Petrol in an average fuel tank provides two billion joules' worth of energy. Let's see how hard (or easy) it is for alternative fuels to match that.

PETROL
Energy: 2 billion joules
Volume: 58 litres
Mass: 43kg
Biggest problem: It’s running out while demand is skyrocketing, plus greenhouse contribution

DIESEL
Energy: 2 billion joules
Volume: 52 litres
Mass: 45kg
Biggest problem: same as petrol, plus the carcinogenic particulate emissions. And additional up-front engine cost

LPG
Energy: 2 billion joules
Volume: 80 litres
Mass: 40kg
Biggest problem: See petrol, plus cost of retrofitting alternative fuel system

UNCOMPRESSED NATURAL GAS (METHANE)
Energy: 2 billion joules
Volume: 56,500 litres
Mass: 37kg
Biggest problem: Where, exactly, do you put 56 cubic metres of gas? (Needs a box seven metres long, four high and two wide.) Even if you compress it to some extent cruising range is severely limited.

LIQUID HYDROGEN
Energy: 2 billion joules
Volume: 199 litres
Mass: 15kg
Biggest problem: Boils at minus 253 degrees C, can freeze air (turn it solid) is currently produced from methane (dirty), uses potentially dirty energy to liquefy, and even the most efficient storage vessels lose 1.7 per cent of the liquid every day via evaporation. No delivery infrastructure, and exceedingly hard to handle.
Conclusion: More than a decade away

COMPRESSED HYDROGEN (5000psi)
Energy: 2 billion joules
Volume: 590 litres
Mass: 15kg
Biggest problem: Dirty production, plus dirty energy used to compress the gas, fuel tank needs to be 10 times bigger than petrol tank for the same onboard energy storage.
Conclusion: More than a decade away

ETHANOL
Energy: 2 billion joules
Volume: 85 litres
Mass: 67kg
Biggest problem: Not really green, yet, although touted as such, competes with food production using current production technology, and intrinsically increases fuel consumption by 30 per cent
Conclusion: Will only stack up when produced from agri-waste using new technology

LEAD-ACID BATTERY
Energy: 2 billion joules
Volume: 8500 litres
Mass: 15,800kg
Biggest problem: Where would you put it; how would you carry it? They die if fully discharged. Anorexic energy storage capacity per unit volume and mass means severely restricted cruising range. Needs to be recharged with potentially dirty energy.
Conclusion: No good even in a golf cart.

LITHIUM-ION BATTERY
Energy: 2 billion joules
Volume: 2060 litres
Mass: 3500kg
Biggest problem: Only looks good when compared with lead-acid batteries. Can’t compete with hydrocarbons on bang for buck, per kilogram, or for compactness. Needs to be recharged with potentially dirty energy.
Conclusion: Only a super-short-haul solution.

SOLAR CELL (Photo-voltaic)
Energy: 2 billion joules
Biggest problem: Cars don’t run on PV cells except as a stunt. Performance drops at night, to zero. For 2 billion joules, you need an array of 300 square metres of reasonably efficient solar cells and seven hours of sunlight – so you can store it in your car’s 3.5-tonne lithium-ion battery (see above).
Conclusion: Solar cars are pie in the sky.

WOOD
Energy: 2 billion joules
Volume: 157 litres
Mass: 133kg
Biggest problem: cars don’t burn wood, but it’s an interesting comparison
Conclusion: Still the number one fuel for billions in the third world, and not at all bad for heating water

COAL
Energy: 2 billion joules
Volume: 76 litres
Mass: 95kg
Biggest problem: Engines don’t burn coal any more but it’s where most of Australia’s electricity and greenhouse emissions stem from
Conclusion: Hampers the transition to clean energy in countries like Australia with vast reserves, and needs more than oxymoronic marketing (think: so-called ‘clean coal’) to overcome poor enviro-fundamentals

URANIUM-238(nuclear fission, 2 billion joules)
Mass: four grams
Volume: tiny
Biggest problem: Turns into a bomb spontaneously if you store 52kg or more in the one place, highly radioactive, hard to dispose of responsibly when spent, lightweight advantage of fuel more than offset by considerable mass (and servicing requirements) of small-scale nuclear reactor required under the bonnet…
Conclusion: Cleaner than coal, but with long-term waste issues