Hybrids 101

What is a Hybrid?
Simply put, a hybrid vehicle is a car, truck, or SUV that has elements of a conventional gasoline or diesel engine drive train, as well as elements of an electric vehicle. Typically, an electric motor provides assistance to the gas engine during acceleration.

Advantages of hybrids
Let’s talk about energy and work for a moment. Every time you accelerate your car away from a stop, the engine has to do work on the car. In physics terms, work is defined as movement of an object through some distance. For work to be done, energy must be expended. The energy source is the gasoline in your tank. Once your car is moving, it contains a significant amount of energy just due to that motion. This is called kinetic energy. In a traditional car, when you slow down, that kinetic energy is wasted. The brakes simply convert it to heat. This means that every time you use your brakes, you are throwing valuable energy (that you paid for with gasoline) out the window.

But what if we could capture that energy when we stop and save it for later? It turns out that in a hybrid vehicle, we can. It is a very fortunate fact that most electric motors will also work as generators. We can use the hybrid’s electric motor as a generator to recharge its batteries some every time we use the brakes. We won’t get all of that energy back, due to various inefficiencies involved, but we’ll get a lot more than none, which is what we get with a conventional car.
Another significant advantage is that since the electric motor can help accelerate the car, the gasoline engine can be significantly smaller. A smaller engine uses less gasoline, everything else being equal.

As an example, consider the Ford Escape. The hybrid version gets 34 miles per gallon (mpg) in the city while the conventional Escape gets 20 mpg. With gas at $4.00 per gallon, that’s a savings of $1000 a year if you drive the national average of 12,000 miles per year.

Disadvantages of hybrids
Unfortunately, you can’t get something for nothing, and hybrids are no exception. All this extra equipment adds complexity and costs money. For example, the hybrid version of Ford’s Escape starts at $26,640 while the similarly optioned Escape XLT starts at $21,140.
Series hybrid vs. parallel hybrid

There are a many different ways to design a hybrid, but they can all be grouped as series or parallel. The terms series and parallel refer to the method by which the gasoline engine and electric motor work together.

Parallel hybrids

All of the hybrids on the market today are parallel hybrids. This means that the gasoline engine and electric motor can both send power to the wheels to move the car. Typically, these hybrids can move under electric motor only, gasoline engine only, or both working together. Some parallel hybrids, such as the Saturn Vue, don’t have a strong enough electric motor to operate in electric-only mode.

One of the benefits of parallel hybrids is that they drive very much like a traditional car. In addition to improved fuel economy, they typically offer improved performance compared to a traditional car, due to the fact that the gasoline engine and electric motor can work together to accelerate the car.

Series hybrids
In a series hybrid, such as the 2010 Chevrolet Volt, the gasoline engine only drives a generator. This generator is used to charge a battery pack to power an electric motor. In this type of hybrid, the gasoline engine cannot directly power the wheels to move the car. This means that the electric motor must be larger and more powerful than in a parallel hybrid, as it must do all of the work of accelerating the car.

The major benefit of this design is that the gasoline engine can be designed to operate at its most efficient point for charging the battery pack. One disadvantage is that the main generator cannot be used as a motor to drive the car. The drive motor can be used as a generator during braking, however.

What about Plug-in Hybrids?

A plug-in hybrid is a hybrid with a battery pack that is large enough to power the car a significant distance without the gasoline engine having to start. The idea is that you keep the car plugged in while it’s at home, and when you drive it for short trips around town, you don’t use any gasoline at all. When you get back home, simply plug back in. If you need to make a longer trip, the gas engine starts and you continue driving normally. The downside is a significantly more expensive battery pack. While there are not any plug-in hybrids on the market yet, the 2010 Toyota Prius will be available as a plug-in in limited quantities. Chevrolet predicts that it’s 2010 Volt plug-in hybrid will go 40 miles on a full charge prior to the gas engine needing to start.