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Comment by anon84873628 | Hacker News Reader

Plus burnt jet fuel weighs nothing, whereas a spent battery weighs the same as a fully charged one.

It seems there needs to be a radical price difference between electrical and chemical energy before the virtues of the rocket equation are overcome for airline travel.

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Considering just how cheap renewable energy can be, even poor efficiency might not matter. If you have process that can be scaled by supply of cheap electric power, it could work even if there is inefficiencies in process and in use.

It's not generating the energy -- it's storing it. Fossil fuels are massively more energy dense than our current electric batteries.

Fossil fuels are literally dead animals pressurized by Earth... all that energy went into the fuel. Planets work on massively larger scales of energy than human society right now and we're using stored energy created by planets to fly.

> Fossil fuels are literally dead animals

By mass, fossil fuels are mostly from plants, algae, and bacteria rather than animals.

The energy is not exactly stored in the fossil fuels directly. Indeed you have to put in extra energy to break those bonds - pulling atoms apart is work. The “stored” energy comes from the fact that long time ago various processes split various compounds into two components, A and B. And putting them back together makes them snap like magnets with enough force to release some extra heat. We call A “fuel” since that’s the part that’s somewhat difficult to come by. We often forget about B altogether as it’s literally all around us. Fossil fuels are fundamentally efficient for flight since the oxygen is something you don’t have to carry around with you (unless of course you’re going to space).

It's not a matter of electricity cost, it's a question of watt hours per Kg. A battery powered plane cannot fly far, no matter how cheap electricity is, because the energy density just isn't there: https://en.m.wikipedia.org/wiki/Energy_density#/media/File%3...

I'm really talking about synthetic fuels made using electric energy.

Traditional fuels would also benefit from the cost savings of cheap renewable energy.

Don't forget watt per volume. H2 has great w/kg but poor w/liter.

A spent battery doesn't weight anything if you drop it once it's done; similarly the spent fuel has weight if you have to store the hot gasses after burning.

Turning a fossil fuel based plane carbon free has the same weight problem

Are you seriously suggesting that airplanes could just drop batteries weighing tons while flying across the sky?

Since this is HN, he probably is. And not only that, he is probably going to select this as his hill to die on. Good luck.

Filled with toxic substances, no less. There’s probably some treaties that would frown upon that.

It'd go over as well as a lead... acid battery

Li-Ion batteries at that! Ibdon't see any reason why regulator wouod object to that. Also, those batteries cost close to nothing, so yeah, just use as consumables...

I think the point was that the only reason burned fuel weighs nothing is because we throw out the waste into the atmosphere.

> a spent battery weighs the same as a fully charged one

A Tesla's battery pack weighs ~3.2 nanograms less when it's fully depleted. Think of the weight savings with a bigger battery pack for a plane! /s

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