How it works: the plug-in hybrid

[sukishan]

How it works: the plug-in hybrid

Thanks largely to the market leading Toyota Prius we're all by now quite accustomed to hybrid cars and most of us probably know to one extent or another how they work. Well, the latest step on our path towards electric cars (or however we'll eventually achieve eco-friendly personal transport) is the plug-in hybrid.

So what's the difference between a conventional hybrid and a plug-in one? Well, we're about to tell you, and believe it or not it's actually a little more interesting than 'one's got a plug' - even though that's true.

Ok, so before we begin remind me how a regular hybrid works?

That question is like asking how a regular engine works - in the same way we have different engine configurations and fuels, so too are there different types of hybrid. Toyota's 'Hybrid Synergy Drive' is an example of a 'full hybrid' system, which means that it has a combustion engine and an electric motor powered by a battery pack. Either the electric motor or the engine can power the car alone, or they can work together.

Some hybrids, like that in the Honda Insight, cannot be driven on electricity alone, but use their electric motor to back up the petrol engine, thus making fuel consumption gains because a smaller engine can be used and isn't as hard worked in pulling the car along.

Excellent, I feel fully clued up now. So how does a plug-in system improve things?

By increasing the range of a full hybrid, thus allowing more electric-only driving and, therefore much improved fuel consumption. In an ideal world, the plug-in hybrid would never need to call on the fuel sloshing about in its tank, which would serve purely as a very wet kind of comfort blanket.

Hang on... a comfort blanket?

Yes indeed. We're so used to the way our cars work - the dynamic of filling up with fuel and knowing we're 'safe' until the gauge needle sinks to zero - that battery power throws us into a collective panic. It's known in the industry as 'range anxiety' and is the main thing that worries us about driving electric only cars; we trust a tank of fuel and the few hundred miles that will get us, but what do we do if our car battery runs out suddenly? Range anxiety is no surprise given electric cars, to date, offer far fewer miles from a charge than a tank of fuel does.

Ah, so having a 'backup' tank of fuel means we're not bothered if the battery runs out?

Exactly. The plug-in hybrid works the same way as a normal hybrid - offering both petrol and electric power, or both - but weans us into electric-only power because it can pull juice from the same socket your toaster's plugged into, and theoretically never needs to use fuel. Toyota's plug-in Prius, for example, replaces the regular car's nickel-metal hydride battery with a lithium ion one (as used in mobile phones), which is more energy intense and can take charge quicker. So, as opposed to the pitiful one-mile electric range of the normal Prius, at speeds up to 31mph, the plug-in version can whirr about for 12.5 miles at up to 60mph. If you live six miles or less from work, Bob's your uncle - no fuel!

What's the next step then?

It's already here, but you can't buy it yet. The Vauxhall Ampera (Chevy Volt in America) is due in 2012 - possibly the time your new Insignia is due for replacement - and can run for 40 miles on its battery before the petrol motor kicks in. The difference is, the petrol unit isn't attached to the wheels, but rather acts as a generator to power the battery for a 300-mile plus total range.

Thus eradicating range anxiety?

Yes indeed. You learn quickly. In the meantime, plug-in hybrids will increase their ranges too so that pretty soon we'll be going to the shops in CO2-free silence, but not worrying if we're all of a sudden called to divert a sudden crisis 100 miles away. Like finding out the bottle bank outside Tesco is closed, prompting a 99-mile round trip to another store in the Range Rover to do some recycling.