Net Calorific Value
Since the beginning of time, mankind had a good selection of fuels at his disposal and Table 1 provides the net calorific value of ancient and modern fuels by mass (kg) and volume (liter). With the exception of hydrogen by mass, hydrocarbons offer the highest energy by weight. Hydrocarbons are petroleum, natural gas and coal, which are derived from living matter of past geological times. The sun, the source of all life, provided these canned energies.
|
Fuel |
Energy by mass (Wh/kg) |
Energy by volume (Wh/l) |
|
Hydrogen (350 bar)* |
39,300 |
750 |
|
Liquid hydrogen* |
39,000 |
2,600 |
|
Propane |
13,900 |
6,600 |
|
Butane |
13,600 |
7,800 |
|
Diesel fuel |
12,700 |
10,700 |
|
Gasoline |
12,200 |
9,700 |
|
Natural gas(250 bar) |
12,100 |
3,100 |
|
Body fat |
10,500 |
9,700 |
|
Ethanol |
7,850 |
6,100 |
|
Black coal(solid) |
6,600 |
9,400 |
|
Methanol |
6,400 |
4,600 |
|
Wood(average) |
2.300 |
540 |
|
Li-cobalt battery |
150 |
330 |
|
Li-manganese |
120 |
280 |
|
Flywheel |
120 |
210 |
|
NiMH battery |
90 |
180 |
|
Lead acid battery |
40 |
64 |
|
Compressed air |
34 |
17 |
|
Supercapacitor |
5 |
7 |
Table 1: Energy densities of fossil fuel and electrochemical batteries.
Fossil fuel carries roughly 100 times the energy per mass compared to Li-ion.
Complied from various sources. Values are approximate.
* Hydrogen has the highest energy to mass ratio (Wh/kg), but energy by volume (Wh/l) reveals a truer picture in terms of storage and delivery. Diesel has almost 14 times the specific energy of pure hydrogen by volume (750Wh/l at 350 bar or 5,000psi).
Oil and natural gas can be drawn from the earth with minimal preparation, but hydrogen needs energy to produce. This is similar to charging a battery, spinning up a flywheel or pressurizing a tank. In addition, the storage and delivery of hydrogen is more difficult than fossil fuels and in terms of yield, energy by volume provides the truer picture.
The deciding factors when choosing a fuel for heating and propulsion are availability, convenience and cost. Fossil fuels are one of the cheapest, most efficient and readily available energies. Pollution and long-term sustainability are less important while the supply lasts.
