[kelnos]

I'm having trouble seeing how it'd be feasible to do all that while expending less energy than you can get out of the resulting gasoline.

But we demonstrably get more energy out of the useful life of a solar panel than we have to put in to manufacture it.

[eru]

Producing synthetic fuels for internal combustion engines doesn't really makes sense for cars: electric cars are good enough.

But it might be necessary for 'green' planes, if the energy density of electric batteries does not improve enough.

[gibolt]

Electric cars are better. Less moving parts/maintenance, quicker, 3x as efficient, can be charged nearly anywhere with existing infrastructure and no ongoing supply chain requirement (fuel delivery).

Energy density is steadily increasing. Hydrogen will be a short-term solution for medium/long haul flights, but will eventually be replaced by batteries.

[eru]

Why would you ever want to use hydrogen? It's essentially a terrible battery with terrible fuel density (if you take into account the weight and volume of the tanks required to contain it).

Either go with an electric battery, or go with a hydrocarbon like kerosene or methane or so.

[_hypx]

You are basically ignore the laws of physics. There will never be a airplane with decent range running on conventional batteries. Even now, battery powered airplanes are just powered gliders or ultra-lights, not something that will send real passengers.

[eru]

What do you mean by 'conventional batteries'? You need to add some assumption so that you can say powering a plane with them is physically impossible.

I made the original comment contemporary batteries ain't good for electric planes. And I would not bet on batteries becoming good enough anytime soon.

But I don't think physics prohibits anything here?

[_hypx]

Anything that works like existing rechargeable batteries. Those would be considered conventional batteries. There is basically no path to a high enough energy density for airplanes for those types of batteries.

Things that involve metal-air reactions are basically fuel cells and don't count. If you go down that route, you'll quickly find yourself working with some kind of chemical fuel. They will suddenly look a lot like existing airplanes in terms of basic concept.

[eru]

> Anything that works like existing rechargeable batteries. Those would be considered conventional batteries.

Ok, that definition works.

I would have gone with 'whatever people (in the future or now) use for powering their phones, laptops and electric cars' is by definition 'conventional' at that point in time.

[matkoniecz]

> I'm having trouble seeing how it'd be feasible to do all that while expending less energy than you can get out of the resulting gasoline.

Use biological solar panels AKA plants.