How much energy in… Cars

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!

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20 Responses to How much energy in… Cars

  1. 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.

    • Bob says:

      Good comment Tony – nice comparisons. But don’t forget you can actually do much better than 100% with electricity.

      It’s counter-intuituve I know but a dual-cycle air-conditioner gets more like 350% efficiency (and even more for ground-sourced versions).

      i.e. you “burn” 1 kWh of electricity and get 3.5 kWh of heat into your house.

      It’s called the “coefficient of performance” … and it’s not anything to do with free-energy… essentially it works because the refrigeration cycle makes the refrigerant extremely cold (say something like -70 degrees). Then, when you put it outside it can gather a huge amount of energy from the relatively hot outdoor air. The air might only be 5 degrees, but that makes it 75 degrees hotter than your refrigerant. There is a lot of energy transfer with such a big temperature difference.

      You then get to put this energy into the house as heat.

      It seems a bit weird, but its perfectly valid and an extremely well-studied process in thermodynamics.

  2. greennav says:

    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

  3. […] numbers of litres. This 1008 litres can be converted to kWh if you have a look at my post on the “How much energy in Cars” post. It works out […]

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  10. car service says:

    I never realized how much energy a car uses. This article helped me realize, thanks

  11. Peter says:

    Very interesting information. It is amazing how people do so much complaining about their electricity bill and yet hardly blink about how much money they spend on fuel. There are some mind games going on here.

  12. Diesel does not have a higher calorific value than gasoline, so this writer does not know what he is talking about.

    • Tony Kruzewski says:

      Hi Colin. You are correct that Diesel has a lower CV, but it also has a lower density. I.E. if petrol is approx 1,368 Ltrs/Tonne and Diesel is approx 1,192 Ltrs/Tonne. Therefore, if CV of Diesel is 11.92kWh/kG then that would be 10kWh/Litre. If petrol CV is 12.44 kWh/kG (higher) then that would be around 9.08 kWh/Litre.
      Though the writer has got the equations wrong in as far as it is 1.29 kWh /Mile and 0.8 kWh/Km.

      • the density of petroleum diesel is about 0.832 kg/L (6.943 lb/US gal), about 11.6% more than ethanol-free petrol (gasoline), which has a density of about 0.745 kg/L (6.217 lb/US gal).

  13. SEFAC USA Inc.

    How much energy in… Cars | GreenNav’s Open Blog

  14. Ussama Ahmad Khan Kirmani says:

    is that universal than 1 litre petrol generate 9.7kwh ?

  15. rmp56 says:

    Something to correct: 0.8 kWh/mile is not equal to 1.29kWh/km.

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