A car running on electricity drawn from the power grid and stored on-board can be fueled at about one-third the cost per mile compared to a gasoline-powered car. We prove this in our recent post Electric Car Cost Per Mile.
There are at least three technologies to store electricity on-board an electric vehicle; hydrogen which is turned into electricity using onbard fuel cells, ultra-capacitors, and batteries. We reject fuel cells for reasons clearly stated in our posts The Hydrogen Hoax, and Fuel Cell Cars Aren’t Ready.
Ultra-capacitors are a wild card – while there probably aren’t nearly insurmountable problems in eventually lowering their manufacturing costs, as there are with fuel cell / hydrogen systems, they have a relatively low energy density. This makes them impractical for vehicle applications. There is some evidence that “nanotube enhanced ultracapacitor” prototypes can now achieve an energy density of 75 watt-hours per kilogram, which lags well behind lithium ion batteries. But the theoretical energy density of ultracapacitors is much higher. Their time may come.
In the race to be the electrical storage mode for the imminent wave of next-generation electric cars, however, the battery continues to show the most promise. The latest lithium ion batteries, used in laptops, display the ability to recharge in minutes instead of hours, and retain 99% of their capacity after 1,000 charge cycles. With a gravimetric energy density approaching 200 watt-hours per kilogram, and a gravimetric output density of over 5 kilowatts per kilogram, these advanced batteries now have solved two of the three inherent problems to-date with batteries; longevity, and ability to produce adequate surges of power.
One of the pioneers in lithium ion batteries is Toshiba, who has already commercialized this advanced battery for use in laptops. Applications for hybrid cars and battery powered cars won’t be far behind, as the laptop battery powered Tesla Roadster will attest.
If battery powered cars have battery packs that can be warrantied for ten+ years, and can be recharged in less than one hour, their third problem of still marginal energy density becomes less significant – particularly since battery energy density has been increasing by 6% per year for decades, with no end in sight.