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First before I say anything else, this is indeed a stupid question. It would be most likely heavy, bulky, and expensive.

But theoretically, is it possible to fly with only Solar energy?

What does it take to accomplish such task? The total cost? Probable shape and size? The power required to lift off such a stupid aircraft?

What does it take to lift off with a single average man piloting the solar-powered aircraft? Without a man?

If you did calculate the amount of power needed, for both lifting a man and not lifting anything but itself, what else could you used that energy for?

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  • $\begingroup$ Have you see this manned plane? Battery power to help with takeoff, solar after that. There was even a Nova show on PBS about it recently. theguardian.com/environment/2016/jul/26/… $\endgroup$
    – CrossRoads
    Apr 11, 2018 at 3:32
  • $\begingroup$ Do gliders count? Technically they fly with atmospheric airflows created by solar power. $\endgroup$
    – Manu H
    Apr 11, 2018 at 5:52
  • $\begingroup$ I believe Facebook is flying one or such planes. They are in the air 24 7. They provide Internet access to remote areas but the goal is to provide global Internet access. They have the wingspan of a 747. They charge their batteries during the day using solar on their body and wings and use that solar to power the aircraft and equipment during the day. At night the batteries take over $\endgroup$
    – securitydude5
    Apr 11, 2018 at 6:22
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    $\begingroup$ As a technology demonstrator, certainly, but not for practical transportation of goods or people. The energy available in sunlight, (~1000 watts/sq meter), even if 100% efficient, is not sufficient to provide enough power to push an aircraft through the air at the speeds necessary to make it useful. An aircraft that can only achieve 20 or 30 mph with a cargo capacity of a few hundred pounds is not going to replace hydrocarbon fueled aircraft. $\endgroup$
    – Charles Bretana
    Apr 11, 2018 at 9:02

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Not a stupid question at all! This was one of the goals that solar impulse I and II set out to show. one thing to keep in mind is that its of course only possible while the sun is shining. It was able to do it but the margin of error was fairly small,

During the day, the plane flies only by the energy from the sun. But in the morning and evening, when sunshine is not so strong, and especially at night, it must tap into its reserve of energy stored in its batteries. So every evening, the pilot must make sure that the plane’s batteries are 100% charged so that it can fly until the next sunrise.

Solar impulse ran on 8HP motors which is not much more than the Wrights first powered aircraft with a cruise speed of 56MPH it was not a terribly fast aircraft either but proved the concept was possible at a small edge of the spectrum.

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Several designs show that solar powered flight is possible. The actual design pretty much depends on the requirements. Solar Impulse 2 is maybe the most famous aircraft, but possible not ready for everday use. The Solar Impulse design resulted from the goal to fly around the earth and especially to be able to fly through the night, based on batteries that are recharged during the day. If you don't need the sustained flight over night, you can come up with other solutions. A pretty good example is the Sunseeker Duo.

The power required for level flight can be estimated by the product of total drag and airspeed. The drag itself can be estimated using aircraft weight and lift over drag ratio. This is why solar aircraft are very similar or even based on gliders, as they are designed for minimum drag as well as low weight.

To get an idea on the electric power and energy required to get a powered glider from the ground you might also have a look at the Lange Aircraft or the Front Electric Sustainer () propulsion concept.

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