Energy Source of Electric Vehicles

Energy Source:

• Different EVS can get the energy required for their operation from different sources which can store energy.
• They are as follows:

1. Batteries
2. Ultracapacitors
3. Flywheels
4. Fuel cells.

Requirements of EVS energy sources:

• The requirements of the energy sources for EVs are as follows:

1. High specific energy and energy density.
2. High specific power and power density.
3. Fast charging and deep discharging capabilities.
4. Long cycle and service lives.
5. Low self-discharging rate and high charging efficiency.
6. Safety and cost-effectiveness
7. Less maintenance.
8. Environmental friendly and recyclable.

• High specific energy from a source is required to provide a long driving range.
• The high specific power helps increase the acceleration.
• The other important characteristics of a perfect energy source are fast charging, long service, and cycle life. Less cost and low maintenance.

1. Battery:

• Batteries are the major energy source for EVs for a long time. They convert the stored chemical energy into electric energy.
• The chemical reaction between the electrodes and electrolyte generates electricity.
• The EVS needs rechargeable batteries that can reverse the chemical reaction by reversing the current.
• The battery is the most important component of an electric vehicle as it constitutes up to about half of the vehicle’s cost and weight.
• The choice of attunes depends on the factors suit as energy density, weight, and costs

Requirement of EV batteries:

• The EV battens should satisfy the following requirements

1. High energy capacity.
2. High peak power output.
3. A stable voltage output.
4. High energy efficiency.
5. Good charge retention when on open-circuited.
6. Ability to recharge at a fast rate.
7. Overcharge and over-discharge withstanding capacity.
8. Wide operating temperature range.
9. Low maintenance
10. Rugged and resistant to rough use.
11. High reliability
12. High safety.
13. Environmental friendly.

Deep cycle batteries:

• Deep cycle batteries are the batteries that can supply a stable voltage even at the deep discharge cycle.
• Deep-cycle batteries are normally available in three-terminal voltages: 6, 8, and 12 V.
• The 6V batteries are used for range whereas 12 batteries are used for performance.
• The battery with 8V terminal voltage offers a good balance between the range and acceleration capabilities.

Types of EV batteries:

• The following four types of batteries are commonly used today in EVS

1. Lead Acid
2. Nickel Cadmium (NiCd).
3. Nickel Metal Hydride (NiMH) and
4. Lithium-ion (Li-ion).

• Most electric vehicles in the early days of EVs have used lead-acid batteries because of their mature technology, easy availability, and low cost.
• However, the recent EVS use the batteries with combinations of lithium-ion and its variations as they possess the following advantages:

1. Higher efficiency,
2. Lower weight,
3. Shorter charging time,
4. Higher power output,
5. Longer lifetime, and
6. Less pollution from battery disposal.

Alternative Energy Storage Devices:

• The alternative energy storage devices are the flywheel and supercapacitors.
• Both these devices have high specific powers that mean that they can take in and give out energy very quickly.
• However, currently, they can store a very small amount of energy.
• That means, they have a good power density but poor energy density.

2. Ultra (Super) Capacitor :

• Ultracapacitors or supercapacitors or electrochemical capacitors are different from batteries.
• Batteries store their energy chemically whereas an ultra-capacitor store it physically.
• The capacity of a capacitor is directly proportional to the area of the conducting plates.
• Hence capacitors with large-area can gain a high storage potential.
• We can use a supercapacitor as an EV battery if its capacity per unit weight is the same or greater than the secondary battery.
• A material whose surface has numerous small noels in it can be used to reduce the size of the capacitor
• In an EV, an ultra-capacitor can be used to provide the power for acceleration and a battery to provide range and to recharge the ultra-capacitor.
• Ultracapacitors charge and discharge very faster as compared to batteries.
• Hence they are very suitable for storing the energy from regenerative braking for climbing hills or sudden acceleration.
• Around the world now, supercapacitors are used as the main power source for electric buses.
• They are charged on their route at intervals very quickly (in about 30 seconds).
• They are also used in buses, trams and trains are increasing.

3. Flywheel:

• The flywheel also is an energy storage device, similar to a battery.
• It stores the energy in the kinetic form in a rotating disc. In its charging process, the rotor is accelerated by an electric motor to store the energy.
• And in its discharging process, it is decelerated when the motor is switched to generative operation.
• This flywheel energy storage system (FESS) is composed of composite rotors spinning at thousands of rpm on frictionless magnetic bearings.
• It can drive a generator to provide power for EVs.
• Energy stored in flywheels increases with an increase in the speed of the rotors.
• As energy is used up, the rotor speed decreases.
• The flywheel manufacturing companies claim that the flywheel of the same size as the 6-volt battery. Weighs much less and can store 3 times the energy and lasts ten times longer.
• The gyroscopic effect is avoided by having two adjoining wheels rotating at identical speeds in opposite directions to each other, on a stationary shaft.
• Friction is reduced to a minimum of suspending the wheels in a vacuum.
• These companies expect that the flywheels can extend the range to 300 miles on a single charge about that of a lead-acid battery.
• The life of the flywheel is very long and no replacement is needed.