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Some notes on Electric Cars



1.ARE ELECTRIC CARS VIABLE?
They are viable if they are charged from off-peak electricity, which is otherwise wasted. Their range is much lower than that of a petrol car, because of the low energy density of the battery compared to that of diesel or petrol.

Diesel contains about 12 kWh per kg.; a charged lead-acid battery holds about 0.05 kWh per kg. Therefore you need a low chassis weight and lots of batteries.

The idea of towing a trailer of batteries was once tried, with a Leyland National bus in the 70s. The trailer weighed more than the bus, and made it more expensive to run than a diesel.

The Nissan Leaf, an electric car currently on the market, runs on lithium ion batteries rated at 24kWh (about 1800 Ah). These have a higher energy density than lead-acid. The price of the car is 28,350 minus a 5000 government subsidy. It weighs 1521kg, most of which is battery weight.

2.HOW QUICKLY CAN AN ELECTRIC CAR BE RECHARGED?
Typically, several hours. The Nissan Leaf takes 8 hours at 12 amps. Fast charging using 480V DC (125 amps) takes about 30 minutes but this shortens battery life and cannot be done from a domestic supply; it needs special charging points and skilled personnel.

Normal charging gives about 5 miles of range per hour, which is equivalent to 3kWh per hour.



3.IS AN ELECTRIC CAR ENVIRONMENTALLY FRIENDLY?
It depends what you mean. If you're referring to saving fossil fuels, no. The large majority of the UK's electricity comes from gas and coal so although the car itself does not use fossil fuel, the same cannot be said of the energy which powers the batteries.

Similarly, gaseous pollution (principally nitrogen oxides) is not produced by an electric vehicle, though the fossil fuels used at the power station produce sulphur and nitrogen oxides in the normal way.

4.HOW DOES ONE KEEP WARM IN AN ELECTRIC CAR?
In a diesel or petrol car, waste engine heat is available to hear the car's interior, via the heating element located under the dashboard, which is effectively a small radiator giving off heat from the car's hot water circuit.

However, in an electric car, there is no engine, just a big electric motor, which doesn't give off any heat. This doesn't matter too much in warm weather, but it's a real problem in winter, because the only solution is to use an electric heater. This decreases the range of the car.

5.WHAT IS THE RANGE OF AN ELECTRIC CAR?
The Nissan Leaf has a measured range of between 50 and 109 miles, according to tests done under a wide variety of conditions. Another way of looking at it - the fully charged batteries can deliver about the same amount of energy as is present in about half a gallon of diesel or petrol. The figure can't be exact, because the energy in the battery isn't all 'available', and the voltage drops as the charge is used up.(1)

6.WHAT DOES IT COST TO CHARGE AN ELECTRIC CAR?
It depends on the cost of the electricity, obviously ... but I pay 25p per unit, (25p per kWh), and 25p x 24 gives 6.00 per charge. You can do the sums. The price per unit is on your electricity bill, and it varies widely between suppliers and schemes. If you're on a white meter then night-time electricity (nuclear baseload, mainly) is about 10p per unit.

7.WHAT ABOUT CARBON EMISSIONS?
There is no proven link between man-made carbon dioxide emissions and the temperature of the planet. However, as regards the conservation of fossil fuel and sustainability, see (3) above.

8.HOW LONG DO THE BATTERIES LAST?
The manufacturers say 10 years. As regards observed figures by the general public - we will have to wait and see.




On 26 Jul 2011, the following contribution on the subject of 'Sustainable Road Transport' was 'phoned in to the BBC programme, You and Yours by a person who has worked on batteries for many years: David Rand.

Here's what he had to say. (reproduced with his permission):

    I'm from Australia and I'm a battery scientist....

    'Sustainable Road Transport' ... it's mooted that this would be electric vehicles; either electrically-driven or hydrogen-based fuel cells.

    First of all, this won't be decarbonising because the energy won't be produced from non-fossil fuels.... most electricity comes from fossil fuel power stations, and in the case of hydrogen, most of it is produced by reforming natural gas.

    Secondly, setting aside the cost, because batteries will be more expensive than internal combustion engines.... I'm in Portmouth, and if I want to come back to my parents' home and part outside their house, I have to do that before six o'clock. Now if I'm then going to be three or four hundred yards away, am I going to have to run a cable into their house to refuel my car with electricity?

    Whatever anyone tells you, batteries will not be recharged in a matter of minutes; it's likely to be hours, unless you have a very specialised and safe high voltage high amperage supply in your house.

    What about people in high rise flats? How are they going to charge their cars? Battery exchange is not a practical proposition.

    I'd like to ask all these European people who talk about road sustainability into the future - how are they going to address the technology that will be required?





ND/ habitat21

(1)Calculation: diesel: energy content approx 12kWh/kg; battery capacity is 24kWh, so equivalent to 2 kg diesel. Volume = mass/density = 2/0.9 = 2.22 litres, = 0.49 gal.

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