Electric Magic: More Ideas for Interdisciplinary Teaching

[Note: I wrote this in 1991. There’s been one vital change since then: the enormous advances in renewable electricity generation, mainly from wind and solar, meaning that there will soon be no filthy exhaust from the power station. There have also been significant advances in battery technology – still a very long way from matching a tankful of petrol or diesel for energy density, but far more usable than in 1991.]

The electric car is a very seductive idea. Electricity is so much cheaper than petrol, and there's no filthy exhaust. For the moment, electric cars don't have much performance – but some of us don't want it, and apart from fire engines and ambulances, none of us need it; so from an individual's point of view, they're probably quite a good idea.

But what about the benefits to the community as a whole? On sober analysis, they're not quite so clear after all. Why is electricity so much cheaper than petrol? Surely because of the economy of scale, converting chemical energy in large quantities all in one place? Green alarms should be ringing already – small is beautiful, isn't it?

Certainly there are real economies in large scale conversion: a carefully designed power station can have an efficiency four times that of a car engine. If you consider losses between the power station and the domestic three-pin socket, it doesn't look quite so good; but actually the losses are genuinely quite small. Even the initial energy cost of building the distribution system is fairly reasonable. But most of the difference in price comes from the purchasing power of electricity companies, and taxation on motor fuel.

Where the energy losses start to mount up is between the three-pin socket and the car wheels: in battery chargers, in the charge-discharge cycle inefficiencies of batteries, in high-current cables, motors, and motor control circuitry on the car. Worst of all, in the energy costs of replacing hefty batteries fairly often.

From the overall community point of view, electric cars are not without a filthy exhaust – it's just that it's at the power station, not at the car. At least it doesn't have lead in it – but even that comes out at the battery factory or in the battery recycling process. (Edit: This is of course slightly out of date. Petrol no longer has lead in it in most countries, and battery manufacture and recycling have moved on a great deal too. Both the oil industry and the battery industry remain major sources of pollution however.)

They (some of them, somewhere) are working on ‘improving’ the electric car. Mainly, what they're trying to do is improve the performance, by which they mean acceleration, top speed, and range. Such energy saving advantages as the electric car has mostly arise from the limitation on its acceleration and top speed – so it’s not really the sort of improvement we actually need.

I'm not trying to say the electric car is necessarily a bad idea – just that there is more to it than meets the eye.

Let us hope they can improve the efficiency of the charge-discharge cycle, and improve the life expectancy of batteries.

Another way to save a tremendous lot of energy would be to reduce the performance of conventional cars. One very worthwhile by-product would be the saving of a great many lives and limbs. Best of all, we could reduce the amount we use cars, and use trains or buses instead.

Another idea which I find seductive is Combined Heat and Power. A nice, well established idea – a pity it isn't a nice, well established practice. But I'm not thinking of miles of pipework connecting everyone's central heating up to the waste heat of the local power station – I'm thinking of replacing my central heating boiler with an old car engine.

I'll just plumb the water cooling system of the engine in in place of the boiler, and run a wee generator off the engine. I'll convert the engine to run off mains gas, so I'm not paying too much of a premium for my fuel. My electricity will still come out a little expensive, but my heating will be free – or vice-versa. Overall I should be well in pocket.

Or will I? Less than half the heat from an engine comes out in the cooling system; most of it comes out in the exhaust. Unless I can retrieve a good proportion of the heat from the exhaust, I may well not end up gaining. So now I'm involved in heat exchanger design – perhaps my old central heating boiler will come in handy?

At least my exhaust will be relatively clean, since I'm using gas as fuel (all that warm carbon-dioxide: would the plants in my greenhouse like it?) – pretty much the same as the flue gas from the old heating system, plus a bit of old engine oil.

Now I'll just plug in my electric car . . .

Just one other thought, while I'm here:

Not tested on cute little fluffy rabbits? So you're going to test it on me? Or is it simply that you're selling nothing but water, which has been fairly thoroughly tested on quite a lot of people, not to mention rabbits; or soap, likewise; or other long-established ingredients. Not that being long-established is any guarantee of benignity.

Thanks, I'll stay dirty.

Green consumerism? There's a contradiction in terms!