Chemical Energy Density Comparison

Jet fuel stores about 43 MJ/kg. Hydrogen stores about 142 MJ/kg. A lithium-ion battery stores about 0.9 MJ/kg. All three are "energy storage," but the two-order-of-magnitude gap between hydrogen and a battery explains why nobody is flying transatlantic flights on batteries.

Chemical fuels store energy in molecular bonds. The energy released per kilogram depends on two factors: how much energy each bond reaction releases, and how heavy the fuel molecule is relative to the energy it contains. Hydrogen wins on a per-kilogram basis because each H₂ molecule is tiny (2 g/mol) and forms a very strong O-H bond when it burns. Diesel is heavier per molecule but packs carbon-hydrogen bonds densely, yielding 45 MJ/kg. Coal, with its complex structure and impurities, delivers only about 24 MJ/kg.

The practical ranking for common fuels:

Fuel	Energy density (MJ/kg)
Hydrogen	142
Natural gas	54
Gasoline	46
Diesel	45
Coal (bituminous)	24
Wood	15
Li-ion battery	~0.9

Worked Example

A long-haul truck needs 3,600 MJ for a 500-mile trip. Compare diesel fuel versus a battery pack.

• Diesel mass. 3,600 / 45 = 80 kg (about 24 gallons).
• Battery mass. 3,600 / 0.9 = 4,000 kg (about 4.4 tons).

The battery weighs 50 times more. What does this mean for payload capacity?

A typical long-haul truck has a maximum payload of about 20,000 kg. A 4,000 kg battery pack consumes 20% of the payload. The 80 kg of diesel consumes 0.4%. This weight penalty is why battery-electric long-haul trucking is viable only for short routes; it is a physics constraint, not just a cost issue.

Engineers can cut costs and improve motors, but they cannot renegotiate what a kilogram of fuel holds. Every electrification debate, from delivery vans to transatlantic flight, starts from this table.

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