Utility defends transmission line at hearings

Germany renewable energy milestone 2019 saw wind, solar, hydropower, and biomass outproduce coal and nuclear, as low gas prices and high CO2 costs under the EU ETS reshaped the electricity mix, per Fraunhofer ISE.

Key Points

It marks H1 2019 when renewables supplied 47.3% of Germany's electricity, surpassing coal and nuclear.

✅ Driven by high CO2 prices and cheap natural gas

✅ Wind and solar output rose; coal generation declined sharply

✅ Flexible gas plants outcompeted inflexible coal units

In Lippendorf, Saxony, the energy supplier EnBW is temporarily taking part of a coal-fired power plant offline. Not because someone ordered it — it simply wasn't paying off. Gas prices are low, CO2 prices are high, and with many hours of sunshine and wind, renewable methods are producing a great deal of electricity as part of Germany's energy transition now reshaping operations. And in the first half of the year there was plenty of sun and wind.

The result was a six-month period in which renewable energy sources, a trend echoed by the EU wind and solar record across the bloc, produced more electricity than coal and nuclear power plants together. For the first time 47.3% of the electricity consumers used came from renewable sources, while 43.4% came from coal-fired and nuclear power plants.

In addition to solar and wind power, renewable sources also include hydropower and biomass. Gas supplied 9.3%, reflecting how renewables are crowding out gas across European power markets, while the remaining 0.4% came from other sources, such as oil, according to figures published by the Fraunhofer Institute for Solar Energy Systems in July.

Fabian Hein from the think tank Agora Energiewende stresses that the situation is only a snapshot in time, with grid expansion woes still shaping outcomes. For example, the first half of 2019 was particularly windy and wind power production rose by around 20% compared to the first half of 2018.

Electricity production from solar panels rose by 6%, natural gas by 10%, while the share of nuclear power in German electricity consumption has remained virtually unchanged despite a nuclear option debate in climate policy.

Coal, on the other hand, declined. Black coal energy production fell by 30% compared to the first half of 2018, lignite fell by 20%. Some coal-fired power plants were even taken off the grid, even as coal still provides about a third of Germany's electricity. It is difficult to say whether this was an effect of the current market situation or whether this is simply part of long-term planning, says Hein.

Activists storm German mine in anti-coal protest

It is clear, however, that an increased CO2 price has made the ongoing generation of electricity from coal more expensive. Gas-fired power plants also emit CO2, but less than coal-fired power plants. They are also more efficient and that's why gas-fired power plants are not so strongly affected by the CO2 price

The price is determined at a European level and covers power plants and energy intensive industries in Europe. Other areas, such as heating or transport are not covered by the CO2 price scheme. Since a reform of CO2 emissions trading in 2017, the price has risen sharply. Whereas in September 2016 it was just over €5 ($5.6), by the end of June 2019 it had climbed to over €26.

Ups and downs

Gas as a raw material is generally more expensive than coal. But coal-fired power plants are more expensive to build. This is why operators want to run them continuously. In times of high demand, and therefore high prices, gas-fired power plants are generally started up, as seen when European power demand hit records during recent heatwaves, since it is worth it at these times.

Gas-fired power plants can be flexibly ramped up and down. Coal-fired power plants take 11 hours or longer to get going. That's why they can't be switched on quickly for short periods when prices are high, like gas-fired power plants. In the first half of the year, however, coal-fired power plants were also ramped up and down more often because it was not always worthwhile to let the power plant run around the clock.

Because gas prices were particularly low in the first half of 2019, some gas-fired power plants were more profitable than coal-fired plants. On June 29, 2019, the gas price at the Dutch trading point TTF was around €10 per megawatt hour. A year earlier, it had been almost €20. This is partly due to the relatively mild winter, as there is still a lot of gas in reserve, confirmed a spokesman for the Federal Association of the Energy and Water Industries (BDEW). There are also several new export terminals for liquefied natural gas. Additionally, weaker growth and trade wars are slowing demand for gas. A lot of gas comes to Europe, where prices are still comparatively high, reported the Handelsblatt newspaper.

The increase in wind and solar power and the decline in nuclear power have also reduced CO2 emissions. In the first half of 2019, electricity generation emitted around 15% less CO2 than in the same period last year, reported BDEW. However, the association demands that the further expansion of renewable energies should not be hampered. The target of 65% renewable energy can only be achieved if the further expansion of renewable energy sources is accelerated.

Related News

• Electricity Forum News

• Power Generation News

U.S. Electricity Trade by State, 2013-2017 highlights EIA grid patterns, interstate imports and exports, cross-border flows with Canada and Mexico, net exporters and importers, and market regions like ISOs and RTOs shaping consumption and generation.

Key Points

Brief EIA overview of interstate and cross-border power flows, ranking top net importers and exporters.

✅ Pennsylvania was the largest net exporter, averaging 59 million MWh.

✅ California was the largest net importer, averaging 77 million MWh.

✅ Top cross-border: NY, CA, VT, MN, MI imports; WA, TX, CA, NY, MT exports.

According to the U.S. Energy Information Administration (EIA) State Electricity Profiles, from 2013 to 2017, Pennsylvania was the largest net exporter of electricity, while California was the largest net importer.

Pennsylvania exported an annual average of 59 million megawatt-hours (MWh), while California imported an average of 77 million MWh annually.

Based on the share of total consumption in each state, the District of Columbia, Maryland, Massachusetts, Idaho and Delaware were the five largest power-importing states between 2013 and 2017, highlighting how some clean states import 'dirty' electricity as consumption outpaces local generation. Wyoming, West Virginia, North Dakota, Montana and New Hampshire were the five largest power-exporting states. Wyoming and West Virginia were net power exporting states between 2013 and 2017.

New York, California, Vermont, Minnesota and Michigan imported the most electricity from Canada or Mexico on average from 2013 to 2017, reflecting the U.S. look to Canada for green power during that period. Similarly, Washington, Texas, California, New York, and Montana exported the most electricity to Canada or Mexico, on average, during the same period.

Electricity routinely flows among the Lower 48 states and, to a lesser extent, between the United States and Canada and Mexico. From 2013 to 2017, Pennsylvania was the largest net exporter of electricity, sending an annual average of 59 million megawatthours (MWh) outside the state. California was the largest net importer, receiving an average of 77 million MWh annually.

Based on the share of total consumption within each state, the District of Columbia, Maryland, Massachusetts, Idaho, and Delaware were the five largest power-importing states between 2013 and 2017. Wyoming, West Virginia, North Dakota, Montana, and New Hampshire were the five largest power-exporting states. States with major population centers and relatively less generating capacity within their state boundaries tend to have higher ratios of net electricity imports to total electricity consumption, as utilities devote more to electricity delivery than to power production in many markets.

Wyoming and West Virginia were net power exporting states (they exported more power to other states than they consumed) between 2013 and 2017. Customers residing in these two states are not necessarily at an economic disadvantage or advantage compared with customers in neighboring states when considering their electricity bills and fees and market dynamics. However, large amounts of power trading may affect a state’s revenue derived from power generation.

Some states also import and export electricity outside the United States to Canada or Mexico, even as Canada's electricity exports face trade tensions today. New York, California, Vermont, Minnesota, and Michigan are the five states that imported the most electricity from Canada or Mexico on average from 2013 through 2017. Similarly, Washington, Texas (where electricity production and consumption lead the nation), California, New York, and Montana are the five states that exported the most electricity to Canada or Mexico, on average, for the same period.

Many states within the continental United States fall within integrated market regions, referred to as independent system operators or regional transmission organizations. These integrated market regions allow electricity to flow freely between states or parts of states within their boundaries.

EIA’s State Electricity Profiles provide details about the supply and disposition of electricity for each state, including net trade with other states and international imports and exports, and help you understand where your electricity comes from more clearly.

Related News

• Electricity Forum News

• Energy Policy News

Germany net-zero roadmap charts coal phase-out by 2030, rapid renewables buildout, energy storage, and hydrogen-ready gas engines to cut emissions and lower LCOE by 34%, unlocking a resilient, flexible, low-cost power system by 2040.

Key Points

Plan to phase out coal by 2030 and gas by 2040, scaling renewables, storage, and hydrogen to cut LCOE and emissions.

✅ Coal out by 2030; gas phased 2040 with hydrogen-ready engines

✅ Add 19 GW/yr renewables; 30 GW storage by 2040

✅ 34% lower LCOE, 23% fewer emissions vs slower path

Germany can achieve significant reductions in emissions and the cost of electricity by phasing out coal in 2030 under its coal phase-out plan but must have a clear plan to ramp up renewables and pivot to sustainable fuels in order to achieve net-zero, according to a new whitepaper from Wartsila.

The modelling, published in Wärtsilä new white paper ‘Achieving net-zero power system in Germany by 2040’, compares the current plan to phase out coal by 2030 and gas by 2045 with an accelerated plan, where gas is phased out by 2040. By accelerating the path to net-zero, Germany can unlock a 34% reduction in the levelised cost of energy, as well as a 23% reduction in the total emissions, or 562 million tonnes of carbon dioxide in real terms.

The modelling offers a clear, three-step roadmap to achieve net-zero: rapidly increase renewables, energy storage and begin future-proofing gas engines in this decade; phase out coal by 2030; and phase out gas by 2040, converting remaining engines to run on sustainable fuels.

The greatest rewards are available if Germany front-loads decarbonisation. This can be done by rapidly increasing renewable capacity, adding 19 GW of wind and solar PV capacity per year. It must also add a total of 30GW of energy storage by 2040.

Håkan Agnevall, President and CEO of Wärtsilä Corporation said: “Germany stands on the precipice of a new, sustainable energy era. The new Federal Government has indicated its plans to consign coal to history by 2030. However, this is only step one. Our white paper demonstrates the need to implement a three-step roadmap to achieve net-zero. It is time to put a deadline on fossil fuels and create a clear plan to transition to sustainable fuels.”

While a rapid coal phase-out has been at the centre of recent climate policy debates, including the ongoing nuclear debate over Germany’s energy mix, the pathway to net-zero is less clear. Wärtsilä’s modelling shows that gas engines should be used to accelerate the transition by providing a short-term bridge to enable net zero and navigate the energy transition while balancing the intermittency of renewables until sustainable fuels are available at scale.

However, if Germany follows the slower pathway and reaches net-zero by 2045, it risks becoming reliant on gas as baseload power for much of the 2030s amid renewable expansion challenges that persist, potentially harming its ability to reach its climate goals. 

Creating the infrastructure to pivot to sustainable fuels is one of the greatest challenges facing the German system. The ability to convert existing capacity to run purely on hydrogen via hydrogen-ready power plants will be key to reaching net-zero by 2040 and unlocking the significant system-wide benefits on offer.

Jan Andersson, General Manager of Market Development in Germany, Wärtsilä Energy added: “To reach the 2040 target and unlock the greatest benefits, the most important thing that Germany can do is build renewables now. 19 GW is an ambitious target, but Germany can do it. History shows us that Germany has been able to achieve high levels of renewable buildout in previous years. It must now reach those levels consistently.

“Creating a clear plan which sets out the steps to net zero is essential. Renewable energy is inherently intermittent, so flexible energy capacity will play a vital role. While batteries provide effective short-term flexibility, gas is currently the only practical long-term option. If Germany is to unlock the greatest benefits from decarbonisation, it must have a clear plan to integrate sustainable fuel. From 2030, all new thermal capacity must run solely on hydrogen.”

Analysis of the last decade demonstrates that the rapid expansion of renewable energy is possible, and that renewables overtook coal and nuclear in generation. Previously, Germany has built large amounts of renewable capacity, including 8GW of solar PV in 2010 and 2011, 5.3 GW of onshore wind in 2017, and 2.5 GW of offshore wind in 2015.

The significant reductions in the cost of electricity demonstrated in the modelling are driven by the fact that renewables are far cheaper to run than coal or gas plants, even as coal still provides about a third of electricity in Germany. The initial capital investment is far outweighed by the ongoing operational expense of fossil fuel-based power.

As well as reducing emissions and costs, Germany’s rapid path to net-zero can also unlock a series of additional benefits. If coal is phased out by 2030 but capacity is not replaced by high levels of renewable energy, Germany risks becoming a significant energy importer, peaking at 162 TWh in 2035. The accelerated pathway would reduce imports by a third.

Likewise, more renewable energy will help to electrify district heating, meaning Germany can move away from carbon-intensive fuels sooner. If Germany follows the accelerated path, 57% of Germany’s heating could be electrified in 2045, compared to 10% under the slower plan.

Jan Andersson concluded: “The opportunities on offer are vast. Germany can provide the blueprint for net zero and galvanise an entire continent. Now is the time for the new government to seize the initiative.”

Related News

• Electricity Forum News

• Power Generation News

Nuclear decarbonization leverages low-carbon electricity, process heat, and hydrogen from advanced reactors and SMRs to electrify industry, buildings, and transport, supporting net-zero strategies and grid flexibility alongside renewables with dispatchable baseload capacity.

Key Points

Nuclear decarbonization uses reactors to supply low-carbon power, heat, and hydrogen, cutting emissions across industry.

✅ Advanced reactors and SMRs enable high-temperature process heat

✅ Nuclear-powered electrolysis and HTSE produce low-carbon hydrogen

✅ District heating from reactors reduces pollution and coal use

By Dr Henri Paillere, Head of the Planning and Economics Studies Section of the IAEA

Decarbonising the power sector will not be sufficient to achieving net-zero emissions, with assessments indicating nuclear may be essential across sectors. We also need to decarbonise the non-power sectors - transport, buildings and industry - which represent 60% of emissions from the energy sector today. The way to do that is: electrification with low-carbon electricity as much as possible; using low-carbon heat sources; and using low-carbon fuels, including hydrogen, produced from clean electricity.
The International Energy Agency (IEA) says that: 'Almost half of the emissions reductions needed to reach net zero by 2050 will need to come from technologies that have not reached the market today.' So there is a need to innovate and push the research, development and deployment of technologies. That includes nuclear beyond electricity.

Today, most of the scenario projections see nuclear's role ONLY in the power sector, despite ongoing debates over whether nuclear power is in decline globally, but increased electrification will require more low-carbon electricity, so potentially more nuclear. Nuclear energy is also a source of low-carbon heat, and could also be used to produce low-carbon fuels such as hydrogen. This is a virtually untapped potential.

There is an opportunity for the nuclear energy sector - from advanced reactors, next-gen nuclear small modular reactors, and non-power applications - but it requires a level playing field, not only in terms of financing today's technologies, but also in terms of promoting innovation and supporting research up to market deployment. And of course technology readiness and economics will be key to their success.

On process heat and district heating, I would draw attention to the fact there have been decades of experience in nuclear district heating. Not well spread, but experience nonetheless, in Russia, Hungary and Switzerland. Last year, we had two new projects. One floating nuclear power plant in Russia (Akademik Lomonosov), which provides not only electricity but district heating to the region of Pevek where it is connected. And in China, the Haiyang nuclear power plant (AP1000 technology) has started delivering commercial district heating. In China, there is an additional motivation to reducing emissions, namely to cut air pollution because in northern China a lot of the heating in winter is provided by coal-fired boilers. By going nuclear with district heating they are therefore cutting down on this pollution and helping with reducing carbon emissions as well. And Poland is looking at high-temperature reactors to replace its fleet of coal-fired boilers and so that's a technology that could also be a game-changer on the industry side.

There have also been decades of research into the production of hydrogen using nuclear energy, but no real deployment. Now, from a climate point of view, there is a clear drive to find substitute fuels for the hydrocarbon fuels that we use today, and multiple new nuclear stations are seen by industry leaders as necessary to meet net-zero targets. In the near term, we will be able to produce hydrogen with electrolysis using low-carbon electricity, from renewables and nuclear. But the cheapest source of low-carbon power is from the long-term operation of existing nuclear power plants which, combined with their high capacity factors, can give the cheapest low-carbon hydrogen of all.

In the mid to long term, there is research on-going with processes that are more efficient than low-temperature electrolysis, which is high temperature steam electrolysis or thermal splitting of water. These may offer higher efficiencies and effectiveness but they also require advanced reactors that are still under development. Demonstration projects are being considered in several countries and we at the IAEA are developing a publication that looks into the business opportunities for nuclear production of hydrogen from existing reactors. In some countries, there is a need to boost the economics of the existing fleet, especially in the electricity systems where you have low or even negative market prices for electricity. So, we are looking at other products that have higher values to improve the competitiveness of existing nuclear power plants.

The future means not only looking at electricity, but also at industry and transport, and so integrated energy systems. Electricity will be the main workhorse of our global decarbonisation effort, but through heat and hydrogen. How you model this is the object of a lot of research work being done by different institutes and we at the IAEA are developing some modelling capabilities with the objective of optimising low-carbon emissions and overall costs.

This is just a picture of what the future might look like: a low-carbon power system with nuclear lightwater reactors (large reactors, small modular reactors and fast reactors) drawing on the green industrial revolution reactor waves in planning; solar, wind, anything that produces low-carbon electricity that can be used to electrify industry, transport, and the heating and cooling of buildings. But we know there is a need for high-temperature process steam that electricity cannot bring but which can be delivered directly by high-temperature reactors. And there are a number of ways of producing low-carbon hydrogen. The beauty of hydrogen is that it can be stored and it could possibly be injected into gas networks that could be run in the future on 100% hydrogen, and this could be converted back into electricity.

So, for decarbonising power, there are many options - nuclear, hydro, variable renewables, with renewables poised to surpass coal in global generation, and fossil with carbon capture and storage - and it's up to countries and industries to invest in the ones they prefer. We find that nuclear can actually reduce the overall cost of systems due to its dispatchability and the fact that variable renewables have a cost because of their intermittency. There is a need for appropriate market designs and the role of governments to encourage investments in nuclear.

Decarbonising other sectors will be as important as decarbonising electricity, from ways to produce low-carbon heat and low-carbon hydrogen. It's not so obvious who will be the clear winners, but I would say that since nuclear can produce all three low-carbon vectors - electricity, heat and hydrogen - it should have the advantage.
We at the IAEA will be organising a webinar next month with the IEA looking at long-term nuclear projections in a net-zero world, building on IAEA analysis on COVID-19 and low-carbon electricity insights. That will be our contribution from the point of view of nuclear to the IEA's special report on roadmaps to net zero that it will publish in May.

Related News

• Electricity Forum News

• Power Generation News

European Green Deal Electrification accelerates decarbonization via renewables, electric vehicles, heat pumps, and clean industry, backed by sustainable finance, EIB green lending, just transition funds, and energy taxation reform to phase out fossil fuels.

Key Points

An EU plan to replace fossil fuels with renewable electricity in transport, buildings, and industry, supported by green finance.

✅ Doubles electricity's share to cut CO2 and phase out fossil fuels.

✅ Drives EVs, heat pumps, and electrified industry via renewables.

✅ Funded by EIB lending, EU budget, and just transition support.

The European Union is preparing an ambitious plan to completely decarbonize by 2050. Increasing the share of electricity in Europe’s energy system – electricity that will increasingly come from renewable sources - will be at the center of this strategy, aligning with the broader global energy transition under way, the new head of the European Commission’s energy department said yesterday.

This will mean more electric cars, electric heating and electric industry. The idea is that fossil fuels should no longer be a primary energy source, heating homes, warming food or powering cars. In the medium term they should only be used to generate electricity, a shift mirrored by New Zealand's electricity shift efforts, which then powers these things, resulting in less CO2 emissions.

“First assessments show we need to double the share of electricity in energy consumption by 2050,” Ditte Juul-Jørgensen said at an event in Brussels this week, a goal echoed by recent calls to double investment in power systems from world leaders. “We’ve already seen an increase in the last decade, but we need to go further”.

Juul-Jørgensen, who started in her job as director-general of the commission’s energy department in August, has come to the role at a pivotal time for energy. The 2050 decarbonization proposal from the Commission, the EU’s executive branch, is expected to be approved next month by EU national leaders. A veto from Poland that has blocked adoption until now is likely to be overcome if Poland and other Eastern European countries are offered financial assistance from a “just transition fund”, according to EU sources.

Ursula von der Leyen, the incoming President of the Commission, has promised to unveil a “European Green Deal” in her first 100 days in office designed to get the EU to its 2050 goal. Juul-Jørgensen will be working with the incoming EU Energy Commissioner, Kadri Simson, on designing this complex strategy. The overall aim will be to phase out fossil fuels, and increase the use of electricity from green sources, amid trends like oil majors pivoting to electric across Europe today.

“This will be about how do we best make use of electricity to feed into other sectors,” Juul-Jørgensen said. “We need to think about transforming it into other sources, and how to best transport it.”

“But the biggest challenge from what I see today is that of investment and finance - the changes we have to make are very significant.”

Financing problems

The Commission is going to try to tackle the challenges of financing the energy transition with two tools: dedicated climate funding in the EU budget, and dedicated climate lending from the European Investment Bank.

“The EIB will play an increasing role in future. We hope to see agreement [with the EIB board] on that in the coming months so there’s a clear operator in the EIB to support the green transition. We’re looking at something around €400 billion a year.”

The Commission’s proposed dedicated climate spending in the next seven-year budget must still be approved by the 28 EU national governments. Juul-Jørgensen said there is unanimous agreement on the amount: 25% of the budget. But there is disagreement about how to determine what is green spending.

“A lot of work has been ongoing to ensure that when it comes to counting it reflects the reality of the investments,” she said. “We’re working on the taxonomy on sustainable finance - internally identifying sectors contributing to overall climate objectives.”

Electricity pact

Juul-Jørgensen was speaking at an event organized by the the Electrification Alliance, a pact between nine industry organizations to lobby for electricity to be put at the heart of the European green deal. They signed a declaration at the event calling for a variety of measures to be included in the green deal, reflecting debates over a fully renewable grid by 2030 in other jurisdictions, including a change to the EU’s energy taxation regime which incentivizes a switch from fossil fuel to electricity consumption.

“Electrification is the most important solution to turn the vision of a fossil-free Europe into reality,” said Laurence Tubiana, CEO of the European Climate Foundation, one of the signatories, and co-architect of the Paris Agreement.

“We are determined to deliver, but we must be mindful of the different starting points and secure sufficient financing to ensure a fair transition”, said Magnus Hall, President of electricity industry association Eurelectric, another signatory.

The energy taxation issue has been particularly tricky for the EU, since any change in taxation rules requires the unanimous consent of all 28 EU countries. But experts say that current taxation structures are subsidizing fossil fuels and punishing electricity, as recent UK net zero policy changes illustrate, and unless this is changed the European Green Deal can have little effect.

“Yes this issue will be addressed in the incoming commission once it takes up its function,” Juul-Jørgensen said in response to an audience question. “We all know the challenge - the unanimity requirement in the Council - and so I hope that member states will agree to the direction of work and the need to address energy taxation systems to make sure they’re consistent with the targets we’ve set ourselves.”

But some are concerned that the transformation envisioned by the green deal will have negative impacts on some of the most vulnerable members of society, including those who work in the fossil fuel sector.

This week the Centre on Regulation in Europe sent an open letter to Frans Timmermans, the Commission Vice President in charge of climate, warning that they need to be mindful of distributional effects. These worries have been heightened by the yellow vest protests in France, which were sparked by French President Emmanuel Macron’s attempt to increase fuel taxes for non-electric cars.

“The effectiveness of climate action and sustainability policies will be challenged by increasing social and political pressures,” wrote Máximo Miccinilli, the center’s director for energy. “If not properly addressed, those will enhance further populist movements that undermine trust in governance and in the public institutions.”

Miccinilli suggests that more research be done into identifying, quantifying and addressing distributional effects before new policies are put in place to phase out fossil fuels. He proposes launching a new European Observatory for Distributional Effects of the Energy Transition to deal with this.

EU national leaders are expected to vote on the 2050 decarbonization target, building on member-state plans such as Spain's 100% renewable electricity goal by mid-century, at a summit in Brussels on December 12, and Von der Leyen will likely unveil her European Green Deal in March.

Related News

• Electricity Forum News

• Climate Change News

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.

Related News

• Electricity Forum News

• Power Generation News