Amongst the various forms of energy in use, electricity is the cleanest and the most easily available energy source. Hence when the question of using eco-friendly hybrid cars arises, the first choice is always given to a Hybrid Electric Vehicle (HEV). It is the combination of the eco-friendliness of the Electric Car and the efficiency of the Gasoline car and thus, a perfect hybrid. Let us discuss some general terms used in HEVs:
- Lead Acid Batteries – They are the old types which are being used in vehicles presently. They are cheap and need to be refilled with water in frequent intervals.
- Nickel-Cadmium and Nickel-Metal Hydride – They are sealed batteries which can store more energy and require almost no maintenance.
- Lithium-Ion Battery – They can store almost 8 times the energy as compared to a lead acid battery of the same weight. It is also maintenance free but its cost is very high.
- Regenerative Braking : Instead of using the mechanical brakes as in conventional cars, Electric cars make use of regenerative brakes. The resistance in the motor stops the car and the generated energy is stored in the battery to be used in case of acceleration.
What are Hybrid Electric Vehicles
A hybrid electric car makes use of two or more sources of energy, one being compulsorily electricity. The other can be gasoline, hydrogen or ethanol. The most common hybrid is the one which uses electricity in combination with gasoline. Some key advantages of Hybrid Electric vehicles are:
- The biggest benefit of using HEVs is the prevention of pollution. Although, pollution occurs in the production of electricity but it is very less as compared to internal combustion engines in gasoline cars.
- HEVs are user friendly. The car itself decides whether to run on electric mode or gasoline mode.
- Features like regenerative braking further leads to saving energy that would otherwise have been wasted.
- HEVs produce no or very little noise.
There are also a few limitations associated with HEVs, they are:
- The greatest disadvantage is that these HEVs are still quite expensive. Moreover, because it is new in the market, it requires high skills to maintain and repair these cars which again adds to the price burden.
- It needs to be recharged time and again, i.e. its range is less.
- The hybrid car makers try to increase the efficiency by using lightweight material which in turn poses safety threats. Also there is a less chance for rescuers to protect the driver in case of an accident, due to electric motor and increased risk of electrocution. Due to high voltage in wires, there is an increased chance of short-circuit.
Working of a Hybrid Electric Vehicle
Almost every HEV uses a power-train combination which consists of a standard gas engine and an electric motor which uses energy from a nickel-metal hydride battery. The engine constitutes the fuel propulsion system while the electric motor and the battery constitute a rechargeable energy storage system (RESS). Small engines, obviously, use less fuel. Hence, hybrid vehicles have a relatively smaller and more efficient gas engine and a larger electric motor.
- Electric Motor Assistance – The instant torque required to accelerate from the stationary state is provided by the electric motor and the vehicle runs on electric power until a specific speed. It is so programmed that the supply shifts to internal combustion engine when required. This transition is managed by a Power-Split device.
- Auto Start/Shutoff – When the vehicle stops, both the engines shut down and it restarts when the accelerator is pressed, automatically. This saves a lot of fuel.
- Regenerative Braking –HEVs extend battery charge by using the Kinetic Energy of the wheels when electric motor applies resistance during application of brakes. At this moment, the regenerative circuit converts the motor into a generator, and converts the wasted energy into electrical energy stored in the battery.
Improved fuel economy, stiffer tires, aerodynamic design, circuits and programming make the hybrid vehicles more efficient than standard cars.
Types of Hybrid Electric Vehicles
Some important types of HEVs available in the market are discussed below. This categorization is based on how the car gets its power.
Mild : Here the electric motor/generator is used to generate energy during deceleration and to give extra output during acceleration. The stored electrical energy can be used in ac, power steering and other electrical components, Examples – Mercedes Benz S 400 Hybrid and BMW-7 Series
Parallel : In this type the electric motor and the internal combustion engine give power to the vehicle individually or simultaneously. The engine is directly connected to the motor. Hence where there is less use of brakes, i.e. in highways, the efficiency is much more than in cities. Example-Honda Insight
Serial : It uses the simplest configuration. The only source to drive the wheels of the car is an electric motor which receives energy from the battery or the generator from gasoline energy. There is a power split device which is controlled by the computer to manage from where the energy is to be taken – from the battery or the internal combustion energy. The engine can charge the battery or drive the motor directly. When large amount of power is required, electric motor can draw electricity from the generator and the battery at the same time. Example – BYD F3DM, urban buses
Serial-Parallel Hybrid : Here there are two electric motors and one internal combustion engine. One electric motor works only as a generator while the other works as a generator as well as a motor. Primary source is the internal combustion energy but in case of extra power required, electric motor is used. Example – Toyota Prius, Ford Escape and Lexus Gs450
Plug-In Hybrid Vehicle (PHEV):
It is the most advanced form of Hybrid Electric Vehicle. It can be connected directly to the mains and the battery will be charged. When the car runs out of the stored electricity, the battery can be recharged by gasoline. It is the ideal HEV but the problem is that it is very expensive. Example – GM Volt, BYD F3DM
Market of Hybrid Electric Vehicles
There has been a tremendous increase in the sales of HEVs in the recent years because of the wide number of options provided to the customer by the car manufacturers. Almost all major car brands have entered into the market of Hybrid Electric Cars. The following graph shows the rise of the sales of some popular HEVs in last few years. It is noteable that Toyota Prius has been the most popular HEV since very long.
Popular Hybrid Vehicles (in terms of units sold) – Toyota Prius Leads the Pack
From the above graph, it is quite clear that Toyota Prius currently rules the market of Hybrid Electric cars. It is because of its low cost and high mileage. The cost and mileage (in MPG – miles per gallon) of the major HEVs have been discussed in the following graphs:
Mileage of Popular Hybrid Vehicles (miles per gallon) – Toyota Prius again Leads the Pack
Price of Popular Hybrid Vehicles (in '000 USD ) – Toyota Prius is amongst the lowest
The range of HEVs offered is very wide. From small cars like Toyota Prius and Honda Civic to expensive luxury models like Mercedes Benz and BMW, the market offers the customer the opportunity to make the choice according to his own needs. This has led to competition in the market which is good for the future of the HEV industry.
Future of Hybrid Electric Vehicles
The future of HEVs depends on the demand of the market and the demand of the society. With the rising fuel prices, shortage of fossil fuels and growing environmental concern amongst the people, it seems that the future belong to hybrid vehicles such as the HEVs.
But some major steps must be taken to insure its position in the market of the future. A lot of investment is required to develop the infrastructure for these vehicles. Also, much research needs to be done in order to eliminate its limitations. This must be accompanied with the lowering in price. If these factors are looked after, there is no doubt that the HEVs will occupy the prime position in the future market. These vehicles will also pave the way for efficient electric vehicles.