On Wed, Jul 09, 2014 at 04:34:07PM -0700, meekerdb wrote: > 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. >
Are you suggesting that the Sun irradiates us with 200W/m^2 on average? That seems a little on the low side - IIRC, the average insolation is something like 1kW/m^2, so that would make John's solar cells around 3% efficient - unless he was planning on locating them on the newly thawed tundra... Plus, the other thing that didn't jibe - I assume that the quoted 333MW engines for a 767 was actually the maximum power, which is only required for take off, and briefly on landing for reverse thrust. On average over a plane's flight, I would guess probably only 15-20% of that figure is required - but I'll defer to wiser heads on this. Cheers -- ---------------------------------------------------------------------------- Prof Russell Standish Phone 0425 253119 (mobile) Principal, High Performance Coders Visiting Professor of Mathematics [email protected] University of New South Wales http://www.hpcoders.com.au Latest project: The Amoeba's Secret (http://www.hpcoders.com.au/AmoebasSecret.html) ---------------------------------------------------------------------------- -- 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.
