On 7/9/2014 10:51 AM, John Clark 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,
That's about 15% efficiency, which is good for photovoltaics, but is way below what
solar-thermal achieves.
Brent
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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