But about midway through the article, I read the following:
He illustrated the challenge of building a battery with the energy density of gasoline by recounting that it took 47 seconds to put 13.6 gallons of gas in his car when he stopped to fill up on the way to San Francisco. That’s the equivalent of 36,000 kilowatts of electricity. An electric car would need to pump 6,000 kilowatts to charge its battery.Does this make sense? Let's parse it.13.6 gallons of gasoline contains (at 125*10^6 joules/gallon) 1.7*10^9 joules. Putting this in the vehicle in 47 seconds yields a "rate of energy transfer" of 1.7*10^9 joules/47 seconds, or 36.2*10^6 joules/second or just over 36,000 kilowatts. OK, so far so good.
But where does the 6,000 kilowatts come in? Well, the internal combustion engine (ICE) in the gas powered car might use energy at something like 22% efficiency, so the 1.7*10^9 joules might translate to 3.74*10^8 joules of useful work. OK, an electric motor with the power to drive a car will typically have a minimum efficiency of 92%, so that means that we'll need 3.74*10^8/.92 = 4.07^10^8 joules of electrical energy put into the battery. Doing this in 47 seconds yields a charging rate of 8.6*10^6 watts or 8,600 kilowatts. Not really so far off, and I guess that that's where the figure came from.
Stepping back, it's a very good illustration of why we love fossil fuels. Suppose IBM and Better Place succeed in creating a lithium air battery with the required energy density and ability to accept a charge at the rate described above. Now, imagine a "charging station" with, say, 4 cars charging their batteries at the rate of 6 megawatts, and imagine that you're at a corner with another station across the street doing the same. As I drive around, this is not at all an unusual circumstance at some times of day. So, at this corner, we'll need to be able to supply at least 48 megawatts of electrical power. That's about 5% of the power from a gigawatt generating station (this is a big facility). Getting energy from a power plant to a charging station at this rate, with the ubiquity of today's gas stations, is an incredibly difficult transmission problem
As I've demonstrated in a previous post, I believe it will be possible to install sufficient capacity to supply electrical energy to a fleet of electric cars. But the ability to deliver it at an acceptable rate to batteries that can store it is definitely the sine qua non of the widespread adoption of electric vehicles.