The Super Capacitor
At about the 2:50 point in the video he says "... eventually we'll get to electric cars.... you'll pull into a charging station and within a minute you'd charge your car..."
Okay, so my distant memory from my electrical engineering degree kicked me when I heard that. Power = volts * amps. So, if you want to charge a car, you have to push volts/amps into the storage device. The question becomes how much power is that?
According to How Stuff Works, one gallon of gas has enough energy to drive a 1500 watt heater for 24 hours. Let's assume that we only need 10 gallons of gas equivalent for a "full tank" for our electric car. Let's also assume lossless transmission. How much power or volts/amps is that? Well, the answer is a TON, especially if delivered in a one minute time frame.
Let's assume we use 440V cables so we don't have to re-engineer the entire electrical grid. At that voltage, the system would need to push thousand of amps into the car's battery (assuming no losses).
Here's the math:
power of the heater = 1500 watts = 120 volts * 12.5 amps (continuously for 24 hours)
1 gallon of gas = 1500 watts for 24 hours = 1500 * 86400 seconds = 129,600,000 W-s
129Megawatt-s * 10 gallons = full tank = Power needed (P = VI)
Keep in mind, we have to deliver that power in "... 60 seconds", not all day long in the case of the heater above. However, let's set voltage at 440 and solve for amps: I = P/V = 294,545 amps. Now divide by our 60 seconds and we get 4909 amps.
Hmmm..
Or, perhaps we go to high voltage systems and get the amps down. Say 33KV like on local subtransmission lines. Then we'd only need 65 amps. Suffice it to say, that skinny little cable they showed in the video would be incapable of delivering that power. And, how safe do you think a 33,000 volt, 65 amp fueling station would be? Better wear your rubber boots!
It is difficult to get around the issue that the energy density of gasoline is very high, perhaps unmatched by any other substance on earth. Delivering that amount of energy into a battery or any other form of storage requires a pretty robust solution.
So, charge a cell phone in 60 seconds? How about that? Well, a brief look at a common Lithium Ion battery shows it runs at 3.7 volts. They also have an amperage measured in milliamp-hours, like this Motorola Razr. It has 3300 mA - hours of power. So, unpacking that:
P = 3.7V * 3.3amps * 60 minutes * 60 seconds = 43,956 W that's a lot in a tiny package.
Now let's charge that in 60 seconds at 3.7 volts (P/V = I):
44KW / 3.7V = 198 amps in one second, but if we have 60 seconds, then we only need 3.3 amps. So, that is possible given the typical house's 15 amp circuits.
Charge a cell phone in 60 seconds? Sure. Charge a car in 60 seconds, that is pure dreamery. A physicist should know better than to talk like that.
One thing that should be abundantly clear is just how amazing gasoline is... Batteries are never going to match it.
