Solar Energy

This hydrogen fuel machine could be the ultimate guide to self-improvement

Published

3 years ago

April 6, 2021

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This hydrogen fuel machine could be the ultimate guide to self-improvement

Three years ago, scientists at the University of Michigan discovered an artificial photosynthesis device made of silicon and gallium nitride (Si/GaN) that harnesses sunlight into carbon-free hydrogen for fuel cells with twice the efficiency and stability of some previous technologies.

Now, scientists at the Department of Energy’s (DOE’s) Lawrence Berkeley National Laboratory (Berkeley Lab) – in collaboration with the University of Michigan and Lawrence Livermore National Laboratory (LLNL) – have uncovered a surprising, self-improving property in Si/GaN that contributes to the material’s highly efficient and stable performance in converting light and water into carbon-free hydrogen. Their findings, reported in the journal Nature Materials, could help radically accelerate the commercialization of artificial photosynthesis technologies and hydrogen fuel cells.

“Our discovery is a real game-changer,” said senior author Francesca Toma, a staff scientist in the Chemical Sciences Division at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). Usually, materials in solar fuels systems degrade, become less stable and thus produce hydrogen less efficiently, she said. “But we discovered an unusual property in Si/GaN that somehow enables it to become more efficient and stable. I’ve never seen such stability.”

Previous artificial photosynthesis materials are either excellent light absorbers that lack durability; or they’re durable materials that lack light-absorption efficiency.

But silicon and gallium nitride are abundant and cheap materials that are widely used as semiconductors in everyday electronics such as LEDs (light-emitting diodes) and solar cells, said co-author Zetian Mi, a professor of electrical and computer engineering at the University of Michigan who invented Si/GaN artificial photosynthesis devices a decade ago.

When Mi’s Si/GaN device achieved a record-breaking 3 percent solar-to-hydrogen efficiency, he wondered how such ordinary materials could perform so extraordinarily well in an exotic artificial photosynthesis device – so he turned to Toma for help.

HydroGEN: Taking a Team Science approach to solar fuels

Mi had learned of Toma’s expertise in advanced microscopy techniques for probing the nanoscale (billionths of a meter) properties of artificial photosynthesis materials through HydroGEN, a five-national lab consortium supported by the DOE’s Hydrogen and Fuel Cell Technologies Office, and led by the National Renewable Energy Laboratory to facilitate collaborations between National Labs, academia, and industry for the development of advanced water-splitting materials.

“These interactions of supporting industry and academia on advanced water-splitting materials with the capabilities of the National Labs are precisely why HydroGEN was formed – so that we can move the needle on clean hydrogen production technology,” said Adam Weber, Berkeley Lab’s Hydrogen and Fuel Cell Technologies Lab Program Manager and Co-Deputy Director of HydroGEN.

Toma and lead author Guosong Zeng, a postdoctoral scholar in Berkeley Lab’s Chemical Sciences Division, suspected that GaN might be playing a role in the device’s unusual potential for hydrogen production efficiency and stability.

To find out, Zeng carried out a photoconductive atomic force microscopy experiment at Toma’s lab to test how GaN photocathodes could efficiently convert absorbed photons into electrons, and then recruit those free electrons to split water into hydrogen, before the material started to degrade and become less stable and efficient.

They expected to see a steep decline in the material’s photon absorption efficiency and stability after just a few hours. To their astonishment, they observed a 2-3 orders of magnitude improvement in the material’s photocurrent coming from tiny facets along the “sidewall” of the GaN grain, Zeng said. Even more perplexing was that the material had increased its efficiency over time, even though the overall surface of the material didn’t change that much, Zeng said. “In other words, instead of getting worse, the material got better,” he said.

To gather more clues, the researchers recruited scanning transmission electron microscopy (STEM) at the National Center for Electron Microscopy in Berkeley Lab’s Molecular Foundry, and angle-dependent X-ray photon spectroscopy (XPS).

Those experiments revealed that a 1 nanometer layer mixed with gallium, nitrogen, and oxygen – or gallium oxynitride – had formed along some of the sidewalls. A chemical reaction had taken place, adding “active catalytic sites for hydrogen production reactions,” Toma said.

Density functional theory (DFT) simulations carried out by co-authors Tadashi Ogitsu and Tuan Anh Pham at LLNL confirmed their observations. “”By calculating the change of distribution of chemical species at specific parts of the material’s surface, we successfully found a surface structure that correlates with the development of gallium oxynitride as a hydrogen evolution reaction site,” Ogitsu said. “We hope that our findings and approach – a tightly integrated theory-experiments collaboration enabled by the HydroGEN consortium – will be used to further improve the renewable hydrogen production technologies.”

Mi added: “We’ve been working on this material for over 10 years – we know it’s stable and efficient. But this collaboration helped to identify the fundamental mechanisms behind why it gets more robust and efficient instead of degrading. The findings from this work will help us build more efficient artificial photosynthesis devices at a lower cost.”

Looking ahead, Toma said that she and her team would like to test the Si/GaN photocathode in a water-splitting photoelectrochemical cell, and that Zeng will experiment with similar materials to get a better understanding of how nitrides contribute to stability in artificial photosynthesis devices – which is something they never thought would be possible.

“It was totally surprising,” said Zeng. “It didn’t make sense – but Pham’s DFT calculations gave us the explanation we needed to validate our observations. Our findings will help us design even better artificial photosynthesis devices.”

“This was an unprecedented network of collaboration between National Labs and a research university,” said Toma. “The HydroGEN consortium brought us together – our work demonstrates how the National Labs’ Team Science approach can help solve big problems that affect the entire world.”

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Solar Energy

3D-printed microstructure forest enhances solar steam desalination

Published

3 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

3 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

3 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