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Topic Review
Energy Storage in Urban Areas
Positive Energy Districts can be defined as connected urban areas, or energy-efficient and flexible buildings, which emit zero greenhouse gases and manage surpluses of renewable energy production. Energy storage is crucial for providing flexibility and supporting renewable energy integration into the energy system. It can balance centralized and distributed energy generation, while contributing to energy security. Energy storage can respond to supplement demand, provide flexible generation, and complement grid development. Photovoltaics and wind turbines together with solar thermal systems and biomass are widely used to generate electricity and heating, respectively, coupled with energy system storage facilities for electricity (i.e., batteries) or heat storage using latent or sensible heat. Energy storage technologies are crucial in modern grids and able to avoid peak charges by ensuring the reliability and efficiency of energy supply, while supporting a growing transition to nondepletable power sources.
  • 443
  • 06 Mar 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.
  • 435
  • 27 Mar 2023
Topic Review
Supercritical CO2 Power Technology
In the late 1960s, a handful of inspired researchers predicted the great potential of supercritical CO2 (“sCO2”) cycles for the production of electricity and highlighted the prospects for dramatic reductions in component sizes and efficiency increases. Since then, considerable development programs have been deployed around the world to “tame” this new technology. 
  • 434
  • 08 Mar 2024
Topic Review
Bubble Dynamics in Proton Exchange Membrane Water Electrolysis
Water electrolysis using a proton exchange membrane (PEM) holds substantial promise to produce green hydrogen with zero carbon discharge. Although various techniques are available to produce hydrogen gas, the water electrolysis process tends to be more cost-effective with greater advantages for energy storage devices. However, one of the challenges associated with PEM water electrolysis is the accumulation of gas bubbles, which can impair cell performance and result in lower hydrogen output. Achieving an in-depth knowledge of bubble dynamics during electrolysis is essential for optimal cell performance.
  • 433
  • 10 Jan 2024
Topic Review
Basics of High-Entropy Materials
High-entropy materials (HEMs) constitute a revolutionary class of materials that have garnered significant attention in the field of materials science, exhibiting extraordinary properties in the realm of energy storage. These equimolar multielemental compounds have demonstrated increased charge capacities, enhanced ionic conductivities, and a prolonged cycle life, attributed to their structural stability. In the anode, transitioning from the traditional graphite (372 mAh g−1) to an HEM anode can increase capacity and enhance cycling stability. For cathodes, lithium iron phosphate (LFP) and nickel manganese cobalt (NMC) can be replaced with new cathodes made from HEMs, leading to greater energy storage. HEMs play a significant role in electrolytes, where they can be utilized as solid electrolytes, such as in ceramics and polymers, or as new high-entropy liquid electrolytes, resulting in longer cycling life, higher ionic conductivities, and stability over wide temperature ranges. The incorporation of HEMs in metal–air batteries offers methods to mitigate the formation of unwanted byproducts, such as Zn(OH)4 and Li2CO3, when used with atmospheric air, resulting in improved cycling life and electrochemical stability.
  • 427
  • 15 Apr 2024
Topic Review
Storage and Transportation Methods of Hydrogen
Hydrogen is one of the most common elements occurring in nature, and its potential as a source of energy has long attracted the attention of scientists and engineers. In addition to environmental cleanliness, one of the main advantages of hydrogen is its high energy density; this means that small amounts of hydrogen can be used to produce a large energy bulk. In addition, hydrogen can be obtained from several sources, including water, biomass, and various gases, such as methane, which makes it more affordable and cost-effective. The great number of different methods of hydrogen production, storage, and transportation dictate the need to develop approaches to selecting the most promising “hydrogen supply chains” in order to identify the most economically advantageous ways to supply fuel to industrial consumers.
  • 425
  • 14 Aug 2023
Topic Review
Technological Innovations in In Situ Leaching
Uranium, a cornerstone for nuclear energy, facilitates a clean and efficient energy conversion. In the era of global clean energy initiatives, uranium resources have emerged as a vital component for achieving sustainability and clean power. To fulfill the escalating demand for clean energy, continual advancements in uranium mining technologies are imperative. Currently, established uranium mining methods encompass open-pit mining, underground mining, and in situ leaching (ISL). Notably, in situ leaching stands out due to its environmental friendliness, efficient extraction, and cost-effectiveness. Moreover, it unlocks the potential of extracting uranium from previously challenging low-grade sandstone-hosted deposits, presenting novel opportunities for uranium mining.
  • 422
  • 12 Mar 2024
Topic Review
Fabrication Techniques of Perovskite Solar Cells
Perovskite solar cells (PSCs) are gaining popularity due to their high efficiency and low-cost fabrication. Researchers are exploring new materials and fabrication techniques to enhance the performance of PSCs under various environmental conditions. The mechanical stability of flexible PSCs is another area of research that has gained significant attention. 
  • 420
  • 22 Feb 2024
Topic Review
CNTs-Supercapacitors
Carbon nanotubes (CNTs), due to mechanical, electrical, and surface area properties and their ability to adapt to different nanocomposite structures, are very substantial in supercapacitor electrodes.
  • 419
  • 12 Jun 2023
Topic Review
Stability and Thermal Conductivity of MWCNT-Based Nanofluid
A nanofluid consisting of 0.5% MWCNTs, water (base fluid), and CTAB (surfactant) was selected with a sonication time of three and quarter hours, considering that these preparation conditions were practically the best. This fluid was circulated in an installed outdoor, weather-exposed PVT system. Experiments were carried out in the harsh weather conditions of Baghdad, Iraq, to test the effectiveness of the PVT system and the nanofluid.
  • 419
  • 18 May 2023
Topic Review
Heat Transfer Limitations in Supercritical Water Gasification
Supercritical water gasification (SCWG) is a promising technology for the valorization of wet biomass with a high-water content, which has attracted increasing interest. Many experimental studies have been carried out using conventional heating equipment at lab scale, where researchers try to obtain insight into the process. However, heat transfer from the energy source to the fluid stream entering the reactor may be ineffective, so slow heating occurs that produces a series of undesirable reactions, especially char formation and tar formation. This paper reviews the limitations due to different factors affecting heat transfer, such as low Reynolds numbers or laminar flow regimes, unknown real fluid temperature as this is usually measured on the tubing surface, the strong change in physical properties of water from subcritical to supercritical that boosts a deterioration in heat transfer, and the insufficient mixing, among others. In addition, some troubleshooting and new perspectives in the design of efficient and effective devices are described and proposed to enhance heat transfer, which is an essential aspect in the experimental studies of SCWG to move it forward to a larger scale.
  • 418
  • 17 Jan 2022
Topic Review
Cooling Techniques in Solar Cells
Non-concentrated photovoltaics (PV) have modest efficiency of up to around 20% because they utilise only a narrow spectrum of solar irradiation for electricity conversion. Therefore, recent advances employed multi-junction PV or concentrated photovoltaic (CPV) to widen the irradiation spectrum for conversion. CPV systems concentrate solar irradiation on the cell’s surface, producing high solar flux and temperature. The efficient cooling of CPV cells is critical to avoid thermal degradation and ensure optimal performance. 
  • 417
  • 27 Mar 2023
Topic Review
Energy Storage Systems for Automotive Applications
In the automotive industry, many devices are used to store energy in different forms. The most commonly used ones are batteries and supercapacitors, which store energy in electrical form, as well as flywheels, which store energy in mechanical form. Other less commonly used storage devices include fuel cell hydrogen tanks and compressed-air systems, which store energy in chemical and mechanical forms, respectively.
  • 417
  • 11 Mar 2024
Topic Review
Optimal Decisions for Deploying Renewable Energy at B&Bs
The adoption of renewable energy (RE) is a promising business strategy for bed and breakfasts (B&Bs) to mitigate climate change while maintaining a competitive edge. Bed and breakfast (B&B) has experienced rapid growth through sharing-economy platforms. The shift to RE has the potential to maintain the B&B’s competitive advantage by offering new service innovations continuously.
  • 415
  • 30 Jun 2022
Topic Review
Electric Vehicle in Energy-V2G, V2H, V2V
Electric vehicles (EVs) are inducing revolutionary developments to the transportation and power sectors. Their innumerable benefits are forcing nations to adopt this sustainable mode of transport. Governments are framing and implementing various green energy policies. Nonetheless, there exist several critical challenges and concerns to be resolved in order to reap the complete benefits of E-mobility. The impacts of unplanned EV charging are a major concern. Accurate EV load forecasting followed by an efficient charge scheduling system could, to a large extent, solve this problem. This entry focuses on short-term EV demand forecasting using three learning frameworks, which were applied to real-time adaptive charging network (ACN) data, and performance was analyzed. Auto-regressive (AR) forecasting, support vector regression (SVR), and long short-term memory (LSTM) frameworks demonstrated good performance in EV charging demand forecasting. Among these, LSTM showed the best performance with a mean absolute error (MAE) of 4 kW and a root-mean-squared error (RMSE) of 5.9 kW.
  • 412
  • 21 Sep 2023
Topic Review
Global Power Scenario
The massive growth in power demand and the sharp decay in the availability of conventional energy sources forces society to move toward renewable power consumption. The rise in renewable energy utilization is one of the greatest strategies involved in making the environment clean, green, and emission-free. The investment cost is slightly high for this kind of resource, but their running costsare very minimal, which encourages power producers to invest in renewable power plants. Power producers always focus on their economic profit and possible feasibilities before the investment in a new power plant setup. Wind, small hydro, and solar photovoltaics have been considered the foremost efficient and feasible renewable sources.
  • 410
  • 28 Jun 2023
Topic Review
Thermoelectric Materials
Solid-state energy conversion has been established as one of the most promising solutions to address the issues related to conventional energy generation. Thermoelectric materials allow direct energy conversion without moving parts and being deprived of greenhouse gases emission, employing lightweight and quiet devices.
  • 406
  • 14 Sep 2023
Topic Review
Terpenic Feedstock as Fuels
“Drop-in” fuels, which can be blended with standard jet fuels without any modification to the current technology in any aspect and also extended to the automotive sector, would ensure a fast implementation into the fuel market. Until today, only six alternative fuels for aircraft have been accepted for blending with jet fuel and mainly biodiesel, bioethanol, and Hydrogenated Vegetable Oils for automotive fuel. In the case of aircraft fuel, some examples of incorporation of Fatty Acid Methyl Esters (FAME) blended with jet fuel are known, but over 5 mg/kg of FAME cannot be used for specific technical reasons. The decarboxylation of fatty acids has produced potential aircraft biofuels, but these have poor cold flow behavior. For fuels derived from the petrochemical industry, aromatic and other cyclic hydrocarbons efficiently increase the fuel density with little loss of gravimetric energy density. However, most alternative fuels have to be blended with their respective standard fuel in order to meet the density requirements. In addition to jet fuels, specialty military fuels have even more demanding density requirements, including the gravimetric net heating value, freezing and flash point, and storage stability, among others. It is essential to evaluate the feedstock sources, extraction, conversion, quality, and final use of biofuels in order to achieve new sustainable and industrially feasible biofuels. One of the most promising feedstocks is terpenic waste.
  • 405
  • 20 Mar 2023
Topic Review
Tin Halide Perovskite-Based Solar Cells
The excellent optoelectronic properties of tin halide perovskites (Sn-PVKs) have made them a promising candidate for replacing toxic Pb counterparts. Concurrently, their enormous potential in photon harvesting and thermoelectricity applications has attracted increasing attention. The optoelectronic properties of Sn-PVKs are governed by the flexible nature of SnI6 octahedra, and they exhibit extremely low thermal conductivity. Due to these two contradictory properties, they are equally explored in solar cell as well as thermoelectric devices.
  • 402
  • 06 Dec 2022
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. 
  • 397
  • 21 Jul 2022
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