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.

Comments

On December 26, 2013 at 2:53pm
stefan wrote:

the newer 18650 have around 3,4 mah at under 50 grams. this would translate to 20batts\kg. so 20 batt x 3,4 mah x 3,7 volt= 252wh/kg. at least. also true capacity 3,6ah 18650’s are on the market. so you could update some figures from the site.