosen up and cause sparking, but that's just because I'm an idiot, and you tighten a bolt and you're back in business."

Khosla has no idea how many electric Gs are out there, because he quit counting after he got to 100. A number of farmers are doing it themselves after reading the directions he posted on the Web with a sustainable farming grant. They can buy conversion kits on the Web from various producers.

Between the tractor and the conversion, Khosla figures a farmer can put one together for about $3,000, though the growing demand for Model Gs is driving up the price.

"The first 100, I was so excited," Khosla said. "Every single person, I remembered their names. I would get every once in a while a little newspaper clipping or e-mail that they were in some parade. It's really amazing."

Jagger stumbled on those directions doing a Google search.

"I was really thinking about doing this, but didn't want to reinvent the wheel, and there it was," Jagger said.

He tracked down a Model G with a blown engine in Corvallis, a city about 200 miles north of his Blue Fox Farm where Jim Corliss was converting them to run on bio-diesel.

"When I bought this thing, it was completely rusted out," Jagger said. "I repacked the bearings, fixed all the joints. The guy said, 'There's no engine on it.' And I said, 'Yeah, that's exactly what I want, because I'm going to be doing this electric conversion to it.'"

Corliss was inspired to start doing electric conversions, too, and has done seven, compared to 155 diesels.

Nearby, Oregon State University has one on its vegetable research farm.

On the other side of the country in Waterford, Maine, retired engineer John Howe has converted a Ford Model 8N tractor and equipped it with a photo voltaic panel that doubles as a sun shade.

"Here is the rub," he said. "It takes about 80 pounds of lead-acid battery to equal one pound of gasoline, to carry the same amount of energy.

"My Ford tractors have 1,200 pounds of lead acid batteries," which is fine, he said, because tractors often need extra weight for traction on soft ground. But, "You can only do serious work for about two hours with the energy you have on board."

That's no problem for the Model G, which is not powerful enough for plowing but well suited for light jobs such as seeding, weeding and cultivating.

Khosla has one Model G with six 8-volt batteries and one with four 12-volt batteries. He finds he can work off-and-on all morning, give it a booster charge over lunch and be back in business.

With old Model Gs becoming harder to find, Khosla has been working on something completely different, designed from the ground up around an electric motor. He wants it to do everything the Model G will do, and be simple enough that a farmer in the developing world can weld a frame together, then mount an electric motor onto it. He has built three prototypes and figures it will be ready to go after two more.

"If you are working with electric motors, it like totally frees your mind," he said. "The new tractors I'm building look really different.

"People are like, 'Yes! Sign me up! That's great, because I can't find a G anywhere,'" he said. "We're mostly there."

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SDG&E Wants More Money From Customers Who Don’t Buy Much Electricity. A Lot More.

SDG&E Minimum Bill Proposal would impose a $38.40 fixed charge, discouraging rooftop solar, burdening low income households, and shifting grid costs during peak demand, as the CPUC weighs consumer impacts and affordability.

 

Key Points

Sets a $38.40 monthly minimum bill that raises low usage costs, deters rooftop solar, and burdens low income households.

✅ $38.40 fixed charge regardless of usage

✅ Disincentivizes rooftop solar investments

✅ Disproportionate impact on low income customers

 

The utility San Diego Gas & Energy has an aggressive proposal pending before the California Public Utilities Commission, amid recent commission changes in San Diego that highlight how regulatory decisions affect local customers: It wants to charge most residential customers a minimum bill of $38.40 each month, regardless of how much energy they use. The costs of this policy would hit low-income customers and those who generate their own energy with rooftop solar. We’re urging the Commission to oppose this flawed plan—and we need your help.

SDG&E’s proposal is bad news for sustainable energy. About half of the customers whose bills would go up under this proposal have rooftop solar. The policy would deter other customers from investing in rooftop solar by making these investments less economical. Ultimately, lost opportunities for solar would mean burning more gas in polluting power plants. 

The proposal is also bad news for people who already have to scrimp on energy costs. Most customers with big homes and billowing air conditioners won't notice if this policy goes into effect, because they use at least $38 worth of electricity a month anyway. But for households that don’t buy much electricity from the company, including those in small apartments without air conditioning, this proposal would raise the bills. Even for customers on special low-income rates, amid electric bill changes statewide, SDG&E wants a minimum bill of $19.20.

Penalizing customers who don’t use much electricity would disproportionately hurt lower-income customers, raising energy equity concerns across the region, who tend to use less energy than their wealthier neighbors. In the region SDG&E serves, the average family in an apartment uses half as much electricity as a single-family residence. Statewide, low-income households are more than four times as likely to be low-usage electricity customers than high-income households. When it gets hot, residential electricity patterns are often driven by air conditioning. The vast majority of SDG&E's customers live in the coastal climate zone, where access to air conditioning is strongly linked to income: Households with incomes over $150,000 are more than twice as likely to have air conditioning than families making less than $35,000, with significant racial disparities in who has AC.

In its attempt to rationalize its request, SDG&E argues that it should charge everyone for infrastructure costs that do not depend on how much energy they use. But the cost of the grid is driven by how much energy SDG&E delivers on hot summer afternoons, when some customers blast their AC and demand for electricity peaks. If more customers relied on their own solar power or conserved energy, the utility would spend less on its grid and help rein in soaring electricity prices over time.

In the long term, reducing incentives to go solar and conserve energy will strain the grid and drive up costs for everyone, especially as lawmakers may overturn income-based charges and reshape rate design. SDG&E's arguments are part of a standard utility playbook for trying to hike income-based fixed charges, and consumer advocates have repeatedly shut them down.  As far as we know, no regulators in the country have allowed a utility to charge customers over $38 for the “privilege” of accessing electric service. 

 

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Ontario Supports Plan to Safely Continue Operating the Pickering Nuclear Generating Station

Pickering Nuclear Generating Station Refurbishment will enable OPG to deliver reliable, clean electricity in Ontario, cut CO2 emissions, support jobs, boost Cobalt-60 medical isotopes supply, and proceed under CNSC oversight alongside small modular reactor leadership.

 

Key Points

A plan to assess and renew Pickering's B units, extending safe, clean, low-cost power in Ontario for up to 30 years.

✅ Extends zero-emissions baseload by up to 30 years

✅ Requires CNSC approval and rigorous safety oversight

✅ Supports Ontario jobs and Cobalt-60 isotope production

 

The Ontario government is supporting Ontario Power Generation’s (OPG) continued safe operation of the Pickering Nuclear Generating Station. At the Ontario government’s request, as a formal extension request deadline approaches, OPG reviewed their operational plans and concluded that the facility could continue to safely generate electricity.

“Keeping Pickering safely operating will provide clean, low-cost, and reliable electricity to support the incredible economic growth and new jobs we’re seeing, while building a healthier Ontario for everyone,” said Todd Smith, Minister of Energy. “Nuclear power has been the safe and reliable backbone of Ontario’s electricity system since the 1970s and our government is working to secure that legacy for the future. Our leadership on Small Modular Reactors and consideration of a refurbishment of Pickering Nuclear Generating Station are critical steps on that path.”

Maintaining operations of Pickering Nuclear Generation Station will also protect good-paying jobs for thousands of workers in the region and across the province. OPG, which reported 2016 financial results that provide context for its operations, employs approximately 4,500 staff to support ongoing operation at its Pickering Nuclear Generating Station. In total, there are about 7,500 jobs across Ontario related to the Pickering Nuclear Generating Station.

Further operation of Pickering Nuclear Generating Station beyond September 2026 would require a complete refurbishment. The last feasibility study was conducted between 2006 and 2009. With significant economic growth and increasing electrification of industry and transportation, and a growing electricity supply gap across the province, Ontario has asked OPG to update its feasibility assessment for refurbishing Pickering “B” units at the Nuclear Generating Station, based on the latest information, as a prudent due diligence measure to support future electricity planning decisions. Refurbishment of Pickering Nuclear Generating Station could result in an additional 30 years of reliable, clean and zero-emissions electricity from the facility.

“Pickering Nuclear Generating Station has never been stronger in terms of both safety and performance,” said Ken Hartwick, OPG President and CEO. “Due to ongoing investments and the efforts of highly skilled and dedicated employees, Pickering can continue to safely and reliably produce the clean electricity Ontarians need.”

Keeping Pickering Nuclear Generating Station operational would ensure Ontario has reliable, clean, and low-cost energy, even as planning for clean energy when Pickering closes continues across the system, while reducing CO2 emissions by 2.1 megatonnes in 2026. This represents an approximate 20 per cent reduction in projected emissions from the electricity sector in that year, which is the equivalent of taking up to 643,000 cars off the road annually. It would also increase North America’s supply of Cobalt-60, a medical isotope used in cancer treatments and medical equipment sterilization, by about 10 to 20 per cent.

OPG requires approval from the Canadian Nuclear Safety Commission (CNSC) for its revised schedule. The CNSC, which employs a rigorous and transparent decision-making process, will make the final decision regarding Pickering’s safe operating life, even though the station was slated to close as planned earlier. OPG will continue to ensure the safety of the Pickering facility through rigorous monitoring, inspections, and testing.

 

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Understanding the Risks of EV Fires in Helene Flooding

EV Flood Fire Risks highlight climate change impacts, lithium-ion battery hazards, water damage, post-submersion inspection, first responder precautions, manufacturer safeguards, and insurance considerations for extreme weather, flood-prone areas, and hurricane aftermaths.

 

Key Points

Water-exposed EV lithium-ion batteries may ignite later, requiring inspection, isolation, and trained responders.

✅ Avoid driving through floodwaters; park on high ground.

✅ After submersion, isolate vehicle; seek qualified inspection.

✅ Inform first responders and insurers about EV water damage.

 

As climate change intensifies the frequency and severity of extreme weather events, concerns about electric vehicle (EV) safety in flood-prone areas have come to the forefront. Recent warnings from officials regarding the risks of electric vehicles catching fire due to flooding from Hurricane Idalia underscore the need for heightened awareness and preparedness among consumers and emergency responders, as well as attention to grid reliability during disasters.

The alarming incidents of EVs igniting after being submerged in floodwaters have raised critical questions about the safety of these vehicles during severe weather conditions. While electric vehicles are often touted for their environmental benefits and lower emissions, it is crucial to understand the potential risks associated with their battery systems when exposed to water, even as many drivers weigh whether to buy an electric car for daily use.

The Risks of Submerging Electric Vehicles

Electric vehicles primarily rely on lithium-ion batteries, which can be sensitive to water exposure. When these batteries are submerged, they risk short-circuiting, which may lead to fires. Unlike traditional gasoline vehicles, where fuel may leak out, the sealed nature of an EV’s battery can create hazardous situations when compromised. Experts warn that even after water exposure, the risk of fire can persist, sometimes occurring days or weeks later.

Officials emphasize the importance of vigilance in flood-prone areas, including planning for contingencies like mobile charging and energy storage that support recovery. If an electric vehicle has been submerged, it is crucial to have it inspected by a qualified technician before attempting to drive it again. Ignoring this can lead to catastrophic consequences not only for the vehicle owner but also for surrounding individuals and properties.

Official Warnings and Recommendations

In light of these dangers, safety officials have issued guidelines for electric vehicle owners in flood-prone areas. Key recommendations include:

  1. Avoid Driving in Flooded Areas: The most straightforward advice is to refrain from driving through flooded streets, which can not only damage the vehicle but also pose risks to personal safety.

  2. Inspection After Flooding: If an EV has been submerged, owners should seek immediate professional inspection. Technicians can evaluate the battery and electrical systems for damage and determine if the vehicle is safe to operate.

  3. Inform Emergency Responders: In flood situations, informing emergency personnel about the presence of electric vehicles can help them mitigate risks during rescue operations, including firefighter health risks that may arise. First responders are trained to handle conventional vehicles but may need additional precautions when dealing with EVs.

Industry Response and Innovations

In response to rising concerns, electric vehicle manufacturers are working to enhance the safety features of their vehicles. This includes developing waterproof battery enclosures and improving drainage systems to prevent water intrusion, as well as exploring vehicle-to-home power for resilience during outages. Some manufacturers are also investing in research to improve battery chemistry, making them more resilient in extreme conditions.

The automotive industry recognizes that consumer education is equally important, particularly around utility impacts from mass-market EVs that affect planning. Manufacturers and safety organizations are encouraged to disseminate information about proper EV maintenance, the importance of inspections after flooding, and safety protocols for both owners and first responders.

The Role of Insurance Companies

As the risks associated with electric vehicle flooding become more apparent, insurance companies are also reassessing their policies. With increasing incidences of extreme weather, insurers are likely to adapt coverage options related to water damage and fire risks specific to electric vehicles. Policyholders should consult with their insurance providers to ensure they understand their coverage in the event of flooding.

Preparing for the Future

With the increasing adoption of electric vehicles, it is vital to prepare for the challenges posed by climate change and evolving state power grids capacity. Community awareness campaigns can play a significant role in educating residents about the risks and safety measures associated with electric vehicles during flooding events. By fostering a well-informed public, the likelihood of accidents and emergencies can be reduced.

 

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Tornadoes and More: What Spring Can Bring to the Power Grid

Spring Storm Grid Risks highlight tornado outbreaks, flooding, power outages, and transmission disruptions, with NOAA flood outlooks, coal and barge delays, vulnerable nuclear sites, and distribution line damage demanding resilience, reliability, and emergency preparedness.

 

Key Points

Spring Storm Grid Risks show how tornadoes and floods disrupt power systems, fuel transport, and plants guide resilience.

✅ Tornado outbreaks and derechos damage distribution and transmission

✅ Flooding drives outages via treefall, substation and plant inundation

✅ Fuel logistics disrupted: rail coal, river barges, road access

 

The storm and tornado outbreak that recently barreled through the US Midwest, South and Mid-Atlantic was a devastating reminder of how much danger spring can deliver, despite it being the “milder” season compared to summer and winter.  

Danger season is approaching, and the country is starting to see the impacts. 

The event killed at least 32 people across seven states. The National Weather Service is still tallying up the number of confirmed tornadoes, which has already passed 100. Communities coping with tragedy are assessing the damage, which so far includes at least 72 destroyed homes in one Tennessee county alone, and dozens more homes elsewhere. 

On Saturday, April 1–the day after the storm struck–there were 1.1 million US utility customers without power, even as EIA reported a January power generation surge earlier in the year. On Monday morning, April 3, there were still more than 80,000 customers in the dark, according to PowerOutage.us. The storm system brought disruptions to both distribution grids–those networks of local power lines you generally see running overhead to buildings–as well as the larger transmission grid in the Midwest, which is far less common than distribution-level issues. 

While we don’t yet have a lot of granular details about this latest storm’s grid impacts, recent shifts in demand like New York City's pandemic power patterns show how operating conditions evolve, and it’s worth going through what else the country might be in for this spring, as well as in future springs. Moreover, there are steps policymakers can take to prepare for these spring weather phenomena and bolster the reliability and resilience of the US power system. 

Heightened flood risk 
The National Oceanic Atmospheric Administration (NOAA) said in a recent outlook that about 44 percent of the United States is at risk of floods this spring, equating to about 146 million people. This includes most of the eastern half of the country, the federal agency said. 

The agency also sees “major” flood risk potential in some parts of the Upper Mississippi River Basin, and relatively higher risk in the Sierra Nevada region, due in part to a historic snowpack in California.  

Multiple components of the power system can be affected by spring floods. 

Power lines – Floods can saturate soil and make trees more likely to uproot and fall onto power lines. This has been contributing to power outages during California’s recent heavy storms–called atmospheric rivers–that started over the winter. In other regions, soil moisture has even been used as a predictor of where power outages will occur due to hurricanes, so that utility companies are better prepared to send line repair crews to the right areas. Hurricanes are primarily a summer and fall phenomenon, and summer also brings grid stress from air conditioning demand in many states, so for now, during spring, they are less of a concern.  

Fuel transport – Spring floods can hinder the transportation of fuels like coal. While it is a heavily polluting fossil fuel that is set to continue declining as a fuel source for US electricity generation, with the EIA summer outlook for wind and solar pointing to further shifts, coal still accounted for roughly 20 percent of the country’s generation in 2022.   

About 70 percent of US coal is transported at least part of the way by trains. The rail infrastructure to transport coal from the Powder River Basin in Montana and Wyoming–the country’s primary coal source–was proven to be vulnerable to extreme floods in the spring of 2011, and even more extreme floods in the spring of 2019. The 2019 floods’ disruptions of coal shipments to power plants via rail persisted for months and into the summertime, also affecting river shipments of coal by barge. In June 2019, hundreds of barges were stalled in the Mississippi River, through which millions of tons of the fossil fuel are normally transported. 

Power plants – Power plants themselves can also be at risk of flooding, since most of them are sited near a source of water that is used to create steam to spin the plants’ turbines, and conversely, low water levels can constrain hydropower as seen in Western Canada hydropower drought during recent reservoir shortfalls. Most US fossil fuel generating capacity from sources like methane gas, which recently set natural gas power records across the grid, and coal utilizes steam to generate electricity. 

However, much of the attention paid to the flood risk of power plant sites has centered on nuclear plants, a key source of low-carbon electricity discussed in IAEA low-carbon electricity lessons that also require a water source for the creation of steam, as well as for keeping the plant cool in an emergency. To name a notable flood example here in the United States–both visually and substantively–in 2011, the Fort Calhoun nuclear plant in Nebraska was completely surrounded by water due to late-spring flooding along the Missouri River. This sparked a lot of concerns because it was just a few months after the March 2011 meltdown of the Fukushima Daiichi nuclear plant in Japan. The public was thankfully not harmed by the Nebraska incident, but this was unfortunately not an isolated incident in terms of flood risks posed to the US nuclear power fleet. 

 

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Electricity Market Headed for a Reshuffle as Province Vows Overhaul

Alberta Electricity Market Overhaul will add renewables like wind and solar, curb price volatility tied to natural gas, boost competition, and reward energy efficiency, while safeguarding grid reliability and investor confidence through a transition roadmap.

 

Key Points

Alberta's 2027 market redesign adds renewables, boosts competition, and cuts volatility to protect reliability.

✅ Integrates wind and solar to meet climate and affordability goals.

✅ Increases competition and efficiency; reduces price volatility.

✅ Plans transition measures to maintain reliability and investment.

 

Alberta's electricity market is on the precipice of a significant transformation. The province, long reliant on fossil fuels for power generation, has committed to a market overhaul by 2027. This ambitious plan promises to shake up the current system, but industry players are wary of a lengthy period of uncertainty that could stifle much-needed investment in the sector.

The impetus for change stems from a confluence of factors. Soaring energy bills for consumers, reflecting rising electricity prices across the province, coupled with concerns about Alberta's environmental footprint, have pressured the government to seek a more sustainable and cost-effective electricity system. The current market, heavily influenced by natural gas prices, has been criticized for volatility and a lack of incentive for renewable energy development.

The details of the new electricity market design are still being formulated. However, the government has outlined some key objectives. One priority is to incorporate more renewable energy sources like wind and solar power into the grid. This aligns with Alberta's climate change goals and could lead to cleaner electricity generation, supporting the province's path to clean electricity in the coming years.

Another objective is to introduce more competition within the market. The current system is dominated by a few large players, and the government hopes increased competition will drive down prices for consumers, as the market needs more competition to function efficiently.

While the potential benefits of the overhaul are undeniable, industry leaders are apprehensive about the transition period, with a Calgary retailer urging the government to scrap the overhaul amid uncertainty. The lack of clarity surrounding the new market design creates uncertainty for power companies. This could discourage investment in new generation facilities, both renewable and traditional, potentially leading to supply shortages in the future.

John Kousinioris, CEO of TransAlta, a major Alberta power generator, expressed these concerns. "We need a clear roadmap for the future," he stated. "Uncertainty makes it difficult to justify significant investments in new power plants, which are essential to ensure a reliable electricity supply for Albertans."

The government acknowledges the need to minimize disruption during the transition. They have promised to engage in consultations with industry stakeholders throughout the redesign process, as the province changes how it produces and pays for electricity to support long-term stability. Additionally, measures may be implemented to ensure a smooth transition and provide some level of certainty for investors.

The success of Alberta's electricity market overhaul will depend on several factors. Striking a balance between environmental sustainability, affordability, and energy security will be crucial. The government must design a system that incentivizes investment in new, cleaner power generation while maintaining reliable electricity supply at a reasonable cost for consumers.

The role of natural gas, a dominant player in Alberta's current electricity mix, is another point of contention. While the government aims to incorporate more renewables, natural gas is likely to remain a part of the equation for some time. Determining the appropriate role for natural gas in the future market will be a critical decision.

The upcoming years will be a period of significant change for Alberta's electricity market. The province's commitment to a cleaner and more competitive system holds promise, but navigating the transition effectively will be a complex challenge. Open communication, collaboration between stakeholders, and a well-defined roadmap for the future will be essential for ensuring a successful electricity market overhaul and a brighter energy future for Alberta.

 

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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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