68,069 research outputs found
Tracking battery state-of-charge in a continuous use off-grid electricity system
The growing importance of batteries in the delivery of primary energy, for example in electric vehicles and isolated off-grid electricity systems, has added weight to the demand for simple and reliable measures of a battery’s remaining stored energy at any time. Many approaches to estimating this battery state-of-charge exist, ranging from those based on a full appreciation of the chemistry and physics of the storage and delivery mechanisms used, and requiring extensive data on which to base an estimate, to the naïve and simple, based only, for example, on the terminal voltage of the battery. None, however, is perfect, and able to deliver a simple percentage-full figure, as in a fuel gauge. The shortcomings are due to a range of complicating factors, including the impact of rate of charge, rate of discharge, battery aging, and temperature, to name just some of these.
This paper presents a simple yet effective method for tracking state-of-charge in an off-grid electricity system, where batteries are in continuous use, preventing static parameter measurements, and where charge/discharge cycles do not necessarily follow an orderly sequence or pattern. A reliable indication of state-of-charge is, however, highly desirable, but need be only of fuel gauge precision, say to the nearest 12-20%. The algorithm described utilises knowledge of the past, and constantly adapts parameters such as charge efficiency and total charge capacity based on this knowledge, and on the occurrence of specific identifiable events such as zero or full charge
Origins of Large Voltage Hysteresis in High Energy-Density Metal Fluoride Lithium-Ion Battery Conversion Electrodes
Metal fluoride and oxides can store multiple lithium-ions through conversion
chemistry to enable high energy-density lithium-ion batteries. However, their
practical applications have been hindered by an unusually large voltage
hysteresis between charge and discharge voltage-profiles and the consequent low
energy efficiency (< 80%). The physical origins of such hysteresis are rarely
studied and poorly understood. Here we employ in situ X-ray absorption
spectroscopy (XAS), transmission electron microscopy (TEM),
density-functional-theory (DFT) calculations, and galvanostatic intermittent
titration technique (GITT) to first correlate the voltage profile of iron
fluoride (), a representative conversion electrode material, with
evolution and spatial distribution of intermediate phases in the electrode. The
results reveal that, contrary to conventional belief, the phase evolution in
the electrode is symmetrical during discharge and charge. However, the spatial
evolution of the electrochemically active phases, which is controlled by
reaction kinetics, is different. We further propose that the voltage hysteresis
in the electrode is kinetic in nature. It is the result of Ohmic
voltage drop, reaction overpotential, and different spatial distributions of
electrochemically-active phases (i.e. compositional inhomogeneity). Therefore,
the large hysteresis can be expected to be mitigated by rational design and
optimization of material microstructure and electrode architecture to improve
the energy efficiency of lithium-ion batteries based on conversion chemistry
Planning Solar in Energy-managed Cellular Networks
There has been a lot of interest recently on the energy efficiency and
environmental impact of wireless networks. Given that the base stations are the
network elements that use most of this energy, much research has dealt with
ways to reduce the energy used by the base stations by turning them off during
periods of low load. In addition to this, installing a solar harvesting sys-
tem composed of solar panels, batteries, charge con- trollers and inverters is
another way to further reduce the network environmental impact and some
research has been dealing with this for individual base stations. In this
paper, we show that both techniques are tightly coupled. We propose a
mathematical model that captures the synergy between solar installation over a
network and the dynamic operation of energy-managed base stations. We study the
interactions between the two methods for networks of hundreds of base stations
and show that the order in which each method is intro- duced into the system
does make a difference in terms of cost and performance. We also show that
installing solar is not always the best solution even when the unit cost of the
solar energy is smaller than the grid cost. We conclude that planning the solar
installation and energy management of the base stations have to be done
jointly
AQUIFER Nano-Electrofuel Energy Economy and Powered Aircraft Operations
The Aqueous, QUick-charging battery Integration For Electric flight Research project is explained and the major subsystems are described, including nano-electric fluid, rim-driven motors, and integration concepts. The nano-electric fluid concept is a new type of aqueous flow battery that could reduce or retire the fire and explosion hazards of conventional batteries and fuel cells. The nano-electric fluid itself could enable energy storage and increased available energy per fuel weight ratios. The rim-driven motor is being developed to improve propulsion system safety and stability and to reduce noise. The rim-driven motor concept could enable motors that are more efficient both electrically and aerodynamically. The Energy Economy of the project concept is presented as a potential renewable or green energy sustainment for utilizing in-place infrastructure. The nano-electric fluid energy charge-use-recharge cycle is presented using renewable energy input from solar, wind, and hydroelectricity. Powered aircraft operations are presented, and the logistics of the new nano-electric fluid technology are explored. Powered aircraft operations topics include weight and balance, fueling, recharging, safety, and derivative considerations
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