GT/ Propeller advance paves way for quiet, efficient electric aviation
Energy & green technology biweekly vol.45, 7th March — 23rd March
TL;DR
- Electrification is seen as having an important role to play in the fossil-free aviation of tomorrow. But electric aviation is battling a trade-off dilemma: the more energy-efficient an electric aircraft is, the noisier it gets. Now, researchers have developed a propeller design optimization method that paves the way for quiet, efficient electric aviation.
- Researchers have engineered a material with the potential to dramatically cut the amount of heat power plants release into the atmosphere.
- Some projections show that widespread adoption of electric vehicles might require costly new power plants to meet peak loads in the evening. A new study shows that placing EV charging stations strategic ways and setting up systems to initiate charging at delayed times could lessen or eliminate the need for new power plants.
- There is currently a large dependence on coal for power generation. As coal-fired plants cause environmental and health hazards, technologies such as swirl flow and air staging have been proposed to mitigate the pollutants in their emissions. However, it is unclear how effective these technologies are in reducing the environmental costs of these plants. Now, researchers have provided insights on this front in a new study, delineating their efficacies with experiments and simulations.
- Solar cells made from metal halide perovskites achieve high efficiencies and their production from liquid inks requires only a small amount of energy. Scientists are investigating the production process. At the X-ray source BESSY II, the group has analyzed the optimal composition of precursor inks for the production of high-quality FAPbI3 perovskite thin films by slot-die coating. The solar cells produced with these inks were tested under real life conditions in the field for a year and scaled up to mini-module size.
- In the event of dry weather and high winds, power system-ignited incidents are more likely to develop into wildfires. The risk is greater if vegetation is nearby. A new study provides the methodology for predicting at what point during a high wind storm, powerline ignition is likely.
- Hydrogen is often heralded as the clean fuel of the future, but new research suggests that leaky hydrogen infrastructure could end up increasing atmospheric methane levels, which would cause decades-long climate consequences.
- Machine learning can be valuable in supporting sustainable development of biomass if it is applied across the entire lifecyle of biomass and biomass-derived products, according to a new study.
- A new study shows what it will take for the plastics industry to become completely sustainable: lots of recycling combined with the use of CO2 from the air and biomass. It is also the image of plastics that need to change.
- Conifers are generally better than broad-leafed trees at purifying air from pollutants. A new study shows that the best trees for air purification depend on the type of pollutant involved.
- And more!
Green Technology Market
Green technology is an applicable combination of advanced tools and solutions to conserve natural resources and environment, minimize or mitigate negative impacts from human activities on the environment, and ensure sustainability development. Green technology is also referred to as clean technology or environmental technology which includes technologies, such as IoT, AI, analytics, blockchain, digital twin, security, and cloud, which collect, integrate, and analyze data from various real-time data sources, such as sensors, cameras, and Global Positioning System (GPS).
Green technology, also known as sustainable technology, protects the environment by using various forms of sustainable energy. Some of the best examples of green technologies include solar panels, LED lighting, wind energy, electric vehicles, vertical farming, and composting.
The global Green Technology and Sustainability market size to grow from USD 11.2 billion in 2020 to USD 36.6 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 26.6% during the forecast period. The growing consumer and industrial interest for the use of clean energy resources to conserve environment and increasing use of Radio Frequency Identification sensors across industries are driving the adoption of green technology and sustainability solutions and services in the market.
The blockchain segment is estimated to grow at the highest CAGR: Energy-intensive cryptocurrency mining has caused a spike in carbon emission, and hence blockchain is capable of driving innovation in the field of green technology.
Latest Research
Blade-Tip Vortex Noise Mitigation Traded-Off against Aerodynamic Design for Propellers of Future Electric Aircraft
by Hua-Dong Yao, Zhongjie Huang, Lars Davidson, Jiqiang Niu, Zheng-Wei Chen in Aerospace
Electrification is seen as having an important role to play in the fossil-free aviation of tomorrow. But electric aviation is battling a trade-off dilemma: the more energy-efficient an electric aircraft is, the noisier it gets. Now, researchers at Chalmers University of Technology, Sweden, have developed a propeller design optimisation method that paves the way for quiet, efficient electric aviation.
In recent years, electrification has been described as having an important role in reducing emissions from future aviation. Due to the challenges posed by longer ranges, interest is chiefly focused on electric propeller planes covering shorter distances. Propellers connected to electric motors are considered the most efficient propulsion system for regional and domestic flights. But while airplanes are electric, propellers cause another kind of emission — noise. The noise from the propeller blades wouldn’t just disturb air passengers. Future electric aircraft will need to fly at relatively low altitudes, with noise disturbance reaching residential areas and animal life.
This is where the research community faces a dilemma. The ambition of developing electric aircraft that are both quiet and energy-efficient is somewhat thwarted by a trade-off problem.
“We can see that the more blades a propeller has, the lower the noise emissions. But with fewer blades, propulsion becomes more efficient and the electric aircraft can fly for longer. In that sense, there is a trade-off between energy efficiency and noise. This is something of an obstacle for electric aircrafts that are both quiet and efficient,” explains Hua-Dong Yao, Associate Professor and researcher in fluid dynamics and marine technology at Chalmers University of Technology.
But now, Hua-Dong Yao and his research colleagues may be one step closer to a solution. They have succeeded in isolating and exploring the noise that occurs at the tip of the propeller blades, or “tip vortices,” a known but less well-explored source of noise. In isolating this noise, the researchers were able to fully understand its role in relation to other noise sources generated by propeller blades. By adjusting a range of propeller parameters, such as pitch angle, chord length and number of blades, the team found a way to optimise the propeller design and even out the trade-off effect between efficiency and noise. The method, described in the study can now be used in the design process of quieter propellers for future electric aircraft.
“Modern aircraft propellers usually have two to four blades, but we’ve found that by using six blades designed using our optimisation framework, you can develop a propeller that’s both relatively efficient and quiet. The propeller achieves a noise reduction of up to 5–8 dBA* with only a 3.5 per cent thrust penalty, compared to a propeller with three blades. That’s comparable to the noise reduction of someone going from speaking in a normal conversation voice to the sound you would perceive in a quiet room,” says Hua-Dong Yao.
Entering new era of thermoelectric oxide ceramics with high power factor through designing grain boundaries
by Cesar-Octavio Romo-De-La-Cruz, Yun Chen, Liang Liang, Sergio A. Paredes-Navia, Winnie K. Wong-Ng, Xueyan Song in Renewable and Sustainable Energy Reviews
Researchers at West Virginia University have engineered a material with the potential to dramatically cut the amount of heat power plants release into the atmosphere.
A team led by Xueyan Song, professor and George B. Berry Chair of Engineering at the Benjamin M. Statler College of Engineering and Mineral Resources, has created an oxide ceramic material that solves a longstanding efficiency problem plaguing thermoelectric generators. Those devices can generate electricity from heat, including power plant heat emissions, which contribute to global warming.
The breakthrough oxide ceramic Song’s team produced “achieved a record-high performance that had been deemed impossible,” she said. “We demonstrated the best thermoelectric oxide ceramics reported in the field worldwide over the past 20 years, and the results open up new research directions that could further increase performance.”
Oxide ceramics are from the same family as materials like pottery, porcelain, clay bricks, cement and silicon, but contain various metallic elements. They’re hard, resistant to heat and corrosion, and well-suited for high-temperature applications in air. They can serve as the material for thermoelectric generator components. However, oxide ceramics have “polycrystalline” structures composed of multiple connected crystals. Engineers run into trouble with large-scale thermoelectric applications for those materials since the “grain boundaries,” the places where those crystals meet, block the current and electron flow that powers thermoelectric generators. Song’s team converted that stumbling block into a stepping stone.
“We intentionally added ‘dopants,’ or metal ions, into the polycrystal ceramics, driving special kinds of dopants to segregate to the grain boundaries,” said postdoctoral researcher Romo de la Cruz. “That’s how we turned the unavoidable and detrimental grain boundaries into electricity-conducting pathways, significantly improving thermoelectric performance.”
The research responds to the growing problem of waste heat, a contributor to climate change and byproduct of most operations that convert fuel into power. When lightbulbs get hot to the touch, they’re giving off waste heat: inefficient extra energy that doesn’t contribute to their primary job of producing light. Waste heat is released into the atmosphere by systems as diverse as power plants, home heating systems and automobiles, and there’s enough of it being emitted that the global market for systems that recover it is projected to exceed $70 billion by 2026.
“Heat is used to make almost everything from food to metals and electricity,” Romo de la Cruz explained. “But during those processes, around 60% of the energy produced is unproductively released to the environment in the form of heat. Waste heat recovery will play an increasingly key role in balancing growing demand for electricity against the carbon footprint of industrial processes. Thermoelectric oxide ceramics like ours come into play by substantially improving the ability of thermoelectric generators to convert waste heat into electricity.”
Thermoelectric generators are a promising technology for waste heat recovery in part because they are simple to operate and maintain. A powerful thermoelectric generator could capture a significant portion of a power plant’s waste heat.
But “for the majority of applications, thermoelectric technology is too inefficient to be economical,” Song said. “Thermoelectric’s lack of effectiveness in converting energy severely hampers the development of thermoelectric devices, even though they are desperately needed.”
Her lab solved that problem using nanostructure engineering — manipulating the ceramic’s crystal structure on an atomic scale that can only be seen using an electron microscope — to create a dense, textured polycrystalline material that outperformed the single-crystal materials that are currently standard.
Although tuning the performance of various materials for thermoelectrics has stimulated intense theoretical and experimental work for decades, Song believes that for bulk oxide ceramics, her lab is the first to demonstrate a significant increase in the efficiency of energy generation from heat through the nano- and atomic-scale engineering of grain boundaries between crystals.
“This work is at the cusp for large-scale, high-temperature waste heat recovery,” she said. “It leads toward a new era for oxide ceramics and aligns with the U.S. Department of Energy’s Industrial Heat Shot initiative to develop cost-competitive industrial heat decarbonization technologies with at least 85% lower greenhouse gas emissions by 2035. Our findings could facilitate and accelerate materials design that is magnitudes higher than the current state of the art.”
Strategies for beneficial electric vehicle charging to reduce peak electricity demand and store solar energy
by Zachary Needell, Wei Wei, Jessika E. Trancik in Cell Reports Physical Science
National and global plans to combat climate change include increasing the electrification of vehicles and the percentage of electricity generated from renewable sources. But some projections show that these trends might require costly new power plants to meet peak loads in the evening when cars are plugged in after the workday. What’s more, overproduction of power from solar farms during the daytime can waste valuable electricity-generation capacity.
In a new study, MIT researchers have found that it’s possible to mitigate or eliminate both these problems without the need for advanced technological systems of connected devices and real-time communications, which could add to costs and energy consumption. Instead, encouraging the placing of charging stations for electric vehicles (EVs) in strategic ways, rather than letting them spring up anywhere, and setting up systems to initiate car charging at delayed times could potentially make all the difference. The study is by Zachary Needell PhD, postdoc Wei Wei, and Professor Jessika Trancik of MIT’s Institute for Data, Systems and Society.
In their analysis, the researchers used data collected in two sample cities: New York and Dallas. The data were gathered from, among other sources, anonymized records collected via onboard devices in vehicles, and surveys that carefully sampled populations to cover variable travel behaviors. They showed the times of day cars are used and for how long, and how much time the vehicles spend at different kinds of locations — residential, workplace, shopping, entertainment and so on.
The findings, Trancik says, “round out the picture on the question of where to strategically locate chargers to support EV adoption and also support the power grid.”
Better availability of charging stations at workplaces, for example, could help to soak up peak power being produced at midday from solar power installations, which might otherwise go to waste because it is not economical to build enough battery or other storage capacity to save all of it for later in the day. Thus, workplace chargers can provide a double benefit, helping to reduce the evening peak load from EV charging and also making use of the solar electricity output. These effects on the electric power system are considerable, especially if the system must meet charging demands for a fully electrified personal vehicle fleet alongside the peaks in other demand for electricity, for example on the hottest days of the year. If unmitigated, the evening peaks in EV charging demand could require installing upwards of 20 percent more power-generation capacity, the researchers say.
“Slow workplace charging can be more preferable than faster charging technologies for enabling a higher utilization of midday solar resources,” Wei says.
Meanwhile, with delayed home charging, each EV charger could be accompanied by a simple app to estimate the time to begin its charging cycle so that it charges just before it is needed the next day. Unlike other proposals that require a centralized control of the charging cycle, such a system needs no interdevice communication of information and can be preprogrammed — and can accomplish a major shift in the demand on the grid caused by increasing EV penetration. The reason it works so well, Trancik says, is because of the natural variability in driving behaviors across individuals in a population.
By “home charging,” the researchers aren’t only referring to charging equipment in individual garages or parking areas. They say it’s essential to make charging stations available in on-street parking locations and in apartment building parking areas as well. Trancik says the findings highlight the value of combining the two measures — workplace charging and delayed home charging — to reduce peak electricity demand, store solar energy, and conveniently meet drivers’ charging needs on all days. As the team showed in earlier research, home charging can be a particularly effective component of a strategic package of charging locations; workplace charging, they have found, is not a good substitute for home charging for meeting drivers’ needs on all days.
“Given that there’s a lot of public money going into expanding charging infrastructure,” Trancik says, “how do you incentivize the location such that this is going to be efficiently and effectively integrated into the power grid without requiring a lot of additional capacity expansion?” This research offers some guidance to policymakers on where to focus rules and incentives.
“I think one of the fascinating things about these findings is that by being strategic you can avoid a lot of physical infrastructure that you would otherwise need,” she says. “Your electric vehicles can displace some of the need for stationary energy storage, and you can also avoid the need to expand the capacity of power plants, by thinking about the location of chargers as a tool for managing demands — where they occur and when they occur.”
Delayed home charging could make a surprising amount of difference, the team found. “It’s basically incentivizing people to begin charging later. This can be something that is preprogrammed into your chargers. You incentivize people to delay the onset of charging by a bit, so that not everyone is charging at the same time, and that smooths out the peak.” Such a program would require some advance commitment on the part of participants. “You would need to have enough people committing to this program in advance to avoid the investment in physical infrastructure,” Trancik says. “So, if you have enough people signing up, then you essentially don’t have to build those extra power plants.”
It’s not a given that all this would line up just right, and putting in place the right mix of incentives would be crucial. “If you want electric vehicles to act as an effective storage technology for solar energy, then the [EV] market needs to grow fast enough in order to be able to do that,” Trancik says.
To best use public funds to help make that happen, she says, “you can incentivize charging installations, which would go through ideally a competitive process — in the private sector, you would have companies bidding for different projects, but you can incentivize installing charging at workplaces, for example, to tap into both of these benefits.” Chargers people can access when they are parked near their residences are also important, Trancik adds, but for other reasons. Home charging is one of the ways to meet charging needs while avoiding inconvenient disruptions to people’s travel activities.
Numerical evaluation of the effect of swirl configuration and fuel-rich environment on combustion and emission characteristics in a coal-fired boiler
by Minsung Choi, Taegam Hwang, Yeseul Park, Xinzhuo Li, Junsung Kim, Kibeom Kim, Yonmo Sung, Gyungmin Choi in Energy
Coal-fired power plants have been in place for a long time to meet the global demands for power generation. Needless to say, there are environmental and human health concerns to be addressed on this front. While there are ongoing efforts to transition to renewable energy resources, coal-fired power plants may not become obsolete just yet. Against this backdrop, it is pertinent to explore how the efficiency of these coal-fired boilers can be improved while mitigating their harmful effects on the environment, namely greenhouse gas emissions, acid rain, and photochemical smog generation, and the human health.
To this end, various combustion methods like air an staging and swirl flow have been proposed. However, the efficacy of these technologies in mitigating the pollutant emissions while maximizing the burnout performance has remained unclear. Now, in a recent study made available online on 31 December 2022 and to be published in Volume 268, Issue 1 of the journal Energy on 01 April 2023, an international team of researchers led by Prof. Gyungmin Choi of Pusan National University, Korea analyzed the effectiveness of combining swirl flow and air staging in improving the combustion performance and reducing pollution.
“The exhaust tube vortex (ETV) structure accompanying the swirl flow improves flame stability and combustion performance, but has the disadvantage of generating a large amount of NOx emissions. In contrast, air staging technology creates a fuel-rich environment in the primary combustion zone, which has a positive effect on NOx reduction but negatively affects combustion performance,” explains Prof. Choi. “Therefore, if these two technologies are appropriately combined and applied in real life, a synergistic effect that reduces the emission of air pollutants as well as improves combustion performance can be expected.”
Accordingly, the team employed both simulations and experiments to study the combined effects of different swirl configurations and air staging within a 16-kWth retrofitted down-fired pulverized coal boiler. The coal boiler was composed of three sections: the swirl burner, the boiler, and the exhaust pipe. For staged combustion, staged air was divided into two sides and injected tangentially into the boiler. Liquified petroleum (LPG) gas was used for preheating and flame stabilization. The staged-air and LPG flow rates were regulated, and for each setting, the temperature was measured using thermocouples. Additionally, the amount of gas-phase species was measured using a multi-gas analyzer.
Air staging with two swirl configurations, namely co-swirling and counter-swirling flames, were evaluated to understand which of these is more beneficial in terms of reducing pollutant emissions. In the case of the co-swirling burner, where the air and fuel circulated in the same sense, the coal particles were evenly distributed owing to the formation of inner circulation zone and the ETV-two vital features for optimizing the design of coal-fired boilers.
Further, the team observed an even burnout zone for the co-swirling configuration, which ensured complete combustion of the fuel, reducing the gas species emissions. It also facilitated an increased conversion of chemical energy into thermal energy, boosting the combustion efficiency. In contrast, counter-swirling burners showed uneven coal particle distribution, uneven burnout, and increased NOx emissions, suggesting that a co-swirling configuration was the better option. Additionally, the team showed that air staging technology reduced the environmental costs from $0.003 to $0.015 per day.
Ink Design Enabling Slot‐Die Coated Perovskite Solar Cells with >22% Power Conversion Efficiency, Micro‐Modules, and 1 Year of Outdoor Performance Evaluation
by Jinzhao Li, Janardan Dagar, Oleksandra Shargaieva, et al in Advanced Energy Materials
Solar cells made from metal halide perovskites achieve high efficiencies and their production from liquid inks requires only a small amount of energy. A team led by Prof. Dr. Eva Unger at Helmholtz-Zentrum Berlin is investigating the production process. At the X-ray source BESSY II, the group has analyzed the optimal composition of precursor inks for the production of high-quality FAPbI3 perovskite thin films by slot-die coating. The solar cells produced with these inks were tested under real life conditions in the field for a year and scaled up to mini-module size.
Metal halide perovskites are considered to be a particularly low-cost and promising class of materials for next-generation solar modules. Perovskite solar cells can be produced with coating processes using liquid inks made from precursor materials and various solvents. After coating, the solvents evaporate and the perovskites crystallise to form a more or less homogeneous layer.
Prof. Dr. Eva Unger’s team at Helmholtz-Zentrum Berlin has extensive expertise in solution-based processing methods and is investigating options for upscaling. “Perovskite photovoltaics is the best solution-processable PV technology available,” says Eva Unger, “but we are only just beginning to understand how the complex interaction of the solvent components affects the quality of the perovskite layers.”
This is because when the halide perovskite layers are coated on large surfaces, unwanted inhomogeneities can occur, for example so-called ribbing structures. “By varying the viscosity of the ink, such effects can be minimised,” says Jinzhao Li, who is doing his PhD with Unger. At BESSY II, he has investigated how different solvent combinations affect the crystallisation of the perovskite films. The best p-i-n-FAPbI3 perovskite solar cells thus achieve a certified efficiency of 22.3 % on a laboratory scale. Jinzhao Li also produced mini solar modules (active area of 12.6 cm2) with colleagues from the HySPRINT innovation lab and PVcomB, which achieved efficiencies of around 17 %.
Dr Carolin Ulbrich’s team tested the optimised solar cells at PVcomB’s outdoor test facility for a whole year: In the process, the efficiency remained almost stable in winter and spring, and only dropped in the warmer summer months. “These tests of larger modules under real conditions give us valuable information on degradation mechanisms to then further improve the long-term stability of halide perovskite photovoltaics,” says Eva Unger.
Predicting wildfire ignition induced by dynamic conductor swaying under strong winds
by Xinyue Wang, Paolo Bocchini in Scientific Reports
Spanning long distances across variable terrains, electric power systems can spark wildfires in the event of dry weather and high winds. This may occur when conductor cables oscillate in such a way to become close to the surrounding vegetation.
Data from the California Department of Forestry and Fire Protection shows that between 2016–2020, at least five of the top 20 most destructive California wildfires started from power systems. Paired with the extreme weather conditions and nearby vegetation, power system-ignited incidents are more likely to develop into large, intense wildfires. To prevent power systems from starting wildfires, California electric utilities are authorized to conduct the preemptive Public Safety Power Shutoffs (PSPS) — causing blackouts that affect millions of people.
“When preventive Public Safety Power Shutoffs are executed, they cause major issues for businesses in the area,” explains Paolo Bocchini, professor of civil and environmental engineering at Lehigh University, founder of Lehigh’s Catastrophe Modeling Center, and one of the study’s authors.
The absence of electricity impacts medical devices, traffic lights, and general illumination, he adds. Approached by a California software company to investigate the policies and if the risk justifies the issues, Bocchini realized an opportunity to better understand the mechanical behavior of conductor cables in extreme wind conditions.
When is a PSPS necessary? And can wildfires caused by power system-vegetation contact be prevented? New research from Bocchini and doctoral student Xinyue Wang provides the methodology for predicting at what point during a high wind storm, powerline ignition is likely.
Through a systematic analysis of the conductor dynamic response under high winds, the researchers found it’s possible to predict the risk of powerline ignition. The researchers explain that encroachment probability is highly sensitive to vegetation clearance and wind intensity. And the duration of the wind event must be taken into consideration as well. The need for accurate risk-analysis is urgent, says Bocchini and Wang.
“Our study is the first of its kind applying a rigorous probabilistic approach to the problem, including consideration of the mechanical behavior of the conductor cables under strong wind,” says Bocchini. “While we appreciate the way in which this serious problem is handled today, we think that our study provides much greater insight. Previous work mostly used data-driven approaches based on historical ignition records.
“In contrast, our research looks at the physical and dynamic interactions between the vegetation and the conductors, in a probabilistic way,” adds Wang.
The researchers hope to see an impact on policy or practice that goes beyond the wildfire itself.
“Since wildfires are closely related to climate change, I think that broader and larger efforts may be needed to fundamentally solve the wildfire problem in California,” says Wang.
Risk of the hydrogen economy for atmospheric methane
by Matteo B. Bertagni, Stephen W. Pacala, Fabien Paulot, Amilcare Porporato in Nature Communications
Hydrogen’s potential as a clean fuel could be limited by a chemical reaction in the lower atmosphere, according to research from Princeton University and the National Oceanic and Atmospheric Association.
This is because hydrogen gas easily reacts in the atmosphere with the same molecule primarily responsible for breaking down methane, a potent greenhouse gas. If hydrogen emissions exceed a certain threshold, that shared reaction will likely lead to methane accumulating in the atmosphere — with decades-long climate consequences.
“Hydrogen is theoretically the fuel of the future,” said Matteo Bertagni, a postdoctoral researcher at the High Meadows Environmental Institute working on the Carbon Mitigation Initiative. “In practice, though, it poses many environmental and technological concerns that still need to be addressed.”
Bertagni is the first author of a research article, in which researchers modeled the effect of hydrogen emissions on atmospheric methane. They found that above a certain threshold, even when replacing fossil fuel usage, a leaky hydrogen economy could cause near-term environmental harm by increasing the amount of methane in the atmosphere. The risk for harm is compounded for hydrogen production methods using methane as an input, highlighting the critical need to manage and minimize emissions from hydrogen production.
“We have a lot to learn about the consequences of using hydrogen, so the switch to hydrogen, a seemingly clean fuel, doesn’t create new environmental challenges,” said Amilcare Porporato, Thomas J. Wu ’94 Professor of Civil and Environmental Engineering and the High Meadows Environmental Institute. Porporato is a principal investigator and member of the Leadership Team for the Carbon Mitigation Initiative and is also associated faculty at the Andlinger Center for Energy and the Environment.
The problem boils down to one small, difficult-to-measure molecule known as the hydroxyl radical (OH). Often dubbed “the detergent of the troposphere,” OH plays a critical role in eliminating greenhouse gases such as methane and ozone from the atmosphere.
The hydroxyl radical also reacts with hydrogen gas in the atmosphere. And since a limited amount of OH is generated each day, any spike in hydrogen emissions means that more OH would be used to break down hydrogen, leaving less OH available to break down methane. As a consequence, methane would stay longer in the atmosphere, extending its warming impacts. According to Bertagni, the effects of a hydrogen spike that might occur as government incentives for hydrogen production expand could have decades-long climate consequences for the planet.
“If you emit some hydrogen into the atmosphere now, it will lead to a progressive build-up of methane in the following years,” Bertagni said. “Even though hydrogen only has a lifespan of around two years in the atmosphere, you’ll still have the methane feedback from that hydrogen in 30 years from now.”
In the study, the researchers identified the tipping point at which hydrogen emissions would lead to an increase in atmospheric methane and thereby undermine some of the near-term benefits of hydrogen as a clean fuel. By identifying that threshold, the researchers established targets for managing hydrogen emissions.
“It’s imperative that we are proactive in establishing thresholds for hydrogen emissions, so that they can be used to inform the design and implementation of future hydrogen infrastructure,” said Porporato.
For hydrogen referred to as green hydrogen, which is produced by splitting water into hydrogen and oxygen using electricity from renewable sources, Bertagni said that the critical threshold for hydrogen emissions sits at around 9%. That means that if more than 9% of the green hydrogen produced leaks into the atmosphere — whether that be at the point of production, sometime during transport, or anywhere else along the value chain — atmospheric methane would increase over the next few decades, canceling out some of the climate benefits of switching away from fossil fuels.
And for blue hydrogen, which refers to hydrogen produced via methane reforming with subsequent carbon capture and storage, the threshold for emissions is even lower. Because methane itself is the primary input for the process of methane reforming, blue hydrogen producers have to consider direct methane leakage in addition to hydrogen leakage. For example, the researchers found that even with a methane leakage rate as low as 0.5%, hydrogen leakages would have to be kept under around 4.5% to avoid increasing atmospheric methane concentrations.
“Managing leakage rates of hydrogen and methane will be critical,” Bertagni said. “If you have just a small amount of methane leakage and a bit of hydrogen leakage, then the blue hydrogen that you produce really might not be much better than using fossil fuels, at least for the next 20 to 30 years.”
The researchers emphasized the importance of the time scale over which the effect of hydrogen on atmospheric methane is considered. Bertagni said that in the long-term (over the course of a century, for instance), the switch to a hydrogen economy would still likely deliver net benefits to the climate, even if methane and hydrogen leakage levels are high enough to cause near-term warming. Eventually, he said, atmospheric gas concentrations would reach a new equilibrium, and the switch to a hydrogen economy would demonstrate its climate benefits. But before that happens, the potential near-term consequences of hydrogen emissions might lead to irreparable environmental and socioeconomic damage.
Thus, if institutions hope to meet mid-century climate goals, Bertagni cautioned that hydrogen and methane leakage to the atmosphere must be held in check as hydrogen infrastructure begins to roll out. And because hydrogen is a small molecule that is notoriously difficult to control and measure, he explained that managing emissions will likely require researchers to develop better methods for tracking hydrogen losses across the value chain.
“If companies and governments are serious about investing money to develop hydrogen as a resource, they have to make sure they are doing it correctly and efficiently,” Bertagni said. “Ultimately, the hydrogen economy has to be built in a way that won’t counteract the efforts in other sectors to mitigate carbon emissions.”
Machine learning for sustainable development and applications of biomass and biomass-derived carbonaceous materials in water and agricultural systems: A review
by Hannah Szu-Han Wang, Yuan Yao in Resources, Conservation and Recycling
Biomass is widely considered a renewable alternative to fossil fuels, and many experts say it can play a critical role in combating climate change. Biomass stores carbon and can be turned into bio-based products and energy that can be used to improve soil, treat wastewater, and produce renewable feedstock.
Yet large-scale production of it has been limited due to economic constraints and challenges to optimizing and controlling biomass conversion. A new study led by Yale School of the Environment’s Yuan Yao, assistant professor of industrial ecology and sustainable systems, and doctoral student Hannah Szu-Han Wang, analyzed current machine learning applications for biomass and biomass-derived materials (BDM) to determine if machine learning is advancing the research and development of biomass products. The study authors found that machine learning has not been applied across the entire life cycle of BDM, limiting its ability for development.
Yao’s research investigates how emerging technologies and industrial development will affect the environment with a focus on bioeconomy and sustainable production. Wang worked in the production of biomaterials during her master’s research. The two researchers said they were interested in pursuing this study to find out if machine learning could help with best practices for creating BDM, a chief component of a bio-based economy, as well as predicting their performance as sustainable materials.
“There are so many combinations of biomass feedstock, conversion technologies, and BDM applications. If we want to try each combination using the traditional trial-and-error experimental approach, this will take a lot of time, labor, effort, and energy. We already generate a lot of data from these past experiments, so we are asking, can we apply machine learning to help us to figure out how we can better design BDM?” Yao explains.
For the study, which was published in Resources, Conservation and Recycling, Yao and Wang reviewed more than 50 papers published since 2008 to understand the capabilities, current limitations, and future potential of machine learning in supporting sustainable development and applications of BDM. What they found is that while a few studies applied machine learning to address data challenges for life cycle assessment, most studies only applied machine learning to predict and optimize the technical performance of biomass conversion and applications. None reviewed machine learning applications across the entire lifecycle, from biomass cultivation to BDM production and end-use applications.
“Most studies are applying machine learning to just a very small part of the entire lifecycle of BDM,” Yao says. “Our argument is that if you really want to incorporate sustainability into development of this material, we need to consider the entire lifecycle of the materials, from how they are generated to their potential environmental impact. We believe machine learning has the potential to support sustainability-informed design for biomass-derived materials.”
Wang said the study has led to further research on data gaps in machine learning on biomass-derived materials.
“We found a future direction that people have not yet explored in terms of sustainability assessments for BDM. There needs to be a full pathway prediction to enhance our understanding of how various factors regarding BDM interact and contribute to sustainability,” she says.
Towards circular plastics within planetary boundaries
by Marvin Bachmann, Christian Zibunas, Jan Hartmann, Victor Tulus, Sangwon Suh, Gonzalo Guillén-Gosálbez, André Bardow in Nature Sustainability
Plastic is everywhere. Our society cannot do without it: plastics have numerous advantages, are extremely versatile, and are also cost effective. Today, plastics are mainly produced from crude oil. When the products reach the end of their life, they often end up in a waste incineration plant. The energy-intensive production of plastics and their incineration release large amounts of CO2 into the atmosphere, making plastic products a major contributor to climate change.
One way out would be to rely on sustainable production methods, such as the circular economy, in which as much plastic as possible is recycled. Then the main raw material for plastic products would no longer be crude oil but shredded plastic waste. But is it even possible to tweak the plastics economy to absolute sustainability? Yes, it is, shows a new study led by André Bardow, Professor of Energy and Process Systems Engineering at ETH Zurich. Gonzalo Guillén Gosálbez, Professor of Chemical Systems Engineering at ETH Zurich, and researchers from RWTH Aachen University and the University of California, Santa Barbara collaborated on the study.
The scientists looked at the complete value chains of the 14 most common types of plastics, including polyethylene, polypropylene and polyvinyl chloride. These 14 bulk plastics account for 90 percent of the plastic products manufactured worldwide. In their study, the researchers investigated for the first time whether it is possible for the plastics industry to respect planetary boundaries. These are a measure of comprehensive sustainability. They go beyond energy and climate issues to include, for example, impacts on land and water resources, ecosystems and biodiversity. In short: processes that adhere to planetary boundaries can be sustained over the long term without depleting the Earth’s resources.
The study finds that circular plastics are feasible within planetary boundaries. This would require at least 74 percent of the plastic to be recycled. By way of comparison, only around 15 percent is recycled in Europe today, and the rate is likely to be much lower in other regions of the world. In addition, the study finds that recycling processes would have to be improved. Specifically, plastics recycling would have to become as efficient as other chemical processes already are today. As things currently stand, not all plastics can be recycled. In the case of polyurethanes used as foams, for example, recycling has yet to be established — a question Professor Bardow is also addressing.
For the remaining maximum 26 percent of plastics, the carbon needed for production could be sourced using two other technologies, according to the study: on the one hand, CO2 captured from combustion processes or from the atmosphere (known as carbon capture and utilisation or CCU), and on the other hand, from biomass. “Recycling alone won’t do it; we need all three pillars,” Bardow says.
“Increasing the recycling rate to 74 percent worldwide is a very ambitious goal,” Bardow admits. As such, it is unlikely to be achieved by 2030, but 2050 is more realistic. Another challenge, however, is that more plastic products are currently being manufactured year after year. If the current trend continues until 2050, it won’t be enough to simply improve recycling processes, as planetary boundaries would still be exceeded in 2050.
That is why the study’s authors suggest also addressing demand as well as assigning a different value to plastic. “Plastic is considered cheap, which for a long time was a blessing but has now become a curse,” Bardow says. “Given its outstanding properties, we should view plastic as the high-quality material it truly is. That way, it would be okay for it to cost a little more, and its recycling, too.”
In the study, the scientists point out that plastic products must be better aligned with the circular economy in future. To this end, manufacturers should work more closely with recyclers. According to the study’s authors, it would be desirable if plastics manufacturers had a wider understanding of the responsibility they hold: Today, responsibility often ends where the product leaves the factory gates. The scientists therefore call for product stewardship to encompass the entire life cycle — including disposal and recycling — as the basis for optimising the design of sustainable processes.
In any case, pushing recycling is the right way to go: given that it has no serious disadvantages, it should be treated as a special case in the transformation of the economy toward sustainability. In many other areas, conflicting goals arise. Take, for example, the production of synthetic fuels, which is extremely energy-intensive, or the use of biomass, which competes with food production. Recycling plastic, on the other hand, does not lead to such a conflict of goals.
“Recycling efforts should be intensified wherever possible,” Bardow says. “As a good rule of thumb: More recycling of plastic always leads to more sustainability.”
Differences in accumulation of polycyclic aromatic compounds (PACs) among eleven broadleaved and conifer tree species
by H. Pleijel, J. Klingberg, B. Strandberg, H. Sjöman, L. Tarvainen, G. Wallin in Ecological Indicators
Conifers are generally better than broad leafed trees at purifying air from pollutants. But deciduous tree may be better at capturing particle-bound pollution. A new study led by the University of Gothenburg shows that the best trees for air purification depend on the type of pollutant involved.
Trees and other greenery in cities provide many benefits that are important for the well-being of residents. Leaves and needles on trees filter air pollutants and reduce exposure to hazardous substances in the air. But which trees purify the air most effectively? Researchers from the University of Gothenburg have collected leaves and needles from eleven different trees growing in the same place in the Gothenburg Botanical Garden’s arboretum (tree collection) to analyse which substances they have captured.
“This tree collection provides a unique opportunity to test many different tree-species with similar environmental conditions and exposure to air pollutants,” says Jenny Klingberg, a researcher at the Gothenburg Botanical Garden.
A total of 32 different pollutants were analysed, some of which are bound to particles of various sizes. Others are gaseous. There is a proven connection between exposure to air pollutants and increased risk of cardiovascular diseases and airway problems. This project has focused on polycyclic aromatic hydrocarbons (PAHs). In cities, traffic is the biggest source of these pollutants, which are released due to incomplete combustion in engines.
“Our analyses show that different tree species have different abilities to absorb air pollutants. Conifers generally absorbed more gaseous PAHs than broadleaved trees. Another advantage of conifers is that they also act as air purifiers in winter, when air pollution is usually at its highest,” says Jenny Klingberg.
The researchers also saw that needles continued to absorb air pollutants for several years, which leaves cannot do for obvious reasons. But broadleaved trees had other advantages. They were more efficient at cleaning the air of particles, which is thought to be due to the leaves having a larger surface area to which particles can attach.
“The various species differed more than we expected. Larch, which is a conifer that sheds its needles each autumn, was best in test. Larch trees absorbed the most particle-bound pollutants, but were also good at capturing gaseous PAHs,” says Jenny Klingberg.
Needles and leaves do not, however, break down pollutants to any greater extent, even if sunlight can start that process. Thus there is a risk that the soil beneath the trees will be contaminated by pollutants when the leaves and needles shed and decompose. This places the ecosystem in the soil at risk of being affected, though this has not been investigated in the current study being published in the journal Ecological Indicators.
“The pollutants do not appear to impact the trees’ photosynthesis; leaf chlorophyll content is just as high in the most polluted areas of Gothenburg compared with trees that grow in less polluted environments. But this likely looks different in cities with even worse air quality,” says project leader Håkan Pleijel, professor of applied environmental science at the University of Gothenburg.
However, you should not simply start filling city streets with trees to improve air quality for residents. Several factors determine the benefit. An alley of trees in a narrow street canyon can reduce air flow, negatively affecting dispersion and dilution of the air pollutants and therefore increase concentrations of contaminants locally on busy streets. This means that on narrow streets sheltered from wind, lower-growing vegetation, like hedges, may be preferable. Careful urban planning is necessary, combining different tree species to optimise air purification and to take into account other functions and benefits of trees, according to the researchers.
“This study contributes to improving our understanding of the ability of trees to clean the air and which species are best at absorbing air pollutants,” says Håkan Pleijel. This knowledge is important for urban planning when designing sustainable cities. While trees and greenery can contribute to better air quality in cities, at the end of the day the most important measure is to reduce emissions.
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