GT/ Bacteria generate electricity from methane
Energy & green technology biweekly vol.22, 8th April — 22d April
TL;DR
- Generating power while purifying the environment of greenhouse gases should be achievable using bacteria. Microbiologists have demonstrated that it is possible to make methane-consuming bacteria generate power in the lab.
- Engineers have developed a heat engine with no moving parts that is as efficient as a steam turbine. The design could someday enable a fully decarbonized power grid, researchers say.
- New research highlights the areas in Europe and North Africa where the construction of wind turbines or power lines is likely to increase the risk of death for migrating birds.
- Researchers have discovered a novel way to combine curcumin — the substance in turmeric — and gold nanoparticles to create an electrode that requires 100 times less energy to efficiently convert ethanol into electricity.
- Drawing on 70 years of historic wind and solar-power data, researchers built an AI model to predict the probability of a network-scale ‘drought,’ when daily production of renewables fell below a target threshold. Under a threshold set at the 30th percentile, when roughly a third of all days are low-production days, the researchers found that Texas could face a daily energy drought for up to four months straight. Batteries would be unable to compensate for a drought of this length, and if the system relied on solar energy alone, the drought could be expected to last twice as long — for eight months.
- A new energy system that makes it possible to capture solar energy, store it for up to eighteen years and release it when and where it is needed has now taken the system a step further. After previously demonstrating how the energy can be extracted as heat, they have now succeeded in getting the system to produce electricity, by connecting it to a thermoelectric generator.
- A research team has developed a highly efficient tandem solar cell composed of perovskite and organic absorbers which can be produced at a lower cost than conventional solar cells made of silicon. The further development of this technology is expected to make solar energy even more sustainable.
- Organic solar cells that are based on nonfullerene-acceptors, or NFAs, have now been found to generate electricity efficiently even with a relatively low offset of 0.1 eV.
- Perovskite materials could potentially replace silicon to make solar cells that are far thinner, lighter, and cheaper. But turning these materials into a product that can be manufactured competitively has been a long struggle. A new system using machine learning could speed the development of optimized production methods, and help make this next generation of solar power a reality.
- After water, sand is the most exploited natural resource on the planet. However, its extraction from seas, rivers, beaches and quarries has an impact on the environment and surrounding communities. A new study has found that a step-change in mineral processing could drastically reduce mineral waste — the world’s largest waste stream — while creating a sustainable source of sand. Coined ‘ore-sand’ this material has the potential to address two global sustainability challenges simultaneously.
- 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
Methane-Dependent Extracellular Electron Transfer at the Bioanode by the Anaerobic Archaeal Methanotroph “Candidatus Methanoperedens”
by Heleen T. Ouboter, Tom Berben, Stefanie Berger, Mike S. M. Jetten, Tom Sleutels, Annemiek Ter Heijne, Cornelia U. Welte in Frontiers in Microbiology
Generating power while purifying the environment of greenhouse gases should be achievable using bacteria. In a new publication, microbiologists from Radboud University have demonstrated that it is possible to make methane-consuming bacteria generate power in the lab.
The bacteria, Candidatus Methanoperedens, use methane to grow and naturally occur in fresh water such as ditches and lakes. In the Netherlands, the bacteria mostly thrive in locations where the surface and groundwater are contaminated with nitrogen, as they require nitrate to break down methane.
The researchers initially wanted to know more about the conversion processes occurring in the microorganism. In addition, they were also curious whether it would be possible to use it to generate power. “This could be very useful for the energy sector,” says microbiologist and author Cornelia Welte. “In the current biogas installations, methane is produced by microorganisms and subsequently burnt, which drives a turbine, thus generating power. Less than half of the biogas is converted into power, and this is the maximum achievable capacity. We want to evaluate whether we can do better using microorganisms.”
Fellow microbiologists from Nijmegen have previously shown that it is possible to generate power using anammox bacteria that use ammonium during the process instead of methane. “The process in these bacteria is basically the same,” says microbiologist Heleen Ouboter. “We create a kind of battery with two terminals, where one of these is a biological terminal and the other one is a chemical terminal. We grow the bacteria on one of the electrodes, to which the bacteria donate electrons resulting from the conversion of methane.”
Through this approach, the researchers managed to convert 31 percent of the methane into electricity, but they aim at higher efficiencies. “We will continue focusing on improving the system,” Welte says.
Thermophotovoltaic efficiency of 40%
by Alina LaPotin, Kevin L. Schulte, Myles A. Steiner, Kyle Buznitsky, Colin C. Kelsall, Daniel J. Friedman, Eric J. Tervo, Ryan M. France, Michelle R. Young, Andrew Rohskopf, Shomik Verma, Evelyn N. Wang, Asegun Henry in Nature
Engineers at MIT and the National Renewable Energy Laboratory (NREL) have designed a heat engine with no moving parts. Their new demonstrations show that it converts heat to electricity with over 40 percent efficiency — a performance better than that of traditional steam turbines.
The heat engine is a thermophotovoltaic (TPV) cell, similar to a solar panel’s photovoltaic cells, that passively captures high-energy photons from a white-hot heat source and converts them into electricity. The team’s design can generate electricity from a heat source of between 1,900 to 2,400 degrees Celsius, or up to about 4,300 degrees Fahrenheit. The researchers plan to incorporate the TPV cell into a grid-scale thermal battery. The system would absorb excess energy from renewable sources such as the sun and store that energy in heavily insulated banks of hot graphite. When the energy is needed, such as on overcast days, TPV cells would convert the heat into electricity, and dispatch the energy to a power grid.
With the new TPV cell, the team has now successfully demonstrated the main parts of the system in separate, small-scale experiments. They are working to integrate the parts to demonstrate a fully operational system. From there, they hope to scale up the system to replace fossil-fuel-driven power plants and enable a fully decarbonized power grid, supplied entirely by renewable energy.
“Thermophotovoltaic cells were the last key step toward demonstrating that thermal batteries are a viable concept,” says Asegun Henry, the Robert N. Noyce Career Development Professor in MIT’s Department of Mechanical Engineering. “This is an absolutely critical step on the path to proliferate renewable energy and get to a fully decarbonized grid.”
Co-authors at MIT include Alina LaPotin, Kevin Schulte, Kyle Buznitsky, Colin Kelsall, Andrew Rohskopf, and Evelyn Wang, the Ford Professor of Engineering and head of the Department of Mechanical Engineering, along with collaborators at NREL in Golden, Colorado.
More than 90 percent of the world’s electricity comes from sources of heat such as coal, natural gas, nuclear energy, and concentrated solar energy. For a century, steam turbines have been the industrial standard for converting such heat sources into electricity. On average, steam turbines reliably convert about 35 percent of a heat source into electricity, with about 60 percent representing the highest efficiency of any heat engine to date. But the machinery depends on moving parts that are temperature- limited. Heat sources higher than 2,000 degrees Celsius, such as Henry’s proposed thermal battery system, would be too hot for turbines.
In recent years, scientists have looked into solid-state alternatives — heat engines with no moving parts, that could potentially work efficiently at higher temperatures.
“One of the advantages of solid-state energy converters are that they can operate at higher temperatures with lower maintenance costs because they have no moving parts,” Henry says. “They just sit there and reliably generate electricity.”
Thermophotovoltaic cells offered one exploratory route toward solid-state heat engines. Much like solar cells, TPV cells could be made from semiconducting materials with a particular bandgap — the gap between a material’s valence band and its conduction band. If a photon with a high enough energy is absorbed by the material, it can kick an electron across the bandgap, where the electron can then conduct, and thereby generate electricity — doing so without moving rotors or blades. To date, most TPV cells have only reached efficiencies of around 20 percent, with the record at 32 percent, as they have been made of relatively low-bandgap materials that convert lower-temperature, low-energy photons, and therefore convert energy less efficiently.
In their new TPV design, Henry and his colleagues looked to capture higher-energy photons from a higher-temperature heat source, thereby converting energy more efficiently. The team’s new cell does so with higher-bandgap materials and multiple junctions, or material layers, compared with existing TPV designs.
The cell is fabricated from three main regions: a high-bandgap alloy, which sits over a slightly lower-bandgap alloy, underneath which is a mirror-like layer of gold. The first layer captures a heat source’s highest-energy photons and converts them into electricity, while lower-energy photons that pass through the first layer are captured by the second and converted to add to the generated voltage. Any photons that pass through this second layer are then reflected by the mirror, back to the heat source, rather than being absorbed as wasted heat.
The team tested the cell’s efficiency by placing it over a heat flux sensor — a device that directly measures the heat absorbed from the cell. They exposed the cell to a high-temperature lamp and concentrated the light onto the cell. They then varied the bulb’s intensity, or temperature, and observed how the cell’s power efficiency — the amount of power it produced, compared with the heat it absorbed — changed with temperature. Over a range of 1,900 to 2,400 degrees Celsius, the new TPV cell maintained an efficiency of around 40 percent.
“We can get a high efficiency over a broad range of temperatures relevant for thermal batteries,” Henry says.
The cell in the experiments is about a square centimeter. For a grid-scale thermal battery system, Henry envisions the TPV cells would have to scale up to about 10,000 square feet (about a quarter of a football field), and would operate in climate-controlled warehouses to draw power from huge banks of stored solar energy. He points out that an infrastructure exists for making large-scale photovoltaic cells, which could also be adapted to manufacture TPVs.
“There’s definitely a huge net positive here in terms of sustainability,” Henry says. “The technology is safe, environmentally benign in its life cycle, and can have a tremendous impact on abating carbon dioxide emissions from electricity production.”
Hotspots in the grid: Avian sensitivity and vulnerability to collision risk from energy infrastructure interactions in Europe and North Africa
by Jethro G. Gauld, João P. Silva, Philip W. Atkinson, et al in Journal of Applied Ecology
New research led by the University of East Anglia (UEA) highlights the areas in Europe and North Africa where the construction of wind turbines or power lines is likely to increase the risk of death for migrating birds.
The study used GPS location data from 65 bird tracking studies to understand where they fly more frequently at danger height — defined as 10–60 metres above ground for power lines and 15–135 metres for wind turbines. This allowed the team to identify the areas where these birds would be more sensitive to onshore wind turbine or power line development. Resulting vulnerability maps reveal that the collision hotspots are particularly concentrated within important migration routes, along coastlines and near breeding locations. These include the Western Mediterranean coast of France, Southern Spain and the Moroccan Coast — such as around the Strait of Gibraltar — Eastern Romania, the Sinai Peninsula and the Baltic coast of Germany.
The GPS data collected related to 1,454 birds from 27 species, mostly large soaring ones such as white storks. Exposure to risk varied across the species, with the Eurasian spoonbill, European eagle owl, whooper swan, Iberian imperial eagle and white stork among those flying consistently at heights where they risk collision.
The study involved an international team of researchers from 15 countries and organisations including the British Trust for Ornithology (BTO) and the RSPB in the UK. The authors say development of new wind turbines and transmission power lines should be minimised in these high sensitivity areas, and any developments which do occur will likely need to be accompanied by measures to reduce the risk to birds. Lead author Jethro Gauld, a PhD researcher in UEA’s School of Environmental Sciences, said, it was thought to be the first time GPS tracking data from multiple species had been used in this way.
“We know from previous research that there are many more suitable locations to build wind turbines than we need in order to meet our clean energy targets up to 2050,” said Mr Gauld. “If we can do a better job of assessing risks to biodiversity, such as collision risk for birds, into the planning process at an early stage we can help limit the impact of these developments on wildlife while still achieving our climate targets.
“Our results will help achieve this and in doing so provide better outcomes for people and wildlife.”
Dr Aldina Franco, the project supervisor at UEA,said: “This collaborative study including research from 51 researchers and 15 countries is a great example of where working together can start to answer some of the big questions around the threats that African-Eurasian migrants face on their long annual journeys.”
Phil Atkinson, project supervisorfrom the BTO, said: “The use of high precision GPS devices allow us to study birds’ movements in huge detail. Birds do not respect country boundaries and power lines and wind turbines impact migratory birds across their annual cycle, especially for large soaring birds such as raptors and storks.”
The researchers combined the sensitivity data with the locations of existing onshore wind farms and power lines to identify where the vulnerability hotspots are for these birds, for example the areas where they are already experiencing high risk of collision due to the presence of wind turbines or power lines.
Mr Gauld added: “Our maps can also help target measures to reduce risks where previously built developments are already causing problems. They highlight the areas where existing energy infrastructure is already providing a source of collision risk for these birds. It is therefore a key conservation priority for additional measures to reduce collision risk are implemented in these vulnerability hotspots.
“Such measures can include marking power lines to make them more visible and implementing systems to allow shutdown of wind turbines during periods of high bird traffic.”
The authors acknowledge that transition to zero carbon energy is essential to avoid runaway climate change. European onshore wind energy capacity is projected to grow nearly fourfold by 2050, and countries in the Middle East and North Africa, such as Morocco and Tunisia, also have targets to increase the share of electricity supply from onshore wind. Alongside this there will be a huge investment in new high voltage power lines, with an estimated fivefold increase in transmission capacity required between 2010 and 2050. However, they warn the expansion of renewable energy infrastructure required to achieve this poses a challenge to wildlife conservation due to collision and electrocution risks, particularly for birds.
The researchers hope the study provides a method which other researchers and practitioners involved in environmental impact assessments for renewables can replicate as more data from tracking studies becomes available.
Green synthesis of a novel porous gold-curcumin nanocomposite for super-efficient alcohol oxidation
by Sai Prasad Nayak, Lakshman K. Ventrapragada, Sai Sathish Ramamurthy, J.K. Kiran Kumar, Apparao M. Rao in Nano Energy
Turmeric, a spice found in most kitchens, has an extract that could lead to safer, more efficient fuel cells.
Researchers at the Clemson Nanomaterials Institute (CNI) and their collaborators from the Sri Sathya Sai Institute of Higher Learning (SSSIHL) in India discovered a novel way to combine curcumin — the substance in turmeric — and gold nanoparticles to create an electrode that requires 100 times less energy to efficiently convert ethanol into electricity. While the research team must do more testing, the discovery brings replacing hydrogen as a fuel cell feedstock one step closer.
“Of all the catalysts for alcohol oxidation in alkaline medium, the one we prepared is the best so far,” said Apparao Rao, CNI’s founding director and the R. A. Bowen Professor of Physics in the College of Science’s.
Fuel cells generate electricity through a chemical reaction instead of combustion. They are used to power vehicles, buildings, portable electronic devices and backup power systems. Hydrogen fuel cells are highly efficient and do not produce greenhouse gases. While hydrogen is the most common chemical element in the universe, it must be derived from substances such as natural gas and fossil fuels because it occurs naturally on Earth only in compound form with other elements in liquids, gases or solids. The necessary extraction adds to hydrogen fuel cells’ cost and environmental impact. In addition, hydrogen used in fuel cells is a compressed gas, creating challenges for storage and transportation. Ethanol, an alcohol made from corn or other agricultural-based feeds, is safer and easier to transport than hydrogen because it is a liquid.
“To make it a commercial product where we can fill our tanks with ethanol, the electrodes have to be highly efficient,” said Lakshman Ventrapragada, a former student of Rao’s who worked as a research assistant at the CNI and is an alumnus of SSSIHL. “At the same time, we don’t want very expensive electrodes or synthetic polymeric substrates that are not eco-friendly because that defeats the whole purpose. We wanted to look at something green for the fuel cell generation process and making the fuel cell itself.”
The researchers focused on the fuel cell’s anode, where the ethanol or other feed source is oxidized. Fuel cells widely use platinum as a catalyst. But platinum suffers from poisoning because of reaction intermediates such as carbon monoxide, Ventrapragada said. It is also costly. The researchers used gold as a catalyst. Instead of using conducting polymers, metal-organic frameworks, or other complex materials to deposit the gold on the surface of the electrode, the researchers used curcumin because of its structural uniqueness. Curcumin is used to decorate the gold nanoparticles to stabilize them, forming a porous network around the nanoparticles. Researchers deposited the curcumin gold nanoparticle on the surface of the electrode at a 100 times lower electric current than in previous studies. Without the curcumin coating, the gold nanoparticles agglomerate, cutting down on the surface area exposed to the chemical reaction, Ventrapragada said.
“Without this curcumin coating, the performance is poor,” Rao said. “We need this coating to stabilize and create a porous environment around the nanoparticles, and then they do a super job with alcohol oxidation.
“There’s a big push in the industry for alcohol oxidation. This discovery is an excellent enabler for that. The next step is to scale the process up and work with an industrial collaborator who can actually make the fuel cells and build stacks of fuel cells for the real application,” he continued.
But the research could have broader implications than improved fuel cells. The electrode’s unique properties could lend itself to future applications in sensors, supercapacitors and more, Ventrapragada said.
In collaboration with the SSSIHL research team, Rao’s team is testing the electrode as a sensor that could help identify changes in the level of dopamine. Dopamine has been implicated in disorders such as Parkinson’s disease and attention deficit hyperactivity disorder. When members of the research team tested urine samples obtained from healthy volunteers, they could measure dopamine to the approved clinical range with this electrode using a cost-effective method compared to standard ones used today, Rao said.
“In the beginning stages of the project, we did not imagine other applications that gold-coated curcumin could support. However, before the end of the alcohol oxidation experiments, we were fairly confident that other applications are possible,” Ventrapragada said. “Although we don’t have a complete understanding of what’s happening at the atomic level, we know for sure that curcumin is stabilizing the gold nanoparticles in a way that it can lend itself to other applications.”
A k-nearest neighbor space-time simulator with applications to large-scale wind and solar power modeling
by Yash Amonkar, David J. Farnham, Upmanu Lall in Patterns
Renewable energy prices have fallen by more than 70 percent in the last decade, driving more Americans to abandon fossil fuels for greener, less-polluting energy sources. But as wind and solar power continue to make inroads, grid operators may have to plan for large swings in availability.
The warning comes from Upmanu Lall, a professor at Columbia Engineering and the Columbia Climate School who has recently turned his sights from sustainable water use to sustainable renewables in the push toward net-zero carbon emissions.
“Designers of renewable energy systems will need to pay attention to changing wind and solar patterns over weeks, months, and years, the way water managers do,” he said. “You won’t be able to manage variability like this with batteries. You’ll need more capacity.”
In a new modeling study, Lall and Columbia PhD student Yash Amonkar, show that solar and wind potential vary widely over days and weeks, not to mention months to years. They focused on Texas, which leads the country in generating electricity from wind power and is the fifth-largest solar producer. Texas also boasts a self-contained grid that’s as big as many countries’, said Lall, making it an ideal laboratory for charting the promise and peril of renewable energy systems.
Drawing on 70 years of historic wind and solar-power data, the researchers built an AI model to predict the probability of a network-scale “drought,” when daily production of renewables fell below a target threshold. Under a threshold set at the 30th percentile, when roughly a third of all days are low-production days, the researchers found that Texas could face a daily energy drought for up to four months straight. Batteries would be unable to compensate for a drought of this length, said Lall, and if the system relied on solar energy alone, the drought could be expected to last twice as long — for eight months. “These findings suggest that energy planners will have to consider alternate ways of storing or generating electricity, or dramatically increasing the capacity of their renewable systems,” he said.
The research began six years ago, when Lall and a former graduate student, David Farnham, examined wind and solar variability at eight U.S. airports, where weather records tend to be longer and more detailed. They wanted to see how much variation could be expected under a hypothetical 100% renewable-energy grid. The results, which Farnham published in his PhD thesis, weren’t a surprise. Farnham and Lall found that solar and wind potential, like rainfall, is highly variable based on the time of year and the place where wind turbines and solar panels have been sited. Across eight cities, they found that renewable energy potential rose and fell from the long-term average by as much as a third in some seasons.
“We coined the term ‘energy’ droughts since a 10-year cycle with this much variation from the long-term average would be seen as a major drought,” said Lall. “That was the beginning of the energy drought work.”
In the current study, Lall chose to zoom in on Texas, a state well-endowed with both sun and wind. Lall and Amonkar found that persistent renewable energy droughts could last as long as a year even if solar and wind generators were spread across the entire state. The conclusion, Lall said, is that renewables face a storage problem that can only realistically be solved by adding additional capacity or sources of energy.
“In a fully renewable world, we would need to develop nuclear fuel or hydrogen fuel, or carbon recycling, or add much more capacity for generating renewables, if we want to avoid burning fossil fuels,” he said.
In times of low rainfall, water managers keep fresh water flowing through the spigot by tapping municipal reservoirs or underground aquifers. Solar and wind energy systems have no equivalent backup. The batteries used to store excess solar and wind power on exceptionally bright and gusty days hold a charge for only a few hours, and at most, a few days. Hydropower plants provide a potential buffer, said Lall, but not for long enough to carry the system through an extended dry spell of intermittent sun and wind.
“We won’t solve the problem by building a larger network,” he said. “Electric grid operators have a target of 99.99% reliability while water managers strive for 90 percent reliability. You can see what a challenging game this will be for the energy industry, and just how valuable seasonal and longer forecasts could be.”
In the next phase of research, Lall will work with Columbia Engineering professors Vijay Modi and Bolun Xu to see if they can predict both energy droughts and “floods,” when the system generates a surplus of renewables. Armed with these projections, they hope to predict the rise and fall of energy prices.
Chip-scale solar thermal electrical power generation
by Zhihang Wang, Zhenhua Wu, Zhiyu Hu, Jessica Orrego-Hernández, et al in Cell Reports Physical Science
The researchers behind an energy system that makes it possible to capture solar energy, store it for up to eighteen years and release it when and where it is needed have now taken the system a step further. After previously demonstrating how the energy can be extracted as heat, they have now succeeded in getting the system to produce electricity, by connecting it to a thermoelectric generator. Eventually, the research — developed at Chalmers University of Technology, Sweden — could lead to self-charging electronics using stored solar energy on demand.
“This is a radically new way of generating electricity from solar energy. It means that we can use solar energy to produce electricity regardless of weather, time of day, season, or geographical location. It is a closed system that can operate without causing carbon dioxide emissions,” says research leader Kasper Moth-Poulsen, Professor at the Department of Chemistry and Chemical Engineering at Chalmers.
The new technology is based on the solar energy system MOST — Molecular Solar Thermal Energy Storage Systems, developed at Chalmers University of Technology. Very simply, the technology is based on a specially designed molecule that changes shape when it comes into contact with sunlight. The research has already attracted great interest worldwide when it has been presented at earlier stages. The new study takes the solar energy system a step further, detailing how it can be combined with a compact thermoelectric generator to convert solar energy into electricity.
The Swedish researchers sent their specially designed molecule, loaded with solar energy, to colleagues Tao Li and Zhiyu Hu at Shanghai Jiao Tong University, where the energy was released and converted into electricity using the generator they developed there. Essentially, Swedish sunshine was sent to the other side of the world and converted into electricity in China.
“The generator is an ultra-thin chip that could be integrated into electronics such as headphones, smart watches and telephones. So far, we have only generated small amounts of electricity, but the new results show that the concept really works. It looks very promising,” says researcher Zhihang Wang from Chalmers University of Technology.
The research has great potential for renewable and emissions-free energy production. But a lot of research and development remains before we will be able to charge our technical gadgets or heat our homes with the system’s stored solar energy.
“Together with the various research groups included in the project, we are now working to streamline the system. The amount of electricity or heat it can extract needs to be increased. Even if the energy system is based on simple basic materials, it needs to be adapted to be sufficiently cost-effective to produce, and thus possible to launch more broadly,” says Kasper Moth-Poulsen.
Molecular Solar Thermal Energy Storage Systems, Most, is a closed energy system based on a specially designed molecule of carbon, hydrogen and nitrogen, which when hit by sunlight changes shape into an energy-rich isomer — a molecule made up of the same atoms but arranged together in a different way. The isomer can then be stored in liquid form for later use when needed, such as at night or in winter. The researchers have refined the system to the point that it is now possible to store the energy for up to 18 years. A specially designed catalyst releases the saved energy as heat while returning the molecule to its original shape, so it can then be reused in the heating system. Now, in combination with a micrometer-thin thermoelectric generator, the energy system can also generate electricity to order.
Perovskite–organic tandem solar cells with indium oxide interconnect
by K. O. Brinkmann, T. Becker, F. Zimmermann, et al in Nature
A German research team has developed a tandem solar cell that reaches 24 per cent efficiency — measured according to the fraction of photons converted into electricity (i.e. electrons). This sets a new world record as the highest efficiency achieved so far with this combination of organic and perovskite-based absorbers. The solar cell was developed by Professor Dr Thomas Riedl’s group at the University of Wuppertal together with researchers from the Institute of Physical Chemistry at the University of Cologne and other project partners from the Universities of Potsdam and Tübingen as well as the Helmholtz-Zentrum Berlin and the Max-Planck-Institut für Eisenforschng in Düsseldorf.
Conventional solar cell technologies are predominantly based on the semiconductor silicon and are now considered to be ‘as good as it gets’. Significant improvements in their efficiency — i.e., more watts of electrical power per watt of solar radiation collected — can hardly be expected. That makes it all the more necessary to develop new solar technologies that can make a decisive contribution to the energy transition. Two such alternative absorber materials have been combined in this work. Here, organic semiconductors were used, which are carbon-based compounds that can conduct electricity under certain conditions. These were paired with a perovskite, based on a lead-halogen compound, with excellent semiconducting properties. Both of these technologies require significantly less material and energy for their production compared to conventional silicon cells, making it possible to make solar cells even more sustainable.
As sunlight consists of different spectral components, i.e. colours, efficient solar cells have to convert as much of this sunlight as possible into electricity. This can be achieved with so-called tandem cells, in which different semiconductor materials are combined in the solar cell, each of which absorbs different ranges of the solar spectrum. In the current study the organic semiconductors were used for the ultraviolet and visible parts of the light, while the perovskite can efficiently absorb in the near-infrared. Similar combinations of materials have already been explored in the past, but now the research team succeeded in significantly increasing their performance.
At the start of the project, the world’s best perovskite/organic tandem cells had an efficiency of around 20 per cent. Under the leadership of the University of Wuppertal, the Cologne researchers, together with the other project partners, were able to increase this value to an unprecedented 24 per cent. ‘To achieve such high efficiency, the losses at the interfaces between the materials within the solar cells had to be minimized,’ said Dr Selina Olthof of the University of Cologne’s Institute of Physical Chemistry. ‘To solve this problem, the group in Wuppertal developed a so-called interconnect that couples the organic sub-cell and the perovskite sub-cell electronically and optically.’
As interconnect, a thin layer of indium oxide was integrated into the solar cell with a thickness of merely 1.5 nanometres to keep losses as low as possible. The researchers in Cologne played a key role in assessing the energetic and electrical properties of the interfaces and the interconnect in order to identify loss processes and further optimize the components. Simulations by the group in Wuppertal showed that tandem cells with an efficiency of more than 30 per cent could be achieved in the future with this approach.
A potential new solution to the mine tailings and global sand sustainability crises. Final Report. Version 1.4
by Golev, A., Gallagher, L., Vander Velpen, A., Lynggaard, J.R., Friot, D., Stringer, M., Chuah, S., Arbelaez-Ruiz, D., Mazzinghy, D., Moura, L., Peduzzi, P., Franks, D.M.
After water, sand is the most exploited natural resource on the planet. However, its extraction from seas, rivers, beaches and quarries has an impact on the environment and surrounding communities. A new study by researchers from the University of Geneva (UNIGE) and the University of Queensland’s Sustainable Minerals Institute (SMI) has found that a step-change in mineral processing could drastically reduce mineral waste — the world’s largest waste stream — while creating a sustainable source of sand. Coined “ore-sand,” this material has the potential to address two global sustainability challenges simultaneously, according to the report ‘’Ore-sand: A potential new solution to the mine tailings and global sand sustainability crises.”
Concrete, asphalt, glass, electronic chips: sand has many applications. Composed of small mineral particles, this granular material comes from sensitive dynamic environments such as seas, beaches, lakes and rivers or, from static land-based environments such as ancient river deposits and rock quarries. It is estimated that 50 billion tons of sand are used each year. Over the past two decades demand has tripled primarily due to urbanisation and population growth, a trend which is expected to continue with aggregates use reaching beyond 50 Bt per year by 2030. In addition to the risks of local shortages, the extraction of such a volume of sand has environmental and societal consequences. For example, it is leading to erosion in river banks, which significantly increases the risk of flooding. In some countries, sand mining has caused loss of livelihoods in communities.
Researchers from the University of Geneva (UNIGE) and from the Sustainable Minerals Institute at the University of Queensland (UQ), Australia, have researched the potential of a viable alternative to naturally occurring sand. This material, presented in a recent report published by the two universities, has been coined “ore-sand’’. UNIGE’s Adjunct Professor at Department F.-A. Forel for environmental and aquatic sciences of the Faculty of Science, Pascal Peduzzi said that “ore-sand has the largest potential in volume for reducing the amount of sand taken in the natural environment. By using what has been so far considered as ‘’left over’’ material, the project gives an important impetus towards a more circular economy.”
The production of ore-sand can help reduce the production of mineral mining waste and thus the further build-up of mine tailings. Mineral wastes from the mining of ores currently represents the largest waste stream on the planet, estimated between 30–60 billion tonnes per year. These residues come from crushing operations to extract certain metals from the rock.
SMI’s Development Minerals Program Leader Professor Daniel Franks said ore-sand has the potential to address two global sustainability challenges simultaneously. “Separating and repurposing these sand-like materials before they are added to the waste stream would not only significantly reduce the volume of waste being generated but could also create a responsible source of sand.”
The 12-month study independently sampled and investigated sand produced from iron ore mining, pioneered by Vale S.A in Brazil, which has previously experienced tailings dam failures. After an analysis of the chemical properties and some refining operations, the researchers were able to demonstrate that part of the material stream which would otherwise end up as mining residues could be used as a substitute for construction and industrial sand, in the same way as recycled concrete and steel slag. “If these results can be replicated with other types of mineral ores there is potential for major reductions in global mine tailings.”
“By mapping mining locations worldwide and modelling global sand consumption, we discovered that almost a third of mine sites can find at least some demand for ore-sand within a 50 km range. This could contribute to at least 10% reduction in the volume of tailings generation at each site. Simultaneously, almost half of the global sand market (by volume) could find a local source of ore-sand. For example, ore-sand could potentially substitute 1 billion metric tons of sand demand in China,” explains Daniel Franks.
In addition, the life cycle assessment of ore-sand, based on the Vale case, shows that substituting naturally sourced sand with ore-sand could potentially lead to net reductions in carbon emissions during sand production. The carbon emissions by transport is however a key consideration.
“Considering the co-production of ore-sand is a significant advantage for mining companies: it reduces the large tailings which hinder operational mining activities, while at the same time can generate additional revenues. Ore-sand is a step towards a “no tailings mine’’, explains Pascal Peduzzi. Developing countries have fewer options for using recycled aggregate materials, given their more recent infrastructure. However, many have mining operations that can generate ore-sand as a by-product.”
Some of the next steps are to collaborate with aggregate market players to demonstrate this substitute material’s ease-of-use, performance and sourcing process. Findings from the study were presented at the 5th United Nations Environment Assembly. A new UNEA resolution (UNEP/EA5/L18/REV.1) on “Environmental aspects of minerals and metals management’’ calls for strengthened scientific, technical and policy knowledge with regard to sand to support global policies and action regarding its environmentally sound extraction and use.
Cascaded energy landscape as a key driver for slow yet efficient charge separation with small energy offset in organic solar cells
by Shin-ichiro Natsuda, Toshiharu Saito, Rei Shirouchi, Yuji Sakamoto, Taiki Takeyama, Yasunari Tamai, Hideo Ohkita in Energy & Environmental Science
Glittering solar-paneled roofs atop residential, commercial, and industrial buildings may soon get a new look with the carbon-based organic solar cell or OSC. Thinness and flexibility partly explain why OSCs may be a better alternative to traditional silicon-based cells.
But not all OSCs are created equal. Those based on nonfullerene-acceptors, or NFAs,have now been found to generate electricity efficiently even with a relatively low offset of 0.1 eV. Compared to conventional fullerene-based types, NFA-based OSCs achieve significantly higher power conversion efficiency.
“We then asked ourselves how this was achieved, and what materials we would need to develop in order to obtain the low offset,” says KyotoU’s Yasunari Tamai, whose team made the discovery.
Traditionally, a combination of so-called p-type polymers with n-type fullerene derivatives have been the preferred semiconductors used in OSCs, also called organic photovoltaics, or OPVs. A difference in the energy levels, or offset, of more than 0.3 eV is generally considered necessary to drive photovoltaic conversion. These conventional polymers can provide up to 10–11% of power conversion efficiency.
Tamai adds, “On the other hand, a large offset also drags down the open-circuit voltage. Efficient power conversion requires a trade-off between electric current and voltage in the form of a low offset.”
The best solutions can sometimes be found by thinking outside the box, or in this case, reversing the thinking: lose the fullerene. Recently, NFA-based OSCs have been found to generate efficient free carriers even with an offset of a mere 0.1 eV, topping regular fullerene-based OSCs by an impressive ten percent or more. The team used transient absorption spectroscopy to track free carrier generation over time. As when a slalom skier glides down the hill from gate to gate, relaxed charges transfer freely down the energy cascade created in the solar cells.
“We hope that our research will help move the world closer to this practical application of organic solar cell technology to harness the virtually non-depletable energy source from our sun,” concludes Tamai.
Machine learning with knowledge constraints for process optimization of open-air perovskite solar cell manufacturing
by Zhe Liu, Nicholas Rolston, Austin C. Flick, Thomas W. Colburn, Zekun Ren, Reinhold H. Dauskardt, Tonio Buonassisi in Joule
Perovskites are a family of materials that are currently the leading contender to potentially replace today’s silicon-based solar photovoltaics. They hold the promise of panels that are far thinner and lighter, that could be made with ultra-high throughput at room temperature instead of at hundreds of degrees, and that are cheaper and easier to transport and install. But bringing these materials from controlled laboratory experiments into a product that can be manufactured competitively has been a long struggle.
Manufacturing perovskite-based solar cells involves optimizing at least a dozen or so variables at once, even within one particular manufacturing approach among many possibilities. But a new system based on a novel approach to machine learning could speed up the development of optimized production methods and help make the next generation of solar power a reality. The system, developed by researchers at MIT and Stanford University over the last few years, makes it possible to integrate data from prior experiments, and information based on personal observations by experienced workers, into the machine learning process. This makes the outcomes more accurate and has already led to the manufacturing of perovskite cells with an energy conversion efficiency of 18.5 percent, a competitive level for today’s market. The research is reported in a paper by MIT professor of mechanical engineering Tonio Buonassisi, Stanford professor of materials science and engineering Reinhold Dauskardt, recent MIT research assistant Zhe Liu, Stanford doctoral graduate Nicholas Rolston, and three others.
Perovskites are a group of layered crystalline compounds defined by the configuration of the atoms in their crystal lattice. There are thousands of such possible compounds and many different ways of making them. While most lab-scale development of perovskite materials uses a spin-coating technique, that’s not practical for larger-scale manufacturing, so companies and labs around the world have been searching for ways of translating these lab materials into a practical, manufacturable product.
“There’s always a big challenge when you’re trying to take a lab-scale process and then transfer it to something like a startup or a manufacturing line,” says Rolston, who is now an assistant professor at Arizona State University. The team looked at a process that they felt had the greatest potential, a method called rapid spray plasma processing, or RSPP.
The manufacturing process would involve a moving roll-to-roll surface, or series of sheets, on which the precursor solutions for the perovskite compound would be sprayed or ink-jetted as the sheet rolled by. The material would then move on to a curing stage, providing a rapid and continuous output “with throughputs that are higher than for any other photovoltaic technology,” Rolston says.
“The real breakthrough with this platform is that it would allow us to scale in a way that no other material has allowed us to do,” he adds. “Even materials like silicon require a much longer timeframe because of the processing that’s done. Whereas you can think of [this approach as more] like spray painting.”
Within that process, at least a dozen variables may affect the outcome, some of them more controllable than others. These include the composition of the starting materials, the temperature, the humidity, the speed of the processing path, the distance of the nozzle used to spray the material onto a substrate, and the methods of curing the material. Many of these factors can interact with each other, and if the process is in open air, then humidity, for example, may be uncontrolled. Evaluating all possible combinations of these variables through experimentation is impossible, so machine learning was needed to help guide the experimental process. But while most machine-learning systems use raw data such as measurements of the electrical and other properties of test samples, they don’t typically incorporate human experience such as qualitative observations made by the experimenters of the visual and other properties of the test samples, or information from other experiments reported by other researchers. So, the team found a way to incorporate such outside information into the machine learning model, using a probability factor based on a mathematical technique called Bayesian Optimization.
Using the system, he says, “having a model that comes from experimental data, we can find out trends that we weren’t able to see before.” For example, they initially had trouble adjusting for uncontrolled variations in humidity in their ambient setting. But the model showed them “that we could overcome our humidity challenges by changing the temperature, for instance, and by changing some of the other knobs.”
The system now allows experimenters to much more rapidly guide their process in order to optimize it for a given set of conditions or required outcomes. In their experiments, the team focused on optimizing the power output, but the system could also be used to simultaneously incorporate other criteria, such as cost and durability — something members of the team are continuing to work on, Buonassisi says.
The researchers were encouraged by the Department of Energy, which sponsored the work, to commercialize the technology, and they’re currently focusing on tech transfer to existing perovskite manufacturers. “We are reaching out to companies now,” Buonassisi says, and the code they developed has been made freely available through an open-source server. “It’s now on GitHub, anyone can download it, anyone can run it,” he says. “We’re happy to help companies get started in using our code.”
Already, several companies are gearing up to produce perovskite-based solar panels, even though they are still working out the details of how to produce them, says Liu, who is now at the Northwestern Polytechnical University in Xi’an, China. He says companies there are not yet doing large-scale manufacturing, but instead starting with smaller, high-value applications such as building-integrated solar tiles where appearance is important. Three of these companies “are on track or are being pushed by investors to manufacture 1 meter by 2-meter rectangular modules [comparable to today’s most common solar panels], within two years,” he says.
‘The problem is, they don’t have a consensus on what manufacturing technology to use,” Liu says. The RSPP method, developed at Stanford, “still has a good chance” to be competitive, he says. And the machine learning system the team developed could prove to be important in guiding the optimization of whatever process ends up being used.
“The primary goal was to accelerate the process, so it required less time, less experiments, and less human hours to develop something that is usable right away, for free, for industry,” he says.
MISC
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