Hybrid car

Figure 1. A 2013 VW Jetta Hybrid.[1]

Hybrid cars are a type of motor vehicle that combines the benefits of both gasoline and electric vehicles. Their goal is to increase the mileage and reduce the emissions of a gas-powered car, while overcoming the shortcomings of electric cars such as short distances for their battery charge.[2] Gas-powered cars have an internal combustion engine and a fuel tank, while electric cars have electric motors and batteries. Both feed power to the transmission which delivers it to their respective drive train in order to move the car. Hybrid cars combine all of these parts into one system.


  • Gas engine- Hybrid cars have similar engines to normal cars, however, they are often smaller in order to reduce emissions and increase fuel efficiency.
  • Fuel tank- Much like normal cars, hybrids use a fuel tank to carry their fuel that supplies the engine. Gasoline's energy density is much higher than typical batteries, as one would need 450 kilograms of batteries to match about 4 liters of gas energy.[2]
  • Electric motor/generator- Sophisticated design allows this part to act as either a motor which gives the car motion from electricity or as a generator which gives the batteries electricity from the motion of the car. In series hybrid cars, the generator and motor are separate components (see below)
  • Batteries- These either supply energy to the motor or draw energy from the generator and take a relatively long time to charge.


The arrangements of these parts differ in hybrid cars and can be arranged either in series or parallel:[2]

  • Series- This configuration doesn't allow both the engine and motor to directly power the wheels. Instead, its power is converted into electricity by the generator, which can either charge the batteries or power the motor. The motor connects to the transmission and powers the wheels. This is more often used in short-range specialty vehicles or industrial equipment.[3]
  • Parallel- This configuration allows both the engine and motor to give power to the transmission, so either can be done independently. This type is more popularly used as it gives the best possible fuel efficiency, however, due to its complexity it has service and repair issues.[3]
Figure 2. Series vs Parallel configuration for hybrid cars.[4]

Improving Fuel Efficiency

There are a few reasons why the hybrid car can be more efficient than normal cars, thereby having a better fuel economy.

Smaller Engines

First of all, the engine is smaller, meaning less weight for the car to have to accelerate. Smaller engine means smaller cylinders and pistons, which require less energy—and therefore fuel—to push them up and down in their reciprocating motion. Smaller engines also mean less cylinders so less fuel is required to give the car motion.[2]

While it may seem that a smaller engine would need more to match the power output of a normal gasoline vehicle, this isn't the case. These smaller engines in a hybrid car only need to achieve the average output of the engine, which allows them to be smaller. A normal gas-powered car must have bigger engines that are designed to achieve the maximum output needed.[2] When the hybrid car needs to achieve more output it doesn't use more fuel, instead it takes advantage of the electrical power from the batteries and motor.

Energy Recovery

When a car brakes, the kinetic energy of its motion is dissipated as heat. Hybrid cars can use the electric motor to slow the car down, and by doing so it acts as a generator supplying the batteries with some of this energy. Read more on the regenerative braking page.

Shutting Off the Engine

Since the engine is not necessarily needed to power the car due to its alternate power source, the engine can be shut off at certain times, for example when the car is stopped at a red light.[2]

Reducing Losses

Hybrid cars are most often shaped to reduce air drag, which acts against the motion of the car. Normal sports cars are shaped as such as well, but larger vehicles like vans or trucks lose a lot of efficiency due to air drag.

Hybrid cars also have special tires that give a smooth ride and give off less noise. They also provide good traction therefore reducing energy losses.

For Further Reading


  1. Wikimedia Commons [Online], Available: http://upload.wikimedia.org/wikipedia/commons/0/04/VW_Jetta_Hybrid_with_badge_WAS_2012_0711.jpg
  2. 2.0 2.1 2.2 2.3 2.4 2.5 Nice, Karim, and Julia Layton. "How Hybrid Cars Work" 20 July 2000. HowStuffWorks.com. <http://auto.howstuffworks.com/hybrid-car.htm> 04 June 2015.
  3. 3.0 3.1 Second Opinion Service, Hybrid and Alternative Fuel Cars [Online], Available: http://sos-inspections.com/articles/hybrid-and-alternative-fuel-cars
  4. Made internally by a member of the Energy Education team, adapted from How Stuff Works. Available: http://auto.howstuffworks.com/hybrid-car2.htm