1. By
Prof. S.K.Biradar
AISSMS COE Pune, India
Introduction to Energy Storage
Systems in Electric & hybrid
vehicles

2. Introduction to Energy Storage Systems in
Electric & hybrid vehicles
 Introduction to energy storage requirements in Hybrid and
Electric vehicles
 Battery-based energy storage
 Ultra capacitor based energy storage
 Flywheel based energy storage system
. Fuel cell based energy storage system
 Hybridization of energy sources for Hybrid and Electric vehicle: -
Hybridization of drive trains in HEVs

3. Energy storage system issues
 Energy storage technologies, especially batteries, are critical enabling
technologies for the development of hybrid vehicles or pure electric vehicles.
 Recently, widely used batteries are three types: Lead Acid, Nickel-Metal
Hydride and Lithium-ion.
 In fact, most of hybrid vehicles in the market currently use Nickel-Metal-
Hydride due to high voltage requirement in its battery system.
Lithium-ion batteries have relatively lighter weight and higher energy
density.
However, there are still many technical barriers which have to be
overcome before the batteries are widely used. These barriers include cost,
performance, life, and durability
Battery storage system

4. Energy storage system issues
 High power density, but low energy density
 can deliver high power for shorter duration
 Can be used as power buffer for battery
 Recently, widely used batteries are three types: Lead Acid, Nickel-Metal
Hydride and Lithium-ion.
 In fact, most of hybrid vehicles in the market currently use Nickel-Metal-
Hydride due to high voltage requirement in its battery system.
Lithium-ion batteries have relatively lighter weight and higher energy
density.
However, there are still many technical barriers which have to be
overcome before the batteries are widely used. These barriers include cost,
performance, life, and durability
Ultra capacitor storage system

5. Basic Secondary Battery

6. Working principle of Battery
• A basic secondary battery cell consists of two electrodes immersed in an
electrolyte.
• The anode is the electrode where oxidation occurs whereby electrons are
transported out of the cell to the cathode via the load circuit.
•The cathode is the electrode where reduction takes place and where electrons
from the external load return to the cell.
.
• Electrons are transported via ion migration from one electrode to the other through
the electrolyte, thus creating a potential across the cell.
•During a battery cell charging operation, the process is reversed.
•Electrons are externally injected into the negative electrode while oxidation takes
place at the positive electrode.
• Reaction rates during charge and discharge are not same
•Generally, the charge release rate of a battery system is higher than the charge
acceptance rate

7. From the electric vehicle designer’s point of view the battery can be
treated as a ‘black box’ which has a range of performance criteria. These
criteria will include:
• specific energy
• energy density
• specific power
• typical voltages
• energy efficiency
• amp hour efficiency
•
• energy efficiency
• commercial availability
• cost, operating temperatures
• self-discharge rates
• number of life cycles
• recharge rates
•
The designer also needs to understand how energy availability
varies with regard to:
• ambient temperature
• charge and discharge rates
• battery geometry
• optimum temperature
• charging methods
• cooling needs.
most of the disappointments connected with battery use, such as their
limited life, self-discharge, reduced efficiency at higher currents.
Battery system performance parameters

8. V = E - IR
External load
Cell and battery voltages
• All electric cells have nominal voltages which gives
the approximate voltage when the cell is delivering
electrical power.
• The cells can be connected in series to give the
overall voltage required.
• The battery is represented as having a fixed voltage
E, terminals is voltage V , because of the voltage
across the internal resistance R.
Battery parameters
Charge (or Ahr) capacity
The electric charge that a battery can supply is clearly a most crucial parameter.
The SI unit for this is the Coulomb, the charge when one Amp flows for one
second. The capacity of a battery might be, say, 10Amphours. This means it can
provide 1Amp for 10 hours.

9. Battery parameters
Energy stored.
The energy stored in a battery depends on its voltage, and the charge
stored. The SI unit is the Joule, but this is an inconveniently small unit,
and so we use the Whr instead.
Energy in Whr = V ´ Ahr
Specific energy
Specific energy is the amount of electrical energy stored for every
kilogram of battery mass. It has units of Wh.kg−1.
Energy density
Energy density is the amount of electrical energy stored per cubic metre
of battery volume. It normally has units of Wh.m−3.

10. Battery Charging/discharging characteristics
Charging
24 volt lead acid battery which has not
been charged or had current drawn from
it for a couple of hours.
Discharging

11. Energy density vs Power density

12. EV Battery types and characteristics
Lead Acid
Lead acid batteries are the most prevalent batteries used for vehicle starting and other ancillary power
functions. They have advantages of low cost per watt-hour, robust, durable, low self-discharge rate, and no
memory effect characteristics. The drawbacks of the lead acid battery include low power and energy densities,
and potential environmental impact, where the lead electrodes and electrolyte can cause environmental harm
if not disposed properly at a recycling facility [30].

13. Energy storage system II: Ultracapacitor
• Capacitors are devices with two conducting plates are separated
by an insulator.
• one plate being positive the other negative,the opposite charges
on the plates attract and hence store energy.
• The charge Q stored in a capacitor of capacitance C Farads at a
voltage of V Volts is given by the equation:
The large energy storing capacitors with large plate areas have
come to be called super capacitors. E =1/2 CV 2
where ε: permittivity
A : plate area
d : distance bet plates
reduce d
high C Ultracapacitor/
supercapacitor
increase A
Low voltage rating leading
to low energy holding capacity
Q = C V
+ C
-V

14. Energy storage system II: Ultracapacitor
• Attractive Features
• typically store 10 to 100 times more enrgy/unit volume
than electrolytic capacitors
• Capacitance ranges to 5000 F.
• No chemical reaction involved.
• Much more effective at rapid,
regenerative energy storage than chemical batteries .
• Works even at low temperatures -40 degrees Celsius.
• Ultracapacitors can store 5 percent as much energy as a modern lithium-
ion battery.
• 5000 farads measure about 5 centimeters by 5 cm by 15 cm, which is an
amazingly high capacitance relative to its volume.
• Can effectively fulfill the requirement of High current pulses that can kill a
battery if used instead.

15. Inside a Ultracapcitor
 Two Electrodes coated with sponge
like activated carbon’
 Electrolyte :Contains free mobile
ions.
 Porous Separator-:Prevents
electrodes from shorting out.
 Originally electrodes were made of
aluminum and coated with activated
carbon
. ESR
EPR
C
Ultracapaci
tor model
EPR :represents the current leakage and
influences the long-term energy storage.
the EPR influences the cell voltage
distribution due to the resistor divider
effect.
ESR : represents static field resistance
Seperator
Electrodes with
activated carbon
layer

16. Energy storage system II: Ultracapacitor
Characteristics of Ultra Capacitor as energy storage system
1. Low energy density compared to Battery, typically holds one-fifth to one-
tenth the energy of an electrochemical battery
2. High power density compared to battery
3. low voltage rating, needs to be connected in series-parallel combination
4. Requires additional Voltage equalisation circuit and sophisticated electronic
control and switching equipment
4. Can rapidly charge and discaharge
4. High self-discharge - the rate is considerably higher than that of an
electrochemical battery
5. Low capacity
6. Low impendence

17. Ragone plot of Batteries and Supercapacitor
Having less energy density, can be hybridised with Battery and can
be used to delivery high current pulses required by vehicle or
regerative pulse current to get charged

18. Sizing of Ultracapacitor:
Power and Energy requirement
• Sizing of an ultracapacitor system requires the specification of the
power and energy requirements.
• For a fixed ultracapacitor bank, these quantities dictate the number
of ultracapacitors needed
• The minimum number of ultracapacitors needed is determined by the
energy profile that the supercapacitive bank has to supply.
• Due to the voltage decay property , all the stored energy can not be
utilised.
• Therefore the sizing is based on the usable energy that the
ultracapacitor bank can transfer.
Energy available is proportional to square of voltage,which decays
over time.
Therefore the available energy of an ultracapacitor bank during
discharge follows

19. Supercapacitors vs Batteries
Chemistry
Nom.
Voltage Energy Power Density Cycle life
(V) Density (W/kg)
(Wh/kg)
Lead-acid 2 30-40 180 ≤800
Ni-Cd 1.2 ~50 150 ≤500
Ni-Mh 1.2 55-80 400-1200 ≤1000
Li-Phosphate 3.2~3.3 80-125 1300-3500 ≤2500
Li-ion 3.6 80-170 800-2000 ≤1500
Li-Manganese 3.7 110-130 ≤2000
Li-polymer 3.7 130-200 1000-2800 ≤1500
Usually when two or more energy sources are involved in a hybrid energy storage system for an electric vehicle, these sources can be

20. Flywheel Energy storage system
• The energy can be captured by connecting an electrical generator
directly to the disc .
• Power converter is used to match the generator output to a form
where it can drive the vehicle motors.
• The flywheel can be re-accelerated, acting as a regenerative brake.
Alternatively the flywheel can be connected to the vehicle wheels
via a gearbox and a clutch.
• Whether mechanical or electrical, the system can also be used to
recover kinetic energy when braking.
• The flywheel can be accelerated, turning the kinetic energy of the
vehicle into stored kinetic energy in the flywheel, and acting as a
highly efficient regenerative brake.

21. Flywheel hybrid mechanism
• Primarily consists of a rotating flywheel, (CVT),
a step up gearing (along with a clutch)
between the flywheel and the CVT and clutch which
connects this system to the primary shaft of
the transmission.
• When the brakes are applied or the vehicle decelerates,
the clutch connecting the flywheel system to the
driveline/ transmission is engaged, causing energy
to be transferred to the flywheel via the CVT.
• When the vehicle stops, or the flywheel reaches its maximum speed, the
clutch disengages the flywheel unit fromthe transmission allowing the
flywheel to rotate independently.
• Whenever this stored energy is required, the clutch is engaged and the
flywheel transmits this energy back to the wheels, via the CVT.

22. Energy storage device III :
Fuel cell
Hydrogen Fuel Cell : Basic principle
Electrode reactions
• fuel cell is the release of energy following a
chemical reaction between hydrogen and oxygen.
• The key difference between this and simply burning
the gas is that the energy is released as an electric
current, rather that heat.
How is this electric current produced?
A cell based on an acid electrolyte, we shall consider the
simplest and the most common type.
• At the anode of an acid electrolyte fuel cell the hydrogen
gas ionizes, releasing electrons and creating H+ ions (or protons).
2H 2 + O2 = 2H 2O
This reaction releases energy. At the cathode, oxygen reacts with electrons taken
from the electrode, and H+ ions from the electrolyte, to form water.

23. Main issues in the fuel cell
There are many problems and challenges for fuel cells to become an alternative to
a Battery.
• Cost: Fuel cells are currently far more expensive than IC engines, and even hybrid
IC/electric systems.
• Water management: It is not at all self-evident why water management should be
such an important and difficult issue with automotive fuel cells
• Cooling: The thermal management of fuel cells is actually rather more difficult
than for IC engines.
• Hydrogen supply: Hydrogen is the preferred fuel for fuel cells, but hydrogen is
very difficult to store and transport. There is also the vital question of ‘where does
the hydrogen come from.
However, there is great hope that these problems can be overcome, and fuel cells
can be the basis of less environmentally damaging transport.

24. Energy storage device III : Fuel cell

25. Fuel cell technology advancement
In Hydrogen fuel cell,
• Hydrogen is fed to one electrode, and oxygen, usually as air (for oxygen) to the
other.
• A load is connected between the two electrodes, and current flows.
• However, in practice reaction of both hydrogen and oxygen is very slow in fuel cell
• Normally the rate of, which results in a low current, and so a low power.
• The three main ways of dealing with the slow reaction rates are which can be
overcome by:
1. use of suitable catalysts on the electrode, (electrode is coated with a catalyst layer)
2. the temperature
3. increasing the electrode area (electrode made highly porous )

26. Types of Fuel cells
• Types of fuel cell are based on different electrolytes
• The situation now is that six classes of fuel cell have emerged as viable systems
for the present and near future
• The PEM fuel cell capitalizes on the essential simplicity of the fuel cell. The
electrolyte is a solid polymer, in which protons are mobile
• In DPEM, hydrogen supply problem is to use methanol as a fuel instead

27. Fuel cell vs Battery/Fossile fuel
• Most fuel cells operate silently, compared to internal combustion engines.
• They can have high energy density and power density as it takes Hydrogen as
input
• Fuel cells can eliminate pollution caused by burning fossil fuels; for hydrogen
fuelled fuel cells, the only by-product at point of use is water.
• Hydrogen is cheaper than Gasoline/Ptrol
• Critics of hydrogen fuel cells argue that although these cells do not emit carbon
after burning, they give out nitrogen dioxide and other emissions.
• transporting hydrogen can be expensive
• Highly Flammable
• battery makes electricity from the energy it has stored inside the battery and a
fuel cell makes its electricity from fuel in an external fuel tank
• This means that while a battery may run dead, a fuel cell will make electricity as
long as fuel is supplied.
• For hydrogen fuel cells, hydrogen is the fuel and it's stored in a tank connected
to the fuel cell. When hydrogen in the tank runs low, you refill it, or replace it
with a full tank.

28. Still Disadvantages

29. Research Status replacing IC engines with Fuel
cell banks

30. FUEL CELL Hybrid Vehicle : Configuration

31. Hybridization of Energy storage systems
Why Hybrid energy storage system (HESS)
• When two or more energy sources are involved in a hybrid energy
storage system (HESS)
• these sources can be distinguished by their energy storage and power
delivery capacities respectively.
• For a pure electric vehicle, sources with high energy density would be
considered as the main energy source such as battery packs and fuel cells.
• Primary Energy source is having high energy density but suffering from
low power delivery problem during vehicle moving from point A to point B
• To boost overall power delivery capacity to a reasonable level, an
auxiliary energy source synonymous with high power density is usually
utilized.
• Popular choices for this source include high power batteries and
supercapacitors.
• So, Battery can be a primary energy source and Ultracapacitor will be
Auxillary source

32. Hybridization of Energy storage systems

33. Hybridization of Energy storage systems
•There are usually N storage devices
( Presently 2)
•W: weight factor for adjusting the rate at which
energy is being drawn (power) from each source.
•∑: algorithm to coordinate the power flow by
dynamically varying the weight factors in load.
• Also taking into consideration the system
constraints such as depletion levels or limits of
the energy storage systems
•The load requests fluctuate through a drive
cycle in the case of an electric vehicle
•the supercapacitor is acting as the auxiliary
source while a battery pack or fuel cell, as the
case may be, is used as the main energy source.

34. Hybridization technique( Implementation circuit)

35. EV drive train with hybrid source configuration

36. Hybridization of Flywheel energy storage system

37. Modified presentation will be uploaded shortly