NREL: Envisioning Net-Zero Emission Energy Systems


NREL researchers contribute to a major journal article describing pathways to net-zero emissions for particularly difficult-to-decarbonize economic sectors

As global energy consumption continues to grow—by some projections, more than doubling by 2100—all sectors of the economy will need to find ways to drastically reduce their carbon dioxide emissions if average global temperatures are to be held under international climate targets. Two NREL authors contributed to a recently published article in Science that examined potential barriers and opportunities to decarbonizing certain energy systems that are essential to modern civilization but remain stubbornly reliant on carbon-emitting processes.

Difficult to Decarbonize Energy Sectors Contribute 27% of Carbon Emissions

Many sectors of the economy, such as light-duty transportation, heating, cooling, and lighting, could be straightforward to decarbonize through electrification and use of low- or net-zero-emitting energy sources. However, some energy uses, such as aviation, long-distance transport and shipping, steel and cement production, and a highly reliable electricity supply, will be more difficult to decarbonize. Together, these sectors contribute 27% of global carbon emissions today. With global demand for many of these sectors growing rapidly, solutions are urgently needed, the article’s authors write.

“The timeframes and economic costs of any energy transition are enormous. Most technologies installed today will have a lifetime of perhaps 30 to 50 years and the transition from research to actual deployment can also be quite lengthy,” said Bri-Mathias Hodge, an author on the paper and manager of the Power Systems Design and Studies Group at NREL. “Because of this we need to be able to identify the most pertinent issues that will need to be solved fairly far in the future and get started now, before we find ourselves heavily invested in even more carbon-intensive, long-term infrastructure.”

Diverse Expert Perspectives Informed Study

Discussion of the article’s underlying issues began at an Aspen Global Change Institute meeting in July 2016. “The diversity and depth of expertise at the workshop—and contributing to the paper—were outstanding,” said Doug Arent, the other NREL researcher to contribute to the paper and deputy associate lab director for Scientific Computing and Energy Analysis. “It was great to hear the different perspectives and learn about new areas that are related to our work at NREL, but that I don’t get to hear about every day at NREL,” added Hodge.

Considering demographic trends, institutional barriers, and economic and technological constraints, the group of researchers concluded that future net-zero emission systems will depend critically on integration of now-discrete energy industries. Although a range of existing low or net zero emitting energy technologies exist for these energy services, they may only be able to fully meet future energy demands through cross-sector coordination. Collaboration could speed research and development of new technologies and coordinating operations across sectors could better utilize capital-intensive assets, create broader markets, and streamline regulations.

Research Should Pursue Technologies and Integration to Decarbonize These Sectors

The article’s authors suggest two broad research thrusts: research in technologies and processes that could decarbonize these energy services, and research in systems integration to provide these energy services in a more reliable and cost-effective way.

The Science article concludes by stating, “if we want to achieve a robust, reliable, affordable, net-zero emissions energy system later this century, we must be researching, developing, demonstrating, and deploying those candidate technologies now.”

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Long-lasting solar cells from and “unexpected gray area” … U of Wisconsin-Madison Make Surprising Discovery


anunexpectedUW-Madison engineers found a way to dramatically extend the lifespan of solar energy-harvesting devices, which use energy from sunlight to generate hydrogen from water. Credit: iStock

University of Wisconsin-Madison materials engineers have made a surprising discovery that could dramatically improve the lifetime of solar energy harvesting devices.

The findings allowed them to achieve the longest-ever lifetime for a key component of some types of photovoltaic cells called the photoelectrochemical electrode, which uses sunlight to split water into its constituent parts of hydrogen and oxygen.

In a paper published July 24, 2018, in the research journal Nano Letters, a team led by UW-Madison materials science and engineering Ph.D. student Yanhao Yu and his advisor, Professor Xudong Wang, described a strategy that extended the lifetime of a photochemical electrode to a whopping 500 hours—more than five times (5X) the typical 80-hour lifespan.

Usually, these types of electrodes are made of silicon, which splits water well, but is highly unstable and quickly degrades when it comes into contact with corrosive conditions. To protect these electrodes, engineers often thinly coat their surfaces.

It’s a tactic that only delays their eventual breakdown—sometimes after a few days and sometimes within hours.

“Performance varies widely and nobody really knows why. It’s a big question,” says Wang, a professor of materials science and engineering at UW-Madison.

Intriguingly, the researchers didn’t make any changes to the coating material. Rather, they boosted the electrode’s lifetime by applying an even thinner coating of  than usual.

In other words, less really was more!

Key to this exceptional performance was the team’s discovery about the atomic structure of titanium dioxide thin , which the researchers create using a technique called .

Previously, researchers believed that the atoms in titanium dioxide thin films adopted one of two conformations—either scrambled and disordered in a state referred to as “amorphous,” or locked into a regularly repeating and predictable arrangement called the crystalline form.

Crucially, researchers were certain that all the atoms in a given thin film behaved the same way. Crystalline or amorphous. Black or white. No in-between.

What Wang colleagues found, however, is a gray area: They saw that small pockets of an in-between state persisted in the final coatings—the  in these areas was neither amorphous nor crystalline. These intermediates have never been observed before.

“This is a cutting edge of materials synthesis science,” says Wang. “We’re thinking that crystallization is not as straightforward as people believe.”

Observing those intermediates was no easy feat. Enter Wang’s colleague Paul Voyles, a microscopy expert who leveraged UW-Madison’s unique facilities to perform sophisticated scanning transmission electron microscopy measurements, enabling him to detect the tiny structures.

From there, the researchers determined those intermediates lowered the lifetime of titanium dioxide thin films by leading to spikes of electronic current that ate tiny holes in the protective coatings.

Eliminating those intermediates—thus extending the ‘s lifetime—is as simple as using a thinner film.

Thinner films make it more difficult for intermediates to form within the film, so by reducing the thickness by three quarters (from 10 nanometers to 2.5), the researchers created coatings that lasted more than five times longer than traditional coatings.

And now that they’ve discovered these peculiar structures, the researchers want to learn more about how they form and influence amorphous film properties. That’s knowledge that could reveal other strategies for eliminating them—which not only could improve performance, says Wang, but also open new opportunities in other energy-related systems, such as catalysts, solar cells and batteries.

“These intermediates could be something very important that has been overlooked,” says Wang. “They could be a critical aspect that controls properties of the film.”

 Explore further: Discovery brings renewable fuel production one step closer to reality

More information: Yanhao Yu et al. Metastable Intermediates in Amorphous Titanium Oxide: A Hidden Role Leading to Ultra-Stable Photoanode Protection, Nano Letters (2018). DOI: 10.1021/acs.nanolett.8b02559

 

Is Reliable Energy Storage (and Markets) On The Horizon?


Green and renewable energy markets are bringing power to millions with virtually no adverse environmental impacts, but before we can count on renewables for widespread reliability, one critical innovation must arrive: storage.

image-223

PetersenDean Inc. employees install solar panels on the roof of a home in Lafayette, California, U.S., Photographer: David Paul Morris/Bloomberg

On Tuesday, May 15, 2018. California became the first state in the U.S. to require solar panels on almost all new homes. Most new units built after Jan. 1, 2020, will be required to include solar systems as part of the standards adopted by the California Energy Commission.

While hydroelectric and some other renewable sources can generate power around the clock, solar and wind energy are irregular and not necessarily consistent sources for 24/7 projections.

Storms and darkness disrupt solar farms, while dozens of meteorological phenomena can impact wind farms. Because these sources have natural peaks, they cannot be made to align with consumer power demand without effective storage. Solar and wind may be able to meet demand during the day or a short period, but when energy is high and demand is low, the power generated must either be used or wasted if it cannot be stored in some type of battery.

According to projections from GTM Research and the Energy Storage Association, the energy storage market is expected to grow 17x from 2017 and 2023. This projection accounts for private and commercial deployment of storage capacity, including impacts from government policies like California’s solar panel mandate.

During the same interval, the energy storage market is expected to grow 14x in dollar value.

The exact type of storage deployments in these projections varies. Recent innovations have included advancements in traditional battery technology as well as battery alternatives like liquid air storage.

In New York, one project included a megawatt scaled lithium-ion battery storage system to replace lead acid schemes. The liquid air storage, however, uses excess energy to cool air in pressurized chambers until it is liquid. Rather than storing electrical or chemical energy like a battery, the process stores potential energy.

When demand arises, the liquefied air is allowed to rapidly heat and expand, turning turbines to generate electricity.

Meanwhile, Tesla has added nearly a third of the annual global energy storage deployments since 2015. Leading the charge with low-cost lithium-ion batteries, Telsla and other innovators are bringing global capacity up quickly.

These energy storage devices are versatile, capable of storing energy from any source–fossil fuel or renewable– and in any place–private homes or industrial operations.

With battery costs continuing to decrease and battery alternatives coming into the fore, projections of storage capacity are indeed quite possible. Assuming the electric industry can indeed upgrade its current infrastructure, new grid connections means that energy will be able to be shared more than ever, perhaps even traveling far distances during peak or be stored for non-peak use anywhere on the grid.

When storage costs and capacity align with market incentives, we may just see a renewable energy revolution, one that makes distributed generation mainstream for all consumers.

** Contributed from Forbes Energy

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Forbes on Energy: We Don’t Need Solar And Wind To Save The Climate — And It’s A Good Thing, Too


France and Sweden show solar and wind are not needed to [+] Special Contributor, M. Shellenberger

For 30 years, experts have claimed that humankind needs to switch to solar and wind energy to address climate change. But do we really?

Consider the fact that, while no nation has created a near-zero carbon electricity supply out of solar and wind, the only successful efforts to create near-zero carbon electricity supplies didn’t require solar or wind whatsoever.

As such solar and wind aren’t just insufficient, they are also unnecessary for solving climate change.

That turns out to be a good thing.

Sunlight and wind are inherently unreliable and energy-dilute. As such, adding solar panels and wind turbines to the grid in large quantities increases the cost of generating electricity, locks in fossil fuels, and increases the environmental footprint of energy production.

There is a better way. But to understand what it is, we first must understand the modern history of renewable energies.

Renewables Revolution: Always Just Around the Corner

Most people think of solar and wind as new energy sources. In fact, they are two of our oldest.

The predecessor to Stanford University Professor Mark Jacobson, who advocates “100 percent renewables,” is A man named John Etzler.

In 1833, Etzler proposed to build massive solar power plants that used mirrors to concentrate sunlight on boilers, mile-long wind farms, and new dams to store power.

Even electricity-generating solar panels and wind turbines are old. Both date back to the late 1800s.

Throughout the 20th Century, scientists claimed — and the media credulously reported — that solar, wind, and batteries were close to a breakthrough that would allow them to power all of civilization.

Consider these headlines from The New York Times and other major newspapers:

• 1891: “Solar Energy: What the Sun’s Rays Can Do and May Yet Be Able to Do“ — The author notes that while solar energy was not yet economical “…the day is not unlikely to arrive before long…”

• 1923: “World Awaits Big Invention to Meet Needs of Masses “…solar energy may be developed… or tidal energy… or solar energy through the production of fuel.”

• 1931: “Use of Solar Energy Near a Solution.” “Improved Device Held to Rival Hydroelectric Production”

• 1934: “After Coal, The Sun” “…surfaces of copper oxide already available”

• 1935: “New Solar Engine Gives Cheap Power”

• 1939. “M.I.T. Will ‘Store’ Heat of the Sun”

• 1948: “Changing Solar Energy into Fuel “Blocked Out” in GM Laboratory”  “…the most difficult part of the problem is over…”

• 1949: “U.S. Seeks to Harness Sun, May Ask Big Fund, Krug Says”

Reporters were as enthusiastic about renewables in 1930s as they are today.

“It is just possible the world is standing at a turning point,” a New York Times reporter gushed in 1931, “in the evolution of civilization similar to that which followed the invention by James Watt of the steam engine.”

Decade after decade, scientists and journalists re-discovered how much solar energy fell upon the earth.

“Even on such an area as small as Manhattan Island the noontime heat is enough, could it be utilized, to drive all the steam engines in the world,” The Washington Star reported in 1891.

Progress in chemistry and materials sciences was hyped. “Silver Selenide is Key Substance,” The New York Times assured readers.

In 1948, Interior Secretary Krug called for a clean energy moonshot consisting of “hundreds of millions” for solar energy, pointing to its “tremendous potential.”

R&D subsidies for solar began shortly after and solar and wind production subsidies began in earnest in the 1970s.

Solar and wind subsidies increased substantially, and were increased in 2005 and again in 2009 on the basis of a breakthrough being just around the corner.

By 2016, renewables were receiving 94 times more in U.S. subsidies than nuclear and 46 times more than fossil fuels per unit of energy generated.

According to Bloomberg New Energy Finance (BNEF), public and private actors spent $1.1 trillion on solar and over $900 billion on wind between 2007 and 2016.

Global investment in solar and wind hovered at around $300 billion per year between 2010 and 2016.

Did the solar and wind energy revolution arrive?

Judge for yourself: in 2016, solar and wind constituted 1.3 and 3.9 percent of the planet’s electricity, respectively.

Real World Renewables

Are there places in the world where wind and solar have become a significant share of electricity supplies?

The best real-world evidence for wind’s role in decarbonization comes from the nation of Denmark. By 2017, wind and solar had grown to become 48 and 3 percent of Denmark’s electricity.

Does that make Denmark a model?

Not exactly. Denmark has fewer people than Wisconsin, a land area smaller than West Virginia, and an economy smaller than the state of Washington.

Moreover, the reason Denmark was able to deploy so much wind was because it could easily export excess wind electricity to neighboring countries — albeit at a high cost: Denmark today has the most expensive electricity in Europe.

And as one of the world’s largest manufacturers of turbines, Denmark could justify expensive electricity as part of its export strategy.

As for solar, those U.S. states that have deployed the most of it have seen sharp rises in their electricity costs and prices compared to the national average.

As recently as two years ago, some renewable energy advocates held up Germany as a model for the world.

No more. While Germany has deployed some of the most solar and wind in the world, its emissions have been flat for a decade while its electricity has become the second most expensive in Europe.

More recently, Germany has permitted the demolition of old forests, churches, and villages in order to mine and burn coal.

Meanwhile, the two nations whose electricity sectors produce some of the least amount of carbon emissions per capita of any developed nation did so with very little solar and wind: France and Sweden.

Sweden last year generated a whopping 95 percent of its total electricity from zero-carbon sources, with 42 and 41 coming from nuclear and hydroelectric power.

France generated 88 percent of its total electricity from zero-carbon sources, with 72 and 10 coming from nuclear and hydroelectric power.

Other nations like Norway, Brazil, and Costa Rica have almost entirely decarbonized their electricity supplies with the use of hydroelectricity alone.

That being said, hydroelectricity is far less reliable and scalable than nuclear.

Brazil is A case in point. Hydro has fallen from over 90 percent of its electricity 20 years ago to about two-thirds in 2016. Because Brazil failed to grow its nuclear program in the 1990s, it made up for new electricity growth with fossil fuels.

And both Brazil and hydro-heavy California stand as warnings against relying on hydro-electricity in a period of climate change. Both had to use fossil fuels to make up for hydro during recent drought years.

That leaves us with nuclear power as the only truly scalable, reliable, low-carbon energy source proven capable of eliminating carbon emissions from the power sector.

Why This is Good News

The fact that we don’t need renewables to solve climate change is good news for humans and the natural environment.

The dilute nature of water, sunlight, and wind means that up to 5,000 times more land and 10 – 15 times more concrete, cement, steel, and glass, are required than for nuclear plants.

All of that material throughput results in renewables creating large quantities of waste, much of it toxic.

For example, solar panels create 200 – 300 times more hazardous waste than nuclear, with none of it required to be recycled or safely contained outside of the European Union.

Meanwhile, the huge amounts of land required for solar and wind production has had a devastating impact on rare and threatened desert tortoises, bats, and eagles — even when solar and wind are at just a small percentage of electricity supplies.

Does this mean renewables are never desirable?

Not necessarily. Hydroelectric dams remain the way many poor countries gain access to reliable electricity, and both solar and wind might be worthwhile in some circumstances.

But there is nothing in either their history or their physical attributes that suggests solar and wind in particular could or should be the centerpiece of efforts to deal with climate change.

In fact, France demonstrates the costs and consequences of adding solar and wind to an electricity system where decarbonization is nearly complete.

France is already seeing its electricity prices rise as a result of deploying more solar and wind.

Because France lacks Sweden’s hydroelectric potential, it would need to burn far more natural gas (and/or petroleum) in order to integrate significantly more solar and wind.

If France were to reduce the share of its electricity from nuclear from 75 percent to 50 percent — as had been planned — carbon emissions and the cost of electricity would rise.

It is partly for this reason that France’s president recently declared he would not reduce the amount of electricity from nuclear.

Some experts recently pointed out that nuclear plants, like hydroelectric dams, can ramp up and down. France currently does so to balance demand.

But ramping nuclear plants to accommodate intermittent electricity from solar and wind simply adds to the cost of making electricity without delivering fewer emissions or much in the way of cost-savings. That’s because only very small amounts of nuclear fuel and no labor is saved when nuclear plants are ramped down.

Do We Need Solar and Wind to Save Nuclear?

While solar and wind are largely unnecessary at best and counterproductive at worst when it comes to combating climate change, might we need to them in support of a political compromise to prevent nuclear plants from closing?

At least in some circumstances, the answer is yes. Recently in New Jersey, for example, nuclear energy advocates had to accept a subsidy rate 18 to 28 times higher for solar than for nuclear.

The extremely disproportionate subsidy for solar was a compromise in exchange for saving the state’s nuclear plants.

While nuclear enjoys the support of just half of the American people, for example, solar and wind are supported by 70 to 80 percent of them. Thus, in some cases, it might make sense to package nuclear and renewables together.

But we should be honest that such subsidies for solar and wind are policy sweeteners needed to win over powerful financial interests and not good climate policy.

What matters most is that we accept that there are real world physical obstacles to scaling solar and wind.

Consider that the problem of the unreliability of solar has been discussed for as long as there have existed solar panels. During all of that time, solar advocates have waved their hands about potential future solutions.

“Serious problems will, of course, be raised by the fact that sun-power will not be continuous,” wrote a New York Times reporter in 1931. “Whether these will be solved by some sort of storage arrangement or by the operating of photogenerators in conjuction with some other generator cannot be said at present.”

We now know that, in the real world, electricity grid managers cope with the unreliability of solar by firing up petroleum and natural gas generators.

As such —  while there might be good reasons to continue to subsidize the production of solar and wind — their role in locking in fossil fuel generators means that climate change should not be one of them.

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High efficiency solar power conversion allowed by a novel composite material


A composite thin film made of two different inorganic oxide materials significantly improves the performance of solar cells, as recently demonstrated by a joint team of researchers led by Professor Federico Rosei at the Institut national de la recherche scientifique (INRS), and Dr. Riad Nechache from École de technologie supérieure (ÉTS), both in the Montreal Area (Canada).

Following an original device concept, Mr. Joyprokash Chakrabartty, the researchers have developed this new composite thin film material which combines two different crystal phases comprising the atomic elements bismuth, manganese, and oxygen.

The combination of phases with two different compositions optimizes this material’s ability to absorb solar radiation and transform it into electricity. The results are highly promising for the development of future solar technologies, and also potentially useful in other optoelectronic devices.

The results of this research are discussed in an article published in Nature Photonics (“Improved photovoltaic performance from inorganic perovskite oxide thin films with mixed crystal phases”) by researchers and lead author Mr. Joyprokash Chakrabartty.

The key discovery consists in the observation that the composite thin film—barely 110 nanometres thick—absorbs a broader portion of the solar spectrum compared to the wavelengths absorbed in the thin films made of the two individual materials. The interfaces between the two different phases within the composite film play a crucial role in converting more sunlight into electricity. This is a surprising, novel phenomenon in the field of inorganic perovskite oxide-based solar cells.

The composite material leads to a power conversion efficiency of up to 4.2%, which is a record value for this class of materials.

Source: INRS

NREL, University of Washington Scientists Elevate Quantum Dot Solar Cell World Record to 13.4 Percent



Researchers at the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) established a new world efficiency record for quantum dot solar cells, at 13.4 percent.

Colloidal quantum dots are electronic materials and because of their astonishingly small size (typically 3-20 nanometers in dimension) they possess fascinating optical properties. 


Quantum dot solar cells emerged in 2010 as the newest technology on an NREL chart that tracks research efforts to convert sunlight to electricity with increasing efficiency. 

The initial lead sulfide quantum dot solar cells had an efficiency of 2.9 percent. Since then, improvements have pushed that number into double digits for lead sulfide reaching a record of 12 percent set last year by the University of Toronto. 

The improvement from the initial efficiency to the previous record came from better understanding of the connectivity between individual quantum dots, better overall device structures and reducing defects in quantum dots.


 NREL scientists Joey Luther and Erin Sanehira are part of a team that has helped NREL set an efficiency record of 13.4% for a quantum dot solar cell.

The latest development in quantum dot solar cells comes from a completely different quantum dot material. The new quantum dot leader is cesium lead triiodide (CsPbI3), and is within the recently emerging family of halide perovskite materials. 

In quantum dot form, CsPbI3 produces an exceptionally large voltage (about 1.2 volts) at open circuit.

“This voltage, coupled with the material’s bandgap, makes them an ideal candidate for the top layer in a multijunction solar cell,” said Joseph Luther, a senior scientist and project leader in the Chemical Materials and Nanoscience team at NREL. 

The top cell must be highly efficient but transparent at longer wavelengths to allow that portion of sunlight to reach lower layers. 
Tandem cells can deliver a higher efficiency than conventional silicon solar panels that dominate today’s solar market.

This latest advance, titled “Enhanced mobility CsPbI3 quantum dot arrays for record-efficiency, high-voltage photovoltaic cells,” is published in Science Advances. The paper was co-authored by Erin Sanehira, Ashley Marshall, Jeffrey Christians, Steven Harvey, Peter Ciesielski, Lance Wheeler, Philip Schulz, and Matthew Beard, all from NREL; and Lih Lin from the University of Washington.

The multijunction approach is often used for space applications where high efficiency is more critical than the cost to make a solar module. 
The quantum dot perovskite materials developed by Luther and the NREL/University of Washington team could be paired with cheap thin-film perovskite materials to achieve similar high efficiency as demonstrated for space solar cells, but built at even lower costs than silicon technology–making them an ideal technology for both terrestrial and space applications.

“Often, the materials used in space and rooftop applications are totally different. It is exciting to see possible configurations that could be used for both situations,” said Erin Sanehira a doctoral student at the University of Washington who conducted research at NREL.

The NREL research was funded by DOE’s Office of Science, while Sanehira and Lin acknowledge a NASA space technology fellowship.

NREL is the U.S. Department of Energy’s primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.

NREL Inks Technology Agreement for High Efficiency Multijunction Solar Cells


October 24, 2017

MicroLink Devices opens the door for new multijunction solar cell applications

October 24, 2017

The U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) has entered into a license agreement with MicroLink Devices, Inc. (Niles, IL) to commercialize NREL’s patented inverted metamorphic (IMM) multijunction solar cells. 

While high-efficiency multijunction solar cells are commonly used for space satellites, researchers have continued to look for ways to improve cost and performance to enable a broader range of applications. 

The IMM technique licensed by MicroLink Devices enables multijunction III-V solar cells to be grown with both higher efficiencies and lower costs than traditional multijunction solar cells by reversing the order in which individual sub-cells are typically grown.



Two hands holding the IMM solar cellA 6-inch MicroLink Devices high-efficiency, lightweight and flexible ELO IMM solar cell wafer. Photo courtesy of MicroLink Devices

The IMM architecture enables greater power extraction from the higher-bandgap sub-cells and further allows the use of more efficient low-bandgap sub-cell materials such as Indium Gallium Arsenide. 

In contrast to traditional III-V multijunction solar cells, IMM devices are removed from their growth substrate, allowing the substrate to be reused over multiple growth runs – a significant component in reducing overall device costs. Removing the substrate also reduces the weight of the solar cell, which is important for applications such as solar-powered unmanned aerial vehicles.

MicroLink Devices is an Illinois-based ISO 9001 certified semiconductor manufacturer specializing in removing active semiconductor device layers from their growth substrate via a proprietary epitaxial liftoff (ELO) process. 

By utilizing its ELO capabilities, MicroLink will be able to make thin, lightweight, and highly flexible IMM solar cells which are ideal for use in unmanned aerial vehicles, space-based vehicles and equipment, and portable power generation applications. 

“IMM makes multijunction solar cells practical for a wide variety of weight-, geometry-, and space-constrained applications where high efficiency is critical,” said Jeff Carapella, one of the researchers in NREL’s III-V multijunction materials and devices research group that developed the technology.

“Former NREL Scientist Mark Wanlass pioneered the use of metamorphic buffer layers to form tandem III-V solar cells with three or more junctions. 

This approach is very synergistic with our ELO process technology, and MicroLink Devices is excited to now be commercializing IMM solar cells for high-performance space and UAV applications,” said Noren Pan, CEO of MicroLink Devices.

MicroLink and NREL have collaborated to evaluate the use of ELO for producing IMM solar cells since 2009, when MicroLink was the recipient of a DOE PV Incubator subcontract from NREL. 

Tests of MicroLink-produced IMM solar cells conducted at NREL have demonstrated multiple successful substrate reuses and efficiencies exceeding 30%.

NREL has more than 800 technologies available for licensing and continues to engage in advanced research and development of next-generation IMM and ultra-high-efficiency multijunction solar cells with both academic and commercial collaborators. 

Companies interested in partnering to advance research on or commercialize renewable energy technologies can visit the EERE Energy Innovation Portal, which features descriptions of all renewable energy technologies funded by the DOE’s Office of Energy Efficiency and Renewable Energy. 

Parties interested specifically in ongoing development of IMM solar cells can contact Dan Friedman, Manager of NREL’s High Efficiency Crystalline Photovoltaics Group, for more information.

NREL is the U.S. Department of Energy’s primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.

Breaking through the sunlight-to-electricity conversion limit



Solar-excited “hot” electrons are usually wasted as heat in conventional silicon solar cells. In a new type of solar cell, known as a hybrid organic-inorganic perovskite cell, scientists found these “hot” electrons last longer. These hot electrons have lifetimes more than a 1000 times longer than those formed in silicon cells. 

The rotation of oppositely charged ions plays a key role in protecting “hot” electrons from adverse energy-depleting interactions (Science, “Screening in crystalline liquids protects energetic carriers in hybrid perovskites”).


In the illustration of a perovskite structure, a “hot” electron is located at the center of the image. Positive molecules (red and blue dumbbells) surround the “hot” electron. The distortion of the crystal structure and the liquid-like environment of the positive molecules (blurred dumbbells at the periphery of the image) screen (yellow circle, partially shown) the “hot” electron. The “shield” protects the hot electron and allows it to survive 1000 times longer than it would in conventional silicon solar cells. (Image: Xiaoyang Zhu, Columbia University)

This research identified a possible route to dramatically increase the efficiency of solar cells. By slowing the cooling of excited “hot” electrons, scientists could produce more electricity. They could devise cells that function above the predicted efficiency limit, around 33 percent, for conventional solar cells.

Hybrid organic-inorganic lead halide perovskites (HOIP) are promising new materials for use in low-cost solar cells. HOIPs have already been demonstrated in solar cells with solar-to-electricity conversion efficiency exceeding 20 percent, which is on par with the best crystalline silicon solar cells.

Research is ongoing to discover why HOIPs work so well for solar energy harvesting and to determine their efficiency limit. A team led by Columbia University has discovered that electrons in HOIPs acquire protective shields that make them nearly invisible to defects and other electrons, which allows the electrons to avoid losing energy. The mechanism of protection is dynamic screening correlated with liquid-like molecular motions in the crystal structure.

Moreover, the researchers discovered that the protection mechanism works for electrons with excess energy (with energy greater than the semiconductor band gap); as a result, these so-called “hot” electrons are very long-lived in HOIPs. In a conventional solar cell, such as the silicon cell widely in use today, only part of the solar spectrum is used, and the energy of the “hot” electrons is wasted. Excess electron energy generated initially from the absorption of high-energy photons in the solar spectrum is lost as heat before the electron is harvested for electricity production.

For conventional solar cells, this loss is partially responsible for the theoretical efficiency limit of around 33 percent, called the Shockley-Queisser limit. However, the long lifetime of “hot” electrons in HOIPs makes it possible to harvest the “hot” electrons to produce electricity, thus increasing the efficiency of HOIP solar cells beyond the conventional limit.

Source: U.S. Department of Energy, Office of Science

Better photovoltaic efficiency grows from enormous solar crystals: MH Perovskites 


In-depth analysis of the mechanisms that generate floating crystals from hot liquids could lead to large-scale, printable solar cells


New evidence of surface-initiated crystallization may improve the efficiency of printable photovoltaic materials.

In the race to replace silicon in low-cost solar cells, semiconductors known as metal halide perovskites are favored because they can be solution-processed into thin films with excellent photovoltaic efficiency. 

A collaboration between King Abdullah University of Science and Technology (KAUST) and Oxford University researchers has now uncovered a strategy that grows perovskites into centimeter-scale, highly pure crystals thanks to the effect of surface tension (ACS Energy Letters, “The role of surface tension in the crystallization of metal halide perovskites”).

In their natural state, perovskites have difficultly moving solar-generated electricity because they crystallize with randomly oriented grains. 

Osman Bakr from KAUST’s Solar Center and coworkers are working on ways to dramatically speed up the flow of these charge carriers using inverse temperature crystallization (ITC). This technique uses special organic liquids and thermal energy to force perovskites to solidify into structures resembling single crystals—the optimal arrangements for device purposes.

While ITC produces high-quality perovskites far faster than conventional chemical methods, the curious mechanisms that initiate crystallization in hot organic liquids are poorly understood. Ayan Zhumekenov, a PhD student in Bakr’s group, recalls spotting a key piece of evidence during efforts to adapt ITC toward large-scale manufacturing. “At some point, we realized that when crystals appeared, it was usually at the solution’s surface,” he says. “And this was particularly true when we used concentrated solutions.”

The KAUST team partnered with Oxford theoreticians to identify how interfaces influence perovskite growth in ITC. They propose that metal halides and solvent molecules initially cling together in tight complexes that begin to stretch and weaken at higher temperatures. With sufficient thermal energy, the complex breaks and perovskites begin to crystallize.

But interestingly, the researchers found that complexes located at the solution surface can experience additional forces due to surface tension—the strong cohesive forces that enable certain insects to stride over lakes and ponds. The extra pull provided by the surface makes it much easier to separate the solvent-perovskite complexes and nucleate crystals that float on top of the liquid.

Exploiting this knowledge helped the team produce centimeter-sized, ultrathin single crystals and prototype a photodetector with characteristics comparable to state-of-the-art devices. Although the single crystals are currently fragile and difficult to handle due to their microscale thicknesses, Zhumekenov explains that this method could help direct the perovskite growth onto specific substrates.

“Taking into account the roles of interfaces and surface tension could have a fundamental impact,” he says, “we can get large-area growth, and it’s not limited to specific metal cations—you could have a library of materials with perovskite structures.”

Source: King Abdullah University of Science and Technology

NREL, Swiss Scientists Power Past Solar Efficiency Records


NREL scientist Adele Tamboli, co-author of a recent article on silicon-based multijunction solar cells, stands in front of an array of solar panels. Credit: Dennis Schroeder

August 25, 2017




Second collaborative effort proves silicon-based multijunction cells that reach nearly 36% efficiency

Collaboration between researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), the Swiss Center for Electronics and Microtechnology (CSEM), and the École Polytechnique Fédérale de Lausanne (EPFL) shows the high potential of silicon-based multijunction solar cells.

The research groups created tandem solar cells with record efficiencies of converting sunlight into electricity under 1-sun illumination. The resulting paper, “Raising the One-Sun Conversion Efficiency of III–V/Si Solar Cells to 32.8% for Two Junctions and 35.9% for Three Junctions,” appears in the new issue of Nature Energy. Solar cells made solely from materials in Groups III and V of the Periodic Table have shown high efficiencies, but are more expensive.

Stephanie Essig, a former NREL post-doctoral researcher now working at EPFL in Switzerland, is lead author of the newly published research that details the steps taken to improve the efficiency of the multijunction cell. While at NREL, Essig co-authored “Realization of GaInP/Si Dual-Junction Solar Cells with 29.8% 1-Sun Efficiency,” which was published in the IEEE Journal of Photovoltaics a year ago.

In addition to Essig, authors of the new research paper are Timothy Remo, John F. Geisz, Myles A. Steiner, David L. Young, Kelsey Horowitz, Michael Woodhouse, and Adele Tamboli, all with NREL; and Christophe Allebe, Loris Barraud, Antoine Descoeudres, Matthieu Despeisse, and Christophe Ballif, all from CSEM.

“This achievement is significant because it shows, for the first time, that silicon-based tandem cells can provide efficiencies competing with more expensive multijunction cells consisting entirely of III-V materials,” Tamboli said. “It opens the door to develop entirely new multijunction solar cell materials and architectures.”

In testing silicon-based multijunction solar cells, the researchers found that the highest dual-junction efficiency (32.8%) came from a tandem cell that stacked a layer of gallium arsenide (GaAs) developed by NREL atop a film of crystalline silicon developed by CSEM. An efficiency of 32.5% was achieved using a gallium indium phosphide (GaInP) top cell, which is a similar structure to the previous record efficiency of 29.8% announced in January 2016. 

A third cell, consisting of a GaInP/GaAs tandem cell stacked on a silicon bottom cell, reached a triple-junction efficiency of 35.9%—just 2% below the overall triple-junction record.

The existing photovoltaics market is dominated by modules made of single-junction silicon solar cells, with efficiencies between 17% and 24%. 

The researchers noted in the report that making the transition from a silicon single-junction cell to a silicon-based dual-junction solar cell will enable manufacturers to push efficiencies past 30% while still benefiting from their expertise in making silicon solar cells.

The obstacle to the adoption of these multijunction silicon-based solar cells, at least in the near term, is the cost. Assuming 30% efficiency, the researchers estimated the GaInP-based cell would cost $4.85 per watt and the GaAs-based cell would cost $7.15 per watt. 

But as manufacturing ramps up and the efficiencies of these types of cells climbs to 35%, the researchers predict the cost per watt could fall to 66 cents for a GaInP-based cell and to 85 cents for the GaAs-based cell. 

The scientists noted that such a precipitous price drop is not unprecedented; for instance, the cost of Chinese-made photovoltaic modules fell from $4.50 per watt in 2006 to $1 per watt in 2011.

The cost of a solar module in the United States accounts for 20% to 40% of the price of a photovoltaic system. Increasing cell efficiency to 35%, the researchers estimated, could reduce the system cost by as much as 45 cents per watt for commercial installations. 

However, if the costs of a III-V cell cannot be reduced to the levels of the researchers’ long-term scenario, then the use of cheaper, high-efficiency materials for the top cell will be needed to make them cost-competitive in general power markets.

The funding for the research came from the Energy Department’s SunShot Initiative—which aims to make solar energy a low-cost electricity source for all Americans through research and development efforts in collaboration with public and private partners—and from the Swiss Confederation and the Nano-Tera.ch initiative.


NREL is the U.S. Department of Energy’s primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.