Colin Bennett
Batteries have to contain all of the chemicals on both sides of their energy releasing equation. The very best batteries available today can store about 0.4 MJ/kg (0.05 kw-hr/lb) including the cases and safety systems. In contrast, gasoline carries about 46 MJ/kg (5.7 kw-hrs/lb).
Even with a 20% efficient IC engine, a gasoline tank stores 20 times as much energy as a battery of equal weight. As the vehicle is moving it gets rid of some of that weight. Battery powered vehicles must carry the full weight of their energy source.
The energy density difference also plays a key role in the time that it takes to put more energy back on the vehicle once a fuel load is consumed. A two minute fill-up of a 12 gallon tank puts the equivalent of 87 kilowatt-hours into the vehicle, again, taking into account the 20% thermal efficiency.
87 kilowatt-hours in 2 minutes works out to 2.6 MegaWatts. Even with a 220 volt connection, that would require about 11,800 amperes of current. Just imagine the size of the electric cables for that current.
There are certainly places and applications where electric vehicles have a role, but it is worth remembering that at least five or six generations of engineers have looked very hard at trying to meet transportation needs and they keep coming back to the same fact - when you want to move a vehicle, you need power, (energy per unit time).
Battery trends
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