Researchers from Shanghai Polytechnic University, Shanghai Engineering Research Center of Advanced Thermal Functional Materials, and Shanghai Solar Energy Research Center Co. Ltd explored how different shade conditions impact performance of single solar cells and two-cell systems connected in series and parallel.

The results have been published by the American Institute of Physics Journal of Renewable and Sustainable Energy.

Large obstacles, like clouds and buildings, can block sunlight from reaching solar cells and even small objects, such as dust and leaves, can block sunlight from reaching solar cells. Understanding how the loss of incoming radiation affects power output is essential for optimizing photovoltaic technology, which converts light into electricity.

The researchers explored how different shade conditions impact performance of single solar cells and two-cell systems connected in series and parallel. They found that the decrease in output current of a single cell or two cells connected in parallel was nearly identical to the ratio of shade to sunlight. However, for two cells running in series, there was excess power loss.

Two solar cells connected in parallel (left) and in series (right) with an obstacle creating shade (brown). Shady conditions caused more power loss in series systems. Image Credit: Shanghai Polytechnic University. Click the press release link above for a larger image and the study paper link with a scroll down to a more completely labeled image.

Author Huaqing Xie, of Shanghai Polytechnic University and Shanghai Engineering Research Center of Advanced Thermal Functional Materials explained, “In the real world, photovoltaic cells are sometimes shaded by obstacles, which significantly alters the amount of incoming light. The degradation effects make power optimization difficult and result in significant power loss.”

Photovoltaics connected in series create a single path with the electrons flowing from one cell into the next. In contrast, cells in parallel provide two lanes for electrons to travel through, then recombine later. In practical applications, networks of solar cells are connected in series and parallel to expand the output current and power capability.

The team found that the decrease in output current of a single cell or two cells connected in parallel was nearly identical to the ratio of shade to sunlight. However, for two cells running in series, there was excess power loss and a rise in temperature, which can cause further output degradation. For example, with 29.6% of the series photovoltaic module in the shade, the current decreased by 57.6%.

Xie noted, “Our study indicates that many factors, including shadow area, shadows on different cells of the module, and the connection of cells and modules, may affect the performance.”

Previous studies have explored the consequences of shade on large photovoltaic modules but have largely ignored single cells and simple systems.

“In these complicated systems, shadows on one single cell may play vital role on the system output and reliability,” said Xie. “Therefore, studying single cells or a simple arrangement of two connected cells is necessary for solar panel development.”

In the future, the authors hope to examine the microscopic interaction behaviors and mechanisms in photovoltaic cells subjected to different shadows.

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One would have thought that this type of research would have been done a long time ago. But serious solar aficionados have come to realize that solar cell quality has more at issue than simply area and price. The installations need maintained regularly. The designs matter. And now we know how they are wired internally has a large effect on the performance.

Knowing this will help consumers make better, more informed decisions about particular solar offerings. One day there might even be label requirements that show just what a panel actually is inside and have actual comparable ratings. Someday. Maybe.

Lets hope the folks in Shanghai keep going. Perhaps they will accumulate enough information that designs improve and perhaps a sensor might be invented to say “Wash Me!”

Waves of magnetic excitation sweep through nickel oxide material whether it’s in superconducting mode or not. Its another clue to how unconventional superconductors carry electric current with no loss.

SLAC National Accelerator Laboratory scientists embedded elementary particles called muons into a many-layered nickel oxide superconductor to learn more about its magnetic properties. They discovered that waves of flip-flopping electron spins create magnetic excitations that sweep through the nickel layer of the compound whether it’s superconducting or not. This is in sharp contrast to what happens in the best-known family of unconventional superconductors, the cuprates, and offers another valuable clue to how these materials can carry electric current with no loss.

Electrons find each other repulsive, it’s just that their negative charges repel each other. So getting them to pair up and travel together, like they do in superconducting materials, requires a little nudge.

In old-school superconductors, which were discovered in 1911 and conduct electric current with no resistance, but only at extremely cold temperatures, the nudge comes from vibrations in the material’s atomic lattice.

But in later, “unconventional” superconductors, which are especially exciting because of their potential to operate at close to room temperature for things like zero-loss power transmission. Although no one knows for sure what the nudge is, researchers think it might involve stripes of electric charge, waves of flip-flopping electron spins that create magnetic excitations, or some combination of things.

In the hope of learning more by looking at the problem from a slightly different angle, researchers at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory synthesized another unconventional superconductor family – the nickel oxides, or nickelates. Since then, they’ve spent three years investigating the nickelates’ properties and comparing them to one of the most famous unconventional superconductors, the copper oxides or cuprates.

In a paper published in Nature Physics, the team reported a significant difference: Unlike in the cuprates, the magnetic fields in nickelates are always on.

Magnetism: Friend or foe?

Nickelates, the scientists explained, are intrinsically magnetic, as if each nickel atom were clutching a tiny magnet. This is true whether the nickelate is in its non-superconducting, or normal, state or in a superconducting state where electrons have paired up and formed a sort of quantum soup that can host intertwining phases of quantum matter. Cuprates, on the other hand, are not magnetic in their superconducting state.

Jennifer Fowlie, a postdoctoral researcher at SLAC’s Stanford Institute for Materials and Energy Sciences (SIMES) who led the experiments said, “This study looked at fundamental properties of the nickelates compared to the cuprates, and what that can tell us about unconventional superconductors in general.”

She noted that some researchers think magnetism and superconductivity compete with each other in this type of system, while others think you can’t have superconductivity unless magnetism is close by.

“While our results don’t settle that question, they do highlight where more work should probably be done,” Fowlie said. “And they mark the first time that magnetism has been examined in both the superconducting and the normal state of nickelates.”

Harold Hwang, a professor at SLAC and Stanford and director of SIMES, commented, “This is another important piece of the puzzle that the research community is putting together as we work to frame the properties and phenomena at the heart of these exciting materials.”

Enter the muon

Few things come easy in this field of research, and studying the nickelates has been harder than most.

While theorists predicted more than 20 years ago that their chemical similarity to the cuprates made it likely that they could host superconductivity, nickelates are so difficult to make that it took years of trying before the SLAC and Stanford team succeeded.

Even then, they could only make thin films of the material – not the thicker chunks needed to explore its properties with common techniques. Hwang noted that number of research groups around the world have been working on easier ways to synthesize nickelates in any form.

So the research team turned to a more exotic method, called low-energy muon spin rotation/relaxation, that can measure the magnetic properties of thin films and is available only at the Paul Scherrer Institute (PSI) in Switzerland.

A muon, center, spins like a top within the atomic lattice of a thin film of superconducting nickelate. These elementary particles can sense the magnetic field created by the spins of electrons up to a billionth of a meter away. By embedding muons in four nickelate compounds at the Paul Scherrer Institute in Switzerland, researchers at SLAC and Stanford discovered that the nickelates they tested host magnetic excitations whether they’re in their superconducting states or not – another clue in the long quest to understand how unconventional superconductors can conduct electric current with no loss. Image Credit: Jennifer Fowlie/SLAC National Accelerator Laboratory. Click the press release link for the largest view.

Muons are fundamental charged particles that are similar to electrons, but 207 times more massive. They stick around for just 2.2 millionths of a second before decaying. Positively charged muons, which are often preferred for experiments like these, decay into a positron, a neutrino and an antineutrino. Like their electron cousins, they spin like tops and change the direction of their spin in response to magnetic fields. But they can “feel” those fields only in their immediate surroundings – up to about one nanometer, or a billionth of a meter, away.

At PSI, scientists use a beam of muons to embed the little particles in the material they want to study. When the muons decay, the positrons they produce fly off in the direction the muon is spinning. By tracing the positrons back to their origins, researchers can see which way the muons were pointing when they winked out of existence and thus determine the material’s overall magnetic properties.

Finding a workaround

The SLAC team applied to do experiments with the PSI system in 2020, but then the pandemic made it impossible to travel in or out of Switzerland. Fortunately, Fowlie was a postdoc at the University of Geneva at the time and already planning to come to SLAC to work in Hwang’s group. So she started the first round of experiments in Switzerland with a team led by Andreas Suter, a senior scientist at PSI and an expert in extracting information about superconductivity and magnetism from muon decay data.

After arriving at SLAC May 2021, Fowlie immediately started making various types of nickelate compounds the team wanted to test in their second round of experiments. When travel restrictions ended, the team was finally able to go back to Switzerland to finish the study.

The unique experimental setup at PSI allows scientists to embed muons at precise depths in the nickelate materials. From this, they were able to determine what was going on in each super-thin layer of various nickelate compounds with slightly different chemical compositions. They discovered that only the layers that contained nickel atoms were magnetic.

Interest in the nickelates is very high around the world, Hwang said. Half a dozen research groups have published their own ways of synthesizing nickelates and are working on improving the quality of the samples they study, and a huge number of theorists are trying to come up with insights to guide the research in productive directions.

Hwang said, “We are trying to do what we can with the resources we have as a research community, but there’s still a lot more we can learn and do.”

***

The superconductor hunt is one of the best stories in energy. Back in 1911 the discovery was astonishing and now its about exotically making wholly new materials. The operating temperatures have come way up and the general interest is improving, which increases the funding going into the hunt.

This research result is important, especially because it breaks the research community’s natural tendency for “tunnel vision”, that human nature where everyone charges in the same direction thinking essentially about the same way.

Now they have data and we can wonder what innovation comes next!

Rice University engineers have shown the manufacture of high-efficiency solar cells with layers of 2D and 3D perovskites may be simplified by solvents that allow solution deposition of one layer without destroying the other. The work solved a long-standing conundrum in making stable, efficient solar panels out of halide perovskites.

The effort took finding the right solvent design to apply a 2D top layer of desired composition and thickness without destroying the 3D bottom one (or vice versa). Such a cell would turn more sunlight into electricity than either layer on its own, with better stability.

Chemical and biomolecular engineer Aditya Mohite and his lab at Rice’s George R. Brown School of Engineering reported in Science their success at building thin 3D/2D solar cells that deliver a power conversion efficiency of 24.5%.

That’s as efficient as most commercially available solar cells, Mohite said.

Mohite noted, “This is really good for flexible, bifacial cells where light comes in from both sides and also for back-contacted cells. The 2D perovskites absorb blue and visible photons, and the 3D side absorbs near-infrared.” The new advance largely removes the last major roadblock to commercial production he added.

Perovskites are crystals with cubelike lattices known to be efficient light harvesters, but the materials tend to be stressed by light, humidity and heat. Mohite and many others have worked for years to make perovskite solar cells practical.

Mohite explained, “This is significant at multiple levels. One is that it’s fundamentally challenging to make a solution-processed bilayer when both layers are the same material. The problem is they both dissolve in the same solvents. When you put a 2D layer on top of a 3D layer, the solvent destroys the underlying layer. But our new method resolves this.”

For background Mohite said 2D perovskite cells are stable, but less efficient at converting sunlight. 3D perovskites are more efficient but less stable. Combining them incorporates the best features of both. “This leads to very high efficiencies because now, for the first time in the field, we are able to create layers with tremendous control. It allows us to control the flow of charge and energy for not only solar cells but also optoelectronic devices and LEDs.”

The efficiency of test cells exposed to the lab equivalent of 100% sunlight for more than 2,000 hours “does not degrade by even 1%. Not counting a glass substrate, the cells were about 1 micron thick.

A discovery by Rice University engineers brings efficient, stable bilayer perovskite solar cells closer to commercialization. The cells are about a micron thick, with 2D and 3D layers. Image Credit: Photo by Jeff Fitlow, Rice University.

How they are made

Solution processing is widely used in industry and incorporates a range of techniques – spin coating, dip coating, blade coating, slot die coating and others – to deposit material on a surface in a liquid. When the liquid evaporates, the pure coating remains.

The key is a balance between two properties of the solvent itself: its dielectric constant and Gutmann donor number. The dielectric constant is the ratio of the electric permeability of the material to its free space. That determines how well a solvent can dissolve an ionic compound. The donor number is a measure of the electron-donating capability of the solvent molecules.

“If you find the correlation between them, you’ll find there are about four solvents that allow you to dissolve perovskites and spin-coat them without destroying the 3D layer,” Mohite said.

Their discovery should be compatible with roll-to-roll manufacturing that typically produces 30 meters of solar cell per minute.

Co-author Jacky Even, a professor of physics at the National Institute of Science and Technology in Rennes, France said, “This breakthrough is leading, for the first time, to perovskite device heterostructures containing more than one active layer. The dream of engineering complex semiconductor architectures with perovskites is about to come true. Novel applications and the exploration of new physical phenomena will be the next steps.”

Mohite added, “This has implications not just for solar energy but also for green hydrogen, with cells that can produce energy and convert it to hydrogen. It could also enable non-grid solar for cars, drones, building-integrated photovoltaics or even agriculture.”

***

Perhaps this is the breakthrough that brings an alternative competitor to the dominating silicon solar cell. If the process engineering can bring the roll to roll manufacturing to commercial scale at great economy, solar energy harvesting might get quite a boost.

This is a big effort that came to fruition. The co-author list is long, so for here is a list of institutions. For the full list of names, please see the press release or the study paper. The institutions are, Rice University, Northwestern University, Purdue University, University of Washington, Seattle, University of Rennes, and the Argonne National Laboratory.

Massachusetts Institute of Technology engineers have designed a battery made from inexpensive, abundant materials, that could provide low-cost backup storage for renewable energy sources. Less expensive than lithium-ion battery technology, the new architecture uses aluminum and sulfur as its two electrode materials with a molten salt electrolyte in between.

The new battery architecture is described in the journal Nature, in a paper by MIT Professor Donald Sadoway, along with 15 others at MIT and in China, Canada, Kentucky, and Tennessee.

Wind and solar advocates are building out ever larger installations of wind and solar power systems, thus need is growing fast for economical, large-scale backup systems to provide power when the sun is down and the air is calm. Today’s lithium-ion batteries are still too expensive for most such applications, and other options such as pumped hydro require specific landscapes that are not always available.

The MIT led group’s chemistry architecture could help to fill the intermittency gaps.

Sadoway, who is the John F. Elliott Professor Emeritus of Materials Chemistry said, “I wanted to invent something that was better, much better, than lithium-ion batteries for small-scale stationary storage, and ultimately for automotive [uses].”

In addition to being expensive, lithium-ion batteries contain a flammable electrolyte, making them less than ideal for transportation. So, Sadoway started studying the periodic table, looking for cheap, Earth-abundant metals that might be able to substitute for lithium. The commercially dominant metal, iron, doesn’t have the right electrochemical properties for an efficient battery, he said. But the second-most-abundant metal in the marketplace – and actually the most abundant metal on Earth – is aluminum.

“So, I said, well, let’s just make that a bookend. It’s gonna be aluminum,” he commented.

Next up was deciding what to pair the aluminum with for the other electrode, and what kind of electrolyte to put in between to carry ions back and forth during charging and discharging. The cheapest of all the non-metals is sulfur, so that became the second electrode material.

As for the electrolyte, “we were not going to use the volatile, flammable organic liquids” that have sometimes led to dangerous fires in cars and other applications of lithium-ion batteries, Sadoway said. They tried some polymers but ended up looking at a variety of molten salts that have relatively low melting points – close to the boiling point of water, as opposed to nearly 1,000° Fahrenheit for many salts. “Once you get down to near body temperature, it becomes practical” to make batteries that don’t require special insulation and anticorrosion measures, he noted.

The three ingredients they ended up with are cheap and readily available – aluminum, no different from the foil at the supermarket; sulfur, which is often a waste product from processes such as petroleum refining; and widely available salts. “The ingredients are cheap, and the thing is safe – it cannot burn,” Sadoway said.

In their experiments, the team showed that the battery cells could endure hundreds of cycles at exceptionally high charging rates, with a projected cost per cell of about one-sixth that of comparable lithium-ion cells. They showed that the charging rate was highly dependent on the working temperature, with 110° Celsius (230° Fahrenheit) showing 25 times faster rates than 25° C (77° F).

Surprisingly, the molten salt the team chose as an electrolyte simply because of its low melting point turned out to have a fortuitous advantage. One of the biggest problems in battery reliability is the formation of dendrites, which are narrow spikes of metal that build up on one electrode and eventually grow across to contact the other electrode, causing a short-circuit and hampering efficiency. But this particular salt, it happens, is very good at preventing that malfunction.

The chloro-aluminate salt they chose “essentially retired these runaway dendrites, while also allowing for very rapid charging,” Sadoway said. “We did experiments at very high charging rates, charging in less than a minute, and we never lost cells due to dendrite shorting.”

“It’s funny,” he said, because the whole focus was on finding a salt with the lowest melting point, but the catenated chloro-aluminates they ended up with turned out to be resistant to the shorting problem. “If we had started off with trying to prevent dendritic shorting, I’m not sure I would’ve known how to pursue that,” Sadoway said. “I guess it was serendipity for us.”

Additionally, the battery requires no external heat source to maintain its operating temperature. The heat is naturally produced electrochemically by the charging and discharging of the battery. “As you charge, you generate heat, and that keeps the salt from freezing. And then, when you discharge, it also generates heat,” Sadoway said.

In a typical installation used for load-leveling at a solar generation facility, for example, “you’d store electricity when the sun is shining, and then you’d draw electricity after dark, and you’d do this every day. And that charge-idle-discharge-idle is enough to generate enough heat to keep the thing at temperature.”

This new battery formulation, he says, would be ideal for installations of about the size needed to power a single home or small to medium business, producing on the order of a few tens of kilowatt-hours of storage capacity.

For larger installations, up to utility scale of tens to hundreds of megawatt hours, other technologies might be more effective, including the liquid metal batteries Sadoway and his students developed several years ago and which formed the basis for a spinoff company called Ambri, which hopes to deliver its first products within the next year. For that invention, Sadoway was recently awarded this year’s European Inventor Award.

The smaller scale of the aluminum-sulfur batteries would also make them practical for uses such as electric vehicle charging stations, Sadoway noted. He points out that when electric vehicles become common enough on the roads that several cars want to charge up at once, as happens today with gasoline fuel pumps, “if you try to do that with batteries and you want rapid charging, the amperages are just so high that we don’t have that amount of amperage in the line that feeds the facility.” So having a battery system such as this to store power and then release it quickly when needed could eliminate the need for installing expensive new power lines to serve those chargers.

The new technology is already the basis for a new spinoff company called Avanti, which has licensed the patents to the system, co-founded by Sadoway and Luis Ortiz ’96 ScD ’00, who was also a co-founder of Ambri. “The first order of business for the company is to demonstrate that it works at scale,” Sadoway said, and then subject it to a series of stress tests, including running through hundreds of charging cycles.

Would a battery based on sulfur run the risk of producing the foul odors associated with some forms of sulfur? Not a chance, Sadoway said. “The rotten-egg smell is in the gas, hydrogen sulfide. This is elemental sulfur, and it’s going to be enclosed inside the cells.” If you were to try to open up a lithium-ion cell in your kitchen, he says (and please don’t try this at home!), “the moisture in the air would react and you’d start generating all sorts of foul gases as well. These are legitimate questions, but the battery is sealed, it’s not an open vessel. So I wouldn’t be concerned about that.”

The research team included members from Peking University, Yunnan University and the Wuhan University of Technology, in China; the University of Louisville, in Kentucky; the University of Waterloo, in Canada; Oak Ridge National Laboratory, in Tennessee; and MIT. The work was supported by the MIT Energy Initiative, the MIT Deshpande Center for Technological Innovation, and ENN Group.

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This sounds pretty good! But no mention of how many watt hours by battery volume or weight. Then there are those “going to scale” things that come up when leaving the lab and getting to a factory setup.

One does hope there will be continued refinement. The press release makes it sound as if the whole thing just fell together by virtue of making low cost choices. One can be certain a lot of thought went into those decisions.

What we do know that gives some pause is this technology needs to be used to stay warm enough to work well. There has to be an energy price in this and that was not revealed or discussed. One might want to be sure these are real cheap as continuous duty with only cycles in the “hundreds” might not actually cut the economic starting ribbon.

University of Technology Sydney (UTS) and Queensland University of Technology (QUT) researchers have announced a new design for solid-state hydrogen storage that could significantly reduce charging times.

Hydrogen is gaining significant attention as an efficient way to store ‘green energy’ from renewables such as wind and solar. Compressed gas is the most common form of hydrogen storage, however it can also be stored in a liquid or solid state.

Dr Saidul Islam, from the University of Technology Sydney, explained solid hydrogen storage, and in particular metal hydride, is attracting interest because it is safer, more compact, and lower cost than compressed gas or liquid, and it can reversibly absorb and release hydrogen.

Dr Islam commented, “Metal hydride hydrogen storage technology is ideal for onsite hydrogen production from renewable electrolysis. It can store the hydrogen for extended periods and once needed, it can be converted as gas or a form of thermal or electric energy when converted through a fuel cell.”

“Applications include hydrogen compressors, rechargeable batteries, heat pumps and heat storage, isotope separation and hydrogen purification. It can also be used to store hydrogen in space, to be used in satellites and other ‘green’ space technology,” he added.

However, a problem with metal hydride for hydrogen energy storage has been its low thermal conductivity, which leads to slow charging and discharging times.

To address this the researchers developed a new method to improve solid-state hydrogen charging and discharging times. The study: “Design optimization of a magnesium-based metal hydride hydrogen energy storage system,” was recently published in the journal Scientific Reports.

Comparison of hydrogen absorption concentration with different designs. Image Credit: Puchanee Larpruenrudee, School of Mechanical and Mechatronic Engineering, University of Technology Sydney. Click the press release link above for a larger image.

First author Puchanee Larpruenrudee, a PhD candidate in the UTS School of Mechanical and Mechatronic Engineering, said faster heat removal from the solid fuel cell results in faster charging times.

Larpruenrudee explained, “Several internal heat exchangers have been designed for use with metal hydride hydrogen storage. These include straight tubes, helical coil or spiral tubes, U-shape tubes, and fins. Using a helical coil significantly improves heat and mass transfer inside the storage.”

“This is due to the secondary circulation and having more surface area for heat removal from the metal hydride powder to the cooling fluid. Our study further developed a helical coil to increase heat transfer performance,” he concluded.

The researchers developed a semi-cylindrical coil as an internal heat exchanger, which significantly improved heat transfer performance. The hydrogen charging time was reduced by 59% when using the new semi-cylindrical coil compared to a traditional helical coil heat exchanger.

The team is now working on the numerical simulation of the hydrogen desorption process, and continuing to improve absorption times. The semi-cylindrical coil heat exchanger will be further developed for this purpose.

As a goal, the researchers aim to develop a new design for hydrogen energy storage, which will combine other types of heat exchangers. They hope to also work with industry partners to investigate real tank performance based on the new heat exchanger.

***

Low pressure metal hydride hydrogen storage has potential. Some of the most difficult problems are reduced to more manageable levels. Yet hydrogen is still the smallest atom and is a devil to contain, and likes to get involved with whatever materials are used in its containment, which is why the metal hydride idea works.

No idea offered for storing hydrogen offers a leak proof long term (days or weeks) solution and hydrogen’s properties are just more than a bit scary if allowed to escape into much of a confined space.

Metal hydride might get to safe practicality someday.

Meanwhile, hundreds of millions of years ago nature figured out what to do. Combine that hydrogen with a bit of carbon and presto, food and fuel and a whole lot of life gets going!


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