The Difference Between Parallel Hybrid & Series Hybrid Cars
- A series hybrid has two power sources linked together in a series, meaning that the output of the first power source feeds into the input of the second, and there is only one power source directly connected to the vehicle's transmission.
The most common example of this type of hybrid is a gasoline or diesel engine turning an electric generator. The electricity powers electric motors, which link to the drive wheels. In this configuration, the gasoline engine and electric motor are in a series, and the gasoline does not connect directly with the drive wheels.
The series hybrid allows both the gasoline engine and electric motor to run at their most efficient setting, maximizing its performance and efficiency of the vehicle. - A parallel hybrid has two power sources connected, through the transmission, to the drive wheels. Each power source may supply some or all of the power needed by the vehicle at any particular moment.
Common examples of parallel hybrids are vehicles in which both a gasoline engine and an electric motor connect to the same transmission. In this design, the amount of power supplied by each source is dependent upon the vehicle requirements at that point. As an example, when accelerating from a start, the parallel hybrid may use both power sources, switching to just one under less demanding highway cruising.
Parallel hybrids may also use an electric motor as a generator to capture energy from the drive wheels during braking. This energy is stored for later use, maximizing efficiency. - The first hybrid vehicles with commercial success have been parallel hybrids. Several manufacturers have introduced models with this technology, and additional models are in design.
Series hybrids are more common in larger and more powerful applications, including most locomotives and many ships. However, their ability to minimize the power requirements on a gasoline engine during stopping and starting makes them a good fit for vehicles commonly used in city traffic. Several major automakers have announced series hybrid vehicles. - Parallel hybrids allow both power sources to work simultaneously, allowing the optimized performance of each. While this strategy allows for increased efficiency and performance, the transmission and drive train are more complicated and expensive.
Series hybrids have only one drive train, but require two distinct energy conversion processes for all operation. These two energy conversions, gasoline to electricity and electricity to drive wheels, each have losses due to inefficiency of energy conversion. - Plug-in hybrids, vehicles that draw and store electricity from the grid, are typically series hybrids. These will likely be the first series hybrid automobiles to be commercially available.
As technology progresses, the distinction between series and parallel hybrids will blur. Mild hybrids, such as a gasoline-powered vehicle where the starter motor can provide added power, will further confuse the terminology.