ARTICLE 1 From his online textbook "Physics for future Presidents" at:
http://muller.lbl.gov/teaching/Physics10/PffP.html

[snipped throughout]

Batteries vs. gasoline

http://muller.lbl.gov/teaching/Physics10/PffP_textbook/Chapter01.htm

A battery stores its energy in chemical form. It can use its energy
to release electrons from atoms. Electrons can carry their energy
along metal wires and deliver their energy at another place; think of
wires as pipes for electrons. The chief advantage of electric energy
is that it can be easily transported along wires and converted to
motion with an electric motor.

Table 1.1 shows that gasoline contains 1000 times as much energy per
gram as in a flashlight battery, and 100 times as much as in an
expensive computer battery. Those facts explain why most automobiles
use gasoline instead of batteries as their source of energy.
Batteries are used to start the engine. A typical car carries about
100 pounds of gasoline. To carry that much available energy in
batteries would take 100 times that weight (10000 lb = 5 tons), much
more than the total weight of a typical car. That's not an attractive
option, even if the batteries were cheap. But batteries have
advantages in some circumstances. In World War II, when submarines
had to submerge and could not obtain oxygen, their energy source was a
huge number of batteries stored beneath the decks. When on the
surface, or "snorkeling depth," the submarines ran on diesel fuel, a
form of gasoline. The diesel fuel also ran generators that recharged
the batteries. So during WWII, most submarines spent most of their
time on the surface, recharging their batteries. Modern nuclear
submarines don't require oxygen, and they can remain submerged for
months. That greatly increases their security against detection.

Electric Car Hype (added 8/25/06)

A student drew my attention to an article that appeared in Wired
magazine about an all-electric car. Here's a link to the article:

http://www.wired.com/news/wiredmag/0,71414-0.html

The article says the car, called the "Tesla Roadster", is powered by
6,831 rechargeable lithium-ion batteries, similar to those found in
laptop computers. The car range is 250 miles. They claim, if you
charge the batteries from your home power plug, that driving the car
costs 1 to 2 cents per mile. Top speed: 130 miles per hour. Wow!
Can't wait to get one? The cars will be built in a factory in England
and available (they say) summer 2007.

But wait a minute. Let's calculate some numbers. My laptop battery
costs $135. For 6,831 batteries, I would have to pay $922,000. Well
– maybe the price will come down? No, probably not by much. Laptop
batteries are already a huge and competitive market, so the price will
not come down very much, at least not in the foreseeable future.

My laptop battery is quite small, with dimensions 14 cm x11 cm x 1.4
cm. That's a volume of 215 cubic cm, or 0.215 liters. If my car
carried 6,831 of these, the total volume would be 1473 liters, or 390
gallons. My Prius has a tank that holds 11 gallons. The batteries
would take 35 times as much space as my present gas tank! There would
certainly be no room for passengers.

Moreover, my laptop battery weighs about one pound. So the batteries
for the Tesla Roadster would weigh 6,831 pounds, well over three tons.
The batteries alone weigh 2.36 times as much as my entire Prius!

Suppose the batteries last 10 years, and the driver goes 50,000 miles
per year. That's 500,000 miles. For a million dollars of batteries,
the cost is about $2 per mile, just for the batteries. The
electricity might cost 1 to 2 cents per mile, but the cost of the
batteries is a hundred times greater. (And who has ever had a laptop
battery last ten years?)

Who will buy this car? Answer: billionaires who want to brag about
their all-electric car. These are the same people who buy flights in
Russian space vehicles so they can claim to be astronauts.

Shouldn't the original article in Wired have contained some of these
numbers?


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ARTICLE 2

http://muller.lbl.gov/teaching/Physics10/old%20physics%2010/physics%2010%20notes\
/Electric%20cars%20.html

Electric 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

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....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.

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).