Ultralight lithium-sulfur batteries for electric airplanes | Hacker News Reader

Ultralight lithium-sulfur batteries for electric airplanes

spectrum.ieee.org

217 pointspross356176 comments

Here's a fun bit: in the article they say that lithium-sulfur is hard to measure charge level for due to the voltage properties of charging and discharging.

"The upshot is that voltage is not a good proxy for the state of charge and, to make things even more complicated, the voltage curve is asymmetrical for charge and for discharge."

Since it would be bad if your battery suddenly died and you dropped out of the sky, they had to develop complex statistical and neural network algorithms to accurately determine state of charge to within a few percent. One black box for staying in the sky and another in case you end up on the ground!

Or you could do what they did on Apollo (forget if it was the CM or LM). They had the problem of measuring how much was in a tank, but the tank was in 0G, so a float is no good. The proposed solution was some sophisticated radiation based thing where they measured the attenuation of some radioactive source through the tank. This wound up being highly complex, and the solution was simply to have a reserve tank. When the main tank ran out, you knew you had exactly the amount in the reserve tank.

This is the solution used on motorcycles (which don't usually have fuel gauges). There's only one tank, but in the normal position you get fuel only to a certain depth.

As you're riding along, if you notice the engine running out of fuel, you reach down and flip the fuel switch and you have access to a little more fuel (and you know to head to a gas station soonish).

For motorcycles people often just use the trip odometer to estimate fuel used. Interestingly, this is similar to coulomb counting which is one of the more common methods of state of charge tracking. Technically coulomb counting would be more analogous to measuring the amount of fuel being pumped out of the tank.

Just for correctness: A vast majority of new motorcycles for quite a while have had fuel gauges. There are only a few brands who are obtuse about it (e.g. Aprilia).

More like sports bikes don't have fuel gauges (saves weight, amirite?) and make do with low fuel warnings instead, which serves the same purpose as a reserve tank without the need for a switch.

Neither my MV Agusta nor my BMW S1000R have fuel gauges. The BMW does the odometer trick itself though to estimate remaining mileage. It's often way out of course, depending on throttle usage.

(It's possible the BMW has a meter but it doesn't present a level, only miles remaining. I still think it's a style thing - something you don't put on sport bikes.)

Pretty sure all the S1000R years have fuel, but yeah it's as miles remaining. S1000RR didn't have anything until 2019.

It never really made any sense, but now that race bikes have tire pressure sensors and full color LCD instruments it is really spectacularly dumb to not have gauges.

Any of the popular crotch rockets have had fuel gauges forever. I think it's mostly just crazy race/rep bikes like BMW and Aprilla (so i guess the guys that only make sport bikes in 300 or 1000+) that don't have gauges

But I bet they still have a reserve and a 3-way fuel knob ( closed, main, reserve ).

On fuel injected bikes, the fuel switch (on/off only) is on the fuel pump, generally bolted to the underneath of the tank, and not reachable while riding.

Oh thanks. My motor-driving skills and knowledge are getting rusty :-)

downsides:

- when you're in heavy complicated traffic and the engine starts cutting out

- when you forget to flip the switch back after filling up

- you more modern motorcycle with a "reserve" indicator below the speedometer (which is below your field of vision when riding and you don't notice)

Another possible solution is to measure how much fuel (or energy) got in and how much is getting out. You know the nominal capacity and you know the flow rate.

That technique is called Coulomb counting and is the standard way of giving a precise battery charge percentage for lithium based batteries. The battery capacity estimate is improved over time based on the previous observed amounts of energy to enter or leave the battery.

You'd have to account for charge losses (Some energy ends up just being heat while charging) but that could probably be simply guestimated on battery temp while charging and some constant factor.

For example, assume a 90% charge efficiency for a battery at 20C... or whatever makes sense.

Same trick is used on some external tanks for outboard engines: the tank has a raised separator in the bottom so that reserve fuel will be caught away from the engine intake. To access the reserve fuel you need to briefly tilt the tank.

See e.g. https://imgur.com/a/9LsrjIR

They could've put a variable-sized bladder in the tank, and measured the internal pressure.

Right?

State of charge tracking is tricky even for lithium ion batteries. I worked on it for a bit as part of a solar car competition. Usually it involves a mix of coulomb counting and voltage measurements. IIRC, a handful of laptops and consumer electronics have trained neural networks to assist in estimating SOC.

As far as aircraft goes, it's sufficient to put a lower bound on the remaining charge. Realistically, the poor (abysmal, really) energy density of batteries pretty much precludes their usage in any serious aircraft. For sustainable air flight I'm more optimistic about syngas or hydrogen.

I've always wondered about those one-use aluminum-air batteries one guy was developing. (search for tevor jackson aluminum air battery)

They might be more palatable for aircraft.

Batteries are fundamentally unsuitable for aircraft. The energy density is easily an order of magnitude lower than thermochemical fuels: https://en.m.wikipedia.org/wiki/Energy_density#/media/File%3...

Furthermore batteries don't get lighter as their charge is expended, as opposed to fuel that gets burned off. This means a plane powered by batteries has to land with the same mass of fuel as it does when it takes off. Many aircraft are worse at decelerating themselves than accelerating. This means they can actually take off with more mass than they can land, thus extending their range. This can't happen for battery powered planes.

Hydrogen powered planes is less far fetched than it seems. The Soviets built a prototype: https://en.m.wikipedia.org/wiki/Tupolev_Tu-155

Cryogenic storage of hydrogen is less difficult than it seems. Because the engines are constantly drawing fuel from the fuel tank, the tank's pressure is constantly dropping which cools it down. Most of the difficulty around hydrogen storage is in long term storage where hydrogen permitting through the vessel is a concern. The main challenge for applying it to aircraft is being able to make a vessel light enough and in a form factor suitable for planes, namely fitting it in the wing.

Let's just use RTGs instead! A gram of Polonium-210 produces 140W of heat. It's also an almost entirely alpha emitter, which means that little shielding is required. At about a 10% efficiency of an RTG you could effectively get 14W out of a single gram of it. A 737-300 seems to require about 7-10 MW of energy at level flight. Put 1 ton of Pu-238 onto a 737-300 and you can run the aircraft (probably) for 6-7 months without refueling. Okay, you probably need a smaller aircraft, because takeoff takes more energy, but still!

While Polonium-210 is incredibly toxic, it does have a half-life of 138 days. If you do have a crash then in <8 years you'd only have about a gram of it left.

The main tricky part is that we produce about 100 grams of it a year. But what's a little scaling up for a startup anyway?

(I'm sure I made a calculation error here somewhere.)

There might not be any math problems, except on how are you going to reject 10MW of thermal heat from inside the airplane at all times

You need 4 engines. After you land, you run 2 engines forward and 2 in reverse.

Note that you will only have 1g of polonium, but dispersed in 1T of lead, which is less toxic, but not really environmentally friendly.

I could make the argument that fuels that burn are unsuitable for automobiles which crash into each other frequently.

But yeah, I think it would need lots of development to get battery technology to do something like a ny-tokyo flight. It might only work for short hop service.

I guess that's how it has worked for battery electric trucks. The first one basically did short, known routes around town with lots of stop/start. That controlled the parameters and made it feasible. I don't know if battery powered trucks will ever replace long-haul trucks unless batteries get lots better or charging gets really fast.

> I could make the argument that fuels that burn are unsuitable for automobiles which crash into each other frequently.

Lithium ion batteries don't like crashing into each other either. The article mentioned that lithium sulfide batteries degrade differently than lithium ion, so fires as a result of heavy use may be reduced, but fires as a result of unscheduled disassembly seem likely, and could be worse than fuel --- you can dump fuel or circle to use it up, but you can't (probably) dump batteries, so you're always going to have lithium available. Not sure if the lithium sulfur compounds are less flamible than the compounds found in lithium ion.

You're correct that batteries are much more suitable for cars, especially commuter vehicle and things like garbage trucks that have relatively limited routes and sit idle for much of the day. There's why were seeing electrification take hold in cars, way before it takes hold in planes (if ever).

Diesel fuel won't burn as gasoline does. Gasoline is ok here to, if compared to a hydrogen-oxygen mixture explosion ;)

Look at some yt videos of li-ion or li-po fires, this will change your mind

Ah, simply have separable battery modules that you drop from the plane as their charge is depleted. Put pop-out wings on them and use gps guidence so that they glide back to recovery centers on the ground, which you've had the foresight (and funding) to build in sufficient density along any likely route your plane might operate. Problem solved.

I'm joking, mostly.

Periodically they would fall over landing on the recovery barge and explode, but that's to be expected. :)

(and your idea is brilliant, it should jokingly be called "blue ice")

I wonder if changing battery packs by drones in-flight would be feasible

No clue how technically feasible this is, but conceptually I like it:

Have 10 small batteries, that you go through one by one, instead of the single big one. You only need to start worrying on the 10th one.

It could work, and it'd certainly give you a good 'ground truth', but there's a couple of reasons currently why it's probably not the best option. Batteries tend to wear out faster when they're deeply discharged, and when they're discharged rapidly. This approach would rapidly, deeply discharge some of your batteries instead of slightly discharging all of them. You could work around it with a sort of 'wear leveling' type battery management system but you'll still be reducing the life of the batteries compared with using the cells all at once.

So it's kinda like RAID 4 then?

In RAID 4 you had a dedicated parity disk. What if you allocated one of your 10 batteries as the "parity". It would not be used until the others had ran out of charge (as originally expressed above)

And to prevent uneven wear levels, each time you plug in to charge, the parity battery changes to one of the other 10 randomly (or on a pattern but the end result is the same).

So over time, assuming your prng was decent, you would have an even wear level.

You'd probably want maybe two batteries as your parity in case of failure but it would still work.

I'm on my first coffee and it hasn't properly kicked in but it sounds plausible in my head :)

This idea certainly has more legs than the first one. It's like a battery equivalent of the reserve tank that motorcycles (used to?) have. You run until the engine cuts out, then you flip the valve to switch to the reserve tank and you know you have at least 100km or whatever left to find a petrol station.

Reserving, say, 10% of your overall capacity would add much less strain on the system and still give you the most important part of the results. Conventional techniques such as Coulomb counting and estimation from voltage are still probably more practical but it's fun to consider alternatives. :)

Also, lithium batteries which have a higher total capacity can deliver more consistent current with less strain and voltage sag, so it's advantageous both for performance and longevity to have bigger cells.

If you have the ability to tell when you get somewhere in the region of 10-30% charge, you could always switch there and not deep discharge unless you really have to.

The discharge rate could still damage the batteries.

Can you just measure the current coming out of the battery and keep track of it?

AKA joule counting- for normal li-ion it gets you to ~5% most of the time, up to 20% off at the start and end. That's assuming the voltage stays constant the entire time- in reality the first bit is at 4.2+ volts, and the last bit is down to ~3 volts. That's a 40% energy difference per electron that leaves the battery.

It's also one of the reasons you get electronics that die suddenly at 5%- current gas gauges usually account for it, but older stuff wasn't always good at knowing when the voltage would drop off. Nowadays (and always, for the most part) the sudden shutoff is because electronics often pull very brief power spikes that drop the battery voltage below the minimum voltage temporarily. The chemistry takes a moment to recover after that.

The problem with Li-S batteries isn't just that they have a goofy curve- that can be charted and saved, even as the battery degrades (Note- I'm mostly up on conventional chemistry. Don't know much about Li-S). It's more have a couple phases they go through during discharge. Impedance and other properties of the battery change, which changes the discharge characteristics of the battery, which changes the voltage. Proportionally, the swing in voltage is also larger (although this kind of thing is always changing, so I may be out of date).

There's also a small amount of self-discharge and parasitic reactions that will consume electrons, but that number is necessarily fairly small and predictable. The main thing is that 50% of the energy variance is in the voltage, and you need to know a lot about the current chemistry inside the battery (as well as the future load profile) to be able to predict the voltage that all the remaining electrons will have as they leave the battery.

Many battery monitoring circuits do this, sampling both voltage and current to compute power over time. With a suitable inductor to limit the rate of current change to be within the nyquist sampling interval of the monitor, you can pretty accurately measure charge going in or coming out of a battery. Combined with a model for the battery and you've got a modern battery monitor circuit.

You could use this technique to estimate the remaining capacity starting from a full charge / known charge, but not to arbitrarily measure the remaining capacity of the battery

It sounds like the voltage curve is all over the place as the battery phases through its chain of different chemical reactions, unlike a normal battery. I take that to mean there's no way to just measure the voltage at a given point of time to estimate capacity, hence why the statistical method was required.

It's a good thing to measure the instant capacity, but the voltage and current (and, hopefully, thermal output) are being measured during the whole flight.

I added a shunt based AH meter to my RV that does this, seems pretty standard tech, not sure what the big deal is:

https://www.magnum-dimensions.com/battery-monitor-kit

This makes me wonder how accurate float bulb based fuel level sensors really are. This sounds like a major problem and the solutions are interesting but potentially even better than what we are used to.

My 1990 Toyota never read full. The buffer on the fuel sender was so extreme that by the time the needle made it to the "F" I had already burned 1/8 of a tank! My current car warns me when I have about 50 miles of fuel left, I wonder how much historical data it uses in that calculation.

None of my motorcycles even have fuel gauges. I just keep an eye on the odometer and when I stop to stretch my legs I give the tank a shake or a peek.

They're pretty inaccurate in light aircraft where you're often flying at an angle / slightly asymmetrically; in commercial airliners, under most flight conditions, they're generally within a couple percent. Aircraft will generally use fuel flow sensors and use those to calculate remaining fuel (by integrating the fuel flow over time) and float/capacitance sensors in tanks are used as verification / a sanity check (which can sometimes only end up being noticed inflight, eg https://www.flightglobal.com/safety/boeing-modifying-777-fue...)

For more than you'd ever want to know about the fuel systems in a modern airliner, see http://www.b737.org.uk/fuel.htm

> This makes me wonder how accurate float bulb based fuel level sensors really are.

They aren't. On light aircraft, the only thing they're good for is as a double check on a manual fuel reading (using a dipstick) or a time-based calculation, and to confirm during flight that the fuel cap wasn't left off. Beyond that, the needles bounce around so much during flight the only thing you can really verify is "yes there's some liquid there; somewhere between empty and full".

Many light aircraft owners have since retrofitted "fuel totalizers" which measure fuel consumption, and are manually reset by the pilot to a dipstick value when fuel is added. My group aircraft's fuel totalizer seems accurate to within at least about 10%. It can be calibrated better, but manual dipstick readings are only accurate to a couple of gallons anyway.

However, one key difference is that I do know, to within about half an hour, my fuel endurance before departure. I'd want the same from a battery.

> float based fuel level sensors

I initially read this comment thinking you meant floating-point based...

Dang floats ruin all calculations!

Hah, didn't even think of that! I made a small edit to clarify.

Just pointing out that the engine dying does not imply you'll free fall from the sky.

I went on a ride in a jet trainer. The instructions I got were "We only bail if there's an engine fire. If the engine goes out an I can't restart it, we glide to one of these airports; this plane is an excellent glider." On bailing out "it came with ejection seats, but the government doesn't like us having explosives, so we use parachutes."

Ejection seats are bad for your body.

> Oxis recently developed a prototype lithium-sulfur pouch cell that proved capable of 470 Wh/kg, and we expect to reach 500 Wh/kg within a year.

Meanwhile, gasoline / petrol / benzin (wherever you are in the world) has an energy density of 12200 Wh/kg.

In other words, even in a world where all petroleum is perfectly depleted, we would still be producing synthetic gasoline for high-demand applications and capturing 100% of the emissions for recycling — essentially using gasoline as a battery. It’s just too good an energy storage to ignore.

I’ve been looking at cars and geeking out on internal combustion engines for the past few weeks since I had to buy a car, and for the usual Silicon Valley guy such as yours truly whose standpoint on cars hadn’t been much more than ‘I want a Tesla’, it was an outright revelation.

ICEs are real technology — and for a software guy it is easy to understand because the complexity is bounded by physical dimensions of parts (i.e they don’t work past a certain small size) so you literally see human-size machinery with human size movements. It’s been a refreshing change from potentially unbounded complexity of software.

Electric motors are simpler, more reliable, smaller, lighter, almost perfectly efficient, and have better torque characteristics than ICE.

You can't compare the energy storage density in isolation. Engines are heavy...Model S's motor generates 362 horsepower (according to the official specs), and only weighs 70 pounds...the equivalent ICE would be 500+ :-)

(Yes, the inverter weighs something, but the transmission is much simpler as well for electric...overall you save a few hundred pounds easily...A Model 3 battery pack is between 600 and 1000 pounds--so pretty close to the crossover point.)

We're still not at the point where weight savings from motor offsets battery. Tesla cars are all extremely heavy for their size

Not by much. The Model 3 is approximately 1 person heavier than a comparable BMW 3 series. The Model 3 Long Range is about one person heavier than a 3 series wagon.

The BMW 330i is about 660lbs lighter according to some questionable internet sources for curb weight

Base Model 3 is 1611kg vs 1545kg for a 330i. I'm looking at both a 330e and a Model 3 at the moment or maybe an M340i xdrive touring.

The mass is a problem of you don't t recuperate braking energy. Tesla's do recuperate braking energy. A heavy ICE driven vehicle in contrast just loses braking energy as heat.

Edit: typo

Energy recovery from regen is minimal unless you're stuck in stop and go traffic. Usually less than 5%.

The argument made wasn't so much about getting more range from regen as about regen lessening the impact of added mass: with perfect regenerative braking, a ten ton vehicle wouldn't use much more energy than a one ton vehicle if they shared the same outer hull.

Real life doesn't have perfect regen, but on the other side of the equation real life ICE cars actually lose more efficiency to added weight than just what is converted to heat while breaking because they tend to compensate worth a bigger engine to get comparable (or better even) acceleration than a lighter counterpart and that means that during cruise where the mass is irrelevant the engine is running at all an even worse load point in terms of efficiency. ICE are terribly inefficient at partial load and when your engine is sized to get decent acceleration despite high total mass you simply can't gear long enough to get the engine to a reasonable load point in a moderate speed cruise. Electric motors don't have this problem (or a much, much smaller version of it), so they wouldn't suffer quite as hard from added mass as ICE even worth no regen at all.

> ICE are terribly inefficient at partial load

Yes, but this doesn't happen much anymore. Torque converter, electronic throttle control, variable valves, and 6+ speed gearboxes means the engine is usually near full throttle even if your foot is barely on the gas.

Turbochargers also help, along with cylinder deactivation for some V8s.

Modern engines are nearly always at a relatively efficient load point. This wasn't true until about a decade ago though.

A Prius or Ford Fusion hybrid get better MPG in city driving than highway. That's because regenerative braking recovers most of the energy needed to get back up to speed. The improved MPG has more to do with higher drag at high speeds which reduces efficiency.

Unless you're stuck in stop&go traffic, the extra energy needed to move the extra mass isn't particularly large either.

It highly, highly depends on motor setup.

Tesla low gearing induction motor is by far not the best here.

Synchronous motors have much better regen capability.

There's just not that much power available for regen. I've done a lot of dicking around with E-scooters. Even at their low speeds with lots of stop and go, regen is less than 10%.

It's only used because dumping excess energy back to batteries is cheaper than including brake hardware. The math may work out the same for EV's. Regen just to decrease the cost of brakes rather than increase range significantly. In the e-scooter world, the cheap ones use regen and more expensive models have traditional disc brakes.

Air resistance burns a ton of energy at any speeds over 20mph.

How much RPM were you getting at your scooter, and what was the vehicle mass?

You say 5% at most... The difference in between, say, 5% and 10%, a bad and good regen is huge.

The RPM's are huge. Like 16k, because smaller motors are lighter for same power. Mass is generally 40lb + rider.

The RPM doesn't matter much though. Regen efficiency is around 80% from wheel to battery. With cars you get much less regen because you lose tons of energy to air at the speeds they travel.

Mass also increases braking distance and reduces handling, no?

First off, 48 volt systems doing regen is already taking off, and there are already many new cars doing it (not just ones that have a hybrid sticker on them either: https://en.wikipedia.org/wiki/Mild_hybrid#Examples)

Second, as other comment says, the idea that braking regen is going to make up for an extra half a ton of batteries is pretty laughable

Also the ice is only 30 percent efficient, where the electric is around 95. So take the energy density /3 for starters.

While your point is arguable what is not arguable is that the weight in a Tesla is very much evenly distributed across the chassis and has a very low center of mass which leads to excellent handling. Whereas an ICE typically has a big heavy engine up high and at the front of the vehicle which puts the vehicle's center of mass way out of whack.

> the equivalent ICE would be 500+

It's not quite that heavy. An LT1 makes 500 horsepower and weighs less than 500 pounds.

It definitely varies, though under 400 lbs would be tough to find....it takes a significant amount of effort to make a light, high power engine. Electric motors OTOH are well understood, and relatively easily engineered.

The point still stands though. You're savings a few hundred pounds compared to an ICE, but you're losing more than in battery weight. An x2 (or maybe even x1.5) increase in battery density, and a (ground up) electric vehicle will almost always be lighter than a similar conventional car with a full tank of gas.

Are you including the transmission?

Teslas have a transmission, but it's not in the same league of complexity or weight.

Forgot about that on my longer reply. EV engines are _tiny_ and incredibly efficient.

However you are ignoring that while you can spin the blades more efficiently, however scaling an electric motor to that size may end up with even more weight, you also have to replace the turbojet portion of these motors. So you will need even more engine. That turbo jet is more efficient at speed while the fan is better at lower speed.

In the end we would have slower planes but we will eventually reach a point where we can do it.

Someone can probably explain it better and my understanding is rough and not current; jets were cool when I was kid

Your speculation about motors is incorrect; motors are actually more efficient the larger you build them. It's a property of the goodness factor: https://en.wikipedia.org/wiki/Goodness_factor

It is profoundly foolish to compare motors and heat engines on first principles like this, obviously. Still, here's a turbine that handles 30x the power of a jet engine, running a generator that is about the same size as a jet engine: https://www.ge.com/news/sites/default/files/Reports/uploads/...

generator is in the upper left. Obviously not at all optimized for size or weight- there aren't even any magnets in that thing.

You're making the parent comment's point, ICE != ICE

Mercedes is selling cars with an engine that weighs 354 lbs, with just 2 liters of volume. Now 354 lbs is still pretty heavy, but it's 354 lbs with fluids and accessories.

Some (many even) of those accessories have equivalents on a Tesla that aren't included in saying it weighs 75lbs, like pumps for coolant and the AC compressor

But the two aren't at odds, o e could use an electric engine and still burn gasoline to produce the electricity, sort of like ships do.

Sure. The average car gets 25 mpg, consuming ~1400 Wh/mi. A Tesla Model 3 uses ~240 Wh/mi. Thats almost a factor of 6 difference. You don't need quite as much energy when you are significantly more efficient and it is only getting more efficient as time goes on. Also add in the factor of recovering energy using regenerative braking which is impossible with ICE.

With a car, unless you have a specific use-case where you are driving 200+ miles a day, an EV is a no-brainer when it comes to efficiency in operating cost as well as emissions and overall energy use.

A Model 3 is smaller than the average car, it should be compared to something like a Honda Accord hybrid. Both have a similar cabin volume of ~100 ft^3. The fuel economy for a hybrid Accord is 48 mpg, or 760 Wh/mile.

The Accord is also $10k cheaper, presumably that is because the Model 3 requires more materials and more embodied energy.

> The Accord is also $10k cheaper, presumably that is because the Model 3 requires more materials and more embodied energy.

Do economies of scale and manufacturing expertise factor in to "embodied energy"?

What are the energy requirements and emissions for just building the vehicle? I've heard rumours that it's non-negligible when considering total emissions that a car will have caused.

Page 9 of https://www.tesla.com/ns_videos/2019-tesla-impact-report.pdf has a chart for that (Average Lifecycle Emissions in New York State (gCO2e/mi)).

Electric: 54 in manufacturing, 74 in use

Gas: 45 in manufacturing, 420 in use

While energy density as an important measure when talking about a fuel source, we can not forget about the other part of the equation. Energy efficiency, of those units of energy in jet fuel, how much of it can we effectively utilize? In other words, what is the distance travelled for a given weight of jet fuel vs the distance travelled for a given weight of batteries.

> Meanwhile, gasoline / petrol / benzin (wherever your are in the world) has an energy density of 12200 Wh/kg.

Yeah, and yet, if you are talking about cars, you are bound by the Carnot efficiency, which is at most 35% no matter what(in reality more like 20% or so). Now gasoline goes to 4270 Wh/kg even assuming the best possible engine. That's without accounting for extraction, refining, transportation losses.

Yes, still 10x more. However, you don't really need 10x, as electric motors are way more efficient (85 - 90%).

The long range Tesla Model 3 only requires a 75kWh (72.5 usable) battery for a 450km (~279 miles). In other words, it uses 161 Wh/km .

> ICEs are real technology

So are EVs. For all the tech they tend to have, it boils down to: Battery and electric motor. There are some pretty reliable solid state electronics to monitor and deliver power, but that's all you really need(even the 'charger' is optional - and for quick charging, it's located outside the vehicle).

You could theoretically use decades old technology to control the amount of power delivered to the motors - so you could see with your naked eye. And, in fact, we have done that! The first cars ever designed were electric, battery tech just wasn't there. It doesn't make sense to do that in this day and age, electronics driven by software work better. We would replace ICE engines with solid state components if it was possible.

Now, for an ICE car, you have valves. You have a crankshaft, controlling said valves (and tied to pistons) - hundreds of moving parts right there. You have spark plugs (and a coil to generate the voltage). Air filters. You have an alternator (usually driven by a belt). You have water pumps (optional on EVs - and for the battery only, when they are used). You need fuel pumps. Fuel filters. Radiators (because of all the engine inefficiency). You need oil - and replace said oil, as well as the oil filter. You have an exhaust with a catalytic converter.

Each one of those things may break and some are even consumables. So much crap EVs don't have.

And you still have software and the tiny electronics you can't see with your eyes ! Unless, of course, you still use carburetors (which add a few hundred more parts each).

EVs are much, much simpler. And more reliable, less parts and most of them don't move. The only thing that degrades is the battery. For now. I drive a Leaf, which is notorious for having no battery thermal management, and degradation is minimal.

> you are bound by the Carnot efficiency, which is at most 35% no matter what(in reality more like 20% or so)

Internal-combustion engines are not limited by the Carnot efficiency; see page 4 of these slides. In fact, latest-generation Priuses gets almost 40% thermal efficiency on the gasoline engine, and large diesel engines -- thanks to lean combustion (favorable ratio of specific heats for the gases that push on the piston), no throttling losses, higher compression ratio -- do even better.

https://www.energy.gov/sites/prod/files/2014/03/f8/deer11_ed...

Not parent commenter (and non mechanically inclined person), but I skimmed through the slides and it seems like a lot of the efficiency increasing techniques involve recapturing lost energy in the form of converting waste heat to electric energy.

Does the 40% for Prius include energy recapturing techniques?

> ICEs are real technology

They are real technology, in the sense that this is where over 100 years of optimising every aspect of ICE has got us to. Fascinatingly complex, extremely well engineered, and depending on the brand still relatively likely to break down within the first few years.

The engines are also longer designed to be maintained without special processes, and are increasingly designed around emission regulations. To the point where a lot of the complexity is in emission systems and the cars are choked by their own extremely lean fuel maps.

Electric motors on the other hand are still relatively unoptimised and the potential in things like torque vectoring is amazing. I'll miss driving manual, but it's getting just about impossible to buy those now anyway.

> Electric motors on the other hand are still relatively unoptimised

Electric motors have huge applications across most industries for longer than combustion engines. Calling them unoptimized is quite a stretch. There're some car specific optimizations to be done, sure, but it's very mature technology, with little potential for breakthroughs.

Those applications generally haven't been focused on putting ridiculous horsepower in a tiny format and then running a highly variable load while dissipating heat.

For example Axial flux motors are still very much being developed with a steady flow of breakthroughs (Magnax, Emrax), and have mind bending power to weight ratios. A lot of the current issues seem to be around heat dissipation, which is where I am hoping some of the next big wins are.

I'm a bit sad that currently easily available motors are currently not in the same league as Tesla (I have a 50kw Me1616 and Sevcon 4 sitting on my bench) but it looks like that is slowly changing.

I drive both ICE cars and electric cars and there is something about ICE engines in cars : they are very unresponsive compared to electric engines. They are fine at high RPMs, but you don't want to and shouldn't drive at high RPM. They have things such as turbo lag or really shitty torque curves. The gearboxes do not help as well. It's weird to wait half a second to get full power when you are used to the instant torque.

You should test drive a random eletric car and a random ICE car.

If you have the opportunity, try comparing your ICE experience with a manual transmission ICE.

Many modern ICE cars are effectively fly-by-wire with eco-junk-softwware in between the accelerator and engine.

Manual transmissions would likely not have the lag that you're experiencing, but I definitely recognize what you're saying w.r.t. torque curves.

I'm not challenging ICE v. Electric, but instead attempting to clarify that there is quite a wide variation in ICE-behavior that is less present in a manual transmission ICE car.

Moving from a manual ICE to electric, it's still night and day. And the manual felt like night and day compared to a lot of automatics...

I own a ICE car with a manual gearbox. The lag is there. The engine needs time to find his torque at low RPM so you need to drop one or two gears if you want some power. Mine doesn't have a turbo, but when I drive manual cars with Turbo, the turbo lag is huge. A manual gearbox doesn't fix this problem. You may drop gears before you need the power, to overtake someone for example, because you plan ahead and want the full power, but that's slow.

And even when I do it fast, I'm much much slower to manipulate the clutch and change gears compared to a modern automatic gearbox.

I doubt that most people can operate a manual transmission significantly better than the "eco-junk software" that controls a modern automatic. Almost nobody is a race driver, but everybody can feel the nicer behavior of an electric engine.

Your statement is utterly incorrect.

1) Electric v. ICE? No contest. Electric wins. Not at dispute.

2) "Manual Transmission" v. "Eco-Junk Software". Please see the following: https://www.motorbiscuit.com/does-sport-mode-really-do-anyth...

At a minimum, some "fly-by-wire" automatic ICE cars default to an "eco" mode which significantly impacts throttle (gas) responsiveness.

No doubt ECO mode does something well, and no doubt that modern automatic transmissions shift well.

My original statement was: "Electric (very responsive) => Manual (...) => Automatic (perceived unresponsiveness of ICE engines)"

Almost nobody is a race car driver, but the fly-by-wire in some ICE cars definitely affects driving feel in a way that is different than both manual transmission ICE and electric cars.

Well engineered ICE cars are the opposite of unresponsive. Gear shifts are in the order of 100ms. Turbocharged engines require some revs to get moving, but good engines rev so fast that unless you have no idea what you're doing this isn't a big problem.

Electric cars are like synthetic computer benchmarks - amazing on paper, but to actually drive? On a real road, with corners and a competent driver? So, so much worse. We'll get there, in time - some hybrids are really great, but we need to work a lot on battery weight before a pure electric car can match an ICE/hybrid car for real world performance. Weight always has been and always will be the enemy, and right now a tesla is closer to a truck than a sports car in terms of weight. The day will hopefully come, but today is not that day.

100ms of gear shifts is 100ms more than an eletric car without multiple gears.

Engines need time to rev fast, that's the problem yes. I don't know what you mean by good engineered ICE engine because I don't drive the worst at all and it's not good. Do you mean the super sporty 600kW ICE engines you find in supercars that cost a fortune to maintain and pollutes a lot?

Hybrids are shit in my humble opinion. You have the worst of both worlds, and not the best.

Weight is a problem but weight distribution is important too. And yes Tesla cars are heavy, as is tradition with American cars : a lot of torque and power, heavy, shitty brakes.

But I think that any car today is much faster than what you need. The roads are not a race.

> 12200 Wh/kg

Most ICE engines have efficiencies from 20 to 35%. Taking an average of 25% effciency, batteries have to essentially aim at about 3000 Wh / kg

Most battery motor systems have a round trip efficiencies of about 80%, so to compete with ICE engines, EV systems have a target of about 4000 Wh/kg.

edit : I also forgot to add about regenerative braking. For on road EV vehicles, regenerative braking can capture about 70% of the energy lost in braking. So, while a battery can store just 450 Wh/kg, averaged total energy, expended from the battery terminals, averaged over time, would have to be higher.

It also makes sense to calculate the average total energy stored in the vehicle, rather than the energy densities of the fuels. For a 300 mile range, assuming an average 30 mpg fuel efficiency, you would need about 10 gallons, about 38 kg. So total stored energy in the vehicle in form of fuel, is 12200 * 38 = ~ 465 kWh. But, of this energy, only 25 % is converted to usable movement, i.e, about 118 kWh.

However on a Model 3 LR, which has a range of 300 miles per charge, the battery capacity is 80 kWh (Tesla claims 75 kWh). So there is no basis to compare energy densities of various fuels directly.

>Meanwhile, gasoline / petrol / benzin (wherever your are in the world) has an energy density of 12200 Wh/kg.

Electric motors are 90% efficient, ICE are less than 20%. So in reality gasoline is 2-3x as energy dense, when you look at how much of the fuel's energy can be used to do useful work.

You also have to factor in the weight reduction as petroleum fuel is consumed vs the fixed weight of a battery.

This is a huge deal for aircraft. Not much for cars, as EVs are not carrying a lot of extra baggage that ICE cars require.

When was the last time you saw an ICE with both a trunk and a frunk? :)

> When was the last time you saw an ICE with both a trunk and a frunk?

Seconds ago -- there's one in my carport :-) (A 1993 Toyota MR2; it's mid-engine. The frunk is small, and completely filled by the spare tire and aftermarket stereo amp.)

Modern gasoline engines are not as heavy as you may think. I once transported 2 liter car engine in the back seat of my civic. Only ~150 lb and quite manageable.

Even monster SUV motors are only ~350 lbs. That doesn't include cooling, oil, accessories, or transmission but EV's have those too.

True, but the effect of this is less than it sounds like, as while the fuel is consumed, in an ICE car the engine is the heavy part and that isn't consumed.

Don't discount this so easily. You can't land a jumbo jet immediately after takeoff because its maximum allowed landing weight is much less than its maximum allowed takeoff weight. So you'll need a stronger fuselage and landing gear for electric plans, which means even more weight

I'd love to see a future where part of a plane's battery pack is a detachable drone that could fly back right after takeoff (most taxing on energy use) and thus decrease the weight of the plane.

You could also have battery swaps during flight as they pass over drone battery depots.

Sounds crazy. Might not be worth the gains for the complexity, but could be worth it across a whole fleet.

Microwave laser groundstations (or solar satellites) could come first, removing much of the battery requirement.

Hah, now you've got me imagining a gentle rain of 18650 batteries following a plane as it travels across the sky.

Yes, gentle :D

Another crackpot idea:

Instead of a catapult or a flying battery pack, go for a tethered launch. The plane taxis onto a platform that is actually a powerful "cable laying UAV" with powerful ducted fans for propulsion and some lift and two big powered spools of copper as heavy as it can carry. The platform arrests the plane's main undercarriage, connects power lines to the plane and raises itself on its own set of wheels. They accelerate together, leave the ground together, all while the powered spools are unrolling the wires to the ground station exactly as fast as needed to avoid mechanical drag (the wires are effectively in free-fall, perhaps issues with the cable landing could be evaded by sending up a chain of "cable carrying (T)UAVs" that take the role of virtual poles). In time before the spools run out, the platform disconnects from the plane slows down the spools so that the inertia and main motors of the platform start pulling on the wires, then reels itself back in while it maneuvers to a point above the base station, finishing the circle with a tail-landing followed by dropping into "platform" position controlled by its secondary fans. Meanwhile, the plane flies of into the sunset on a fresh set of batteries.

But the battery tender UAV actually sounds far more practical, I guess I just like ideas involving tethered UAV.

(and somehow I feel almost entitled do spew out the most improbable ideas, since seeing footage of the successful dual suicide burns of the Falcon Heavy boosters - if that's possible, why isn't everything else as well?)

Seems like you'd be better off with a ground-based catapult system to get the plane up to speed and in the air where the on-board motors could take over.

Catapult really paints the wrong picture... but if you say ballista and actually mean a maglev rail accelerator then I'm down

If these are passenger aircraft, that probably wouldn't fly

> If these are passenger aircraft, that probably wouldn't fly

Well, it doesn't need to have the same rate of acceleration as a carrier's, but honestly it just doesn't make sense in general.

Right -- you could use the full length of an existing runway to have a gentle acceleration , bt I'd argue this makes a lot more sense than some sort of drone delivered jettisoned/retrieved battery if your goal is to reduce on-board energy expended for takeoff. Much less complex and the wear parts would be fixed at the airport rather than on every single airplane.

> I'd argue this makes a lot more sense than some sort of drone delivered jettisoned/retrieved battery..

Oh absolutely, it compares favourably to one of the most asinine first-pass approaches to this problem I've ever seen, heheh.

The real solution is to find a way to produce good liquid fuel from a cheap and abundant source of overprovisioned baseline power (maybe make hydrogen† from your nuclear power in off-peak hours).

Batteries are mostly composed of matrix, so even if you could extract energy as efficiently from the non-matrix materials in the battery as you can from hydrocarbon combustion, you would still be lugging around all that matrix.

† Yes, I get that it's 3 times less energy dense than good hydrocarbons, but it's a start when compared to batteries.

Might make more sense that you suspect. An airport designed to land uphill and takeoff downhill actually makes huge a difference in operating costs for heavy aircraft. Takeoff and initial climb are huge fuel burners.

My SUV is 4500 lbs and has a 17 gallon tank. Gasoline weighs ~6lbs/gallon, so it only factors for about 2% of total mass between a full and empty tank. Seems safe to mostly ignore it.

Yes, that's true. And the cost of electricity vs. fuel. Safety is another factor. The point is there's a lot more to it than Wh/kg of the energy source.

Electric vehicles have range problems in cold climates because you don't have waste heat.

On a very cold day 60% of that waste heat might be used to warm the cabin. This translates to up to 50% range reduction in electric vehicles.

This is a myth. It is not nearly that bad. I own a Model 3 in a place where it is frequently below 30F in the winter. My last road trip when it was 17F throughout I consistently got around ~250-270 miles out of 310 rated range. The new hybrid heat-pump based system in the newer models makes it even more efficient.

I'm not sure how much it would matter, but it's probably worth pointing out that 17F is nearly shorts weather in the middle of the brutally cold winters a lot of places experience.

It shouldn't matter that much in that case too, especially if you have home charging. The lowest I have gone is minus 40 F during a cold snap last year. I had no problems starting up the car and going. The acceleration/regen was limited for a bit in the beginning to protect the battery. I lived in an apartment at the time and so I couldn't "pre-condition" the battery and interior from wall-power. But even then I had no problems after everything warmed up. Sure I used a bit more energy at the beginning to warm up the interior since I couldn't plug in.

On longer trips, the waste heat from motors are cycled through the battery to bring it to ideal temperatures. Even in extreme cold weather, you get full "regen" capability (meaning battery is warmed up), just from the waste heat from the motors. There is also an option to pre-condition the battery for fast charging by intentionally driving the motors less efficiently to generate more heat.

Isn't the range penalty a lot worse on short trips? When I was researching Leaf I noped out of buying one because range penalty in the cold for daily commutes was almost 50%

Depends on the generation of Leaf. The older ones had a big problem with thermal management. Teslas on the other hand has a cooling loop that takes in excess heat from the motor (in some cases, intentionally running the motor inefficiently to generate more heat), to "condition" the battery to the ideal temp. Ideally this is done while plugged in if for short trips. The car essentially stalls the motor with just enough current to generate heat. On long trips, the heat generated during the drive is enough to take care of this and the battery stays at the optimum temperature even if it is extremely cold outside.

Top-level ev's like the Model 3 are already superior for most drivers. The only problem is cost, and that is being fixed in the coming years through steadily falling battery prices.

Other use cases like aviation and ocean boats are more difficult. It may well be that synfuels made with renewable energy will be the solution there.

True but gas turbines (not ICEs, those are mainly used on small aircraft) can reach a theoretical efficiency of 30% while electric motor efficiency of 92…93% is quite common. So you can multiply that number by 1/3 since 2/3 becomes heat.

With turbofans and turbojets it gets a little harder as well, since unlike stationary turbine generators, not all "waste heat" is actually wasted, when considering thrust-specific fuel consumption.

ICEs are way heavy for their power.

I agree that we will produce and burn synthetic fuel for flight long into the future. But this is going to burn in turbines for flying in atmosphere, and in rocket engines for getting to orbit.

The only metric with planes that matters is $/mile. A soon as something flies far enough with enough payload, energy density stops being an issue. It doesn't matter that the plane is going to be four times the weight if it gets from A to B at a fraction of the cost. Think 100$ hamburgers turning into 5$ coffee runs because of vastly reduced fuel cost and maintenance cost.

You see the same pattern with EVs. All of the cool ones are really heavy compared to the ICE cars they compete with. But they still go really fast and pretty far. So, you see much heavier Tesla's making formerly cool ICE sports cars look sluggish and outdated. And lets be honest, those never had any kind of fuel economy (or range) worth talking about because they burn fuel at obscene rates to get that speed. Being obscenely noisy and inefficient was kind of the point of owning one.

Higher energy density makes electric planes a little bit more reasonable, but they'd still be quite range-limited compared to gas. For some use cases, that might be okay.

I'm more interested in how this affects cars. Getting four or five hundred miles out of a battery pack that's lighter than what's in a typical Tesla would be a great thing, especially if it's cheap.

I'm currently working on an electric conversion of a Mazda RX-8. I just bought about 450 pounds of lithium iron phosphate batteries. They're the most expensive component, and provide about 27kwh; maybe enough for 100 miles if I'm lucky. I sort of assumed that in about ten years or so I'll probably replace the whole pack with whatever great new technology can provide more range with less weight, and probably cost less too. It would be wonderful if we had awesome batteries now.

(I considered used tesla modules; they have much better energy density, but they're more dangerous and they wouldn't have fit well in the odd-shaped places I wanted to put them.)

Any range you can achieve with batteries in a plane it's basically going to decimate operational cost and be unbeatable from that point of view for missions falling into that range. There are a number of products in development that have interesting enough range that they are pre-selling well because there are companies out there that can fit that in their missions. Double the range, and there are going to be more such companies.

There are a number of battery companies looking to improve energy densities by a factor of 2x to 7x. It's increasingly looking like a matter of when; not if we hit 2x-3x. Five years seems reasonable; even quite long given the constant barrage of announcements from various companies and research groups. These improved batteries will likely be expensive initially and not produced in mass volumes right away. But could be perfect for niche markets where volume and cost are less of a concern; i.e. aviation.

Tesla's battery day next month is going to be interesting as well. Rumors are currently flying about longevity and energy density of that particular battery. It's clearly going to be better than what they are currently shipping and some insiders seem to hint it's quite close to the magical 400 wh/kg that e.g. Elon Musk has been citing as a minimum viable battery for electric flight.

Another thing to consider is that a lot of already announced electrical airplanes are equipped with what are now already obsolete batteries. That's not because the companies behind them are stupid but because certifying planes just takes a very long time and does not allow for massive technical overhauls in between. So, there are some gains to be had by simply updating existing designs with newer off the shelf technology as it becomes available. Second and third generations of a lot of the products that are close to production ready are going to be interesting in the next few years and in some cases, manufacturers are already planning such products. Doubling or tripling ranges is going to be very disruptive in that market.

Sweet project! How much did the batteries cost? I see this works out to ~130 Wh/kg--did you avoid batteries with higher energy density for cost reasons, or are they just difficult to get?

The batteries cost me about six thousand dollars. Lithium iron phosphate is generally recommended for conversions because they're about as safe as you can reasonably expect a battery to be and tolerant of abuse.

Used tesla packs have much higher energy density and are actually reasonably inexpensive, but I couldn't really figure out how to make them work in my setup. They're awkwardly long and don't really fit where I wanted to put them, and need liquid cooling. They're also quite a bit more dangerous if they're damaged or catch on fire, which is unlikely in a vehicle carefully designed to protect them but considerably more likely in conversion. So I went with the simpler, safer option.

LG Chem has some pretty good batteries as well, but I would have needed multiple series groups connected in parallel, which would have required a pretty complicated battery management system to keep everything balanced.

I have a largish 20AH 48V LiFePO4 I bought from PingBattery.com ten years ago for powering a dual motor e-bike project. I ended up also using it to power a mobile robot (rover) project, and sometimes used it for emergency power during blackouts.

I went with lithium iron phosphate because it was perceived safer and more durable. Over the past ten years when it wasn't bouncing around inside a rover or e-bike it spent months or years on a shelf when I forgot about it. Most recently I've dusted it back off and use it to power a large shop fan. Because of it's long storage and infrequent charging/balancing the subset of cells that actually power the microcontroller in the BMS were alarmingly low compared to the others, but after a few cycles it seems to have recovered and all but one of the low cells has balanced to the others. The battery still seems to perform well overall.

Everyone is talking energy density but nobody is talking about Urban Air Mobility.

Electric is the name of the game for a VTOL plane that will take you from SFO to downtown or Santa Cruz. They don't have to have all the performance in the world, they just need to have enough performance to do their job.

Also, pilots will appreciate the operating costs and simplicity of these aircraft. Student pilots will love a plane that costs $10/hr instead of $100/hr in the Bay Area. 90 minutes of flight time (1 hour lesson + 30 minute VFR 'fuel' reserve) is all it needs.

Neighbors will appreciate higher torque motors that turn modern props at 1500 RPM instead of 2200 for the noise reduction.

> nobody is talking about Urban Air Mobility.

Because flying cars have always been just behind fusion.

Five years away, my friend. Five years. I know it's true because I've been reading the same figure since about 1972, and much earlier if you count old copies of Popular Science I bought at garage sales.

Except there are only a few rooftops in cities where you could land such a plane, and that real estate is very expensive. It doesn't scale.

It's not the scale that I'd be worried about. I see enough idiots in land-based vehicles, last thing we want is a load of air-based vehicles flying around. Learners trying to hover over your house and youths joy-flying.

And let's not neglect that those rooftops are going to be plastered in solar panels anyway...

How much of a prop plane's noise is from its propeller vs its engine?

Depends on the size of the propeller. The main issue is the tip of the propeller breaking the sound barrier. This limits the RPM. Bigger propellers mean more noise at lower RPM. Smaller propellers enable higher RPM.

So the noise profile of a plane with smaller, faster propellers and engines is going to be very different from a big noisy helicopter where you can clearly hear the engine over the already substantial noise of the very loud propeller. Faster also means the noise is of a higher frequency and carries less far.

Comparatively the engine noise for electrical engines is not going to be a factor. Think of the noise level of your vacuum cleaner; most of which is in fact the spinning blade inside hitting a few thousand rpm; 3-5K is pretty common for vacuum cleaners. Dysons apparently go way beyond that. A typical Cessna would max out at around 2700 RPM and be cruising at around 2200.

This varies extremely widely depending on engine selection and propeller design. Urban air mobility vehicles are also very likely to be loudest during vertical take-off and landing, which is not comparable to a conventional small aircraft.

With every lithium-sulfur battery I've come across you need to have a lot of steel clamping plates together because they expand so much when charging, and will otherwise delaminate. So ultimately they become the same mass.

This includes the oxis energy battery mentioned here.

This might sound crazy but is it possible to do that in some way such that the clamping plates etc. are only there during the charging process? Prevent the delamination during charging and then remove the prevention mechanism?

Or just charge really really slowly? Airports etc. could just have terminals full of trickle-charged batteries to swap in and out.

That was my first thought as well. But I don't have a clue if it's practical.

Is there some way to embrace this in the design of the plane? Could the wing structure be built in such a way that an expanding battery actually adds strength?

The idea of making a battery a structural part of an aircraft wing has come up before, e.g. https://newatlas.com/axial-stack-battery-supersonic-electric.... I'm not sure if any progress has been made on this front recently, or whether they've come up against a materials-science roadblock!

Can I just say this was an extremely well-written article? Each time a question came to mind, it was answered within the next two sentences.

For speculative (near future) fiction, that uses a lightweight electrically-powered aircraft as a linking device, "News From Gardenia" by Robert Llewellyn, is a good read.

Just yesterday I threw out a print of a DoE paper from 1997 that talked about lithium-sulfur as imminent new storage tech.

Impressed with the persistence here.

Surely hydrogen makes more sense for electric airplanes?

Wow. So much geekery comparing ICE to electric, without a single mention of global warming.

Big oil has done an amazing job making the subject unmentionable.

Still orders of magnitude less energy-dense than jet fuel.

IIRC real-engineering on youtube did a detailed analysis of the current operating limitations with electric planes: https://www.youtube.com/watch?v=VNvzZfsC13o

He also identified a couple of sweet spots where electric flight would make sense factoring in engine efficiency & cost of fuel etc. bottom line is that the picture is more complex than just comparing energy density of jet-fuel & batteries. with batteries becoming much lighter IMO it should open up many more use cases for short haul frequent flights without the need of big central hub airports. which is good. an more importantly give the trajectory of battery energy density it should provide enough justification for heavy investment into research into electric planes so i wouldn't dismiss it out of hand.

Yes but presumably electricity is order(s) of magnitude cheaper than jet fuel. And also order(s) of magnitude more available than jet fuel. And also order(s) of magnitude cleaner than jet fuel (depending on the source).

>Yes but presumably electricity is order(s) of magnitude cheaper than jet fuel.

It's really not even about the cost of fuel. With aviation it's all about maintenance costs. Electric aircraft will be orders of magnitude simpler and cheaper to maintain than jet turbines. This is what will unlock cost effective small scale commuter routes, allowing you to just hop on a small 10 passenger plane at a neighborhood airport and take a 300 mile flight with no need for security.

I'd debate the 'more available' statement. It is more widely available overall but not in the places you'd want it. Of course that can be fixed but someone will have to build out that infrastructure to make electric planes viable.

It's a bit like Tesla. Prior to them building out their charging network, electric cars had a bit of a chicken and the egg problem. You might buy a car but have no where to charge it, but nobody wanted to build places to charge them because nobody has an electric car.

That’s not the case at all. Everyone has electricity at their home. You can charge basically any electric car from a domestic wal socket and higher power chargers are easily available. Commercial charge points only really need to be used for long distance travel. Most EV owners can do the majority of charging at home.

One confounding factor is parking arrangements. If you have a garage then a wall socket is reasonable, but for many years the only place i could park a car was somewhere on the street, hopefully within 100m of my address. In that situation commercial charge points (hopefully near my employer, if lucky) would be the only reasonable charge point.

> Everyone has electricity at their home.

I do. But I can't get the car up the stairs. :-(

Yeah basically all airports that have commercial service also have access to power. There are exceptions like seaplane bases and small country strips, but there are more than enough airports with access to commercial or even industrial grade power to make electric airplanes that require charging viable. The final step of linking up the airport power supply to the airplane charger is peanuts in the world of aviation. Almost all airports have a fleet of fuel trucks, therefore, the cost of buying a fuel truck is the low end of the acceptable cost for ground infrastructure investment to open a new route for an airline.

I just reread what I wrote and I think maybe I wasn’t very clear.

There’s electricity at every single gas station in the US. Why can’t we pull into any gas station in the US and charge an electric car? Even now that electric cars are gaining market share and becoming more common.

Someone has to build, supply, and hook up high power charging systems. You can’t just fly your $5 million eJet into any airport in the US and run a 100’ extension cord into the FBO. If that’s the plan, you certainly can’t hope to leave the same day. It will take at least 3 days for your 1 MWh eJet to finish charging.

We’re in the pre-Tesla days of electric aircraft. There’s a few players working on the aircraft and they’re getting close. However, until a ‘Tesla’ comes along where they also install charging infrastructure at the airports their customers are planning on using, we’re not going to see a commercially viable electric aircraft.

The best way to do it would be start in the corners and cross in the middle. Seattle/SF/LA => { colorado? vegas? texas? chicago? } => NY/DC/Miami

If you can link up some sort of route(s) to deal with range-anxiety / weather, and can criss-cross the country, you're in business.

Once your route is built, it's straightforward to manage capacity/flight-plans (reservations / networks / routing), and then you move directly to demand-generation, but you'll have a real tough time competing directly with coast-to-coast direct flights.

Yeah, I think you're mostly right. I suspect it's going to start with seaplanes (oddly) because they fly short hop routes that are ideal for electric aircraft. Then you'll start to see new routes made economic by electrification, such as; Marin County->Palo Alto, SurfAir routes (like linking up the dozen airports sprinkled around Los Angeles area), generally linking up small hops. At the beginning electric aircraft won't be competing with existing airline routes, they'll be expanding coverage and reducing prices for local area hops.

Jet fuel is ~36 kWh/gallon raw energy density (13 kWh/gallon mechanical power assuming 35% engine efficiency). The pre-covid jet fuel price was $2/gallon, or $.15/kWh. The average price of commercial electricity is $.06/kWh in America, or $.08/kWh including charging/motor efficiency. This cost will definitely be higher if you only buy clean electricity, and this ignores battery wear out.

But where the economics break down is aircraft utilization. If charge time is greater than ~1 hour typical turn time, all of your costs will grow. Capital cost, crew costs, and airport infrastructure cost will increase. To charge in <1 hr is a challenge, you need a huge power source (tens of megawatts per plane) and serious cooling.

Or swap the component, although that introduces its own design challenges and provenance risks.

Aircraft refueling generally runs in-ground (at the largest airports), then 5-10k gallon trucks (~20-40k liters), then ~500-2000 gallon smaller trucks (2k-10k liters) for smaller aircraft or smaller airports.

If you reimagined refueling trucks as "forklifts carrying batteries" instead of "tubes of gasoline on wheels" then you'd likely end up with similar delivery practices (central charging, swap/refuel, discard/recharge batteries instead of refilling the fuel tank on a fuel truck).

Effectively it would be standardizing on some way to slot-in pre-charged batteries, and treat them similar to a propane tank rental company, where each removed battery is considered suspect and tested/refurbished/recharged after each use.

Otherwise, yeah, putting a bunch of 220v outlets in the ground around an airport... you're going to be sitting there a while to recharge the ten planes that landed that day. It'd effectively be untenable for smaller airports to be able to provide "quick-turn" refueling services, and potentially risky to be able to guarantee overnight refueling.

This is all nudging towards personal / corporate aircraft, not commercial aircraft operations, which would "never" want the plane in more than one spot for more than one hour, which would require something similar to battery-swaps that they control, OR some very fancy electrical and heat management associated with the airport/jetbridge that the plane pulls up at.

To be fair, you need to compare a complete workflow including the renewable production of the jet fuel.

If the overhead of heavy batteries does not annihilate the benefit of the carbon-neutral production rendered possible by using electricity (and associated carbon-neutral sources like photovoltaic etc... heck, even nuclear fission), then batteries are still the path to go.

If there are carbon-neutral ways to produce the jet-fuel, and to have a completely carbon-neutral(or even negative) cycle production+consumption, then why not. If it could be done without turning the Earth into a giant bio-fuel crop, that would be nice.

>> Still orders of magnitude less energy-dense than jet fuel.

Does that matter, if other aspects of the system compensate with lighter weight? For example, lighter weight electric engines versus heavier fuel-burning engines along with exhaust and cooling systems.

A PW150 turboshaft engine is ~5 kW/kg. Some electric motors are up to ~10 kW/kg. But, as an example, engines on a Q400 regional airliner are only ~5% of the total weight. Fuel is up to 15% of total weight. So the savings are not significant.

Also, the batteries will likely require a cooling solution. This can be challenging (heavy) for high altitudes (where air is cold but very low density). Jet fuel requires no cooling.

https://en.wikipedia.org/wiki/Power-to-weight_ratio

If it's anything like ships/yachts then the lighter weight doesn't come anywhere close to making up for the loss of energy.

Could still be very useful for flights between nearby cities e.g. LAX to SF.

Reply on news.ycombinator.com