Why battery-powered aircraft will never have significant range

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BJC

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I think where it went off the rails was their underestimation of tire technology. The world of the 1950's could not even conceive of the tires we take for granted today. That's the parallel to this thread: Like them, we are basing our understanding on the known realities of today. There may be an enabling technology that comes along which will turn our "reality" into laughable ignorance.
See post #76 for one potential enabling technology.


BJC
 

proppastie

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There may be an enabling technology that comes along which will turn our "reality" into laughable ignorance.
I read about the limit of the chemistry, while watching some very impressive chemical reactions lots more powerful than gas in the news. Seems to me harnessing these explosive chemicals is an engineering problem, and perhaps we are just suffering from a lack of imagination.
 

12notes

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My general conclusion is that, for 'GA' distances about 400 miles(w/o reserves) you need about 400 Wh/kg. Tesla batt, without all the support equipment, are running around 250ish
Tesla uses a version of Panasonic 18650 batteries to make their battery packs, the Panasonic's 18650B, available to consumers since 2008, has an independently tested energy density of 252 Wh/kg, so 250 is a much more accurate current starting point than the initial figure of only 100, and is probably too low since that was 9 years ago. Batteries are an industrial technology that increases in energy density 3-5% a year, although the last decade or so has been more like 5-8% per year. Although this doesn't sound like much, using the most conservative 3%, we should be at 400Wh/kg in 16 years. If you're an optimist and use 8%, that goes down to 6 years.

We were at around 100 Wh/kg in 1990, we were at least at 252 Wh/kg in 2008. If you predicted a 3%/year increase in 1990 we should've been expected to be at 229 Wh/kg in 2008, so the gain over 30 years is most likely over 3%, and the trend has been accelerating.

Sorry for the years, I couldn't easily find more recent data that was reputable.
 

12notes

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I just watched the video, and they really phrase things in the worst possible way to make the energy densities look low. But if you just keep track of the statements it makes, it really should have the complete opposite conclusion for batteries.

Statements on the left are from the video, the right is the equivalent statement about density:
Lithium ion with the same energy can theoretically be 50% of the weight of current batteries = Lithium ion can have 2x the density of current batteries
Lithium sulfur can weigh 30% of the Lithium ion = Lithium sulfur is 3x the density of the theoretical maximum of lithium ion (6x current batteries).
Lithium oxygen is 25% weight of lithium sulfur = 4x the density (24x current batteries).
Lithium fluorine (if possible) is 5% weight of lithium oxygen = 10 x the density (240x current batteries).

So the theoretical limit of batteries, using the video's own numbers, is 60,000 Wh/kg. Even ignoring lithium fluorine, you'd still get 6,000 Wh/kg as the theoretical maximum. I have no idea how he gets the 5% number at the end of the comparisons, it's not consistent with the comparisons before that. That's still 20x current, or 5,000 Wh/kg.

With the most pessimistic, out of nowhere 5% current figure, the Hummelbird that needs 20kW to fly for an hour? That's 8.8 lbs of battery, or 3.2 lbs less than the gasoline that would be needed.

Even if the development only got as far as lithium sulfur, at 1,500 Wh/kg, the Hummelbird would need 29 lbs. of batteries for an hour. Assuming a 25 lb electric motor plus 10 lbs of controller and wiring replaces the 85 lb 1/2 VW plus full 6 gallon tank, you would have 2.7 hours with batteries instead of 3 hours with gas at the exact same weight.

I can't vouch for these figures, I got them from the video and they didn't list sources. The video is inconsistent, and uses percentages in a way that supports the most pessimistic view of batteries in a biased way at best. And his math sucks. But the end result is that batteries theoretical limits are well in the range that will be useful.

It's likely to be a long wait to get to these limits, but his conclusion isn't consistent with his data in any way.
 

Doggzilla

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Ya, those numbers just don't seem right.

But do remember that the weight of the electric motors save about 30 pounds and that they are about 3 times as efficient even without drag reduction.

I'm betting our current engines don't even get 30% efficiency, while electric can be over 90%.

So the effective energy density is much higher.

So in order to match the energy density of gasoline, a battery would "only" require about 4300 wh/kg

Then take into account the drag reduction and it's probably closer to 3000. Or even lower if the aircraft can operate at higher altitudes. Could be closer to 2500 then.
 

12notes

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Lithium fluorine (if possible) is 5% weight of lithium oxygen = 10 x the density (240x current batteries).

So the theoretical limit of batteries, using the video's own numbers, is 60,000 Wh/kg.
Ok, so my math sucks, too, but my error only reinforces the argument. This should be:

Lithium fluorine (if possible) is 5% weight of lithium oxygen = 20 x the density (480x current batteries).

So the theoretical limit of batteries, using the video's own numbers, is 120,000 Wh/kg.

That would be 10 times the energy density of jet fuel burning at 100% efficiency.
 
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pictsidhe

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Fluorine batteries. Umm, wouldn't want to be around a malfunctioning one...
Considering electrode cost, Aluminium is a strong contender for future batteries, it's much more plentiful than lithium. In a battery, it would have maybe half the energy density, depending on the other electrode, but lithium isn't close to potential energy so it may not work out that bad. magnesium isn't as cheap as Aluminium, but offers energy density between Aluminium and Lithium.
If you want the absolute lightest, Beryllium Fluoride is likely near the top of the pile. That's nasty stuff and really nasty stuff, so safety is a big concern.
If you can make use of atmospheric gases, you can store fuel in the air. Hydroxylamine sheds nitrogen and water as it used up, the battery would get lighter as it discharges. Oxygen to Ozone is also electrochemically interesting, but a battery that converts oxygen to ozone isn't going to be safe to have around people.
 

RJW

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The world of the 1950's could not even conceive of the tires we take for granted today. That's the parallel to this thread...
I understand the analogy. And I feel that impossibility proofs should be reserved for formal systems (predicate logic, etc.). Still the argument in the video is very persuasive if you accept the assumptions of fundamental chemistry and trust that the guy did his homework.

Here is a clearer discussion of the topic than that of the video: https://thebulletin.org/limits-energy-storage-technology

The only way to get around a theoretical limit is to abandon the theory. It’s very difficult to imagine throwing out fundamental physics and chemistry for some new theory. My guess is that if a new theory of the universe where to replace what we currently use to understand things, we won’t be much interested in chemical batteries and airplanes anymore.

Rob
 
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Aesquire

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Neither is burning hydrocarbons. So what is the difference?

Tim
The difference between coughing, asphyxiation if you have a really bad design, CO poisoning, eventual cancer, vs. Bursting into flames.


Here's some fun stuff for the lunatics that want to play with Flourine chemistry.

http://blogs.sciencemag.org/pipeline/archives/2010/02/23/things_i_wont_work_with_dioxygen_difluoride

A few nit picks.

90% efficiency? Bull patties. There's enough bad math in Kickstarter Electric whatsit garbage, and EPA mileage ratings without ignoring the production of electricity.

Energy density of Chemical Batteries may indeed DOUBLE in your children's lifetimes. They still are going to be a poor choice for replacing combustion engines. And any bets we make today will be paid by & to our estates. ( I'll try and keep a steak dinner's worth in trust before I pass )

You are thinking like a Verne era enthusiast. Better and Better Steam Engines will Bring Us To The Heavens! New! Electric! Power! After all, Robur the Conqueror and Captain Nemo used the mysterious power of Electricity!

Chemical Batteries! Bah! Humbug!

Super capacitors. Quantum Storage. Why waste Fullerenes holding H2 when they can store electrons?

Sure, you'll use a chemical battery with low self discharge to start your combustion engine for decades to come. The trainers may use them, the self launching sailplanes are Now. But the tech is a dead end. As energy density rises, so does the danger. Compare an Iron-Air battery where you need to safely get rid of the hydrogen it produces as a byproduct, ( making it a better hybrid choice than you, or Edison, ever considered ) to a Lithium Cobalt cell that bursts into flames when over charged. Double that density, square that risk? Cube? or just Double?

No, we stand on the edge of a new era, but what seems shiny today will be silly tomorrow. Feel free to design for today's tech, and leave room for better in your plans, but designing for an imaginary tomorrow's tech will leave you grounded. BD-5? Designing for unproven engines is a proven losing proposition.

The self discharge question may make early super capacitors a pain to use, you may need to show up at the airport an hour or 2 before flight to throw on the charger. Instead of the day before on the way home from work with chemical batteries.

However, you guys are on the right track by looking to use car & motorcycle tech, just as home builders are today with Subaru/Honda/Chevy engines.

In ten years I bet we have thread on the best way to layer super capacitor cloth between fiberglass/resin layers so the whole wing is a storage device.

Or I could be wrong. Fuel cells that run on alcohol might be the future.
 

blane.c

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I am liking the anti gravity pill idea, the drug company's are profit motivated enough to pull it off. You know something like a reverse Bean-o would aid in propulsion as well.
 

tspear

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Here's some fun stuff for the lunatics that want to play with Flourine chemistry.
I know Flourine is bad stuff. I was asking about Ozone compared to the exhaust coming out of our existing tailpipe. SO2, CO, CO2, NOx, Particulates....

Otherwise, I think pure EV is gonna work for the 100 buck hamburger run.
Then it will be hybrid solutions, where batteries allow for better efficiency.
1. Only need to plan for cooling drag in cruise, not max power. This can be a significant reduction in drag, and tighter tolerances for the engine resulting in better efficiency
2. better placement of engines versus prop, weight...
3. More modular designs

Tim
 

saini flyer

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Let me add some real numbers from the world of electric motorcycles!

Instead of electric cars, IMHO electric motorcycle development in past 5 years show how battery capacity has changed without liquid cooling as they need to keep volume, weight, and cost down.

Here is a snapshot of the 2013 Zero powertrain battery specification.
2013 -Zero Battery pack information.jpg

The 2013 battery with BMS is 42 lbs and 2.8KWhr (132Whr/Kg)
The new 2018 battery with BMS is 42 lbs and 3.6KWhr (188 Whr/Kg)
The volume & weight of the battery pack is the same year over year as the frame remained the same. This is a 42% increase over 5 years.

I have yet to see an aircraft using a Nissan Leaf or BMW i3 powertrain but the egull and its derivatives have flown with the 2013 Zero powertrain. Also the Windward Goshawk will use the new Zero powertrain. There is a Belite here on HBA that is using zero too.
 

Doggzilla

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90% efficiency? Bull patties. There's enough bad math in Kickstarter Electric whatsit garbage, and EPA mileage ratings without ignoring the production of electricity.
That is true, but for this conversation we are only examining the efficiency between the batteries and drive motors, which do in fact reach more than 90% in some cases.

So the effective energy density is much higher.
 

Aesquire

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Fair enough. The efficiency lets you reduce cooling drag. Good.

I was going to do a rant on how hybrids for cars use a different set of power percentage ratios than airplanes. Take off at 100%, cruise at 75%, much higher than cars.

Then I realized that doesn't matter so much. So I'm sold on hybrids for the near future.

You guys just keep on thinking. An electric motor glider works for me and locally I figure 50-70 miles range at minimum consumption, which is max L/D speed, including a couple of climbs of ? 3000 feet? Gives Me the range I need. Which I far less than a Cessna 172 replacement.

Assuming a plane equiv. To a Xenos from Sonex, will current gear work for electric & batteries?
 

rdj

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Super capacitors. Quantum Storage. Why waste Fullerenes holding H2 when they can store electrons?
Because electrons are negatively charged particles and of the four forces of nature the electromagnetic force is the second most powerful, one order of magnitude less than the strength of the strong nuclear force that keeps atomic nuclei together but 4-7 orders of magnitude greater than the weak nuclear force responsible for the radioactive decay of said nuclei. Storing actual electrons--which desperately want to repel each other--in anything other than their orbital clouds around an atomic nucleus involves the application of serious magnetic fields and lots of exciting physics. But since this is Homebuilt Airplanes dot com and not a Physics Today forum I won't belabour the point any further :)
 

pictsidhe

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I know Flourine is bad stuff. I was asking about Ozone compared to the exhaust coming out of our existing tailpipe. SO2, CO, CO2, NOx, Particulates....

Otherwise, I think pure EV is gonna work for the 100 buck hamburger run.
Then it will be hybrid solutions, where batteries allow for better efficiency.
1. Only need to plan for cooling drag in cruise, not max power. This can be a significant reduction in drag, and tighter tolerances for the engine resulting in better efficiency
2. better placement of engines versus prop, weight...
3. More modular designs

Tim
It wouldn't be Ozone in small quantities, it would be Ozone coming out the tailpipe like CO2 comes out of a hydrocarb tailpipe. Ozone isn't nice stuff to breathe and a serious pollutant in small doses. No way would it be allowed to spew out in quantity. There may be some catalyst tech that could deal with it, though.
I was reading a patent for ammonia fuel cells last night, theoretical energy density of 3kWhr/kg Get something like that working at 20% of theoretical, and Bob's your mother's brother!
We really have no clue what might be invented in 1-5-10-20 years. We merely have some idea of some possibilities. I'm seeing some awfully high figures for cooling drag in this thread. It really shouldn't be over 10% if you do a half way decent job.
 

Aesquire

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https://www.graphenea.com/pages/graphene-supercapacitors

https://en.m.wikipedia.org/wiki/Supercapacitor


Serious magnetic fields? That's not the storage mechanism I'm talking about.

Commercial production at the density we need isn't there yet. The promise is big. Time will tell.

I suspect you'll be able to store more power per pound but not per volume in the next gen graphene capacitors, compared to this generation of lithium ion batteries.

Hence my reference to building capacitor materials into wing skins. Perhaps custom shapes that could replace foam in a D tube leading edge? Time will tell.
 
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