[Kelbit]

Quick back of the envelope calculation:

Wing area of a Cessna 172 (representative GA aircraft) is 16 m^2.

Best-case insolation on a sunny day with no clouds at high noon is around 1000 W/m^2.

Best commercially available solar cells are the triple-junction cells used on commercial satellites, at about 30% efficient. They are horrendously expensive (around $50-100k per square meter), but we will ignore economics for now.

16 m^2 * 1000 W m^2 * 0.3 = 4.8 kW.

Powerplant for a Cessna 173 is a 160 hp piston engine, or 120 kW. So, we're about an order of magnitude and a half off. The cells also aren't massless, so they will add weight and reduce range... you'd need to do a cost/benefit there.

There are a couple solar UAVs in existence (example: https://en.wikipedia.org/wiki/Qinetiq_Zephyr) which use super lightweight materials and have very large wing areas to support solar cells. Even then, they are really on the hairy edge of where physics works in your favor.

[mrfusion]

Does it use the full 160hp while cruising though? I’d imagine most of that peak power is for take off.

[plantain]

Most of it is still used while cruising. 100hp+ depending on cruise speed. The excess power for climb is very small, which is why weight/loading is so critical in aviation.

[Gibbon1]

> The excess power for climb is very small, which is why weight/loading is so critical in aviation.

This is one of the reasons in favor hybrid electric aircraft. The marginal hp to weigh ratio of an electric motor is about 3 hp/lb or ~5.5 kw/kg. And partial load efficiency is high. Means you potentially have a lot more hp available on take off.

For commecial passenger aircraft hybrid turbofans wouldn't have spooling up lag like straight turbofans. Turbine engines take seconds to spool up. This big big problem with jet aircraft during landing. If you hit wind shear and/or need to go around you need to apply more power and sometimes the lag is fatal.

[AshleyGrant]

Aviation is an expensive market, so in some future world where a 75% efficiency of solar cells was available, it would be possible. And maybe even economically feasible at some point. Not any time soon though.

And the great thing about flying is that it's pretty much always a sunny day when you're in cruise.