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

[Robert G Kennedy III, PE]

On 2014-07-10 08:00, John Clark <johnkclark at gmail.com> wrote:

> 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.

No, there are 3:

space-based photovoltaic satellites.

either in GEO as the late great Peter Glaser invented/envisioned, or at 
the Sun-Earth L1 point as we and a few others have proposed. See for 
example our "Dyson Dots and Geoengineering: The Killer App to Bootstrap 
Us Ad Astra" article in JBIS vol.66, no.10-11, Oct-Nov 2013. Our 
geoengineering with SBSP work has also appeared in Acta Astronautica in 
2012 (another refereed journal), as well as the Whole Earth Review way 
back in the summer of 2001. Also Stanford webcast us back then right 
after 9/11. Also we were published by the Russian Academy of Sciences / 
Rosgidromet (their national weather service) in 2011. Yes, the Russkiis 
have all of a sudden got serious about climate change.

And I would substitute fast breeders for the fusion reactors, since we 
do already know how to build and operate the former, but not the latter. 
We'd just have to be honest and call it as the "plutonium economy", 
since that's what it is.

But of all of these, solar is the one with the most "headroom" for the 
human race, even just down here on /terra firma/. The United States 
alone encompasses 2 billion acres. The "built environment" (buildings, 
parking lots, roads, but not farms) covers about 5% of that, ~100 
million acres. One acre in the temperate zone can host 1/6th to 1/4th of 
a MW(e) of solar electric generating capacity, depending on technology 
and latitude and cloud cover. Now, nameplate capacity of the US grid is 
1 terawatt; steady state generation is closer to just half of that, 0.5 
TW or 500 GW(e). The global grid is less than 4 TW(e); steady-state 
about 2 TW(e). These rough figures suggest that there's sufficient area 
just on the parking lots and rooftops (that happen to be pointing the 
right way) of America to host solar equivalent to the world's grid 
several times over. That's without covering up one single square meter 
of grass or productive farmland, which the Germans mistakenly did.

In space, a single Dyson Dot the size of Texas could host enough PV on 
its sunny side to provide the entire planetary primary energy that we 
forecast by the year 2050. Meanwhile the Dot is also providing a bit of 
shade, 1/4th of one percent, enough to cool down the Earth just enough 
to offset AGW, about 2 deg. C worth.

Btw, LNG would be an even better aviation fuel, especially for 
professional (non-amateur) flyers, with far less difficult handling and 
density problems than LH2. Expect to see LNG-fueled a/c in the next 
decade.

Robert

-- 
Robert G Kennedy III, PE
www.ultimax.com
1994 AAAS/ASME Congressional Fellow
U.S. House Subcommittee on Space


> 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