From: Stirling Westrup (sti@cam.org)
Date: Thu Feb 03 2000 - 04:23:24 MST
Robert J. Bradbury wrote:
>
> On Wed, 2 Feb 2000, Stirling Westrup wrote:
>
> >
> > The ultimate problem with solar power is that there isn't enough of it.
> > I've seen projections in which the planet's power needs by 2050 will be
> > such that a band of 100% efficient solar cells 10 miles wide and wrapping
> > the whole equator will not give enough power. So, even if we converted
> > all highways and all roofing materials to 98% efficient solar cells,
> > we're *still* going to have to go out and find other fuel sources.
>
> Well, my comment would be -- *never* believe everything you read.
> As I said at Extro3 -- "Trust but verify"...
>
> Draging up an Excel sheet (I just love Excel...),
> Earth's Circumference: 6378 km x 10 mi, gives about 2*10^9 km^2
> Assume perhaps 30% of it is getting sunlight at a rate of about
> 750 w/m^2 that is being harvested at an efficiency of about 20%
> (after all if we are enginering for planetary power we can afford
> the "good" solar cells...). That gives you ~10^10 W (J/sec).
> Assuming maybe 8 hours of light per day gives you an annual
> production of ~1000 EJ.
>
> According to "Energy: A Guidebook", in 1974, our annual energy
> consumption was 370 EJ (year round constant drain of 12 TW).
> So even with some pretty pessimistic assumptions we should be
> able to harvest 2-3x the amount of energy we are currently consuming.
Okay, so the numbers are more or less as I assumed.
> So, I think there are some interesting built-in assumptions
> in your claim, like:
As always. And note that this is not *my* claim, just something I read a while
ago, and thought worth repeating.
> (a) You can't put power collectors in the ocean...
> Yet here in Washington State we have several "floating"
> bridges...
Why would such an assumption be required? I just implied that 10^9 km^2 isn't
enough. Your numbers aren't that far off considering I was pulling numbers out
of a rather leaky memory...
> (b) That power consumption will continue to grow at past
> historic rates... But in the developed countries per
> capita power consumption seems to have leveled off...
Granted. Still, I have a feeling that that will be compensated for by the sheer
number of third-world countries that enter the computer age in the next few
decades.
> (c) That there will be no improvements in energy efficiencies
> (automobiles, electric lights, etc.) [LEDs for example
> are 50%+ efficient, new electrodeless sodium vapor lamps
> are 2-3x as efficient as incandescent.]
Yup. Oh, I think the *technology* will improve, but I'm not forcasting the
arrival of *commercially viable* new technology. There just doesn't seem to be
enough demand (sad to say) to cause the improvements in cost per unit that will
be sufficient to convince people to switch to alternative methods. I'd love to
be proved wrong on this point, BTW.
> (d) The solar cells are the really crappy 8% efficient versions
> rather than the 30+% efficient versions that we can build...
Hmmm. I think that was most likely part of the assumption. Then again, what's
the current per-capita cost of 10^9 km^2 of the expensive kind of solar cell...
> (e) That we don't use other more efficient technologies such
> as heliostats and heat pumps to harvest the solar power...
These devices tend to be more expensive and require more maintenance, no? Are
they really cheaper when the energy cost of their manufacture and maintenace
are factored in? My guess is yes, but not by the margin you believe.
> But we are talking 50 years here. Everyone always assumes the same
> thing when discussing these limits -- the population grows, energy
> consumption grows and technology stands still. Makes me want to gag.
Granted. My point was just that there just isn't as much solar energy reaching
the planet as some people seem to think. Putting a solar cell on top of every
car won't suffice. Neither will paving all our roads and rooftops with solar
cells.
> And 10 miles wide is nothing, we've got agriculture production over
> much of the land area of the Northern hemisphere hundreds to thousands
> of miles wide! I've previously discussed how terribly poor our
> agricultural efficiencies are.
Don't get me started on the ecological wasteland that USED to be praries in
North America and is now monocultural bio-factories for as far as the eye can
see. Slightly more picturesque than the smokestacks of New Jersey, but no
better for the ecology of the region... One of the things *I've* been hoping
that nanotech would give us is a food production system efficient enough to let
most of the grain belt be returned to its natural state.
> > (Note that I'm assuming we don't get around to huge solar collectors in
> > space. THAT way we could get enough power for the planet.)
>
> Agreed. Though the power delivery area requirements remain a concern.
Ever since I've heard about the plans to use phase conjugation systems to steer
the energy beams, I'm far more comfortable with the idea of giant power beams
being aimed at the hearts of our cities...
> However, if we get to the point of building interesting diamondoid
> things out of oil, I can see the carbon supplies going rapidly.
> But by then it will be a very different economy, so it really
> won't matter.
I dunno there is one heck of a *lot* of carbon on the planet, not just as oil.
--
Stirling Westrup | Use of the Internet by this poster
sti@cam.org | is not to be construed as a tacit
| endorsement of Western Technological
| Civilization or its appurtenances.
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