[ExI] How will air travel work in a green solar economy?

Mark Walker markalanwalker at gmail.com
Wed Jul 9 19:09:24 UTC 2014

I'm not sure pessimism about solar's potential is the right conclusion from
John's back-of-the-envelop calculations. New Mexico is 121,593 square
miles, which means that it should be sufficient to keep 40k planes in the
air. Estimates of the number of planes in the air at anyone time world wide
are in the neighborhood of 10 to 20K. So, covering half of New Mexico
should about write the check. And of course, most of these planes are much
smaller than a 747.



Dr. Mark Walker
Richard L. Hedden Chair of Advanced Philosophical Studies
Department of Philosophy
New Mexico State University
P.O. Box 30001, MSC 3B
Las Cruces, NM 88003-8001

On Wed, Jul 9, 2014 at 11:50 AM, John Clark <johnkclark at gmail.com> wrote:

> Liquid Hydrogen would be a pretty good fuel for airplanes, so let’s see
> how many solar cells would be needed to make the fuel to keep one in the
> air. A 747 jet uses on average 140 megawatts of power, incidentally even
> the old fashioned nuclear reactor on a Nimitz class aircraft carrier  can
> generate 190 megawatts, a LFTR could be much smaller because it's much more
> energy dense. The electrolysis process to make hydrogen from water is only
> about 60% efficient so that brings the power requirement up to 233
> megawatts, but then you need another 30% to liquefy the hydrogen (it’s not
> easy to do) so the grand total is you need a  solar cell installation that
> on average produces 333 megawatts each and every hour to keep a hydrogen
> powered 747 in the air.
> Averaged over 24 hours a square meter of solar cells might produce 30
> watts each hour, so you’d need 11,100,000 square meters of solar cells,
> that’s a square 2787 meters on a side. We conclude that to keep just one
> jet in the air we need a fuel factory that covers 3 square miles of the
> Earth’s surface. And that is why I don’t think solar is the answer to all
> our energy needs.
> There are only 2 other sources that have the potential to power our
> civilization for the next billion years:
> 1) Fusion reactors, but nobody is close to figuring out how to build even
> a working model much less a practical machine.
> 2) Thorium fission reactors, and we’ve known how to build them for half a
> century.
>   John K Clark
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