Authored by Michael Kelly
Next time you stand for 90 seconds filling your petrol tank, you might think of the enormity of what is happening, in energy terms. Chemical energy is entering your tank at a rate of typically 17 million Joules/second, or 17 megawatts—equivalent to the energy given off by 17,000 one-bar electric heaters! This large number is the basis of many difficulties, much glossed over in the rush to all-electric cars.
In making personal mobility all-electric, two important considerations must be weighed. The first is that electric motors convert electricity to motion three times more efficiently, in energy terms, than the internal-combustion engine does with gasoline. The second is that we do not recharge an electric battery in 90 seconds. Neither of these avoid the difficulties I now describe.
When electronics first became portable in the early 1970s, the battery was a carbon-zinc type. All the global research in the fifty years since then has produced a lithium-ion battery, which has six times the density of energy storage; this, in turn, is still more than forty times less dense than the energy stored in petrol. For direct comparability in performance, the car battery has to be forty times bigger in volume than the gasoline tank!