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Thursday, 5 April 2012

Electric cars.

Thinking of buying an electric car and saving the planet?transmission

If you look at the diagram above (Sorry for the poor quality), you’ll see what is required to get the power for the car battery from the source.

Lets look at the efficiencies of the various parts of the diagram, starting with the generating station first. Even a non CO2 emitting nuclear plant is at best 30% efficient due to the lower steam temperatures employed. That’s a start down the slope.

Next comes the step up transformer. Ever wondered why they have to be oil cooled? Using a step up transformer to increase the voltage does not give you something for nothing. As the voltage goes up, the current goes down by the same proportion. The power equation shows that the overall power remains the same.

P=V x I  Power = Voltage x Current

In reality, the power output is always less than the power input because the changing magnetic field in the core creates currents (called eddy currents) which heat the core.  This heat is then lost to the environment, it is wasted energy. It’s actually not too bad at 2%. But 2% never the less.

Now we come to transmission of this power. This is usually transmitted at voltages of around 133kv in the UK for long distances. Here again we lose energy. Estimated at approximately 6%.

Of course we now have to transform it down again to a realistic voltage for consumers to use. Another 2% lost.

Bearing in mind  charging the batteries of your electric car is going to involve turning that AC voltage into a DC voltage and step down to a voltage that will be suitable for your battery, the efficiency falls further. Lets say another 2%.

Overall by my reckoning that makes the whole jiggery pokey to have you on the road is about 58% efficiency overall.

Contrasting that to a modern common rail fuel injected diesel engine at 50% efficiency,  the efficiency is not vastly better.

Of course you have to buy the car first before you can drive an electric vehicle on the open road. Now the agony really becomes real. Even with a generous government subsidy (£5,000), a Nissan Leaf is going to set you back a whopping £25,990.

And for that price you only (On a good day) get a mileage of 109 miles between charges.  


And finally the cost of a replacement battery will set you back over £5,000. (Conservative price. Some sites have reckoned it could be as high as £8,000).

Still want to buy one? Me. I’m sticking to my diesel powered car, which has a range of 350 miles even when my heater is on in the winter. I don’t want to take 3 days to visit my son. (And three days back) After all, who would feed the cats?


  1. And amongst other good news about Electric Cars is this:’-green-‘investment’-battery-company-withers

    A company that received $279million in grants from US taxpayers.

  2. The link didn't work, Joe. Still I get your point.

  3. Topical - from a report of just yesterday!

    ? 2nd time lucky?’-green-‘investment’-battery-company-withers

  4. And then there's this bollocks..

  5. The energy losses in a transformer are down to hysteresis.

    At last those electrotechnology lectures in the late 70s are becoming useful!

  6. my diesel powered car, which has a range of 350 miles

    Actually, your diesel car is better than that. Given that diesel recharging points are distributed at a spacing very much shorter than the average journey, and that recharging your diesel battery takes very much less time than the average journey, the effective range of your diesel car is infinite.

  7. "Ideal driving conditions, constant speed,38mph" - Yeah I LOVE twats like that blocking the roads up...

    You forgot to include the considerable chemical and heat losses involved in charging and discharging the batteries. There was a post on WUWT (I think) which had calculations showing the real overall efficiency & CO2 output compared to a modern diesel car, and this showed electric to be worse...

  8. MD

    "You forgot to include the considerable chemical and heat losses involved in charging and discharging the batteries."

    I left that as I couldn't find any reliable figures.

    Patently. You're right of course.

  9. You have forgotten that the actual electric car itself is not 100% efficient. The best electric motors in the best operating conditions may achieve 90% efficiency but this is unlikely in a road car. So now the system performance is lower than a decent diesel engine.


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