2.1.2 Energy use and energy units
Course subject(s)
2. Accounting energy use and GHG emissions
The video you are about to see will be about energy use and energy units
Key takeaways:
- The unit of energy is the Joule, J
- Power is equal to energy per unit time, it has the unit Watt, W
- The kilowatt hour is another unit of energy. 1 kWh is equal to 3.6 MJ
- There are numerous other units of energy which can all be expressed in an equivalent number of Joules.
Summary of some important data and equations:
Overview of units of energy use and their conversion to the SI-unit joule.
| Unit | Conversion to joules (multiply by…) | Remarks |
|---|---|---|
| calorie (cal) | 4.1868 | Old unit for quantiles of heat |
| tonne of oil equivalent (toe) | 41.868 x 109 | Defined as 107 kcal. The toe is widely used in international energy statistics |
| barrel of oil equivalent (boe) | approx. 6.1 x 109 | Conversion values ranging from 6.06 to 6.12 x 109 |
| tonne of coal equivalent (tce) | 28.6 x 109 | Used as the main unit of energy in China |
| kilowatt-hour (kWh) | 3.6 x 106 | Used mainly for electricity |
| British-thermal-unit (BTU) | 1.055 x 103 | Used in the USA; other units include the therm (105 BTU) and the quad (1015 BTU) |
| watt-year (Wyr) | 31.5 x 106 | Useful unit for analytical applications; if one uses 1 W on average, one uses 1 Wyr in a year |
Energy content for a number of energy carriers. For fuels, the energy content is given on the basis of the lower heating value.
| Energy content (MJ/kg unless indicated otherwise) | |
|---|---|
| Hard coal (coking coal and bituminous coal) | 23 – 30 |
| Brown coal (sub-bituminous coal and lignite) | 5 – 17 |
| Crude oil | 42 – 44 |
| LPG, Ethane | 46 – 47 |
| Gasoline/petrol | 44.8 (33 MJ/litre) |
| Aviation turbine fuel | 43.9 |
| Diesel fuel (Gas/diesel oil) | 43.4 (36 MJ/litre) |
| Heavy fuel oil (low sulphur) | 40.2 |
| Natural gas | 31 – 36 MJ/m3 |
| Wood pellets | 17 |
| Methanol | 19.9 (15.7 MJ/litre) |
| Ethanol | 26.8 (21.2 MJ/litre) |
| Electricity | 3.6 MJ/kWh |
| Hot water 90℃ (reference to 10℃) | 0.34 |
| Steam, depending on pressure and temperature | 2.7 – 3.5 |
| Steam, for heating applications | 1.9 – 2.2 |
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