First published in the September 2012 issue of Desig, Mensa’s Design Special Interest group.
Following on from my previous post on the matter, the Nissan Leaf was been robustly advertised over Christmas 2011 on UK television, proudly announcing its status as “2011 Car Of The Year”. Now, the Vauxhall Ampera is “2012 Car Of The Year”.
While alternative fuel cars (hydrogen?) are probably the future, I have to question these.
First, the Nissan Leaf costs £23,990. That’s about 30% more than a reasonably specified MINI Cooper D, with similar on road performance. The Vauxhall costs £32,250. These figures are including a government £5,000 subsidy for purchasing an electric car. I’ll concentrate on the cheaper Nissan Leaf in the examples below.
It does benefit from a zero road tax rating, but then, so does the MINI. But, there are some big downsides. The quoted range is about 100 miles and reviewers have had ranges of about 47 miles in city driving. So, it’s not one for the motorways, and not really one for the cities either. I live about thirty miles from the centre of London, so it would be a sixty mile round trip – and I don’t think my nerves could stand the adventure of the possibility of getting stranded on the M3.
Then, there’s the issue of a British winter. When it gets cold, ‘normal’ cars use excess engine heat to warm the cabin. This one will have to use battery power, reducing the range even further.
They say you could save about £1,500 a year on fuel. Let’s do some maths.
To save this sort of money, you’d need to do almost 14,000 miles a year. That’s 38 miles every day, quite a lot for a car with a short range. That’s an average, many people will have driving patterns that include days with no driving and others with hundreds of miles. I’ve calculated this against a car doing 40mpg, petrol at £1.40 a litre and a charge costing £2.40 (the battery is 24KW/h).
Now, the car is warranted for 3 years or 60,000 miles, and the drive train and battery for 5 years / 60,000 miles. That means if you DO use the car for 14,000 miles, the battery will be out of warranty just after four years.
What will the battery cost? I’ve seen rumours of £7,000. Being generous, if it’s £4,000, then your average mileage of 10,000 miles will save £1,080 a year, so £5,400 after five years. Murphy’s law dictates that the battery will need replacing once the warranty has expired, so that should leave you £1,400 better off than a 40mpg car.
The MINI does average 50mpg, that will save you that extra money in the first place, and the car is cheaper to start.
So unless you are a raving ecologist and willing to pay significantly more to feel good about doing your bit, what’s the point?
You might say that electric power is greener, but again, I’m not so sure.
One benefit of a vehicle that uses an engine is that the fuel is stored in the vehicle and goes through a single process to produce mechanical energy to the wheels. We could probably assume that this is 70% efficient.
But, electricity in the UK is mostly produced by fossil fuels too. About 74% of our electric power is from oil, gas and coal, 20% from nuclear, and the remaining amount from ‘green’ sources such as wind.
So, for the purposes of calculations, let’s consider that nuclear is ‘green’.
Our electric car will need power from the grid. We could be generous and say that the battery to motor power conversion will be 80% efficient. But we need to charge that battery from the mains, that is generally considered about 70% efficient. Getting that power to the house requires transmission, which involves conversion to and from high voltage and transmission itself. 70% efficient would be good. Then, the power needs to be generated in the first place. Lets say 80% efficient.
So, for each unit of fossil fuel in our petrol car, 0.7 would get to the wheels using our 70% efficiency guess above.
But, for the electric car, we need to apply 80%, 70%, 70% and 80% as above. Allowing for the 26% of fuel which we consider ‘green’, we can apply a 1.35 multiplier which improves things a bit, but we get .42 of each unit getting to the wheels of our electric car. We’re burning more fossil fuels as a result, so how is this greener?
Unless we charge our electric cars from home using entirely wind or solar power I can’t see how electric cars make sense. They just move pollution out of the cities and cause us to burn more fossil fuels than we already do with our current petrol and diesel cars. The idea of calling electric cars ‘zero emission’ is just propaganda in my opinion, until we have renewable energy for the majority of our electricity needs.
The Nissan Leaf is only greener because if you buy one, you’ll probably end up using it a lot less than you would a normal car…