Marshall Brain's Blog

>it could make electric cars feasible

This is true. One funny thing about cars though is that the recharge time might still be high.

A typical car uses about 15 horsepower to cruise on a flat freeway. Let's say an electric car is more efficient, so it needs 10 HP, and let's say this is the average. A HP equals about 750 watts. If you assume normal inefficiencies in the batteries, the converter, etc. let's say it's 1,000 watts per HP.

If you want the car to have a three hour range, what this means is that you need to be able to pump 30 kilowatt-hours of electricity into the car to fully recharge it.

I went out and looked at the circuit breakers for my house. The biggest one is 40 amps at 220 volts (for the air conditioner). That's roughly 8,000 watts. In other words, if I plugged the car directly into the biggest circuit breaker in my house, it would take about four hours to fully recharge. Even if I plugged it directly into the 200-amp main coming into the house, it would take perhaps an hour. And I would not be able to trn on anything else in the house.

I don't ever think we will have quick-recharge electric cars. It is always going to take at least an hour to recharge an electric car with any kind of range.
 

The car would have to be a "plug in hybrid" to replace driving with electricity. If you have "plug in" cars, you can surely make a cheaper all electrical one. Keep in mind that motors are about 3-4x as efficient as internal combustion. Fuel-cell battery hybrids (with plug-in and solar re-charging and super-capacitors for rapid acceleration?) might be the long-run direction of choice. Keep all the systems electrical and you don't need the redundancy of motor and engine, and you can afford a more powerful motor for better acceleration. If you don't use it to accelerate or decellerate at all or to climb hills, how powerful a fuel cell do you need just to maintain an aerodynamic car's velocity at 80mph? For a perfectly non-aerodynamic car, this is almost the same question as "how much energy does an 80mph wind contain and what is the cross-section of a car" the answer to these questions is 75mW/m^2 x about 2m^2 = about 77kW, which with a 77% efficient (about average) electric motor means that about 100kW of power is needed. A Honda Insight has a drag coefficient of .25 and a cross-section of 1.6 square meters, so it could drive at 80mph relative to the surrounding air using 20kW of power. Since the DOE expects fuel cells to cost about $400/kw (http://www.fossil.energy.gov/programs/powersystems/fuelcells/) by 2010, this would imply a total cost of $8000 for the fuel cell, still too high, but another factor of 4 would make it cheaper than the engine in most current cars, which it would be replacing. History suggests that a factor of 4 price decrease can be met by a 64 fold increase in scale of production so long as use of valuable materials can be minimized (difficult since most current fuel cell proposals use platinum catalysts).
 

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