SEMINAR REPORT

ON

SUPERCAPACITORS FOR HYBRID

ENERGYSTORAGE APPLICATIONS

SUBMITTED BY

V.Naveen Kumar

09711A0249

EEE

CONTENTS

ABSTRACT

INTRODUCTION

REPORT

CONCLUSION

ABSTRACT

Super capacitor 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

This paper offers a concise review on the use of a super

capacitor in various energy storage applications. Super capacitor is also

known as Electric/electrochemical double layer capacitor (EDLC) is a

unique electrical storage device, which can store much more energy than

conventional capacitors and offer much higher power density than batteries.

Electric double-layer 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 double layer capacitors have capacities as high as 5,000 farads.

These particularities make them very attractive for some applications as

vehicle, electric grid, UPS, etc. So, this component can used with battery to

supply the high power needed for the vehicle starting-up and acceleration,

what can reduce the maximum power given by the battery and improves the

lifetime of this last one.

These super capacitors fill up the gap between the batteries

and the conventional capacitor, allowing applications for various power and

energy requirements i.e., back up power sources for electronic devices,

engine start or acceleration for hybrid vehicles.

This paper deals with the the construction and working of

super capacitors and its application in various electronics energy storage

applications and hybrid power supply for the vehicles. For that the battery is

used us energy tank and supercapacitors to ensure the phases which need

high power (startup, acceleration etc.).

REPORT

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

In general, electric double-layer capacitors improve storage

density through the use of a nanoporous material, typically activated

charcoal, in place of the conventional insulating barrier. Activated charcoal

is a powder made up of extremely small and very "rough" particles, which in

bulk form a low-density volume of particles with holes between them that

resembles a sponge. The overall surface area of even a thin layer of such a

material is many times greater than a traditional material like aluminum,

allowing many more charge carriers (ions or radicals from the electrolyte) to

be stored in any given volume. The downside is that the charcoal is taking

the place of the improved insulators used in conventional devices, so in

general electric double-layer capacitors use low potentials on the order of 2

to 3 V.

Super capacitor is a double layer capacitor; the

energy is stored by charge transfer at the boundary between electrode and

electrolyte. The amount of stored energy is function of the available

electrode and electrolyte surface, the size of the ions, and the level of the

electrolyte decomposition voltage.

Super capacitors are constituted of two electrodes, a

separator and an electrolyte. The two electrodes, made of activated carbon

provide a high surface area part, defining so energy density of the

component. On the electrodes, current collectors with a high conducting part

assure the interface between the electrodes and the connections of the

supercapacitor. The two electrodes are separated by a membrane, which

allows the mobility of charged ions and forbids no electronic contact. The

electrolyte supplies and conducts the ions from one electrode to the other.

Usually super capacitors are divided into two types:

double-layer capacitors and electrochemical capacitors. The former depends

on the mechanism of double layers, which is result of the separation of

charges at interface between the electrode surface of active carbon or carbon

fiber and electrolytic solution. Its capacitance is proportional to the specific

surface areas of electrode material. The latter depends on fast faraday redox

reaction. The electrochemical capacitors include metal oxide supercapacitors

and conductive polymer supercapacitors. They all make use of the high

reversible redox reaction occurring on electrodes surface or inside them to

produce the capacitance concerning with electrode potential. Capacitance of

them depends mainly on the utilization of active material of electrode.

When metal oxides/ metal oxide and carbon

composite/conducting polymer and carbon composite are used as electrodes

for the construction of EDLCs, the charge storage mechanism includes both

double layer capacitance and pseudo capacitance which result in higher

capacitance output and the EDLCs are termed as supercapacitors (SCs). One

major disadvantage of carbon based EDLC is the lower specific stored

energy.

DIFFERENCES BETWEEN

SUPERCAPACITORS AND BATTERY

Charge Cycles:

Ultracapacitors can be charged and discharged hundreds of

thousands (and millions) of cycles without losing performance. A battery

is only good for a limited amount of charge and discharge cycles. You

probably notice this now with your cell phone or if you have a cordless

phone at the house. The longer you have and more you use the less

effective the battery holds the charge.

Charging Time:

As we know, batteries rely on chemical reactions and take

more time to charge unlike ultracapacitors which charge and discharge

very quickly.

• Size / Weight:

Batteries are larger and heavier where ultracapacitors tend

to be smaller and lighter.

Energy Density:

Typically ultracapacitors hold one fifth to one tenth the

energy of an electrochemical battery. This will be changing though as the

development of ultracapacitors continue.

Energy Release:

Batteries release energy on a slower longer period of time

while capacitors release stored energy very quickly. For an electric

vehicle, this quick burst will give the energy needed for passing other

cars or going up a hill

ADVANTAGES

Long life, with little degradation over hundreds of thousands of

charge cycles. Due to the capacitor's high number of charge-discharge

cycles (millions or more compared to 200 to 1000 for most

commercially available rechargeable batteries) it will last for the

entire lifetime of most devices, which makes the device

environmentally friendly. Rechargeable batteries wear out typically

over a few years, and their highly reactive chemical electrolytes

present a disposal and safety hazard. Battery lifetime can be optimised

by charging only under favorable conditions, at an ideal rate and, for

some chemistries, as infrequently as possible. EDLCs can help in

conjunction with batteries by acting as a charge conditioner, storing

energy from other sources for load balancing purposes and then using

any excess energy to charge the batteries at a suitable time.

Low cost per cycle.

Good reversibility.

Very high rates of charge and discharge.

Extremely low internal resistance (ESR) and consequent high cycle

efficiency (95% or more) and extremely low heating levels.

High output power.

High specific power. According to ITS (Institute of Transportation

Studies, Davis, California) test results, the specific power of electric

double-layer capacitors can exceed 6 kW/kg at 95% efficiency.

Improved safety, no corrosive electrolyte and low toxicity of

materials.

Simple charge methods—no full-charge detection is needed; no

danger of overcharging.

DISADVANTAGES

The amount of energy stored per unit weight is generally lower than

that of an electrochemical battery (3–5 W·h/kg for a standard

ultracapacitor, although 85 W.h/kg has been achieved in the lab as

compared to 30-40 W·h/kg for a lead acid battery), and about

1/1,000th the volumetric energy density of gasoline.

Typical of any capacitor, the voltage varies with the energy stored.

Effective storage and recovery of energy requires complex electronic

control and switching equipment, with consequent energy loss.

Has the highest dielectric absorption of any type of capacitor.

High self-discharge - the rate is considerably higher than that of an

electrochemical battery.

Cells hold low voltages - serial connections are needed to obtain

higher voltages. Voltage balancing is required if capacitors are

connected in series.

Very low internal resistance allows extremely rapid discharge when

shorted, resulting in a shock hazard similar to any other capacitor of

similar voltage and capacitance (generally much higher than

electrochemical cells).

APPLICATIONS

Applications of super capacitors in the field of consumer

electronics and vehicles etc.

Consumer electronics

Automotive application

Consumer electronics

Super capacitors can be used in PC Cards, flash

photography devices in digital cameras, flashlights, portable media players,

solar power calculator, electronic toy, internet equipments and in automated

meter reading, particularly where extremely fast charging is desirable.

In 2007, a cordless electric screwdriver that uses an EDLC for energy

storage was produced. It charges in 90 seconds, retains 85% of the charge

after 3 months, and holds enough charge for about half the screws a

comparable screwdriver with a rechargeable battery will handle. Two LED

flashlights using EDLCs were released in 2009. They charge in 90 seconds.

Cordless electric screwdriver

AUTOMOTIVE APPLICATION

In the automotive domain the supercapacitor applications

are classified in three categories:

Onboard electrical systems:

Electromagnetic valve control, catalysts preheating, brake

actuators, steering.

Micro hybrid:

Integrated starter-generator, electro-hydraulic or mechanical

braking.

Mild hybrid:

Energy storage for the traction assistance.

Strong hybrid:

Energy storage for the traction.

TOPOLOGY OF A SERIES HYBRID SUPPLY FOR

AUTOMOTIVE APPLICATIONS.

Enhanced starting of automobile engines is another

attractive application for double-layer capacitors. Today the energy required

to crank an internal combustion engine, is stored in batteries, either Pb or Ni.

Because of their high internal resistance, which limits the initial peak

current, they have to be oversized. The fast battery discharging and the cold

environmental temperature affect heavily its properties.

The use of supercapacitors like power sources allows us to

reduce considerably the size of the battery which will be used just like an

energy source. On the other hand, the use of the converters ensures a good

control of the starting-up dynamics (control of the current). Two topologies

can be distinguished for the power supply which depends to the association

BATTERY CON 1DC/DC

SUPER CAPACITORS

CON 2DC/AC

STARTR ALTERNATOR

of the two storage components (battery and supercapacitors): in series or

parallel.

For the series topology the two storage systems are putted

in series. In this case, the supercondensator module is charged by the battery

through a chopper (Boost). The starting-up is only assured by the

suspercapacitors through a chopper in the case of the starter and through the

inverter in the case of the starter-alternator. This topology allows us to

reduce the size of the coil which is sized for a current of 20A.

Mild and strong hybrid vehicles

These environmentally friendly drives are based on the combination of an

internal combustion engine with an electric power train. The double-layer

capacitors absorb the kinetic energy from braking and release it later to

accelerate the vehicle. In addition, they cover the energy requirements of

auxiliary electrical power equipment. The duration and magnitude of typical

acceleration and braking events determines the size of the double-layer

capacitor bank. The double-layer capacitors can be also a device to improve

the lifetime of a storage system as they present a high number of

charge/discharge cycles, withstand wide temperature ranges, require little

maintenance, and be placed more optimally for vehicle ergonomics.

Fuel cell vehicles

In the future the combustion engine mechanical energy obtained from the

fuel combustion could be replaced electrical engine supplied by electricity

produced by a fuel cell. The promise of fuel cell technology has had a recent

resurgence due to new advancements not in fuel cells, but in the double-

layer capacitors. Indeed, high power energy storage is required in all types

of fuel cell applications and double-layer capacitors are ideally suited to

provide it. These improvements open up opportunities for the development

of new power train and subsystem architectures utilizing both double-layer

capacitors and fuel cells which can improve performance, efficiency, and

cleanliness in electric and hybrid vehicle technology.

In collaboration with the Paul Scherrer Institute, the Volkswagen group and

other partners, a fuel cell vehicle has been built up with BOOSTCAPs .The

fuel cell, which acts as a primary power source, is sized for the continuous

load requirement. The super capacitor bank, which acts as the secondary

power source, is sized for peak load leveling events such as fuel starting,

acceleration and braking. These short duration events are experienced many

thousands of times throughout the life of the vehicle and require relatively

little energy but substantial power.

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.

CONCLUSION

In this paper the use of super capacitor for various

energy storage applications is described. They 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. The specific Power of

the super capacitors and its lifetime (1 million of Cycles) is very high. These

peculiarities make it very attractive for various energy storage applications

and the startup of the automobiles etc. The power density of super capacitors

makes them very interesting for the applications which need high power

during short time. The use of this component technology allows reducing the

battery size and optimizing the lifetime of the supply.