From: Eugene Leitl (eugene.leitl@lrz.uni-muenchen.de)
Date: Thu Sep 07 2000 - 02:54:26 MDT
Spike Jones writes:
> Granted, growing corn and distilling the result is not the best way to
> capture solar energy, but it does give one a feel for orders of magnitude.
> When one hears some yahoo say: "Hey, if we put solar panels on our
> cars, and let them charge during the day, we could run our cars on
> electricity." After this exercise, we know that that person isnt even in
This is silly. Why would one want to cover your car with solar cells?
It hardly produces enough power to directly drive an ultralite
manta-style vehicle during high summer in Oz. The only reason to put
thin-film cells on your roof, is to ventilate/cool your car in the
parking lot while trickle-charging your battery.
> the right order of magnitude. Another way to look at it is this: if a
> parking lot capable of comfortably holding about 600 cars were to
> be dug up, planted in corn and the result distilled, the ethanol produced
> could be used to power one of those 600, assuming it is an average
> American guzzler driven an average amount.
>
> That same area, covered with solar cells would be able to power
> about 15 of those 600 cars. If the cars were all state of the art
> electrics, the parking lot could power about 25 of em.
A fairly average U.S. family has 2-3 cars (I know, I've seen
them. Dunno about trailer trash, though). Most of them stand around in
the residential area during most of the day. Assuming a residential
roof area of 100 m^2 (I have no idea how accurate that is), our 10% of
500 W average insolation gives us 50 W*100 = 5 kW during most of the
daytime. Now most normal (gasoline-guzzling, steel coffin) type of car
do quite ok on an energy budget of 30-40 kW. A composite (hybrid)
electrical car with spike cache should do nicely (i.e. have a kick-ass
acceleration and very acceptable (for the U.S., that is) cruise speed)
on a fraction of that. Given that you can't recharge your EV battery
with full juice without damaging it, 5 kW sustainable performance
during daylight hours seems the optimal ballpark figure to recharge
your 2-3 cars hanging around in the residential area.
See, I can twist numbers, too :p
> Conclusion: petrol is your friend. spike
Energy is your friend.
Gasoline has a relatively high power density, but is lousy if you want
to burn it just in carbon dioxide and water (what I would call zero
emission, only idiots without common sense would still point at the
faint whiff of carbon dioxide still emitted) in a non-Carnot process,
and it has a nasty tendency that you have to drill (and sometimes
shoot) for it in faraway places, generate a lot of muck in situ and
during the transport, and suffer the refined product to be under the
control of a monopoly-type of distributors, and the feds holding out
their greedy little paws (70% of fuel costs in Germany are diverse
*taxes*).
Methanol has a slightly less power density, but you can easily make it
from any organic material (including gas, oil, coal and renewables) in
the country, it readily mixes with water, is rapidly fully
biodegradable, is less toxic than gasoline (unless drunk), can be
consumed both in the ICU (with less emissions than gasoline), unlike
hydrogen can be stored in a normal fuel tank, can be readily reformed
into fuel-cell-grade hydrogen/carbon dioxide in small onboard reactors
and also can directly power alcohol fuel cells. Yeah, and in the
future with engineered photosynthesis you can make solar panels which
fix carbon dioxide from air (or other sources) and generate methanol
directly on your roof.
Dunno, looks like a winner to me.
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