There are two types of hybrids: parallel hybrids and series hybrids. The parallel version (Fig 2.3) has a fuel tank for the gas engine and batteries for the electric motor. Both the engine and the electric motor can turn the transmission and power the vehicle. The small gas engine runs the car and the electric motor comes on when needed to boost power. This is typically needed for increasing speed, merging and passing other vehicles. Honda currently uses this technology.

Series hybrids (Fig. 2.2) have a gas engine that powers a generator. The generator then charges the batteries and powers the electric motor. The gasoline engine does not power the vehicle on its own. The electric motor runs all the time and the gas engine comes on only when needed. This vehicle gets better mileage around town, where the electric motor is doing most of the work. Alternate Propulsion currently uses this technology.

Hybrid cars get significantly better gas mileage than the traditional internal combustion engine. Most get between 20 and 30 miles per gallon more than standard automobiles. All hybrids shut off the gas engine automatically when the car is stopped. This saves fuel and is better for the environment. On some hybrid vehicles when you press the gas pedal, the engine turns back on automatically. The gas engine will also come on to start charging the batteries when they become low on power.

Because less gasoline is burned in these vehicles, there is less pollution causing emissions released into the atmosphere. In addition, there is a lower level of carbon dioxide released into the atmosphere. Many scientists and environmentalists link carbon dioxide to global warming.

Hybrids recover energy from the electric motor to the battery. When you step on the brake, the energy from the motor is transmitted back to the battery. This process is known as regenerative braking. This helps to recharge the batteries and keep them in good working order.