You wouldn't have 747s, you would have dirigibles. (Read more SF! :-) Especially since a green economy would imply that everyone telecommutes, and most people live on locally grown produce. So far less air travel. (Although this is a bit of a pipe dream because it looks like climate change will make growing *anything* more difficult... except perhaps seaweed.)
But anyway ... an airship could be perhaps solar powered. On 10 July 2014 06:19, 'Chris de Morsella' via Everything List < [email protected]> wrote: > > > ------------------------------ > *From:* John Clark <[email protected]> > *To:* [email protected] > *Sent:* Wednesday, July 9, 2014 10:51 AM > *Subject:* How will air travel work in a green solar economy? > > >>Liquid Hydrogen would be a pretty good fuel for airplanes, > > > Liquid hydrogen is hard to make and store (it needs to be liquefied to > near absolute zero -- an energy intensive process all by itself); the > volumetric density of liquid hydrogen is not all that impressive either. > Liquid hydrogen is also aggressive chemically and causes metal tank walls > to become brittle over time. Biofuels seem superior -- much easier to store > and handle -- as a future fuel source for aviation needs. The US Navy and > Air force (and Virgin Airways among others) are experimentally blending it > into jet fuel. Jet engines, apparently burn the mixes, quite well with no > modifications required. Thus the entire existing infrastructure and stock > of jets (and jet engine/ fuel systems) can be modified in an evolutionary > sense to add support for biofuels. Going with liquid hydrogen is a radical > departure from the current installed base. > Chris > > > > 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 > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
