Mercedes Hyper concept cutaway showing major components.

If you listen to the makers, hybrid cars are the best invention since sliced bread. While there are many reasons to buy a hybrid car, including a new tax incentive for US owners, it helps to have a good understanding of how they work. This article explores the myths, benefits and drawbacks of owning one of these new “green” vehicles.

First off: What is a hybrid car? Basically, it’s a normal, fuel efficient car that has two motors - an electric motor and a gasoline powered motor. It also has a special system to capture braking energy to store in an onboard battery.

Why a hybrid? Why not a straight gas or electric powered car? After all, one of the basic rules of science is the more complex the system - two motors instead on one - the more often it will break down. This is the main reason many boat owners prefer one motor instead of the “double trouble” of two - despite the obvious safety advantages. This is a hard question and, in the minds of some experts, not fully answered.

• Join PhysOrg.com on Facebook!
• Follow PhysOrg.com on Twitter!

The reason for two motors is in the strengths and weaknesses of both types. Specifically, electric motors use no energy during idle - they turn off - and use less than gas motors at low speeds. Gas motors do better at high speeds and can deliver more power for a given motor weight. That means during rush hour stop and go driving, the electric motor works great and, as an added benefit, does not produce any exhaust thus reducing smog levels. At higher speeds - above 40 mph - the gas motor kicks in and gives that peppy feel so many car owners look for when driving on the highway.

Another benefit of having the gas motor is it charges the batteries while it’s running. Many an electric car owner has been stranded just out extension cord range of an outlet. Hybrid owners can forget about this annoyance; the gas motors starts automatically when the battery gets low and proceeds to charge the battery - a hybrid never needs to be plugged into an outlet. Of course, if you forget to fill the tank…. Still, you can carry a gas can a half mile while a tow truck is necessary in a straight electric car.

Honda Insight

All this new technology comes at a price: a hybrid car is complex and expensive. It has two motors and all the ancillary systems to manage them plus a heavy battery and a regeneration system used to produce electricity during breaking.

All of these systems must work together, adding complexity. While cars and, just as importantly, the computers that control them, have become more reliable, they still suffer from failures. So owners of hybrids can expect more time in the shop and larger repair bills.

Hybrids are the most gasoline efficient of all cars - they typically get 48 to 60 mpg (claimed). Not bad, but only about 20% to 35% better than a fuel efficient gasoline powered vehicle - like the Honda Civic, for example, that gets 36 mpg. But, when comparing prices - hybrids cost from $19,000 to $25,000 and gas saver cars cost $14,000 to $17,000 - the justification to buy becomes less clear.

Indeed, the difference in average annual fuel bills - $405 for a Honda Insight versus $635 for a Honda Civic - means you may never recoup the added initial cost of a hybrid. Over a ten year period owning a hybrid will save you only $2,300 - less than the cost difference for comparably equipped cars.