[Plasmoid]

We're actually not that far off.

Right now, liquid fuels have about 10x the energy density of batteries. Which absolutely kills it for anything outside of extreme short hop flights. But electric engines are about 3x more efficient than liquid fuel engines. So now we're only 3x-4x of a direct replacement.

That means we are not hugely far off. Boeing's next major plane won't run on batteries, but the one afterwards definitely will.

[WalterBright]

> So now we're only 3x-4x of a direct replacement.

The math leads out an important factor. As the liquid fuel burns, the airplane gets lighter. A lot lighter. Less weight => more range. More like 6x-8x.

Batteries don't get lighter when they discharge.

[Qwertious]

It's not that simple.

Batteries are inherently more aerodynamic, because they don't need to suck in oxygen for combustion, and because they need less cooling than an engine that heats itself up by constantly burning fuel. You can getvincredible gains just by improving motor efficiency - the difference between a 98%-efficient motor and a 99%-efficient motor is the latter requires half the cooling. That's more important than the ~1% increase in mileage.

Also, the batteries are static weight, which isn't as nightmarish as liquid fuel that wants to slosh around in the exact directions you want it not to. Static weight means that batteries can be potentially load-bearing structural parts (and in fact already are, in some EV cars).

The math leaves out a lot of important factors.

[giobox]

Not to mention that jet planes routinely take off heavier than their max safe landing weight today too, relying on the weight reduction of consuming the fuel to return the plane to a safe landing weight again while enjoying the extra range afforded. This trick doesn't work well with batteries either.

[breve]

> Boeing's next major plane won't run on batteries, but the one afterwards definitely will.

Jet engines work better. Boeing's next major plane will have jet engines, just like their previous major planes.

Synthetic, carbon neutral jet fuel will be the future for commercial jets.

[capitainenemo]

Well, there's also burning regular fuel in a fuel cell, a FCEV. That doubles the efficiencies over ICE, so I guess that bumps it back up to 8x away?

Given the great energy densities and stability in transport of hydrocarbons, there's already some plants out there synthesising them directly from green sources, so that could be a solution if we don't manage to increase battery densities by another order of magnitude.

[WalterBright]

> there's already some plants out there synthesising them directly from green sources

I didn't realize that a "green" carbon atom is different from a regular carbon atom. They both result in CO2 when burned.

[rgmerk]

Hmmm. If we do simple extrapolation based on a battery density improvement rate of 5% a year, it takes about 30 years to get there. So it's not as crazy as it sounds - and it's also worth noting that there are incremental improvements in aerodynamics and materials so that gets you there faster...

However, as others have pointed out, the battery-powered plane doesn't get lighter as it burns fuel.

[crote]

If we do simple extrapolation, a cellphone-sized battery will reach the 80kWh needed to power a car in as little as 180 years.

Expecting a 5% / year growth rate sustained for 30 years is very optimistic. It is far more likely that we'll hit some kind of diminishing return well before that.

[TheSpiceIsLife]

More accurately, the calculation needs to factor in the fact that battery weight doesn’t decrease as charge is used.

Commercial aviation’s profitability hinges on being able to carry only as much fuel as strictly[1] required.

How can batteries compete with that constraint?

Also, commercial aviation aircraft aren’t time-restricted by refuelling requirements. How are batteries going to compete with that? Realistically, a busy airport would need something like a closely located gigawatt scale power plant with multi-gigawatt peaking capacity to recharge multiple 737 / A320 type aircraft simultaneously.

I don’t believe energy density parity with jet fuel is sufficient. My back of the neocortex estimate is that battery energy density would need to 10x jet fuel to be of much practical use in the case of narrow-body-and-up airliner usefulness.

[WalterBright]

You laid it out better than I. Thank you!

[abdullahkhalids]

An A320 can store 24k liters of fuel. Jet fuel stores 35 MJ/L. So, the plane carries 8.4E11 J of energy. If that was stored in a battery that had to be charged in an hour 0.23GW of electric power would be required.

So indeed, an airport serving dozens or hundreds of electric aircrafts a day will need obscene amounts of electric energy.