Making gasoline for cars from renewable energy isn't going to happen. The end to end efficiency of that process (Hydrolysis, CO2 capture, Fischer Tropf) would likely measure in the single digit percentages. Charging a car battery (especially from local solar) can be over 90% efficient.

When you include the very low tank to wheels efficiency of an ICE vehicle, the overall efficiency is even worse.

> Hydrolysis

Self-correction: I meant electrolysis, not hydrolysis

That isn't really "renewing", though. If part of the process involves the substance being dispersed in the environment and then extracted again, that's different from capturing waste as it's produced. Furthermore, you're not necessarily capturing the same carbon dioxide that you released, but when you recycle a battery, it's the same lithium. And getting the lithium from a battery should take less energy than mining it, while capturing and reducing carbon dioxide definitely requires more energy than pumping oil from the ground.

So I don't think this analogy holds up.

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.

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.

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.

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.

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.

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?

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.

> 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.

> 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.

[delayed]

Yeah, I meant figuring out how to do it so efficiently that it becomes preferable to batteries for powering cars. We talk like it is certain that battery-powered cars will win out, but I haven't seen a proof that that is how it must turns out if we learn to create nanomachines that use solar energy to suck carbon from air.

Unfortunately, physics says battery-powered cars have won.

Using solar to power a process to make a fuel before burning a fuel that at best (way less in reality) uses 2x more energy than just powering an electric motor directly is not sensical.

And the battery makes the car 1.3 times the weight of a gas-powered car. Making the battery requires much more energy than making a gas tank. The charging infrastructure might prove more expensive than a network of gas stations. Long trips are punctuated by idle periods needed for the battery to charge, so the car's "utilization rate" is lower than a gas-powered car. All I am saying is that it is not 1.00 certain which technology will retain the lowest total cost of ownership as both technologies improve, although yeah battery tech is the likely winner.