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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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.
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.
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
Actually interesting figures. Probably it is common on the list of cosmood buy and sell
[…] 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 […]
[…] For more on driving -see here […]
oil…
[…]How much energy in… Cars « GreenNav’s Open Blog[…]…
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Yes! Finally someone writes about Cars.
I never realized how much energy a car uses. This article helped me realize, thanks
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.
Diesel does not have a higher calorific value than gasoline, so this writer does not know what he is talking about.
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).
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How much energy in… Cars | GreenNav’s Open Blog
is that universal than 1 litre petrol generate 9.7kwh ?
Something to correct: 0.8 kWh/mile is not equal to 1.29kWh/km.
rmp56 is right, it’s /1.609344 , not *1.609344
so it’s 0.5kWh/km
“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.
You have got 0.8 kWh/mile, or 1.29kWh/km. around the wrong way.”
Yes, great article! finally, I got what you need through your article, thank you for writing it. And hope to read more articles from you
It’s more like about 800 globes
I don’t know where you went off the rails, but if the consumption is 35 miles to the gallon, and say to car goes at 70 miles per hour, the consumption is 2 gallons. This is 2 x 3.8 x 9.7 = 74kw in 1 hour That is 74kw per hour. That is 74,000 / 60 = 1250 globes
Hey moron, are those thermal energy or kinetic energy in your imbecilic table?
My ev uses about 180wh/km. So, basically, it uses 10% – 20% of the energy of an internal combustion vehicle.
“This is incorrect
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.”
A mile is longer than a km
Selling a transportable Hummingbird Fishfinder.
My delivered cost for Natural Gas is about $6.00 per GJ.
My delivered cost for electricity is about $0.20/kwhr.
If the conversion is 1GJ = 277 KWhr, let’s look at the cost.
1 GJ = $6.00
277kwhr @ .20 = $55.40
Based on this, heating with electricity is about 9 time as expensive as heating with natural gas. That is why I converted my hot tub to run on using a dedicated natural gas hot water heater. It’s much cheaper!
With gasoline conversion from liters to Kwhrs (1 liter = 9.7 kwhr) and with gas in Canada costing $1.10/liter and 9.7 Kwhr @$0.20 = $1.94,
driving and electric vehicle (and charging it up at home) I can’t see how an EV is cheaper to run than driving a gas powered vehicle. And given that electricity is now being mostly (here anyway) generated by natural gas fired systems, why drive an EV? It’s just an emissions shift from the car to a power plant.There are a lot of inefficiencies in power transmission and in electric motors as well as the inefficiencies of gas powered vehicles. What am I missing?
And right now there is no road tax on electricity. Wait until enough people switch to electric vehicles and the Govt will add a road tax to the electricity as there is on gasoline – they want their tax revenue. This is what killed propane powered vehicle conversions.Just my thoughts…
Hi Brian
Just seen your comments and you have fallen into the same old trap of assuming petrol/gas cars use energy like electric cars.
In the UK at the moment petrol is about £1.10 per litre, electricity 14p per kWh. So doing the calculation 14p x 9.7kwh= £1.36.
However a petrol/gas engine is about 15% to 20% efficient (lots of waste energy in the form of heat), electric motors are 90% to 95%. efficient, so the energy put into an electric car takes you further.
In terms of generating the power for electric cars, in the UK the last coal powered station just closed, natural gas traditionally low cost can’t compete with wind/solar/hydro costs. I use solar PV to charge my car when I have surplus power so my cost is the opportunity cost of selling energy back to the grid in my case 5.38p per kwh.
In my car it’s about a fifth of the cost of using petrol if I charge from the grid, if I charge from solar its about twelfth of the cost.
In the UK you can use a smart electricity tariff with market rate pricing, these tariffs are often around 3p overnight and on some occasions have gone negative, so the electricity suppler pays you to take electricity and electric cars are ideal for taking the extra energy.
Looking at the numbers in 2020 with lower cost electric cars on the market, I really can’t understand why anyone would buy a new petrol car unless they have money to burn.
There is almost no-where in Australia that you can charge an electric car and if two people in the street install charging stations, the transformer down the end of the road will overheat. It’s just a dream toy for the few show-offs that live in our society. It is entirely impractical for even 10% of the population to invest in.
1GJ in Australia is about $24.00 not $6.00
Plus delivery cost of about 70 cents per day
So reading that above 1 mile needs 0.8kwh or 1609m will need 0 8kwh.
And 1km needs 1.29kwh?…
So reading that above 1 mile needs 0.8kwh or 1609m will need 0 8kwh.
And 1km needs 1.29kwh?…
NO
Maths are wrong per mile and per km back ways