Oh burger it... I'll stay at home

The folk at the Energy Efficiency and Conservation Authority (EECA) are nothing if not innovative and enthusiastic, and you don't get much more enthused than EECA Chairman Roger Sutton.

Keen to ensure Kiwis understand the cost of their power, Sutton has translated electricity, petrol and even human muscle into Big Mac equivalents.

Sutton cycles 7km to work each day, but has calculated he spends the same in food equivalents as he would on petrol.

His sums assume his car drinks petrol at 10l/100km, at 15.9 cents a kilometre assuming petrol at $1.59 per litre. Fuel consumption for the bicycle depends on your size, bike and how fast you ride.

Sutton reckons a man of his weight cycling at 30km/h burns 64 kilojoules per kilometre. The cost of that depends on what you eat.

Sutton used Big Macs for his calculations, " because ... their cost and energy value is well known". A Big Mac costs $4.90 and contains 2050kJ of energy, at 0.24c/kJ.

Sutton's cycle ride would cost 15.4 cents a kilometre - "So it costs almost exactly the same to drive as it does to bike at 30km/h, assuming Big Macs are the fuel. A car that does more than 10l/100 will cost more and vice versa."

A slower rider will be more efficient - at 20km/h he'll burn 34kJ/km, or 8.16c/km, equivalent to a petrol car using 5.6l/100km. Whereas Sutton reckons a Tour de France entrant pedaling at about 50km/h will burn as much energy as a Lamborghini Murcielago.

How come a bicycle can cost more than a car to power? "It's because food energy is comparatively expensive compared to petrol," Sutton says. "The burger fuel is more than 51 times more expensive per unit of energy than petrol. The equivalent amount of energy in a litre of petrol equates to about 17 Big Macs. Petrol as a form of energy is very cheap," he says.

Sutton admits his calculations aren't perfect.

Most people carry auxiliary energy in the form of fat; cars cost more to run than just the pure fuel cost; and of course you can choose to eat cheaper food.

Sutton got the idea from the Burgernomics Big Mac Index that compares purchasing parity across different economies using local Big Mac prices as a common link.