What's a Hybrid? A Brief Overview
A hybrid-electric vehicle, or HEV, is a vehicle that operates on both electric power and something else. In many cases, that something else is internal combustion, and can involve the combustion of gasoline as well as natural gas, hydrogen, or propane.
The advantages of an HEV are plentiful. Besides being much more fuel efficient than their fully internal combustion counterparts, hybrids are much cleaner and are better for the environment. Electric drivetrains are well suited to reclaiming energy that is usually completely lost in other varieties of vehicles. Braking, for instance, is usually a complete loss of the vehicle's kinetic energy. With an electric or hybrid-electric drivetrain, a process called regenerative braking can convert a vehicle's motion to electric energy to use later.
Most of the commercially available hybrids (such as the Toyota Prius or the Honda Insight or Hybrid Civic) have drivetrains that incorporate regenerative braking as their primary source of electric energy. This means that the battery pack does not get charged unless the vehicle is being slowed with the brakes. It is for this reason that these hybrids excel in stop-and-go city driving, while on the highway (with no braking or electric assist) their fuel economy is more comparable to vehicles with more traditional drivetrains. This is called a 'parallel' arrangement (see diagram to the right).
The design that I plan on using for my hybrid is a 'series' arrangement, which takes a full-electric platform and essentially adds a small generator for on-the-fly charging. This arrangement has a few advantages over the parallel arrangement, especially in the case of added efficiency. This is due to a smaller gasoline engine, and to the fact that the engine is allowed to run at a constant speed. Unfortionately, I will not be able to take advantage of regenerative braking with the truck's initial configuration. This is something that will have to be added on later, when the budget is larger and the time is more plentiful.
For short range requirements, my vehicle will be able to run on electric power alone. This is a definite advantage for a utilitarian vehicle like a truck, which is often used around town and may not have to cover long distances on a regular basis. Operating solely on electric power is much more cost effective and is cleaner than always having to fuel an internal combustion engine.