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4,725 result(s) for "Energy accumulation"
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Carbon-Based Supercapacitors Produced by Activation of Graphene
Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp 2 -bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.
Reliability evaluation of generating systems containing wind power and energy storage
Global environmental concerns associated with conventional energy generation have led to the rapid growth of wind energy in power systems. Many jurisdictions around the world have set high wind penetration targets in their energy generation mix. Wind speed is variable in nature, and power output from a wind farm is not readily controllable. High wind penetration can lead to high-risk levels in power system reliability and stability. In order to maintain the system stability, wind energy dispatch is usually restricted and energy storage is considered to smooth out the fluctuations and improve supply continuity. The benefits from using energy storage are highly dependent on the operating strategies, associated with wind and storage in the power system. A simulation technique that can consider wind farm and energy storage operating strategies is presented. The system impacts of energy storage capacity and operating constraints, wind energy dispatch restrictions, wind penetration level, and wind farm location on the reliability benefits from energy storage are illustrated.
Mixed-integer linear model for transmission expansion planning with line losses and energy storage systems
In this study, a deterministic single-stage transmission expansion planning model considering line losses and deployment of energy storage systems (ESSs) is proposed. A piecewise linearisation approach using secant segments is adopted to estimate non-linear line losses, and the optimal partitioning method is studied. ESSs are introduced to reduce the overall cost, and their siting and sizing are determined by nodal power balance and load duration curve. The effectiveness of the proposed model is shown through case studies simulated on two test systems, and the potential of ESSs reducing network investment costs is illustrated in a quantitative manner.
Optimal driving strategy for traction energy saving on DC suburban railways
Energy saving on electrified railways has been studied for many years and the technical solution is usually provided by a combination of driving strategy (e.g. coasting), regenerative braking and energy storage systems. An alternative approach is for the driver (or automatic train operation system if fitted) to manage energy consumption more efficiently. A formal method for optimising traction energy consumption. during a single-train journey by trading-off reductions in energy against increases in running time, has been demonstrated. The balance between saving energy and running faster has been investigated by designing a fitness function with variable weightings. Energy savings were found, both qualitatively and quantitatively, to be affected by acceleration and braking rates, and, by running a series of simulations in parallel with a genetic algorithm search method, the fitness function was used to identify optimal train trajectories. The influence of the fitness function representation on the search results was also explored.
A metal-free organic–inorganic aqueous flow battery
Flow batteries, in which the electro-active components are held in fluid form external to the battery itself, are attractive as a potential means for regulating the output of intermittent renewable sources of electricity; an aqueous flow battery based on inexpensive commodity chemicals is now reported that also has the virtue of enabling further improvement of battery performance through organic chemical design. Go with the flow batteries Flow batteries differ from the conventional type in that the electro-active components of flow batteries are held in fluid form external to the battery itself, enabling such systems to store arbitrarily large amounts of energy. Flow batteries are therefore attractive as a potential means for regulating the output of intermittent sources of electricity such as wind or solar power. But an important limitation of most such systems is the abundance and cost of the electro-active materials. To overcome this limitation, Brian Huskinson and colleagues have developed an aqueous flow battery on the basis of inexpensive, non-metallic commodity chemicals, with the added advantage of enabling the tuning of key battery properties through chemical design. As the fraction of electricity generation from intermittent renewable sources—such as solar or wind—grows, the ability to store large amounts of electrical energy is of increasing importance. Solid-electrode batteries maintain discharge at peak power for far too short a time to fully regulate wind or solar power output 1 , 2 . In contrast, flow batteries can independently scale the power (electrode area) and energy (arbitrarily large storage volume) components of the system by maintaining all of the electro-active species in fluid form 3 , 4 , 5 . Wide-scale utilization of flow batteries is, however, limited by the abundance and cost of these materials, particularly those using redox-active metals and precious-metal electrocatalysts 6 , 7 . Here we describe a class of energy storage materials that exploits the favourable chemical and electrochemical properties of a family of molecules known as quinones. The example we demonstrate is a metal-free flow battery based on the redox chemistry of 9,10-anthraquinone-2,7-disulphonic acid (AQDS). AQDS undergoes extremely rapid and reversible two-electron two-proton reduction on a glassy carbon electrode in sulphuric acid. An aqueous flow battery with inexpensive carbon electrodes, combining the quinone/hydroquinone couple with the Br 2 /Br − redox couple, yields a peak galvanic power density exceeding 0.6 W cm −2 at 1.3 A cm −2 . Cycling of this quinone–bromide flow battery showed >99 per cent storage capacity retention per cycle. The organic anthraquinone species can be synthesized from inexpensive commodity chemicals 8 . This organic approach permits tuning of important properties such as the reduction potential and solubility by adding functional groups: for example, we demonstrate that the addition of two hydroxy groups to AQDS increases the open circuit potential of the cell by 11% and we describe a pathway for further increases in cell voltage. The use of π-aromatic redox-active organic molecules instead of redox-active metals represents a new and promising direction for realizing massive electrical energy storage at greatly reduced cost.
Energy storage application in low-voltage microgrids for energy management and power quality improvement
The study deals with the application of energy storage connected to the low-voltage microgrid by coupling inverter for simultaneous energy management and ancillary services that include the compensation of power quality disturbances. The usefulness of storage equipment as a solution to various problems that accompany microgrid development is discussed. Then, the idea is presented to join different tasks the storage can perform in one application. Control algorithm is presented for storage inverter, which enables storage unit to be charged or discharged according to assumed schedule and to contribute to power quality improvement through the compensation of reactive power, current harmonics and unbalance. Effectiveness of compensation is examined on the simulation model of test microgrid. Moreover, the results of tests performed in real test microgrid configured in the Laboratory of Distributed Generation at the Lodz University of Technology are presented in the study.
Porphyrin-Sensitized Solar Cells with Cobalt (II/III)-Based Redox Electrolyte Exceed 12 Percent Efficiency
The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co (II/III) tris(bipyridyl)—based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.
Electrocatalyst approaches and challenges for automotive fuel cells
Although automotive fuel-cell catalyst development has come a long way in the past fifteen years, more research is needed for oxygen reduction electrocatalysts to be successfully commercialized. Fuel cells stuck in the slow lane In the face of dwindling oil reserves and concerns about climate change, vehicles powered by fuel cells that use hydrogen from renewable sources and emit only water seem ideal. Small test fleets of fuel-cell vehicles have shown impressive performances, but in this Review Mark Debe reminds us that significant obstacles need to be overcome before the technology becomes genuinely practical. In particular, it will not be enough to develop oxygen-reduction electrocatalysts, the crucial components at the heart of fuel cells, with high activity. As important — and more challenging — is the need to ensure that these catalysts are highly durable, fault tolerant and can be mass-produced with high yields and exceptional quality. Many of the catalyst systems currently being explored seem unlikely to meet these criteria. Fuel cells powered by hydrogen from secure and renewable sources are the ideal solution for non-polluting vehicles, and extensive research and development on all aspects of this technology over the past fifteen years has delivered prototype cars with impressive performances. But taking the step towards successful commercialization requires oxygen reduction electrocatalysts—crucial components at the heart of fuel cells—that meet exacting performance targets. In addition, these catalyst systems will need to be highly durable, fault-tolerant and amenable to high-volume production with high yields and exceptional quality. Not all the catalyst approaches currently being pursued will meet those demands.