Solar Energy

Squeezing a rock-star material could make it stable enough for solar cells

Published

3 years ago

February 8, 2021

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Squeezing a rock-star material could make it stable enough for solar cells

Among the materials known as perovskites, one of the most exciting is a material that can convert sunlight to electricity as efficiently as today’s commercial silicon solar cells and has the potential for being much cheaper and easier to manufacture.

There’s just one problem: Of the four possible atomic configurations, or phases, this material can take, three are efficient but unstable at room temperature and in ordinary environments, and they quickly revert to the fourth phase, which is completely useless for solar applications.

Now scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have found a novel solution: Simply place the useless version of the material in a diamond anvil cell and squeeze it at high temperature. This treatment nudges its atomic structure into an efficient configuration and keeps it that way, even at room temperature and in relatively moist air.

“This is the first study to use pressure to control this stability, and it really opens up a lot of possibilities,” said Yu Lin, a SLAC staff scientist and investigator with the Stanford Institute for Materials and Energy Sciences (SIMES).

“Now that we’ve found this optimal way to prepare the material,” she said, “there’s potential for scaling it up for industrial production, and for using this same approach to manipulate other perovskite phases.”

A search for stability

Perovskites get their name from a natural mineral with the same atomic structure. In this case the scientists studied a lead halide perovskite that’s a combination of iodine, lead and cesium.

One phase of this material, known as the yellow phase, does not have a true perovskite structure and can’t be used in solar cells. However, scientists discovered a while back that if you process it in certain ways, it changes to a black perovskite phase that’s extremely efficient at converting sunlight to electricity. “This has made it highly sought after and the focus of a lot of research,” said Stanford Professor and study co-author Wendy Mao.

Unfortunately, these black phases are also structurally unstable and tend to quickly slump back into the useless configuration. Plus, they only operate with high efficiency at high temperatures, Mao said, and researchers will have to overcome both of those problems before they can be used in practical devices.

There had been previous attempts to stabilize the black phases with chemistry, strain or temperature, but only in a moisture-free environment that doesn’t reflect the real-world conditions that solar cells operate in. This study combined both pressure and temperature in a more realistic working environment.

Pressure and heat do the trick

Working with colleagues in the Stanford research groups of Mao and Professor Hemamala Karunadasa, Lin and postdoctoral researcher Feng Ke designed a setup where yellow phase crystals were squeezed between the tips of diamonds in what’s known as a diamond anvil cell. With the pressure still on, the crystals were heated to 450 degrees Celsius and then cooled down.

Under the right combination of pressure and temperature, the crystals turned from yellow to black and stayed in the black phase after the pressure was released, the scientists said. They were resistant to deterioration from moist air and remained stable and efficient at room temperature for 10 to 30 days or more.

Examination with X-rays and other techniques confirmed the shift in the material’s crystal structure, and calculations by SIMES theorists Chunjing Jia and Thomas Devereaux provided insight into how the pressure changed the structure and preserved the black phase.

The pressure needed to turn the crystals black and keep them that way was roughly 1,000 to 6,000 times atmospheric pressure, Lin said – about a tenth of the pressures routinely used in the synthetic diamond industry. So one of the goals for further research will be to transfer what the researchers have learned from their diamond anvil cell experiments to industry and scale up the process to bring it within the realm of manufacturing.

The researchers described their results in Nature Communications.

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Solar Energy

3D-printed microstructure forest enhances solar steam desalination

Published

2 days ago

July 24, 2024

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3D-printed microstructure forest enhances solar steam desalination

by Clarence Oxford

Los Angeles CA (SPX) Jul 24, 2024

To address the global freshwater scarcity issue, researchers in Singapore have developed advanced solar steam generators (SSGs) for seawater desalination. This method, powered by renewable energy, mimics the natural water cycle by using solar energy to evaporate and purify water, offering a potentially cost-effective solution compared to traditional, energy-intensive desalination techniques. However, current SSG technologies face limitations due to the complexity of fabricating designs that maximize surface area for optimal water evaporation.

Drawing inspiration from nature, the team utilized 3D printing to create innovative SSGs. Their findings, published in Applied Physics Reviews, highlight a novel technique for manufacturing efficient SSGs and introduce a groundbreaking method for printing functional nanocomposites using multi-jet fusion (MJF).

“We created SSGs with exceptional photothermal performance and self-cleaning properties,” said Kun Zhou, a professor of mechanical engineering at Nanyang Technological University. “Using a treelike porous structure significantly enhances water evaporation rates and ensures continuous operation by preventing salt accumulation – its performance remains relatively stable even after prolonged testing.”

The technology works by converting light to thermal energy, where SSGs absorb solar energy and convert it to heat to evaporate water. The porous structure of the SSGs aids in self-cleaning by removing accumulated salt, ensuring sustained desalination performance.

“By using an effective photothermal fusing agent, MJF printing technology can rapidly create parts with intricate designs,” Zhou added. “To improve the photothermal conversion efficiency of fusing agents and printed parts, we developed a novel type of fusing agent derived from metal-organic frameworks.”

The SSGs feature miniature tree-shaped microstructures that mimic plant transpiration, forming an efficient, heat-distributing forest.

“Our bioinspired design increases the surface area of the SSG,” Zhou explained. “Using a treelike design increases the surface area of the SSG, which enhances the water transport and boosts evaporation efficiency.”

In both simulated environments and field trials, the SSGs exhibited a high rate of water evaporation. The desalinated water consistently met drinking water standards, even after extended testing.

“This demonstrates the practicality and efficiency of our approach,” Zhou said. “And it can be quickly and easily mass-produced via MJF commercial printers.”

The team’s work shows significant potential for tackling freshwater scarcity.

“Our SSGs can be used in regions with limited access to freshwater to provide a sustainable and efficient desalination solution,” said Zhou. “Beyond desalination, it can be adapted for other applications that require efficient solar energy conversion and water purification.”

Research Report:3D printing of bio-inspired porous polymeric solar steam generators for efficient and sustainable desalination

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Solar Energy

Renewables overproduction turns electricity prices negative

Published

2 days ago

July 24, 2024

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Renewables overproduction turns electricity prices negative

By Nathalie Alonso and Catherine Hours

Paris (AFP) July 24, 2024

With the proliferation of solar panels and wind turbines an unusual phenomenon is becoming more and more frequent: wholesale electricity prices turn negative.

While that may brighten the mood of consumers whose power bills have surged in recent years, it could undermine the further development of renewables, a key element in the fight against global warming.

The increasingly frequent phenomenon is “extremely problematic” for the wind and solar sector, said Mattias Vandenbulcke, strategy director of the renewables industry group France Renouvelables.

“It allows some to have harmful, even dangerous rhetoric which says ‘renewables are useless’,” Vandenbulcke said.

In southern Australia, wholesale electricity prices have been negative some 20 percent of the time since last year, according to the International Energy Agency.

The share of negatively priced hours in southern California was above 20 percent in the first half of the year, more than triple from the same period in 2023, the IEA said.

In the first six months of the year in France, there were negative prices around five percent of the time, beating the record set last year, according to the electricity grid operator RTE.

In Switzerland the price tumbled as far as -400 euros (-$436) per megawatt hour on July 14. The lowest prices are usually recorded around midday during the summer when solar production is at its peak.

– ‘A warning signal’ –

The trend has been accelerating for the past three years as demand in Europe has unexpectedly dropped since the Covid pandemic and the war in Ukraine.

Prices turn negative on the spot wholesale electricity market when production is strong while demand is weak.

Around a fifth of the total is traded on this market, where electricity is bought for the following day.

Negative prices help reduce the bills of consumers, said Rebecca Aron, head of electricity markets at French renewables firm Valorem, but the impact is delayed and difficult to discern among the other factors that send prices higher and lower.

Large, industrial consumers that can shift production to times when prices are negative and buy on wholesale markets can reap the biggest rewards.

Negative prices are “a warning signal that there is way too much production on the electrical grid”, said energy analyst Nicolas Goldberg at Colombus Consulting.

Electricity grids need to be kept constantly in balance. Too much can lead to the electricity to increase in frequency beyond norms for some equipment. Too little can lead to some or all customers losing power.

There are currently few options to stock surplus electricity production so producers have to reduce output.

Many renewable producers stop their output when prices are set to turn negative. It takes one minute to stop output at a solar park, two to three minutes for a wind turbine.

But not all stop their production.

– Tripling renewables –

“Renewable energy can be controlled, but depending on production contracts, there might not necessarily be an incentive to stop,” said Mathieu Pierzo at French grid operator RTE, which has the responsibility for balancing the electricity load.

Some producers are paid a fixed price under their contract or are compensated by the state if prices fall below a certain level.

Fossil fuel and nuclear power plants can adjust their production to some extent, but halting and restarting output is costly.

In the future, solar and wind will also have to “participate more in balancing the electricity system”, Pierzo said.

Solar and wind production is set to rise further as nations agreed at the COP28 climate conference last year to triple renewable energy capacity by 2030 as part of efforts to limit warming to 1.5 degrees Celsius compared with pre-industrial levels.

“Rising frequency of negative prices sends an urgent signal that greater flexibility of supply and demand is needed,” the Paris-based IEA warned last week.

“The appropriate regulatory frameworks and market designs will be important to allow for an uptake in flexibility solutions such as demand response and storage,” it said.

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Solar Energy

NREL explores long-term strategies for sustainable perovskite solar panels

Published

2 days ago

July 24, 2024

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NREL explores long-term strategies for sustainable perovskite solar panels

by Clarence Oxford

Los Angeles CA (SPX) Jul 24, 2024

Researchers at the National Renewable Energy Laboratory (NREL) are examining the future of perovskite solar panels, focusing on scaling, deploying, and designing panels to be recyclable.

Perovskite solar panels could play a key role in global efforts to reduce greenhouse gas emissions. With the technology still in its developmental stages, researchers are emphasizing the importance of designing these panels to minimize environmental impact.

“When you have a technology in its very early stages, you have the ability to design it better. It’s a cleaner slate,” said Joey Luther, a senior research fellow at the U.S. Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) and coauthor of the newly published article in the journal Nature Materials. “Pushing perovskite PV toward enhanced sustainability makes more sense at this stage. We’re thinking about how we can make sure we have a sustainable product now rather than dealing with sustainability issues toward the end of its practical life.”

The article highlights the PV research community’s influential position to prioritize remanufacturing, recycling, and reliability efforts, aiming to make perovskite PV one of the most sustainable energy sources available.

“Perovskites could unlock the next evolution of high-efficiency PV, and it is our responsibility to assure they are manufactured, used, and recycled sustainably,” said the lead author of the study, Kevin Prince, a former graduate researcher at NREL who now researches perovskites at Helmholtz Zentrum Berlin in Germany.

While silicon solar panels dominate the industry and cadmium telluride (CdTe) panels have established recycling programs, perovskites are at a critical point where sustainability issues can be addressed from the start.

The most effective circular economy begins at the design stage, considering materials sourcing, product lifetime, and end-of-life management. Researchers suggest assessing environmental impacts by looking at carbon emissions during production, embodied energy, sustainable material sourcing, and module circularity.

The journal article identifies critical sustainability concerns for each component of a perovskite solar panel. For instance, lead can be diluted with metals like tin to reduce lead content, though this may affect PV efficiency and durability. Expensive precious metals such as silver and gold could be replaced with cheaper alternatives like aluminum, copper, or nickel. Fluorine-tin oxide is recommended over the scarcer indium-tin oxide for front electrodes.

“We want to have the lowest amount of embodied energy in the fabrication,” Luther said. “We want to have the lowest amount of emissions in the fabrication. At this stage, now is the chance to look at those components. I don’t think we have to change anything. It’s more a matter of what decisions should be made, and these arguments should certainly be discussed.”

The authors discuss various ways to improve the circularity of perovskite panels. Remanufacturing involves reusing parts from old modules to make new ones, while recycling converts waste materials into raw materials for reuse. Attention is needed for the specialized glass used in perovskite modules, which is crucial for structural support and protection while allowing maximum sunlight penetration. Establishing a recycling pathway for this glass will be essential as PV deployment increases.

Silvana Ovaitt, a PV researcher and coauthor of the paper, noted that cleaner electricity grids will lead to cleaner manufacturing processes, further reducing emissions.

“Another concern is the transportation of the final modules and the raw glass because those are the heaviest items,” Ovaitt said. “Local manufacturing will be a great way to reduce those carbon impacts.”

The researchers explain that increasing the durability of PV modules, thereby extending their useful life, is a more effective approach to reducing net energy, energy payback, and carbon emissions than designing for circularity alone. A longer lifespan means panels won’t need to be recycled as often.

“Ultimately, we want to make them as durable as possible,” Luther said. “But we also want to consider the aspects of whenever that time does come. We want to be deliberate about how to take them apart and to reuse the critical components.”

Research Report:Sustainability pathways for perovskite photovoltaics