The future of hybrid road cars


Just when you thought you’d mentally sorted your plug-in hybrids from your range extenders, your NiMh batteries from your lithium-ions, steel yourself for another twist in the hybrid tale, heading your way with gathering speed. What’s more is that we have Formula 1 to thank for it, in part at least. Which is just one reason it’s fascinating.

When we think of ways of temporarily storing energy, a battery is quite naturally the first thing that springs to mind. But in the context of a car, a flywheel will do it far more simply and efficiently. Instead of converting kinetic energy into chemical energy and thence into electricity which can then be used to generate kinetic energy, as does a conventional hybrid car, using a flywheel instead of a battery merely transfers the kinetic energy from one place to another.

Williams selected this mechanical energy recovery system when KERS was mandated in 2009 and now Porsche has a highly evolved system in its GT3R Hybrid prototype, which I was lucky enough to drive late last year. So long as you have a long enough stab at the brakes, it will recover enough energy and store it in a flywheel sitting next to you in the cockpit to provide a 200bhp burst of power for seven seconds. Which, aside from the added weight of the flywheel and some frictional losses, is essentially free power.

The advantage to a lap time in a racing car is clear, but it could be equally effective in slashing fuel consumption and therefore CO2 emissions from road cars.

The reason flywheels are only reaching the agenda now, well over a decade after hybrid first got a grip, is that they are not without their problems. Clearly they cannot store power for as long as a battery. But their real drawback until now is that for a flywheel to be effective, it needs either to be extremely heavy (which would negate its point) or spin so fast it could fly apart.

Happily physics lends a hand, because while the energy a flywheel can store increases in direct proportion to its weight, it squares in proportion to its speed. So if you double its speed, you can store four times the energy. Which means it’s now possible and far more efficient to build small fast carbon-fibre flywheels that won’t self-destruct, than big, heavy steel ones that will.

The other potentially huge benefit will come when people realise how environmentally unfriendly is the process required to make and eventually scrap large battery packs such as those used in hybrids for the last decade. There are no nasty chemicals in a flywheel, just a single clean disc of carbon fibre.

Will flywheels take over the world, and make wasted all those billions poured into conventional hybrid systems? Clearly not: right now it is hard to see how a flywheel will be able to combat the new generation of green machines that derive most of their power from neither energy recovery nor an internal combustion engine, but by plugging into the national grid.

But these systems are fiendishly expensive and the more affordable conventional hybrids below them are soon to be obsolete. What is needed is something simple, affordable, clean and effective to plug the gap they will leave. And what could have greater potential than the simple, humble flywheel to do just that?

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