Tuesday, 25 May 2010

More thinking re Electric Cars

An interesting article has come out referring to comments by Professor Roger Kemp of the Electric Vehicles Working Group of the Royal Academy of Engineering.

In summary, he says that there is little to be gained by the adoption of electric vehicles over those powered by the latest efficient internal combustion engines. I suspect this is down to mainly transmission losses and maybe some generation losses.

Yet again we see comments such as the need for vast improvements in battery technology (in terms of cost, weight and bulk), a distribution network to charge them.

What is being missed here yet again is the very commonsensical "next step" to series hybrid. Series hybrids are different to vehicles like the Toyota Prius.

A Prius is a parallel hybrid. It has a traditional engine connected to a sophisticated transmission that can juggle this and an electric motor/generator, so that the engine can power the car, the engine can power and charge (the electric motor operating as a generator), have the electric motor operating on its own in all electric mode, have the electric motor assist the engine and have the electric motor in regeneration mode during braking. And for what? The Prius has lousy efficiency, is very complex, not very fast and has a derisory all-electric performance and range. Lets face it, the Prius is a vanity purchase.

So what with the Series Hybrid?

The Series hybrid uses purely electric traction, has batteries and capacitors for storing electrical energy and a generator, typically a small petrol or diesel engine of around 40hp/kWh, so around 1litre in capacity. Due to the steady speeds ideal for a generator, two stroke designs might even make an appearance, being smaller and more mechanically simple. A sensible series hybrid will have a very powerful electric drive or even one motor on each wheel, enabling significant amounts of regeneration to occur in braking. A Prius cannot regenerate much because the motor is not that powerful. A Series hybrid with 600hp of in-wheel traction can also absorb that amount, potentially doing away with friction brakes altogether.

In contrast to the parallel hybrid efforts, a series hybrid can be very fast indeed, very efficient at around 100mpg equivalent when relying on the generator, operate without recharging for 500, 800 or even 1000 miles if need be. All that last number would need is a 10 gallon tank. It can also operate in all electric mode using batteries. As it regenerates so well, the penalty for heavy batteries is significantly minimised as the inertia is re-converted to electricity during braking. This means it is not so tempting to skimp the battery packs, so facilitating electric only range to grow. With a very powerful electric motor set-up, performance will not be too adversely affected by this.

Series hybrids are more efficient, faster, have a longer range and a far simpler than Parallel hybrids.

Series hybrids are more efficient, faster, have a longer range than electric only cars and do not rely on a charging network and can be refuelled for instant use just like a normal vehicle.

The beauty of Series hybrids is as the electric charging stations grow, one can use electricity more and more, relying on petroleum less and less and eventually only for long trips.

If the good professor is right, that electric cars are little better than the current efficient internal combustion engined vehicles, then, by that measure, series hybrids are more efficient still.

I suppose, though, series hybrids are pesky things to vested interests. They do not need complex and finely balanced engines, exhausts and carburation able to deliver smooth power over wide speed ranges. They do not require cleverly chosen gear ratios or forgiving clutches. Most of all, from a political perspective, they do not require vast infrastructure changes that only a State deems itself capable of doing. Therefore politicians might not be bothered with series hybrids, preferring to focus on electric vehicles, where their decision has more, how can I say it, value.

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