In the automobile’s earliest days, you had your choice of propulsion. Along with gasoline, you could also go for steam or electric power—or if you were a purist, a horse.

Gasoline eventually eclipsed all of those, but everything goes in cycles, and drivers can once again choose some type of electric power. Although hybrids have been on the scene for more than a decade, they’re complicated, and they’re not all the same. We’ve put together a bit of info on the systems you’ll see.

The general definition of a hybrid is a car that operates on both gasoline and electricity, but of course there’s more to it than that. The driveline includes an internal combustion engine, an electric motor, and a storage battery—which, these days, is usually some form of lithium ion. A hybrid doesn’t get plugged in, but recharges the storage battery itself (although there are plug-in hybrids, and we’ll get to them later).

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2013 Toyota Prius C Hybrid Synergy Drive system- Photo: Toyota

There are two basic types of hybrids, popularly called “full” or “mild” hybrids. A full hybrid is capable of running on electricity alone, while a mild hybrid can’t, and its electric motor is used to supplement the gasoline engine when more power is needed. Full hybrids are more popular, but mild hybrids—also called light electrification—generally cost less.

Full hybrids are amazingly complicated machines. They switch automatically between electricity and gasoline, and while they’re programmed to prioritize electricity whenever possible, there are numerous factors that have to be constantly analyzed. These include ambient temperature, the battery’s state of charge, how fast you’re driving or how hard you’re accelerating, and how many power accessories you’re running.

The system will try to stay on electricity alone as much as possible—obviously, because if the engine isn’t running, you aren’t using any fuel. You may be able to stay on the battery alone during gentle acceleration, but if you put your foot into it, the electric motor won’t be enough and the gasoline engine will kick in. Once you reach your cruising speed and back off the throttle, the gas engine will likely shut off again. The battery-only top speed was low on the earliest hybrids, but many can now cruise along with highway traffic on electricity.

The battery is recharged via two methods: regenerative braking, and engine power. Regenerative braking captures the kinetic energy when you slow down, converts it to electrical energy, and stores it in the battery. The more you coast, the more energy you capture. The most efficient hybrid drivers are those who look far ahead and get off the throttle as early as possible when they know they’ll have to stop. On some hybrids, such as the Toyota Prius, the shifter can be slipped into a “Brake” mode that makes the regenerative process even more aggressive, slowing the car down faster but feeding more power into the battery.

If regenerative braking isn’t enough, the engine will come on to recharge the battery. While driving on electricity-only in stop-and-go traffic is the most satisfying, it may not always be the most economical: since you don’t get in a lot of regenerative braking, the engine will start when the battery depletes, and you’ll be almost exclusively using gasoline to power the battery back up. The optimal driving condition is with moderate speeds in light traffic, where you can run on electricity but still benefit from regenerative braking.

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Mazada’s i-ELOOP is a regenerative braking system that converts kinetic energy into electricity as teh vehicle slows down – Photo: Mazda

After many years of having to convince customers that hybrids didn’t have to be plugged into a wall, some manufacturers now offer ones that do. The various plug-in hybrid models may have slight differences, but essentially, you plug them into a wall and recharge the battery, and then drive using only that stored power. Once that depletes, usually after 30 kilometres or less, the vehicle reverts to regular hybrid operation, where it recharges its battery with the engine and regenerative braking. These are more expensive than regular hybrids, but depending on your daily commute, you could potentially drive almost exclusively on plug-in power.

An extended-range vehicle, such as the Chevrolet Volt, is also a type of hybrid but has a major difference. You also plug it in and run on the stored charge, and when it depletes, the gasoline engine starts up. However, instead of powering the wheels, it acts like a generator to produce more electricity for the car’s electric motor. Extended-range vehicles also take advantage of regenerative braking for recharging.

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The Chevrolet Volt (Extended Range Vehicle) – Photo: Chevrolet

The main advantage of plug-in hybrids and extended-range vehicles is that if the stored charge runs out before you can plug the car back in, you’re not stranded. You can drive these without plugging them in at all, but they really don’t make sense unless you do. If you don’t charge them up regularly, they’re just hybrids that cost and weigh more.

But you definitely have to plug in an electric vehicle, which contains only an electric motor and battery. These also use regenerative braking to top up the battery when they can, but ultimately, you will deplete the charge, and if you don’t plug it back in again, you’re not going anywhere. The range will depend on the vehicle, but no matter what, there’s a limit to how far you can go, and your commute and driving habits will have to fit the car, rather than the other way around.

Steam won’t make a comeback, and the horse remains primary transportation mainly amongst Amish farmers, but it looks like while electricity is still in the minority on our roads, it’s definitely here to stay.