GT/ Renewable grid: Recovering electricity from heat storage hits 44% efficiency
Energy & green technology biweekly vol.71, 6th June — 21st June
TL;DR
- Closing in on the theoretical maximum efficiency, devices for turning heat into electricity are edging closer to being practical for use on the grid, according to new research.
- A perspective piece describes innovative strategies that significantly reduce both resource consumption and fossil fuel emissions.
- Boilers are a major source of greenhouse gas emissions. In a recent study, researchers developed a method to convert CO2 emissions from small boilers into methane, which makes use of an optimized reactor design that evenly distributes the CO2 feed. This, in turn, results in significantly lower temperature increments and a boost in methane production. This innovative technique could pave the way for reducing greenhouse gas emissions.
- Engineers have helped design a new method to make hydrogen gas from water using only solar power and agricultural waste such as manure or husks. The method reduces the energy needed to extract hydrogen from water by 600%, creating new opportunities for sustainable, climate-friendly chemical production.
- Offshore wind could have prevented the Fukushima disaster, according to a review of wind energy.
- And more!
Green Technology Market
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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.
Latest Research
High-efficiency air-bridge thermophotovoltaic cells
by Bosun Roy-Layinde, Jihun Lim, Claire Arneson, Stephen R. Forrest, Andrej Lenert in Joule
Closing in on the theoretical maximum efficiency, devices for turning heat into electricity are edging closer to being practical for use on the grid, according to University of Michigan research.
Heat batteries could store intermittent renewable energy during peak production hours, relying on a thermal version of solar cells to convert it into electricity later.
“As we include higher fractions of renewables on the grid to reach decarbonization goals, we need lower costs and longer durations of energy storage as the energy generated by solar and wind does not match when the energy is used,” Andrej Lenert, U-M associate professor of chemical engineering and corresponding author of the study.
Thermophotovoltaic cells work similarly to photovoltaic cells, commonly known as solar cells. Both convert electromagnetic radiation into electricity, but thermophotovoltaics use the lower energy infrared photons rather than the higher energy photons of visible light.
The team reports that their new device has a power conversion efficiency of 44% at 1435°C, within the target range for existing high-temperature energy storage (1200°C-1600°C). It surpasses the 37% achieved by previous designs within this range of temperatures.
“It’s a form of battery, but one that’s very passive. You don’t have to mine lithium as you do with electrochemical cells, which means you don’t have to compete with the electric vehicle market. Unlike pumped water for hydroelectric energy storage, you can put it anywhere and don’t need a water source nearby,” said Stephen Forrest, the Peter A. Franken Distinguished University Professor of Electrical Engineering at U-M and contributing author of the study.
In a heat battery, thermophotovoltaics would surround a block of heated material at a temperature of at least 1000°C. It might reach that temperature by passing electricity from a wind or solar farm through a resistor or by absorbing excess heat from solar thermal energy or steel, glass or concrete production.
“Essentially, using electricity to heat something up is a very simple and inexpensive method to store energy relative to lithium ion batteries. It gives you access to many different materials to use as a storage medium for thermal batteries,” Lenert said.
The heated storage material radiates thermal photons with a range of energies. At 1435°C, about 20–30% of those have enough energy to generate electricity in the team’s thermophotovoltaic cells. The key to this study was optimizing the semiconductor material, which captures the photons, to broaden its preferred photon energies while aligning with the dominant energies produced by the heat source. But the heat source also produces photons above and below the energies that the semiconductor can convert to electricity. Without careful engineering, those would be lost.
To solve this problem, the researchers built a thin layer of air into the thermophotovoltaic cell just beyond the semiconductor and added a gold reflector beyond the air gap — a structure they call an air bridge. This cavity helped trap photons with the right energies so that they entered the semiconductor and sent the rest back into the heat storage material, where the energy had another chance to be re-emitted as a photon the semiconductor could capture.
“Unlike solar cells, thermophotovoltaic cells can recuperate or recycle photons that are not useful,” said Bosun Roy-Layinde, U-M doctoral student of chemical engineering and first author of the study.
A recent study found stacking two air bridges improves the design, increasing both the range of photons converted to electricity and the useful temperature range for heat batteries.
“We’re not yet at the efficiency limit of this technology. I am confident that we will get higher than 44% and be pushing 50% in the not-too-distant future,” said Forrest, who also is the Paul G. Goebel Professor of Engineering and professor of electrical engineering and computer science, materials science and engineering, and physics.
Demand-side strategies key for mitigating material impacts of energy transitions
by Felix Creutzig, Sofia G. Simoes, Sina Leipold, et al in Nature Climate Change
A perspective research describes innovative strategies that significantly reduce both resource consumption and fossil fuel emissions.
The study led by Felix Creutzig from the Mercator Research Institute on Global Commons and Climate Change (MCC) in Berlin, with the collaboration of IIASA researchers Alessio Mastrucci, Charlie Wilson, and Volker Krey, as well as many collaborators from the IIASA-led CircEUlar and EDITS research projects, discusses an optimistic scenario from a climate protection perspective, in which the use of fossil fuels can be rapidly reduced.
By phasing out fossil fuels, the production of raw materials is reduced as the extraction of natural gas, oil, and coal is no longer necessary. This also reduces emissions of greenhouse gases and other pollutants. However, the key question is whether the demand for raw materials and land for renewable energies, electric cars, and sustainable transport infrastructure will lead to additional social and environmental impacts.
“Material extraction and waste streams, the construction of new infrastructure, the associated land use changes and the provision of new types of goods and services related to decarbonization will create social and environmental pressures at local to regional levels,” explains Krey, who leads the Integrated Assessment and Climate Change Research Group at IIASA. “So-called rare earths are, for example, needed for wind turbines and electric cars, lithium and cobalt for batteries, and construction materials for green infrastructure.”
“Our study provides an overview of the social, ecological, and geopolitical risks of these materials. These include the displacement of people from residential areas where the raw materials are extracted, health effects due to toxic emissions, injuries, and deaths due to occupational accidents, cartel structures, corruption, and other grievances,” adds coauthor Helmut Haberl from the University of Natural Resources and Life Sciences (BOKU), Vienna.
To limit these problems, it is necessary to keep energy and resource requirements as low as possible through demand-side measures.
“Our study shows that there is considerable potential to reduce energy and resource consumption without having to impose restrictions,” notes Creutzig.
While the need for materials to support a clean energy infrastructure is substantial, it remains significantly lower than the demand generated by the ongoing reliance on fossil fuels. Demand-side strategies, such as improving resource efficiency, replacing individual mobility with shared or public transport, reusing or recycling existing materials, and the thermal refurbishment of buildings play a decisive role here.
The study highlights models that promote shared mobility (including car and ride sharing), which drastically reduces the need for private vehicles. This significantly reduces both material consumption and emissions.
“Our study emphasizes the dual benefits of demand-side solutions in mitigating climate change and reducing material consumption,” says Creutzig. “By focusing on efficiency and circular economy principles, we can achieve significant environmental and social benefits.”
The research team calls for increased interdisciplinary cooperation and new ideas in policy design to make effective use of these demand-side measures. They underscore the importance of integrating such strategies into global climate protection plans to ensure a holistic approach to sustainable development.
Unveil carbon dioxide recycling potential throughout distributor-type membrane reactor
by Yuya Sato, Marcin Moździerz, Katarzyna Berent, Grzegorz Brus, Mikihiro Nomura in Journal of CO2 Utilization
Boilers are a major source of greenhouse gas emissions. In a recent study, researchers from Japan and Poland developed a method to convert CO2 emissions from small boilers into methane, which makes use of an optimized reactor design that evenly distributes the CO2 feed. This, in turn, results in significantly lower temperature increments and a boost in methane production. This innovative technique could pave the way for reducing greenhouse gas emissions.
Reducing carbon emissions from small-scale combustion systems, such as boilers and other industrial equipment, is a key step towards building a more sustainable, carbon-neutral future. Boilers are widely used across various industries for essential processes like heating, steam generation, and power production, making them significant contributors to greenhouse gas emissions.
Boilers are generally quite efficient. As a result, it is difficult to reduce CO2 emissions simply by improving the combustion efficiency. Therefore, researchers are exploring alternative approaches to mitigating the environmental impact of CO2 emissions from boilers. One promising strategy to this end is to capture the CO2 emitted from these systems and convert it into a useful product, such as methane.
To implement this strategy, a specific type of membrane reactor, called the distributor-type membrane reactor (DMR), is needed that can facilitate chemical reactions as well as separate gases. While DMRs are used in certain industries, their application for converting CO2 into methane, especially in small-scale systems like boilers, has remained relatively unexplored.
The team conducted a two-pronged approach to the problem through numerical simulations and experimental studies to optimize the reactor designs for efficient conversion of CO2 from small boilers into methane. In their simulation, the team modeled how gases flow and react under different conditions. In turn, this enabled them to minimize the temperature variations, ensuring that energy consumption is optimized while methane production remains dependable.
The team further found that, unlike traditional methods that channel gases into a single location, a distributed feed design could spread the gases out into the reactor instead of sending them in from one place. This, in turn, results in a better distribution of CO2 throughout the membrane, preventing any location from overheating. “This DMR design helped us reduce temperature increments by about 300 degrees compared to the traditional packed bed reactor,” explains Prof. Nomura.
Beyond the distributed feed design, the researchers also explored other factors influencing the reactors efficiency and discovered that one key variable was the CO2 concentration in the mixture. Changing the amount of CO2 in the mixture affected how well the reaction worked. “When the CO2 concentration was around 15%, similar to what comes out of the boilers, the reactor was much better at producing methane. In fact, it could produce about 1.5 times more methane compared to a regular reactor that only had pure CO2 to work with,” highlights Prof. Nomura.
Additionally, the team investigated the impact of reactor size, finding that increasing the size of the reactor facilitated the availability of hydrogen for the reaction. There was, however, a tradeoff to be considered as the benefit of higher hydrogen availability required careful temperature management to avoid overheating.
The study thus presents a promising solution to the problem of tackling a major source of greenhouse gas emissions. By utilizing a DMR, low-concentration CO2 emissions can be successfully converted into usable methane fuel. The benefits gained thereof are not limited to methanation alone but can also be applied to other reactions, making this method a versatile tool for efficient CO2 utilization even for households and small factories.
Sub-volt conversion of activated biochar and water for H2 production near equilibrium via biochar-assisted water electrolysis
by Nishithan C. Kani, Rohit Chauhan, Samuel A. Olusegun, Ishwar Sharan, Anag Katiyar, David W. House, Sang-Won Lee, Alena Jairamsingh, Rajan R. Bhawnani, Dongjin Choi, Adam C. Nielander, Thomas F. Jaramillo, Hae-Seok Lee, Anil Oroskar, Vimal C. Srivastava, Shishir Sinha, Joseph A. Gauthier, Meenesh R. Singh in Cell Reports Physical Science
University of Illinois Chicago engineers have helped design a new method to make hydrogen gas from water using only solar power and agricultural waste, such as manure or husks. The method reduces the energy needed to extract hydrogen from water by 600%, creating new opportunities for sustainable, climate-friendly chemical production.
Hydrogen-based fuels are one of the most promising sources of clean energy. But producing pure hydrogen gas is an energy-intensive process that often requires coal or natural gas and large amounts of electricity.
In a paper f, a multi-institutional team led by UIC engineer Meenesh Singh unveils the new process for green hydrogen production. The method uses a carbon-rich substance called biochar to decrease the amount of electricity needed to convert water to hydrogen. By using renewable energy sources such as solar power or wind and capturing byproducts for other uses, the process can reduce greenhouse gas emissions to net zero.
“We are the first group to show that you can produce hydrogen utilizing biomass at a fraction of a volt,” said Singh, associate professor in the department of chemical engineering. “This is a transformative technology.”
Electrolysis, the process of splitting water into hydrogen and oxygen, requires an electric current. At an industrial scale, fossil fuels are typically required to generate this electricity.
Recently, scientists have decreased the voltage required for water splitting by introducing a carbon source to the reaction. But this process also uses coal or expensive chemicals and releases carbon dioxide as a byproduct. Singh and colleagues modified this process to instead use biomass from common waste products. By mixing sulfuric acid with agricultural waste, animal waste or sewage, they create a slurry-like substance called biochar, which is rich in carbon.
The team experimented with different kinds of biochar made from sugarcane husks, hemp waste, paper waste and cow manure. When added to the electrolysis chamber, all five biochar varieties reduced the power needed to convert water to hydrogen. The best performer, cow dung, decreased the electrical requirement sixfold to roughly a fifth of a volt.
The energy requirements were low enough that the researchers could power the reaction with one standard silicon solar cell generating roughly 15 milliamps of current at 0.5 volt. That’s less than the amount of power produced by an AA battery.
“It’s very efficient, with almost 35% conversion of the biochar and solar energy into hydrogen” said Rohit Chauhan, a co-author and postdoctoral scholar in Singh’s lab. “These are world record numbers; it’s the highest anyone has demonstrated.”
To make the process net-zero, it must capture the carbon dioxide generated by the reaction. But Singh said this too could have environmental and economic benefits, such as producing pure carbon dioxide to carbonate beverages or converting it into ethylene and other chemicals used in plastic manufacturing.
“It not only diversifies the utilization of biowaste but enables the clean production of different chemicals beyond hydrogen,” said UIC graduate Nishithan Kani, co-lead author on the paper. “This cheap way of making hydrogen could allow farmers to become self-sustainable for their energy needs or create new streams of revenue.”
Greener Is Cheaper: An Example From Offshore Wind Farms
by Subhamoy Bhattacharya, Dan Kammen in National Institute Economic Review
Offshore wind could have prevented the Fukushima disaster, according to a review of wind energy led by the University of Surrey.
The researchers found that offshore turbines could have averted the 2011 nuclear disaster in Japan by keeping the cooling systems running and avoiding meltdown. The team also found that wind farms are not as vulnerable to earthquakes.
Suby Bhattacharya, Professor of Geomechanics at the University of Surrey’s Department of Civil and Environmental Engineering, said: “Wind power gives us plentiful clean energy — now we know that it could also make other facilities safer and more reliable. The global review finds that greener really is cheaper — thanks to falling construction costs and new ways to reduce wind turbines’ ecological impact.”
One of the report’s starkest findings was that new wind farms can produce energy over twice as cheaply as new nuclear power stations. The lifetime cost of generating wind power in the UK has fallen dramatically, from £160/MWh to £44/MWh. This includes all the costs of planning, building, operating and decommissioning the wind farm over its entire life. By comparison, the UK Government agreed to pay £92.50/MWh for energy produced at Hinkley Point C nuclear power station.
Professor Bhattacharya said: “What makes wind so attractive is that the fuel is free — and the cost of building turbines is falling. There is enough of it blowing around the world to power the planet 18 times over. Our report shows the industry is ironing out practical challenges and making this green power sustainable, too.”
Although less power is generated in calmer conditions, the electricity generated could be stored in batteries — as planned for the Ishikari project off the coast of Hokkaido, Japan. Or it could be used to produce hydrogen from seawater — giving us the fuel of the future.
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