Energy cost calculator

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General comments

Fuel Fuel price Cost per GJ Firewood $160/tonne $10 Brown coal briquettes $350/tonne $16 Compressed natural gas (CNG) $16.95/GJ $17* Liquified petroeum gas (LPG) $0.54/Litre $21 Oil $1.15/Litre $29 Electricity $0.18/kWh $50* *A substantial supply charge also had to be paid for connection to the CNG and electricity supply systems.

In the Mid-North of South Australia in May 2005 I calculated the approximate energy costs, in Australian dollars (Au$1 ~ US$0.75), shown on the table at the right. The per gigajoule costs shown in this box were based on what seemed the most reliable prices I was able to find at the time.

As the peak of oil production is approached and passed, we must expect the price of oil and LPG to rise. As governments begin to take global warming (and global dimming and ocean acidification) seriously, coal will become scarcer and more expensive.

Electricity, especially in Australia, is commonly generated by burning fossil fuels; this is obviously unsustainable from several points of view. Electricity is more efficient for heating than the calculated cost indicates because no heat goes up the flew, unlike those fuels that are burned. Also, if it powers a reverse cycle air conditioner its efficiency can be even higher. See my page Heating Efficiency.

Considering the above factors, Firewood will probably become more important as a fuel in the Western World in future. Firewood generally needs to be chopped into smaller pieces than those that you will get from the wood merchant. This might be thought of as a disadvantage or as a useful source of exercise.

Coal also requires manual handling.

All the fossil fuels add to the greenhouse problem when burned. Using electricity might also add to greenhouse depending on how your electricity is generated.

Europeans and others who do not use the dollar can simply enter prices in their own monetary unit; the answers will be in the same units.

For USAzians who do not use metric units I can only say: learn metric and move into the twentieth century (I would say the twenty-first century, but it would be safer for you to move a small step at a time).

Some energy units, conversions and definitions are given on my Energy Units page.

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Cost of energy per gigajoule from firewood

Enter a value in the top box and click on the 'Calculate' button

The price you pay for one tonne of firewood = $

Cost of energy from firewood = $ per GJ

Example calculation: Enter 160, answer will be $10

Explanation The energy content of 'dry' firewood is 16GJ/tonne, so if the price is $X/tonne, then the price per GJ is X/16. In the example above, $160/16=$10

The calculation of the energy cost from firewood assumes that the firewood is air-seasoned (that is, it had been dried by allowing air to freely circulate around it for long enough to remove most of the moisture). Air-seasoned wood releases about 16GJ/tonne when burned; see Wikipedia. For comparison, green wood releases about 10GJ/t, oven-dry wood 20GJ/t (Clean Energy Future Report by the Clean Energy Future Group.)

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Cost of energy per gigajoule from coal

Enter a value in the top two boxes and click on the 'Calculate' button
The price you pay for one tonne of coal = $	Energy content of your coal in GJ/tonne For brown coal briquettes enter 22, for black coal 28
Cost of energy from coal = $ per GJ
Example calculation: Enter 350 and 22, the answer will be about $15.91
Explanation The energy content of briquettes is 22GJ/tonne, so if the price is $X/tonne, then the price per GJ is X/22. In the example above, $350/22=$15.91 (approximately)

Please note that the energy content of coal can vary greatly. If your coal has an energy content very different from the figure that you enter then the calculated energy cost will be wrong to the same extent. The moisture content of the coal will also effect its energy content. Some coal has an energy content as low as 15GJ/tonne.

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Cost of energy per gigajoule from heating oil

Enter a value in the top box and click on the 'Calculate' button

The price you pay for a litre of heating oil = $

Cost of energy from heating oil = $ per GJ

Example calculation: Enter 1.15, answer will about $31

Explanation The energy content of heating oil is 37.3MJ/Litre, so if the price is $X/L, then the price per GJ is X/37.3*1000. In the example above, $1.15/37.3*1000=$31 (approximately). Multiplying by 1000 converts the price per MJ to the price per GJ

The calculation works on the energy in a litre of heating oil being around 37.3MJ.

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Cost of energy per gigajoule from ethanol (ethyl alcohol)

Enter a value in the top box and click on the 'Calculate' button

The price you pay for a litre of ethanol = $

Cost of energy from ethanol = $ per GJ

Example calculation: Enter 1, answer will be about $43

Explanation The energy content of ethanol is 23.4MJ/Litre, so if the price is $X/L, then the price per GJ is X/23.4*1000. In the example above, $1/23.4*1000=$43 (approximately). Multiplying by 1000 converts the price per MJ to the price per GJ

The calculation works on the energy in a litre of ethanol being 23.4MJ. (I do not know what price fuel ethanol sells for in Australia.)

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Cost of energy per gigajoule from liquified petroleum gas (LPG)

Enter a value in the top box and click on the 'Calculate' button

The price you pay for a litre of LPG = $

Cost of energy from Gas = $ per GJ

Example calculation: Enter 0.54, answer will be about $21

Explanation The energy content of LPG is 25.4MJ/Litre, so if the price is $X/L, then the price per GJ is X/25.4*1000. In the example above, $0.54/25.4*1000=$21 (approximately). Multiplying by 1000 converts the price per MJ to the price per GJ

The calculation works on the specific gravity of LPG being 0.52 and the energy in a tonne of LPG being around 49.4GJ.

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Cost of energy per gigajoule from electricity

Enter a value in the top box and click on the 'Calculate' button

The price you pay for a kilowatt hour of electricity = $

Cost of energy from electricity = $ per GJ

Example calculation: Enter 0.18, answer will be about $50

Explanation One KWh of electricity equals 3.6MJ, so if the price is $X/KWh, then the price per GJ is X/3.6*1000. In the example above, $0.18/3.6*1000=$50. Multiplying by 1000 converts the price per MJ to the price per GJ

This calculation works on one megawatt hour of electricity being equal to 3.6GJ. In South Australia there is also a substantial supply charge for electricity, and 10% goods and services tax. These can increase the effective price that you pay for your electricity by 40% or more.

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Technical notes

My source for the energy content of fossil fuels and ethanol was the Australian Bureau of Agricultural and Resource Economics (ABARE) document titled Energy Definitions.

Information on the energy content of firewood came from Wikipedia.

Another source I used for the energy content of liquid fuels was Wikipedia.

While petrol (automotive gasoline) is not used for heating, the reader might be interested to know that, by volume, automotive diesel contains 17% more energy than petrol. By weight petrol contains 2% more energy than diesel.

Related pages

External pages...

Green Resources: A number of useful home energy guides.

Related pages on this site...

Energy units and conversions

Weight-to-Power Ration

Payload Ratio

Firewood as a fuel

A list of pages on this site relating to energy in an international context and in an Australian context

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