The Achilles heel of electric aviation is that batteries don’t shed weight as they discharge. A fundamental aspect of Aerospace engineering is that rockets/planes shed a lot of weight during flight by by burning fuel. Many big jets take off at weights far too heavy to land and long ranges are only possible because of all the weight shed in flight.

Until that issue can be addressed with electric aviation, electric planes will be a concept limited to very short range flying.

Rockets solve this problem by dumping the dead weight overboard but not sure a bunch of dead airplane batteries parachuting back to earth is a viable approach.

Don’t conflate rockets and airplanes. Most of the energy an airplane uses is to overcome parasitic drag – to overcome the air resistance caused by moving forward through the air mass. While some of the energy is used to keep the plane in the air, that is not dominant. Yes, planes have a higher maximum takeoff weight then maximum landing weight, but that has to do with the design of the landing gear, in some hypothetical world where jet fuel did not shed weight, planes would only have slightly worse range.

The real problem with electric aviation is that batteries have terrible weight to energy ratios compared to fossil fuels.

It’s pretty clear that battery technology and cost efficiency is going to have to advance substantially before it can have a meaningful impact on air transport.

Blimps might be a slight exception.

I remember Sid Smith saying that we have enough lithium in known reserves to replace every car on earth one time.

https://www.youtube.com/watch?v=5WPB2u8EzL8&t=35m29s

https://www.cell.com/joule/pdf/S2542-4351(18)30292-7.pdf : "Lithium Metal Extraction from Seawater"

> Based on the consumption rate projected for 2050, the residual lithium reserve on land will be exhausted by 2080

> In contrast, the ocean contains 230 billion tons of lithium, an amount four orders of magnitude larger than the lithium reserves on land

> our prototype device can be powered by a solar panel and metallic lithium can be directly generated during the lithium extraction process

What exactly do they mean by "seawater"? Not all seawater is exactly the same, chemically speaking. I have actually measured "seawater" before, and the chemistry of the water at a single location can vary wildly from day to day. I just want to know under what conditions they tested their prototype!

THIS IS NOT BAD FAITH FAUX IGNORANCE. I AM ACTUALLY CURIOUS ABOUT THIS.

Lithium content varies as much as salt content, but one thing is certain: the open seas are consistently salty.

That's only if you take the average of all the measurements collected across the entire ocean for decades. In one spot, salinity is not consistent. Patterns of evaporation and rainfall affect not only salinity but also the presence of organic matter and other random contaminants. Such fluctuations are most pronounced at the surface, where this device is meant to operate.

It's the substance that composes those 75% of the surface of our planet that we call "sea".

How much seawater does that process per day?

Yesterday I learned that Sodium batteries might become a contender to Lithium batteries. And they are safer.

Sodium is very clearly a contender for stationary batteries. It may even be competitive for surface mobile applications like cars... But there is just no way it can compete on air transport.

I keep being intrigued by vanadium redox flow batteries, and I've seen some in the real world in stationary applications. And the prospect of instant charging by spit-swapping in a mobile application is pretty wild.

How scarce is vanadium, though?

Vanadium has an horrible weigh/charge ratio. That's why it's used in stationary applications.

Sodium redox flow batteries are all the hype nowadays, because sodium is much cheaper, sulfur for the oxydizer is also very cheap, weight/charge is very high, and volume/charge (important for stationary applications) is also much higher. But I think it's stuck in a patent minefield.

It’s like 2 percent by mass of spent iron slag.

Now now, no need to be rude.

/

Or just use hydrogen, it's a much denser energy storage medium, and airflight is less cost sensitive than ground transportation.

> just use hydrogen

At that point, why not package the hydrogen on a carbon chain...oh wait.

A lot of these schemes compare poorly against synthetic jet fuel manufactured from atmospheric carbon.

Likely the issue is cost. We can make liquid H2 pretty cheaply these days. We don't know if synfuel can get close to that price.

Or not bother with air taxis, civilisation won't collapse because some rich arsehole can't get across New York in five minutes.

It also won't collapse because some rich arsehole won't be able to post comments on Hackernews from their smartphone.

Sure, but on another hand we should encourage the rich asshole to spend his money so it could be useful to the rest of the economy.

But does it?

Just because it got a battery, it doesn't mean it actually solves the issue "getting around without taking forever and wasting resources" well. In the long run, it would be better to reduce commutes. And that's something we can do with some policies, on paper. No need to invent human slingshots or anything.

If climate casualties become serious, people might start questioning whether allowing people to be rich and be assholes and not contribute to solving the problem is sustainable...

Universal basic income and massive carbon taxes to pay for it!

It’s about time we tax actual destruction, not a minimum wage earner’s Netflix subscription.

Best way to do it I've ever seen is the automated transactions tax, whereby you replace most taxes with a small percentage taken on every financial transaction (plus a larger one when converting to/from cash to account for the black economy).

It's progressive because poor people will only pay twice (once on their salary/benefits, once when buying stuff), whereas rich people will pay several times when moving money around.

Expect a new class of companies to spring up overnight that are dedicated to bundling transactions to avoid this new tax. For instance, I could make a single transaction to my broker that covered all of my expected expenditures for the month, and that broker would then disburse it to my payees, bundling it with funds from other payers to avoid the tax on the other end.

I am strongly in favor of a tax on all stock market transactions, though—anything to deter HFT, which IMHO has little societal benefit while externalizing a ton of risk.

Wouldn't work. Tax law can tell the difference between an individual transaction and bundled transactions. It's also the only area of law that allows for ex post facto changes to the criminality of acts.

Tax law already handles much more complex schemes. Admittedly nowhere near perfectly, but then this scheme being simple frees up resources for policing, and the tax code being much simpler makes it less easy to exploit.

Why tax the income side when you could just tax the consumption side?

Taxing consumption is regressive; Bill Gates can't eat that many more hamburgers than the average person.

Write everyone a cheque.

Taxing income is quite regressive too: it’s how people with nothing can survive.

Taxing income at a few % as this scheme intends is not regressive.

For simplicity's sake. All transactions are taxed equally, no way to evade it by making false or borderline claims about the nature of exchange, and no resource have to be wasted on optimizing or litigating them.

Hydrogen is denser by weight, but by volume the story is completely different. The tanks need to be large.

What if most of the aircraft was hydrogen tank or bag? Then it could use the hydrogen for some of its lift! We can call it an "airship".

Or compress the hydrogen, but then you have 700 PSI handling issues and the tanks have to be very strong.

> We can call it an "airship".

Yeah, let's make a huge one and call it the Hindenburg! That sounds like a foolproof plan.

Too bad that there hasn't been decades of materials science improvements, including and in particular to handling flammable materials, between some highly propagandized disaster and today.~

(Almost every modern cruise ship is bigger than the Titanic, imagine if people acted like the Titanic was the last word on how big a cruise ship could get.)

In the chart from the article I see that capacitors are shown as having high specific power. Would it not work to use a hybrid approach of capacitors for takeoff and then Li-ion for most of the flight? I know it would make the system more complicated and therefore more expensive up front, but I wonder if it's an option or if it's out of the question for one reason or another. I've read that supercapacitors are being used for busses and other applications. https://en.wikipedia.org/wiki/Supercapacitor

Capacitors are great for high load requirements but not great as an energy storage device. i.e. if you wanted to draw several hundred amps for a second or two with relatively low heat waste, an ultra-capacitor arrangement would be the way to go, but for energy storage, a battery wins hands down. There's huge research going into expanding the capacity of capacitors.

Check out this video about capacitors: https://www.youtube.com/watch?v=EoWMF3VkI6U

PS -- author here, happy to discuss.