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Topic Review
Hydrogen-Based Energy Systems
The current state of hydrogen as an energy vector is marked by its growing importance and recognition worldwide. Despite its still formidable challenges, once it achieves some maturity, it might be seen as a promising solution to address climate change, reduce emissions, and facilitate the transition towards a sustainable energy future. Collaborative international efforts highlight its significance. While challenges exist and these should not be underestimated, the momentum behind hydrogen suggests that policymakers all around the world see a promising future in the global energy transition towards a cleaner future for both developed and developing countries, and thus for the world.
  • 680
  • 12 Jan 2024
Topic Review
Energy Grid Applications
In the energy usage scenario, the demands on energy load and the tariffs on the usage of electricity are two main areas that require a lot of attention. Energy forecasting is an ideal solution that would help us to better understand future needs and formulate solutions accordingly. Some important factors to investigate are the quantity and quality of smart grids as they are significantly influenced by the transportation, storage, and load management of energy.
  • 679
  • 26 Oct 2023
Topic Review
Economics of Hydrogen Generation
Hydrogen is known as the lightest and the most abundant element. It supplies energy to fuel the stars and the Sun. It is considered non-toxic, odorless, colorless, highly combustible, and unpolluted.
  • 666
  • 07 Feb 2024
Topic Review Peer Reviewed
Application of Nanoparticles in Bioreactors to Enhance Mass Transfer during Syngas Fermentation
Gas–liquid mass transfer is a major issue during various bioprocesses, particularly in processes such as syngas fermentation (SNF). Since SNF involves the movement of gases into the fermentation broth, there is always a rate-limiting step that reduces process efficiency. Improving this process could lead to increased efficiency, higher production of ethanol, and reduced energy consumption. One way to improve fluid transfer between gas and liquid is by incorporating nanoparticles (NPs) into the liquid phase. This entry describes recent advances in using NPs to improve gas–liquid mass transfer during SNF. The entry also describes the basics of SNF and the impact of NPs on the process and suggests areas for future research. For example, carbon nanotubes have been found to elevate the available surface area needed for gas–liquid transfer, thus improving the process efficiency. Another area is the use of NPs as carriers for enzymes involved in syngas fermentation.
  • 659
  • 27 Mar 2023
Topic Review
End-of-Life Photovoltaic Modules
More than 78 million tons of photovoltaic modules (PVMs) will reach their end of life (EOL) by 2050. If they are not responsibly managed, they can (a) pollute our terrestrial ecosystem, (b) indirectly encourage continuous mining and extraction of Earth’s finite resources, and (c) diminish the net environmental benefit of harvesting solar energy. Conversely, successfully recovering them could reduce resource extraction and waste and generate sufficient economic return and value to finance the production of another 2 billion PVMs by 2050. Therefore, EOL PVMs must participate in the circular economy, and business and political leaders are actively devising strategies to enable their participation. 
  • 658
  • 21 Jul 2022
Topic Review
Intelligent Micro-Cogeneration Systems for Residential Grids
Historical residential grid data were analysed to develop a machine learning-based demand prediction model for electricity and hot water. Thermal energy storage was integrated into the Micro-cogeneration system to enhance flexibility. An optimization model was created, considering efficiency, emissions, and cost while adapting to real-time demand changes. A control strategy was designed for the flexible operation of the Micro-cogeneration system, addressing excess thermal energy storage and resource allocation. The proposed solution’s effectiveness was validated through simulations, with results demonstrating the Micro-cogeneration system’s ability to efficiently address high electricity and hot water demand periods while mitigating power demand failures from renewable energy sources.
  • 653
  • 14 Jul 2023
Topic Review
Electric and Hydrogen Automobile
The negative consequences of toxic emissions from internal combustion engines, energy security, climate change, and energy costs have led to a growing demand for clean power sources in the automotive industry. Developing eco-friendly vehicle technologies, such as electric and hydrogen vehicles, has increased. The researchers investigate whether hydrogen vehicles will replace electric vehicles in the future. The results showed that fuel-cell cars are unlikely to compete with electric cars. This is due to the advancements in electric vehicles and charging infrastructure, which are becoming more cost-effective and efficient. Additionally, the technical progress in Battery Electric Vehicles (BEVs) is expected to reduce the market share of Fuel-Cell Electric Vehicles (FCEVs) in passenger vehicles. However, there are significant investments in hydrogen cars. Many ongoing investments seem to follow the sunk cost fallacy, where decision-makers continue to invest in an unprofitable project due to the already invested resources. Furthermore, even with megawatt charging, fuel-cell trucks cost more than battery-powered electric trucks. The use cases for fuel-cell electric trucks are also much more limited, as their running expenses are higher compared to electric cars. Hydrogen vehicles may be beneficial for heavy transport in remote areas. However, it remains to be seen if niche markets are large enough to support fuel-cell electric truck commercialization and economies of scale. In summary, researchers believe hydrogen vehicles will not replace electric cars and trucks, at least before 2050.
  • 652
  • 25 Apr 2023
Topic Review
Heavy-Metal Contaminated Input along Liquid Biofuel Value Chains
The main types of contaminants include inorganic (mostly heavy metals—HMs) and organic pollutants (petroleum, pesticides, polycyclic aromatic hydrocarbons—PAHs, etc.). The presence of contamination in the value chains examined is assessed in order to identify the corresponding effects and implications. Their effect is studied in each of the typical stages of the existing value chains, including pre-processing, conversion and post-processing steps. Special focus is assigned to the gasification and pyrolysis conversion processes, reviewing the fate of contaminants along each process. In the gasification process, parameters such as temperature, pressure, HM type and concentration are evaluated. At the same time, in pyrolysis, the major parameters considered were residence time and reactor temperature.
  • 642
  • 08 Oct 2022
Topic Review
Hydrogen Fuel for Future Mobility
Hydrogen fuel for sustainable mobility has its own effectiveness in terms of its generation and refueling processes. As the fuel requirement of vehicles cannot be anticipated because it depends on its utilization, choosing hydrogen refueling and onboard generation can be a point of major concern.
  • 642
  • 07 Oct 2023
Topic Review
Hydrogen Carriers
Hydrogen carriers are one of the keys to the success of using hydrogen as an energy vector. Indeed, sustainable hydrogen production exploits the excess of renewable energy sources, after which temporary storage is required. The conventional approaches to hydrogen storage and transport are compressed hydrogen (CH2) and liquefied hydrogen (LH2), which require severe operating conditions related to pressure (300–700 bar) and temperature (T < −252 °C), respectively. To overcome these issues, which have hindered market penetration, several alternatives have been proposed in the last few decades.
  • 638
  • 28 Aug 2023
Topic Review
Valorisation of Waste Heat in District Heating Systems
To recover thermal energy from different sources, its quality and possibilities for utilisation are essential. The wide range of engineering solutions includes a direct connection to the district heating (DH) system and the integration of low-quality heat using heat pumps to increase the temperature level of recoverable heat. 
  • 634
  • 10 Oct 2023
Topic Review
Electrochemical Energy and Carbon Cycle
Green hydrogen, green ammonia, and green methanol are being widely discussed for shipping. Because green methanol and ammonia have higher energy densities and are relatively easier to transport and store on ships, they have become the most promising near-zero-emission marine fuel. In addition, since most of the production pathways for green fuel require green power, the production methods for green power are analyzed in detail.
  • 627
  • 31 Mar 2023
Topic Review
Hydrogen Energy Eco-System
Climate change primarily caused by the greenhouse gases emitted as a result of the consumption of carbon-based fossil fuels is considered one of the biggest challenges that humanity has ever faced. Moreover, the Ukrainian crisis in 2022 has complicated the global energy and food status quo more than ever. The permanency of this multifaceted fragility implies the need for increased efforts to have energy independence and requires long-term solutions without fossil fuels through the use of clean, zero-carbon renewables energies. Hydrogen technologies have a strong potential to emerge as an energy eco-system in its production-storage-distribution-utilization stages, with its synergistic integration with solar-wind-hydraulic-nuclear and other zero-carbon, clean renewable energy resources, and with the existing energy infrastructure.
  • 625
  • 27 Apr 2023
Topic Review
Sustainable Energy Technologies in Buildings
The building sector accounts for a significant proportion of global energy usage and carbon dioxide emissions. It is important to explore technological advances to curtail building energy usage to support the transition to a sustainable energy future. 
  • 624
  • 24 Oct 2023
Topic Review
Graphene-Based Materials for Tribological Engineering Applications
Graphene and graphene-based materials are relatively novel 2D materials with great tribological potential. Graphene is inherently low-friction, very high stiffness, and its thermal conductivity may reduce friction and wear.
  • 623
  • 17 Nov 2023
Topic Review
Two-Sided Matching in Coal Mining and Power Generation
Under the current marketized coal and planned electricity price systems, barriers to price shifting between coal and electricity are created and conflicts between the two sectors are aggravated. The stable trading matching between coal mining and power generation companies is not only an effective means to resolve the conflict in the coal trading market, but also a ballast stone for price stabilization and supply guarantees in coal trading.
  • 620
  • 28 Apr 2022
Topic Review
Advanced Supercritical CO2 Thermodynamic Power Cycles
CO2 is a natural, non-toxic and non-flammable working fluid that possesses excellent thermophysical properties, including higher density, latent heat, specific heat, thermal conductivity and volumetric cooling capacity, along with lower viscosity.
  • 616
  • 04 Dec 2023
Topic Review
Data-Driven Methodologies Used for Wind Turbines O&M Tasks
 Wind power is one of the most sustainable and eco-friendly energy sources. With the rapid development of wind turbines (WTs), there is an increasing need to lower the Cost of Energy (COE) of wind power. Predictive maintenance techniques that leverage past failures to learn from and forecast failure and the remaining usable life of various wind turbines can significantly reduce operation and maintenance (O&M) expenses. Recent advancements in data-driven models for condition monitoring and predictive maintenance of wind turbines’ critical components (e.g., bearing, gearbox, generator, blade pitch) are reviewed. The entry categorizes these models according to data-driven procedures, such as data descriptions, data pre-processing, feature extraction and selection, model selection (classification, regression), validation, and decision making. The findings after reviewing extensive relevant articles suggest that (a) SCADA (supervisory control and data acquisition) data are widely used as they are available at low cost and are extremely practical (due to the 10 min averaging time), but their use is in some sense nonspecific. (b) Unstructured data and pre-processing remain a significant challenge and consume a significant time of whole machine learning model development. (c) The trade-off between the complexity of the vibration analysis and the applicability of the results deserves further development, especially with regards to drivetrain faults. (d) Most of the proposed techniques focus on gearbox and bearings, and there is a need to apply these models to other wind turbine components. 
  • 611
  • 13 Mar 2023
Topic Review
Electric Vehicle Battery Systems Thermal Issues
Electric vehicles battery systems (EVBS) are subject to complex charging/discharging processes that produce various amount of stress and cause significant temperature fluctuations. Due to the variable heat generation regimes, latent heat storage systems that can absorb significant amounts of thermal energy with little temperature variation are an interesting thermal management solution. 
  • 609
  • 24 Mar 2023
Topic Review
Renewable Energy Transition
The renewable energy transition of oil- and gas-producing countries has specific peculiarities due to the ambivalent position of these countries in the global energy market, both as producers and consumers of energy resources. This task becomes even more challenging when the share of oil and gas in the country’s GDP is very high. These circumstances pose serious challenges for long-term energy policy development and require compromising decisions to better align the existing and newly created energy policies of the country. The scale, scope, and pace of changes in the transition process must be well balanced, considering the increasing pressure of economic and environmental factors.
  • 605
  • 10 Jan 2024
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