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

John Clark johnkclark at gmail.com
Wed Jul 9 17:50:36 UTC 2014

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

  John K Clark
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