Friday, April 01, 2005

Electricity, gasoline and uranium

The previous post on Toshiba's new batteries (with one-minute recharge times) prompted a question that then led to an email exchange. The question is, "Can't we now use these batteries to create electric cars that recharge in a minute or two?"

The answer to that question is "probably not." One funny thing about electric cars is that the recharge time might still be high even with batteries that take only one minute to recharge.

A typical car uses about 15 horsepower to cruise on a flat freeway. The power is needed to cut through aerodynamic drag, overcome rolling resistance, run the air conditioner and other appliances in the car and so on. Let's say an electric car is more efficient, so it needs 10 HP. 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. That means the car needs about 10 kilowatt-hours per hour to go down a flat highway at a reasonable speed.

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.

The biggest circuit breaker in a typical house might be 50 amps at 220 volts (probably for the air conditioner). That's roughly 10,000 watts. So, if you plug an electric car directly into the biggest circuit breaker in a typical house, it would take about three hours to fully recharge the car. It has nothing to do with the batteries -- it has to do with the amount of time it takes to move electricity across a wire into the car.

Even if you plug an electric car directly into the 200-amp main coming into the house, all you can pump is 40 kilowatt-hours of electricity per hour into the car. It would still take perhaps 45 minutes to recharge an electric car with 150 to 200 mile range. And you would not be able to turn on anything else in the house while recharging the car.

I don't ever think we will have quick-recharge electric cars. It is always going to take at least an hour or so to recharge an electric car with any kind of range if "plugging it in" is the way you do the recharging.

It is when you think about this that you realize the miracle of gasoline. When you pump 20 gallons of gas into your car in 5 minutes, you are transferring an amazing amount of energy into the gas tank. A gallon of gas, if you could convert it completely to electricity in a 100% efficient process, contains about 36.6 kilowatt-hours of energy. Twenty gallons of gas therefore contains about 730 kilowatt-hours of electricity. And it all comes into the car in 5 minutes.

As you can see, gasoline has a good energy density that it makes it easy to move a fair amount energy into a car's fuel tank quickly. Is there anything with a better energy density? One year ago today I wrote an April-Fool's article on a vehicle called the NCar. The NCar is powered by enriched uranium, and it is such an appealing idea. A pound of highly enriched uranium contains the energy equivalent of about one million gallons of gasoline. If we could somehow tap into that incredible energy density in a safe way using a small (big as a typical car engine, say) reactor, we would be set. You would never have to refuel your car. If we could make small nuclear-powered AA batteries, they would potentially last for decades in a cell phone or laptop without ever needing recharging.

Alas, it does not appear that we will be seeing uranium batteries any time soon...

Comments:
Can you imagine the stories in the media about uranium powered cell phone induced brain tumors...?

:-)
 
I don't think I'm that keen on enriched uranium becoming a consumer product. The potential for abuse is staggering.
 
You could have very large roadside supercapacitors that discharged rapidly into the car's battery, though heat and other things might make this problematic. They could stabilize the grid and provide re-charge potential simultaniously.
Probably impractical though.
 
Automotive innovations:

- Concept plug-in hybrids tout 180 mpg ratings.

- Every additional 10 miles of vehicle range in electric mode adds about $1,000 to the cost.

- The Toyota Prius already has a "secret button" that lets it operate in full electric mode.

- Tangos seem to solve a variety of transportation problems but will enough people want to drive them to make them cheap?

- A hydrogen economy would be great but the costs are currently staggering and need to come way down. $1,000,000 for the car, billions for the infrastructure, energy loss producing hydrogen, etc

- Interesting report describes more options for increasing the efficency of cars and decreasing emissions. Ultra-light materials and biofuels add a bunch of nice effects. Could implementing these options and others push efficency to 300 mpg or higher?


Plug-in hybrids seem to have some great potential. Sure, you can't charge them as fast as you can pump gasoline(unless maybe you can run a booser cable to a high voltage line), but an instant charge is not the end of the world.

Keep your fingers crossed for crude to go above $100/barrel asap. That should push all this innovation into overdrive.
 
Perhaps we'll have hydrogen hybrids? You could tank-up quickly on hydrogen, but stretch it out longer by coupling it with a battery.
 
Automobiles utilize about 10% of the potential energy of gasoline. The rest is dispersed as heat, CO2, water, etc. Not very efficient and it requires large volumes of gasoline. 50% efficiency might mean a four-gallon gas tank, maybe?
 
A car going 60 mph has an effective wind of 60 mph passing over it. If you put up a few small wind powered generators on the car the wind would activate them and make electricity. This electricy can then charge the battery or power the motor as needed.

Simple solution to many problems. So why don't the car companys do this? Because they are in cahoots with the oil companys and there is no money to be made.

Duh!
 
Its true that if we had batteries that could be recharged within minutes we would have problems charging quickly enough from home grid power unless we used a secodary battery system in the home (made from the same batteries/ultracapacitors) that would slowly fill during the day and then quickly discharge the power into the vehicle when you come home.
 
Re wind-powered generator on automobile:

The drag produced by the vanes or blades has to be overcome by an equivalent amount of energy to continue propelling the vehicle. You have no net gain. Seems good but defies physics.
 
They already have Uranium batteries. in Nuclear subs and the reactors are only about the size as a small rubbish bin. And run on 1kg (2pounds) or enriched uranium.
 
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Electric Cars are the best because they are Eco-friendly and they are best for the nature
 
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