Originally Posted by
FlightlessParrot
I don't think car hybrids have got very much to do with aviation. I sit in my Nissan Note serial hybrid and glance happily at the gauge showing the battery recharging as I coast down a hill or slow to a stop at the traffic lights, and that's where most of the efficiency comes from: there isn't really anything like that in aviation. Electric motors have lots of advantages, some of which probably would apply in aircraft, and there might be wins in a hybrid configuration from having a reservoir of electric power (battery or capacitor) for peak loads, but not the big advantage of regenerative braking in city driving (hybrids are not any more efficient than ICEs at steady-speed highway cruising, which is a better analogy to most aviation). Also, that VW prototype applies standards of light-weight construction and aerodynamics which are already in use in aircraft design.
Further, solar panels are not going to make a big contribution. I gather that NASA estimates the total solar power available at the "top of the atmosphere" (this is a quick google-search, so I don't know exactly what height that is, but presumably above normal flight altitude) as 1,360 Watts per square metre. Just for a quick guide to the limits, I worked out a solar panel DC-3 replacement. The DC-3 has a wing area (according to Wikipedia) of 91.7 square metres, so the maximum available solar power, if the whole of the upper wing surface is harvesting power, is about 125kW. The engines on a typical DC-3 are rated at 1,200 hp each = 890 kW. I believe an assumption of 65% power for the cruise is reasonable, which means the venerable aircraft, flying much slower than modern airliners, is using 1,157 kW. So the available energy is less than the needed energy by an order of magnitude even before beginning to account for losses. The 1.36 kW per square metre is available energy: the best panels at the moment would only actually gather about 25% of that, and then there would be other losses in the motor(s) and transmission. Oh, and this is only for daytime operations, too, which might be a further problem.
It looks like aviation is one of those areas where there is no alternative to fossil fuels except for synthetic hydrocarbons made in a carbon-neutral way, or just maybe hydrogen. Making synthetic aviation fuel would be an inefficient way of using sustainable power (wind, solar, hydro, geothermal, nuclear, whatever), but sometimes you have to accept inefficiency, and the power might be used in a form of load spreading.
The consequence of this is that the aviation industry and its supporters should not be engaged in climate change denial (which only encourages the flight-shamers), but instead should be making the case for aviation as a (temporary) special case, while at the same time investing heavily in realistic sustainable alternatives that are not defeated from the start by physical constraints. The sad present state of the Boeing company shows the consequences of short-termist denial of social responsibility.
"The real downside of biofuel for aircraft is the amount of arable land that would have to be taken away from growing food crops to provide the materials for biofuels.
Fuel consumption for international
aviation could be as high as 852 million tonnes (Mt) by 2050 (ICAO, 2016), and could
require 426 Mt of
bio-jet to meet the GHG emissions-reduction goals. Current
production, however, is currently very limited, at less than 0.1% of global total consumption of all types of jet fuels."
Foillowing is a goto to a paper on the subject:
https://www.irena.org/documentdownlo...ation_2017.pdf