seminars: December 2012

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SuperCapacitor:

Supercapacitor also known as electric double-layer capacitor (EDLC), super condenser, pseudo capacitor, electrochemical double layer capacitor, or ultracapacitors, is an electrochemical capacitor with relatively high energy density. Compared to conventional electrolytic capacitors the energy density is typically on the order of hundreds of times greater. In comparison with conventional batteries or fuel cells, EDLCs also have a much higher power density.

In this article the use of super capacitors likes hybrid power supply for various applications is presented. The main application is in the field of automation. The specific Power of the super capacitors and its high lifetime (1 million of Cycles) makes it very attractive for the startup of the automobiles. Unfortunately, the specific energy of this component is very low. For that this technology is associated with battery to supply the starter alternator.

Introduction of Super Capacitor

Super capacitors also known as Electric double-layer capacitors, or electrochemical double layer capacitors (EDLCs), or ultracapacitors, are electrochemical capacitors that have an unusually high energy density when compared to common capacitors, typically on the order of thousands of times greater than a high capacity electrolytic capacitor. For instance, a typical electrolytic capacitor will have a capacitance in the range of tens of millifarads. The same size super capacitor would have a capacitance of several farads, an improvement of about two or three orders of magnitude in capacitance but usually at a lower working voltage. Larger, commercial electric doublelayer capacitors have capacities as high as 5,000farads.

In a conventional capacitor, energy is stored by the removal of charge carriers, typically electrons, from one metal plate depositing them on another. This charge separation creates a potential between the two plates, which can be harnessed in an external circuit. The total energy stored in this fashion increases with both the amount of charge stored and the Potential between the plates. The amount of charge stored per unit voltage is essentially a function of the size, the distance, and the material properties of the plates and the material in between the plates (the dielectric), while the potential between the plates is limited by breakdown of the dielectric. The dielectric controls the capacitor's voltage. Optimizing the material leads to higher energy density for a given size of capacitor.

EDLCs do not have a conventional dielectric. Rather than two separate plates separated by an intervening substance, these capacitors use "plates" that are in fact two layers of the same substrate, and their electrical properties, the so-called "electrical double layer", result in the effective separation of charge despite the vanishingly thin (on the order of nanometers) physical separation of the layers. The lack of need for a bulky layer of dielectric permits the packing of plates with much larger surface area into a given size, resulting in high capacitances in practical-sized packages.

Super capacitor technology is based the electric double layer phenomenon that has been understood for over a hundred years. However, it has only been exploited by commercial applications for about ten years. As in a conventional capacitor, in an ultracapacitor two conductors and a dielectric generate an electric field where energy is stored. The double layer is created at a solid electrode-solution interface - it is, then, essentially a charge separation that occurs at the interface between the solid and the electrolyte. Two charge layers are formed, with an excess of electrons on one side and an excess of positive ions on the other side. The polar molecules that reside in between form the dielectric. In most ultracapacitors, the electrode is carbon combined with an electrolyte. The layers that form the capacitor plate's boundaries, as well as the small space between them, create a very high capacitance. In addition, the structure of the carbon electrode, which is typically porous, increases the effective surface area to about 2000 m2/g

Green Technology Super Capacitors :

Activated carbon used is unsustainable and expensive. Biochar is viewed as a green solution to the activated carbon currently used in super capacitor electrodes. Unlike activated carbon, biochar is the byproduct of the pyrolysis process used to produce biofuels and it is nontoxic and will not pollute the soil when it is tossed out. Biochar costs almost half as much as activated carbon, and is more sustainable because it reuses the waste from biofuel production, a process with sustainable intentions to begin with.

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Electric drive vehicles can be thought of as mobile, self-contained, and-in the aggregate-highly reliable power resources. "Electric-drive vehicles" (EDVs) include three types: battery electric vehicles, the increasingly popular hybrids, and fuel-cell vehicles running on gasoline, natural gas, or hydrogen. All these vehicles have within them power electronics which generate clean, 60 Hz AC power, at power levels from 10kW (for the Honda Insight) to 100kW (for GM's EV1). When vehicle power is fed into the electric grid, we refer to it as "Vehicle-to-Grid" power, or V2G.

With the popularization of electric vehicles and the construction of charging stations, the understanding of people to the electric vehicle and the changing station is not only confined to the transportation and the "gas station". It is desired to exploit more extensive application. The concept of V2G was firstly brought out by Willet Kempton of the Delaware University. The initial goal of V2G was to provide peak power, that is, the electric vehicle owners charging the vehicles in low load with lower price and discharging the vehicles in peak load with higher price. Then, the vehicle owners can get the profits from the V2G project. The functions of the vehicle in power grid were expanded, and the conclusion was get that benefit of providing peak power is significantly less than providing auxiliary services to the power grid . The V2G research also was carried out in some other countries such as Denmark, Britain and Germany, etc .

Introduction of Vehicle-to-Grid V2G

The first V2G requirement is the power connection. Battery vehicles must already be connected to the grid inorder to recharge their batteries; to add V2G capability requires little or no modification to the charging station and no modification to the cables or connectors, but on board power electronics must be designed for this purpose had "zero incremental cost."

The second requirement for V2G is control, for the utility or system operator to request vehicle power exactly when needed. This is essential because vehicle power has value greater than the cost to produce it only if the buyer (the system operator) can determine the precise timing of dispatch. The automobile industry is moving towards making real-time communications a standard part of vehicles. This field, called "telematics" has already begun with luxury vehicles; over a period of time it will be available for most new car models. Whether using built-in vehicle telematics, or in the interim using add-on communications, the vehicle could receive a radio signal from the grid operator indicating when power is needed.

The third element of precision, certified, tamper-resistant metering, measures exactly how much power or ancillary services a vehicle did provide, and at which times. The telematics could again be used to transmit meter readings back to the buyer for credit to the vehicle owner's account

Thinking about the metering of V2G expands the usual concept of a "utility meter." Electronic metering and telemetric appear to have efficiency advantages in eliminating the meter reader, transfer of billing data to the central computer, and the monthly meter-read cycle. More unnerving, electronic metering and telemetric also eliminates the service address! An onboard meter would transmit its own serial number or account number with its readings, via telemetric, and presumably this would be billed in conjunction with a traditional metered account with a service address. A large-scale V2G system would automate accounting and reconciliation of potentially millions of small transactions, similar to the recording and billing of calls from millions of cellular phone customers.Thus the mobile metered KWhs or ancillary services wold be added or subtracted to the amount registered on the fixed meter to reconcile both billing amounts.

Concept Of V2G :

Figure schematically illustrates connections between vehicles and the electric power grid. Electricity flows one-way from generators through the grid to electricity users. Electricity flows back to the grid from EDVs, or with battery EDVs, the flow is two ways (shown in Fig. as lines with two arrow ). The control signal from the grid operator (labelled ISO, for Independent System Operator) could be a broadcast radio signal, or through a cell phone network, direct Internet connection, or power line carrier. In any case, the grid operator sends requests for power to a large number of vehicles.

The signal may go directly to each individual vehicle, schematically in the upper right of Fig. , or to the office of a fleet operator, which in turn controls vehicles in a single parking lot, schematically shown in the lower right of Fig. , or through a third-party aggregator of dispersed individual vehicles' power (not shown). (The grid operator also dispatches power from traditional central-station generators using a voice telephone call or a T1 line, not shown in Fig .)

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Bubble Power:

In sonofusion a piezoelectric crystal attached to liquid filled Pyrex flask send pressure waves through the fluid, exciting the motion of tiny gas bubbles. The bubbles periodically grow and collapse, producing visible flashes of light. The researchers studying these light emitting bubbles speculated that their interiors might reach such high temperature and pressure they could trigger fusion reaction. Tiny bubbles imploded by sound waves can make hydrogen nuclei fuse- and may one day become a revolutionary new energy source.

When a gas bubble in a liquid is excited by ultrasonic acoustic waves it can emit short flashes of light suggestive of extreme temperatures inside the bubble. These flashes of light known as sonoluminescence, occur as the bubble implode or cavitates. It is show that chemical reactions occur during cavitations of a single, isolated bubble and yield of photons, radicals and ions formed. That is gas bubbles in a liquid can convert sound energy in to light.

Sonoluminescence also called single-bubble sonoluminescence involves a single gas bubble that is trapped inside the flask by a pressure field. For this loud speakers are used to create pressure waves and for bubbles naturally occurring gas bubbles are used. These bubbles can not withstand the excitation pressures higher than about 170 kilopascals. Pressures higher than about 170 kilopascals would always dislodge the bubble from its stable position and disperse it in the liquid. A pressure at least ten times that pressure level to implode the bubbles is necessary to trigger thermonuclear fusion. The idea of sonofusion overcomes these limitations.

Introduction of Bubble Power

Sonofusion is technically known as acoustic inertial confinement fusion. In this we have a bubble cluster (rather than a single bubble) is significant since when the bubble cluster implodes the pressure within the bubble cluster may be greatly intensified. The centre of the gas bubble cluster shows a typical pressure distribution during the bubble cluster implosion process. It can be seen that, due to converging shock waves within the bubble cluster, there can be significant pressure intensification in the interior of the bubble cluster. This large local liquid pressure (P>1000 bar) will strongly compress the interior bubbles with in the cluster, leading to conditions suitable for thermonuclear fusion. More over during the expansion phase of the bubble cluster dynamics, coalescence of some of interior bubbles is expected, and this will lead to the implosion of fairly large interior bubbles which produce more energetic implosions.

The apparatus consists of a cylindrical Pyrex glass flask 100 m.m. in high and 65m.m.in diameter. A lead-zirconate-titanate ceramic piezoelectric crystal in the form of a ring is attached to the flask's outer surface. The piezoelectric ring works like the loud speakers in a sonoluminescence experiment, although it creates much stronger pressure waves. When a positive voltage is applied to the piezoelectric ring, it contracts; when the voltage is removed, it expands to its original size.

The flask is then filled with commercially available deuterated acetone (C 3 D 6 O), in which 99.9 percent of the hydrogen atoms in the acetone molecules are deuterium (this isotope of hydrogen has one proton and one neutron in its nucleus). The main reason to choose deuterated acetone is that atoms of deuterium can undergo fusion much more easily than ordinary hydrogen atoms. Also the deuterated fluid can withstand significant tension (stretching) without forming unwanted bubbles. The substance is also relatively cheap, easy to work with, and not particularly hazardous.

Applications :

• Thermonuclear fusion gives a new, safe, environmental friendly way to produce electrical energy.

• This technology also could result in a new class of low cost, compact detectors for security applications. That use neutrons to probe the contents of suitcases.

• Devices for research that use neutrons to analyze the molecular structure of materials.

• Machines that cheaply manufacture new synthetic materials and efficiently produce tritium, which is used for numerous applications ranging from medical imaging to watch dials.

A new technique to study various phenomenons in cosmology, including the working of neutron star and black holes.

With the steady growth of world population and with economic progress in developing countries, average electricity consumption per person has increased significantly.

There fore seeking new sources of energy isn't just important, it is necessary. So for more than half a century, thermonuclear fusion has held out the promise of cheap clean and virtually limitless energy. Unleashed through a fusion reactor of some sort, the energy from 1 gram of deuterium, an isotope of hydrogen, would be equivalent to that produced by burning 7000 liters of gasoline. Deuterium is abundant in ocean water, and one cubic kilometer of seawater could, in principle, supply all the world's energy needs for several hundred years.