Electric cars?

There was an interesting article in the Sept 6, 2000 Chronicle: Automobile Industry's Electric-Car Power Play. You will recall from my lecture that the fundamental difficulty in using electric cars is the size of the battery needed. A better article was published on Sept 9 in the New York Times: California Upholds Rule for Pollutionless Car by '03

I will discuss several aspects:

Energy in a gasoline tank
"Non-polluting" cars and Hybrid cars
Is there a future for pure battery-driven cars?

Energy stored in a gasoline tank.
I won't "look up" the numbers, but I will just work them out. I remember the old saying from cooking, "a pint is a pound, the world around." Gasoline is a little less dense than water, so a pint of gasoline weighs less than a pound -- but let's approximate that they are the same. Then a 15 gallon fuel tank holds 60 quarts = 120 pints = 120 pounds of gasoline.

Recall that the enegy stored in a lead-acid battery is 400 times less than that of an equal weight of gasoline (0.025 Cal/gm vs 10 Cal/gm). So a lead-acid battery equivalent to one tank of gas would weigh 120 lb x 400 = 48,000 lb = 24 tons. A typical auto weighs 1-2 tons.

We could use better batteries. The lithium batteries in our portable computers are about 10x better than lead-acid batteries. Therefore the weight of lithium batteries equivalent to one gas tank is only 4,800 lb = 2.4 tons. This is a reasonable weight; it only doubles the present car weight. The present cost of such batteries is about $100/lb (a typical computer battery weighs about a pound). So the cost of batteries is 4,800 lb x $100/lb = $480,000. The cost might be reduced a little because of the large size, but not much: the battery business is already very very competitive. This is too expensive for most of us. The solution is to use less battery, and reduce the range of the car. Instead of being able to go 400 miles on a tank of gas, let the car go only 40 miles on a fully charged battery. By reducing the range by a factor of 10, we reduce the cost from $480,000 to $48,000. Some people think the cost for the batteries could soon be brought down to $20,000, perhaps by using cheaper batteries.

This calculation should make it clear why we have not already converted. The students at Cal decided to be on the forefront of electric cars by making the bus that goes to campus from BART into an electric vehicle. Since it goes less than 40 miles per day, it could be charged at night. (Charging takes typically 4 hours.) It was called the "Campus Conductor" to brag about its use of electricity. After several years of operation, the cost was found to be so high, and the pollution saved so minimal, that we have now switched, and the Campus Conductor burns gasoline.

Non-polluting cars

As the Chronicle article points out, California has passed a law saying that by 2003, at least 10% of the automobile company sales must be "non polluting" vehicles. By this, everyone assumes they mean battery powered cars. (Solar powered cars can get about 300 watts of power from a square meter of solar cells; this is equivalent to about a half horsepower per square meter.) However, electric battery cars are not really non-polluting, since they must be charged from electricity, and most electricty in California is produced by the burning of fossil fuels. When these burn, the carbon in them is converted to carbon-dioxide, and that is believed by many (including Al Gore) to be the source of "green-house warming." So even battery cars are responsible for polluting carbon dioxide into the atmosphere.

So how can such cars be called non-polluting? Electric car advocates argue that electricity is produced in power plants with high efficiency, so although those plants pollute, they pollute less than automobiles. Opponents argue, okay, that's true, but they are still not zero pollution. Suppose we could make gasoline cars as efficient (i.e. as pollution free) as the electric-power/electric-car combination. Shouldn't that also be considered as non-polluting? Maybe we should change the name to "minimally polluting".

Does the technology exist to produce such a minimally-polluting car? Many people think it does. It is called the gas-electric "hybrid." A hybrid car runs on electricity, but it has a gasoline engine to recharge the battery. Doesn't that defeat the purpose of electricity? No, surprisingly. The gasoline engine can run at a constant speed (unlike an automobile engine), and thanks to that, it can be made much more efficient. In fact, when you consider that some electricity is lost in the powerlines, the proponents argue that hybrid autos are less polluting than the supposedly "non-polluting" pure battery cars.

Ten years ago, I predicted to my classes that hybrid cars would begin to take over in about a decade. (This wasn't great insight on my part -- I had spoken about the subject with experts, and I knew that all the major car companies already had reached this conclusion themselves.) Hybrid cars are now being sold by Honda and Toyota, and Ford and General Motors have hybrid cars almost ready for the market. I predict that California will decide that hybrid autos satisfy the 2003 law, and that in 10 years hybrid cars will be a major fraction of the auto market in California.

Is there a future for battery-driven cars?

For the last ten years, there has been an enormous incentive to develop better batteries: the portable computer market. People were willing to spend up to $200 per pound of batttery if their laptops could be lighter, and as a result, there has been rapid development in this field. The first light-weight batteries were "nicad" (stands for Ni-Cd, which stands for Nickel-Cadmium), and everybody who used them, hated them. They were unreliable, and could not be recharged until they had been completely drained, for otherwise the battery would be degraded. In the recent past, the advent of light weight cell phones has added stimulus to developing better batteries. The use of hybrid automobiles in the next few years will stimulate the development even further.

Will this stimulus for research result in batteries as good (in Calories per gram) as gasoline? Unfortunately, the factor of 400 (gasoline, compared to cheap lead-acid batteries) is hard to overcome. If lithium batteries become significantly cheaper, we still have a factor of 40 to overcome (gasoline has 40x the energy per gram, compared to lithium batteries). Battery development is an area of technology in which I find it hard to make predictions. A good bet for the future are fuel cells, which burn hydrogen gas. Since no carbon is burned, no carbon-dioxide is produced, only water (H2O). Therefore, hydrogen fuel cells are clean. Hydrogen is light, but hard to store. At room temperature it is a gas. Methods for storing hydrogen in a condensed form are being sought by many companies. A real scientific breakthrough is needed. Some people think the hydrogen can be absorbed into a solid carbon block (maybe made out of nanotubes, also called Buckminsterfullerines).