A query came my way to explain kWh again, and its relevance when it comes to automotive fuels. Well. I hope this explains
So here we go.
kWhs are the most common unit electricity is measure in. For me the easiest way to think about it is to think about light bulbs. If you had ten 100W bulbs, and you left them on for 1 hour, they would have consumed 1000Wh (Watt-hours), or 1kWh (kilo meaning thousand). An old one bar heater is usually a 1kW heater, meaning if it was on for one hour, that would be 1kWh. Finally if you left one 100W bulb on for 10 hours, you would consume 1kWh.
Joules is just another unit that energy is measure in. 1 kWh = 3600kJ (kilo-Joule)
So here is a small table:
|
|
|
kWh |
|
1kWh |
Electricity |
1 |
|
1m3 |
Gas |
11 |
|
1 litre |
Petrol |
9.7 |
|
1 litre |
Diesel |
10.7 |
|
1 litre |
Biodiesel |
9.9 |
|
1 litre |
Kerosene |
10.5 |
|
1 kg |
Coal |
6.64 |
So, to take that in Car mode. A petrol car that gets 35 miles/gallon would equate to about 0.8 kWh/mile, or 1.29kWh/km.
So driving your car for 1 km, and leaving 21 X 60Watt bulbs lighting for one hour… is about the same.
Or look another way… to drive 1 km takes about 36 seconds. In lighting terms that is equivalent to 2150 X 60watt bulbs… Yes.. your car is equivalent to 2150 light bulbs. Far more if we were to consider the energy efficient type of bulbs!
greennav
martinfaulkner
micallc
thenewoil
ciablasar
March 4, 2008 at 8:43 pm |
Your clear and simple comparisons on the fuels set me thinking about the relative cost of heating a small home with what are perhaps the three most common power sources, Oil, Coal, and Electricity.
If I got my math correct, taking 10.5 Kw hours as the reference,
It would take 1 litre of OIL to heat a small home for 1 hour at a cost of roughly 72cent.
It would take 10.5 units of ELECTRICITY at roughly 15.03 cent per unit. thats €1.58
It would take 1.58 Kgs of COAL at roughly 40 cent per Kg. that comes to 63 cent.
I know we are talking relative efficiencies with the different forms of heat. With ELECTRICITY being 100%. OIL comes in around 90%. Coal in a closed burner can give 80% And you would be lucky to get 55% in a fire with a good surround boiler.
It would be daft to think of using electricity to heat except for very occasional heating needs. Coal is a very good bet in an Aga or similar high efficiency burner. But despite the price oil still comes out the best value for money.
Wood-pellet boilers looked at one time like they would beat the lot at cost efficiency. However because the price of wood-pellets has tracked oil price rises almost to the cent, and because most people depend on the more expensive bagged pellets, there is little or no price advantage over oil. This is very disappointing because there is such potential in this form of heating both in terms of cost advantage and in enviormental protection.
March 4, 2008 at 11:39 pm |
Hi Tony,
Those are interesting figures. I agree, but I suppose as you say the flexibility of electricity is hard to beat. But in the long run, heating by electricity is crazy
Patrick
March 10, 2008 at 7:40 pm |
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