Transport : sustainable energy

Transport : sustainable energy

Updated 15-Oct-2003 17-Oct-2003 21-Oct-2003

I have been trying to put together some calculations to determnine if it is
viable for cars to be run on rapeseed oil. I am trying to answer the question:
how many acres of farmland would it take to run a car for a year, and how much
would it cost? Any help in making that determination would be gratefully
received. Send comments to xs@ukmail.com. Assume that the average yearly
mileage is 10,000 miles, and the fuel consumption is 30 mpg (miles per gallon).
That equates to about 333 gallons of petrol.

Personally, I do many more than 10k miles in a year, but I reckon that I do
much better than 30mpg.

Here are some statistics

[S1] 1 gallon of petrol contains about 31 million calories
Source:
http://www.heartratemonitors.co.uk/calories.htm

[S2] 1 calory = 4.184 joules
Source: as [S1]
A calorie is the amount of energy, or heat, it takes
to raise the temperature of 1 gram of water 1 degree Celsius.

[S3] 100g pure vegetable oil contains 900kcal
Source: the side of a bottle of Tesco Pure Vegetable oil.

[S4] Britain has 2.7m hectares of woodland (11.9% of the surface area of Great
Britain)
Source:
www.forestry.gov.uk
I really wanted to  know the amount of arable farmland in Britain, but didn't
quite get around to finding it. If anyone knows, then please drop be a line.

[S5] 1 gallon = 4.5 litres

[S6] Rapeseed costs 264.50 EUR / kg
Source: FT website on 14-Oct-2003
EUR means Euro. The settlement price is based on 8,000 kg.

[S7] 1 EUR = 0.693100 GBP
Source: ICAEW prices for 01-Oct-2003 to 31-Oct-2003
GBP means Great British Pounds.

[S8] 2.471 acres = 1 hectare
Imperial measurement, don't you just love it.

[S9] Rapeseed yields about 100kg of oil per hectare.
Source:
http://journeytoforever.org/biodiesel_yield.html

A scan of the site reveals that all biodiesel oils have, litre for litre, about
the same energy value as petrol. It's not exact, but it's about right.
This suprised me somewhat, as I expected petrol to have much more energy. But
someone told me that although petrol is definitely more volitile, that doesn't
mean it contains more energy. What makes a crop more valuable, therefore, is
its yield per acre - making yield proportional to energy value (to a reasonable
order of approximation). Cashew nuts and avocados have exceptionally high
yields - but of course we can't grow them in this country.

[S10] Vegetable oil weighs about 800g per litre
I don't remember where I got that value from, or whether it was a derived
value. I need to check it out.

[S11] Petrol costs 76p per litre
Source: petrol receipt dated 16-Oct-2003

[S12] Vegetable oil costs 63p per litre
Source: Safeway vegetable oil costs £1.88 for 3 litres [=63p/l], or 65p for 1
litre, as at 21-Oct-2003. Safeways is notorious for being expensive, so it
ought to be possible to buy it at a lesser price.

I concluded that it would take about 4 acres of rapeseed to fuel a car for a
year - which seemed quite reasonable. The value was calculated by mental
arithmetic, which may well be wrong. I need to check it out.