4 ms·
Batteries are (in theory) optional and irrelevant for solar planes. The 747 uses about 80MW of power on takeoff, and maybe half that for cruising. The 747 has
by keenerd 10y ago
Batteries are (in theory) optional and irrelevant for solar planes. The 747 uses about 80MW of power on takeoff, and maybe half that for cruising. The 747 has 525 m^2 of wing surface area. The sun blankets the earth with 1kW per square meter.
Solar cell efficiency is the limiting factor, if you are willing to fly only at day. No batteries needed. And it will never be enough with current designs, since 500kW is well under 40MW.
Of course a solar plane can cruise much higher since it doesn't need oxygen for the motors. And it gets more range traveling westward. At a fast enough speed (tantalizing "easy" mach 1.4) a plane on the equator could cruise under high noon forever. Wing size tends to go down with speed, so I doubt that design will ever be possible.
- vkou 10y agoEdit: You were originally off by three orders of magnitude. Solar flux at 1 AU is ~1.3 KW/m^2. At sea level, due to atmospheric absorbtion, it is between 1 KW/m^2 and 500 W/M^2. And yeah, 500 KW of power is probably enough to get a Cessna off the ground... Not so much a useful aircraft.
- keenerd 10y agoSorry, I think I fixed it while you were typing out your post? Atmosphere conditions are usually a bit better at 9km up than at sea level. If the numbers weren't quite so bad there would be a case for detachable JATO units to get a solar plane off the ground, which then fly back to the airport to launch the next plane. ... and I forgot the speed of sound gets slower at altitude. It would need to do mach 1.6 to stay under the sun.