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Why does 500wh/kg make electric aircraft possible? 6x less than kerosene. Is that the break even on cost if you can source very cheap electricity? Seems like i

Why does 500wh/kg make electric aircraft possible? 6x less than kerosene. Is that the break even on cost if you can source very cheap electricity? Seems like it would still annihilate the payload/range.

ralusek 4y ago
I assume it's a limit motivated more by how far you can go rather than the cost of fueling/charging. Like, above a certain weight/energy store ratio, it's either too heavy to fly or would just have an incredibly limited range.
nvy 4y ago
Seems like marketing hype to me. An 8-hour transatlantic flight requires something like 600MWhr of energy. That's about 75MW, which is in small nuclear reactor territory.
- kolinko 4y ago
  Closer to 200MWh - jet engines are ~30% efficient
- rgmerk 4y ago
  Not every flight is transatlantic. These batteries, if they deliver on the advertised specs and aren’t too expensive should make short-range electric aviation possible. The electric air taxis that Joby and others are working on suddenly have a lot bigger margin to work with, as do electric regional airliners.
- Epa095 4y ago
  Replacing transatlantic flights is out of the question (for batteries for now). But there exists shorter routes, and according to this list [1] on Wikipedia, the busiest route in the world is 449km long. That's probably also not doable now, but maybe in some years? For the first years it will probably only be a few wierd, short routes in rich countries like Norway with 110% financial support from the state. But when they can safely fly 5-600km there is a actually quite a number of routes with a lot of passengers out there. 1: https://en.m.wikipedia.org/wiki/List_of_busiest_passenger_air_routes https://en.m.wikipedia.org/wiki/List_of_busiest_passenger_ai...
- fwlr 4y ago
  The US very nearly built a 60MW nuclear reactor for use in airplanes after their scaled down design at 2.5MW was successfully built, ran, and tested. This was done in the 1950s and, incidentally, required inventing molten salt reactors. https://en.m.wikipedia.org/wiki/Aircraft_Reactor_Experiment https://en.m.wikipedia.org/wiki/Aircraft_Reactor_Experiment (They actually planned to go all the way to 350MW, which could theoretically run a transatlantic passenger jet with 2,000 passengers, assuming it’s even possible to build such an airframe.)
sdenton4 4y ago
ICE engines only manage to turn ~15% of the stored energy in gasoline into actual work. A bit of googling suggests that jet engines are about 35% efficient. Stored electricity is much more efficiently turned into mechanical work... Electric engines have 75-90% efficiency. So, you get a lot more work or unit of stored energy.
- jansan 4y ago
  That factor 6 already seems to include the efficiency of the engine. Pure chemical energy density of kerosene is 12000 W/kg, 24x the new battery's energy densitiy.
- thedrbrian 4y ago
  table on wikipedia says the 15% thing might be out of date. https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption?useskin=vector https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio...
kpw94 4y ago
> Why does 500wh/kg make electric aircraft possible? 6x less than kerosene Where did you read that kerosene is at 3000Wh/kg? My googling says 12,000Wh/kg The tweet thread from TFA and its replies just says that for aircraft, weight impact is important. See https://twitter.com/__bdimitrov__/status/1298753593638440960 https://twitter.com/__bdimitrov__/status/1298753593638440960: "260 to 400 Wh/kg should lengthen flight time by 90.8% --- assuming that 100% of the drone weight is from the battery." But going from 400 to 500 Wh/kg adds another 39% on top of that, so 2.6x longer total
- DrSAR 4y ago
  Yes. 12kWh/kg chemical energy for kerosene, a little more for avgas. But with a 25% efficiency you are only getting 3kWh out of a kg of fuel. Electric motors tend to have higher efficiency -- maybe up to 75% so you might nearly get 500Wh from a kg of battery.
  - oblio 4y ago
    Electric motors are over 85%, some reaching 95%, from what I remember.
krasin 4y ago
Let's consider Cessna-172S ([4]). Its characteristics: - 130 kW engine, Lycoming_O-360 that weighs 117 kg. For comparison, an electric motor of this range would weigh 11-13 kg (at 10-12 kW/kg, [2]). That saves 100+ kg weight immediately and we can put 50+ kWh batteries instead. - It carries up to 200 liters of kerosene ([3]), which weighs 164 kg. We can place 82 kWh of batteries instead. - The engine consumes around 30 liters/hour ([1]), which gives us ~6.7 hours of flight time or the equivalent of 6.7*130=871 kWh for an electric-power plane. - The fuel tank weighs about ~14 kg (source: an LLM, sorry) and gives us another 7 kWh. So, we can put 50+82+7=139 kWh. By using modern materials, we can probably increase it to ~180 kWh, which will give us about 1.5 hours of flight time / 300 km range. This is much less than 6.7 hours, but quite practical for recreation and short flights. And it would be much cheaper to run too. That said, still not practical for medium and long flights. 1. https://en.wikipedia.org/wiki/Lycoming_O-360 https://en.wikipedia.org/wiki/Lycoming_O-360 2. https://cleantechnica.com/2021/03/25/groundbreaking-h3x-motor-brings-electric-aircraft-one-step-closer-to-reality/ https://cleantechnica.com/2021/03/25/groundbreaking-h3x-moto... 3. https://www.globalair.com/aircraft-for-sale/specifications?specid=131 https://www.globalair.com/aircraft-for-sale/specifications?s... 4. https://en.wikipedia.org/wiki/Cessna_172 https://en.wikipedia.org/wiki/Cessna_172
- Someone 4y ago
  The airplane would be a bit heavier at landing, though. I expect that will require a somewhat heavier landing gear. I also think taking out the weight of the tank is unfair if you don’t add weight for the structures for holding the batteries. But yes, for many smaller planes, we’re close to flying electric on shorter flights being economically feasible.
  - krasin 4y ago
    Fair points. But the point that CATL makes with this announce is that before this capacity boost, electric planes were a complete joke. Now, they are only somewhat funny. What I am more excited about is that electrically pumped rockets are now a lot more practical. As an example, Electron is such a rocket ([1]). It can now reduce the weight of the battery pack and increase payload. 1. https://en.wikipedia.org/wiki/Rutherford_(rocket_engine) https://en.wikipedia.org/wiki/Rutherford_(rocket_engine)
pcurve 4y ago
Yep. Also... kerosene gets spent. Pilots can also dump fuel in emergency when it's too heavy to land. Battery powered planes can't dump electricity, so I'd imagine some trade offs that have to be made.
- thriftwy 4y ago
  Electric engines may be much more reliable than kerosene engines.
  - Toutouxc 4y ago
    This is more about day to day operations than emergencies. For an electric plane, your MTOW (max takeoff weight) is equal to your MLW (max landing weight). An ICE plane can take off with "bonus" fuel that it can't land with for structural reasons, while an electric plane can't.
  - pcurve 4y ago
    I would hope so, considering this is what it looks like inside. https://en.wikipedia.org/wiki/Rolls-Royce_Trent_1000#/media/File:Trent_1000_GoodwinHall_VirginiaTech.jpg https://en.wikipedia.org/wiki/Rolls-Royce_Trent_1000#/media/... But. Turbine engine is actually very reliable and doesn't need overhaul for 20,000 flight hours.
    - thriftwy 4y ago
      The problem here is single-engine planes losing engine on takeoff. Would be almost non-issue with electrics.
- jansan 4y ago
  That is a very good and often overlooked point. So in average on a flight one has to calculate maybe with 60% weight of kerosene, while the battery keeps 100% of its weight during the entire flight.
  - tjmc 4y ago
tormeh 4y ago
We're talking short flights here.
- gibolt 4y ago
  Not at this density. This is the minimum requirement for medium length large airplanes. Small aircraft are already viable with mass produced batteries. As they scale production of these, hopefully they can get 20% additional improvements at the cell/pack level, reaching potential to replace the most common flights.
jl6 4y ago
I feel that synthetic kerosene via electrolysis is a far more viable path to sustainable aviation than battery-electric engines. The energy-inefficiency doesn’t really matter as long as you can keep the total cost of the flight within consumer reach.
- Toutouxc 4y ago
  Carbon neutral synthetic fuels might make sense for airliners, because they're already pretty efficient, reliable and incomprehensibly powerful and there's tons of other stuff in them that'd require maintenance even if you took out the engines. They don't make sense for general aviation planes that are usually a fifty year-old engine design that requires expensive overhauls and guzzles expensive fuel wrapped in a bit of aluminum.
  - someweirdperson 4y ago
    Compated to jet fuel, avgas is more expensive today because there's almost no market for it. When synthesized, it's probably cheaper to produce than jet fuel.
  - dx034 4y ago
    But do we really need to focus on general aviation? I don't have numbers but believe it to be a pretty small part overall. In transportation, it's also fine if we keep some gasoline speciality vehicles for a long time, as long as we're able to convert the vast majority of cars and trucks.
dzhiurgis 4y ago
Well we had electric aircraft for half a century, but thats just toys. The variable is how many passengers can you fit.
- jillesvangurp 4y ago
  Nope, the variable is cost per passenger. Large jets only exist because fuel is really expensive. The cost per passenger gets astronomical with smaller planes. That's why only rich people can afford that. Big planes are more economical. Because of the fuel. This is simply not true with electrical planes. A mega watt hour of power is about 60-100$. And much cheaper than that with renewables. Not at retail prices of course. But if you consume power by the mwh, you'd be investing in your own generation (solar + storage) pretty soon. A mwh is about what you need to move a small electrical plane a few hundred miles. The kerosene cost for a similar journey in a small jet is going to be hundreds of dollars, even for a small jet. The smallest jets burn 50-100 gallons of fuel per hour (in cruise). Depending where you get your fuel, that ranges from 3-5$ per gallon. That's why small jets are only for rich people. Even a very short flight sets you back hundreds of dollars. A simple propeller plane is cheaper. But we're still talking 5-10 gallons per hour. That's why people talk about 100$ hamburgers. Because that's what it costs to take your tiny plane out to grab a burger somewhere. Big big jets are a bit more economical with fuel than small ones. But they only makes sense if you can distribute fuel cost among many passengers. With electrical, you can use lots of smaller planes cost effectively rather than having to put lots of people in a few bigger ones. For the same reason, you don't need big airports either. Or worry about pollution. And even the noise of small electrical planes is not as much of a problem. And with autonomous flight, we won't even need pilots long term. Small electrical planes are good enough and much nicer for passengers, more flexible to operate, etc.
  - Maxion 4y ago
    Nail on the head. Airliners have already moved away from the hub-and-spoke model to a point-to-point model where smaller narrowbodies fly direct from small airport to small airport (E.g. Southwest in the US). They do this specifically because of the increased efficiencies of smaller aircraft. If you can further lower the per passanger cost of small planes, you can make smaller airports more viable, and fly point-to-point from more odd routes. Think Oxford, UK (OXF), to Gothenburg, Sweden (GSE).
jillesvangurp 4y ago
Well, they were already possible and being sold. But with relatively short but usable ranges. Those now more than double with this battery. Which makes those planes usable in a lot more scenarios. Consider the Eviation Alice, one of the 9 passenger prototype electrical planes that is currently undergoing test flights (i.e. it definitely works). The advertised range is 250nm. Not amazing. But far enough for a lot of regional flights. What would happen if you double the battery capacity without increasing the weight? You more than double that range. This is counter intuitive until you realize that you are not going to need more energy for taking off, or reserves. All that extra energy goes into extending cruise range. So you get more than 250nm extra. Basically, it's probably getting closer to 600nm. That's still not amazing but there are a lot of flights every day that are much shorter than that. All of those are now doable with electrical planes. At a fraction of the fuel cost. Most flights are short haul. And they are, well, short. Which means, all of those are in scope for electrical planes. Small planes work well for these too. You don't have to cram hundreds of people in a plane if you eliminate fuel cost as a major cost factor. That's the only reason we do that. It's not like it's pleasant or comfortable. 20 ten passenger planes can do the work of one passenger jet. But it can do it more flexible and cover more destinations too. Electrical planes are not about doing exactly the same things that we do with traditional planes but about doing a lot more than that. Basically, less noise, less pollution, less cost, means that a whole lot of flights that would be considered decadent and obscene right now become perfectly feasible and reasonable. A ten minute hop across town. Why not? Live 70 miles from your office? Not a problem, you commute there in under 15 minutes. For the price of a few cups of coffee.
- vidarh 4y ago
  > Most flights are short haul. And they are, well, short. Which means, all of those are in scope for electrical planes. Exactly. In the EU, Eurocontrol (European Organisation for the Safety of Air Navigation) says 30.6% of flights in 2020 were 0-500km, roughly within the range of the Eviation Alice currently. A further 43.6% of flights in the EU are between 500 and 1500km. Source [1] > You don't have to cram hundreds of people in a plane if you eliminate fuel cost as a major cost factor. That's the only reason we do that. Not only. Gate capacity and runway capacity is an issue too. But that might also be easier to resolve with smaller electric planes. E.g. there's Liliums approach of vertical takeoff from little more than a helipad-sized platform, but even non VTOL planes capable of taking off from short runways would be helpful. [1] https://www.eurocontrol.int/publication/eurocontrol-data-snapshot-co2-emissions-flight-distance https://www.eurocontrol.int/publication/eurocontrol-data-sna...
fwlr 4y ago
I don’t think Musk has given a writeup of his reasons for thinking 400wh/kg is the magic number, but a lot of research has been done that says similar numbers. This paper https://www.sciencedirect.com/science/article/pii/S2666691X2200032X https://www.sciencedirect.com/science/article/pii/S2666691X2... is a good review; it cites researchers saying 800wh/kg for an electric Airbus A320, NASA saying 400Wh/kg for general aviation and 750Wh/kg for regional aviation, and other researchers saying 600Wh/kg for commercial regional aircraft and 820Wh/kg for commercial narrow-body aircraft. That paper also sketches out the argument for electric flight at close to current battery densities rather than close to kerosene energy densities. It goes: Jet fuel gets roughly 28% final efficiency while electric gets roughly 90%, so divide jet fuel by 3 to get 4,000 effective Wh/kg. Alternate aerodynamic designs and especially distributed propulsion are much more achievable with electric engines. Imagine the difficulty of making a 14-, 24-, or even 36-turbine aircraft, yet all of those have been built and flown with electric engines already (https://en.m.wikipedia.org/wiki/NASA_X-57_Maxwell https://en.m.wikipedia.org/wiki/NASA_X-57_Maxwell, https://en.m.wikipedia.org/wiki/Aurora_XV-24_LightningStrike https://en.m.wikipedia.org/wiki/Aurora_XV-24_LightningStrike, and https://en.m.wikipedia.org/wiki/Lilium_Jet https://en.m.wikipedia.org/wiki/Lilium_Jet respectively). Gains of 3-5x have been observed here and higher is predicted, the conservative mean is 4x, so divide again by 4 to get jet fuel to 1,000 effective Wh/kg. That is getting close to current energy densities of batteries. You only need to find one more ~2x improvement that electric flight can obtain over jet fuel to bring it into the range of 500Wh/kg, which CATL is saying they have in production right now. (Presumably Musk’s magic 400Wh/kg number involved another 2.5x improvement, though I don’t know where specifically he thought it would come from. The internet seems to think he said you can go higher because you don’t need oxidizer from the air to burn jet fuel, but that doesn’t sound right since you still need to push on the air with your fans and you’ll run out of that at high altitude before you run out of oxygen, so it must be coming from somewhere else. Regardless, the point is that jet fuel imposes design constraints that trap you in a local maximum of aircraft efficiency, and electric engines allow you to explore a wider space which may have much much higher maximums.)
- someweirdperson 4y ago
  > Jet fuel gets roughly 28% final efficiency while electric gets roughly 90% 90% likely doesn't include the efficieny of the prop?
chemmail 4y ago
My house alone makes 12-14kWh of electricity a day. Do that to some land near an airport and it will be almost free.
elihu 4y ago
The point isn't necessarily to equal or beat kerosene in terms of weight and range, but rather to be good enough that electric aircraft are usable for many or most use cases. Planes tend to be very expensive to operate, due to maintenance and fuel costs. Some people would be happy to trade range for dramatically lower operating costs.
fh973 4y ago
Soaring is currently making the switch, not only as sustainers, but also for starting. There are models from major manufacturers, like the Schleicher AS 33/34 me [1] or Antares [2]. [1] https://www.alexander-schleicher.de/en/flugzeuge/as-34-me/ https://www.alexander-schleicher.de/en/flugzeuge/as-34-me/ [2] https://www.lange-aviation.com/antares-serie/antares-21e/ https://www.lange-aviation.com/antares-serie/antares-21e/
ortusdux 4y ago
The best application I've seen for the currently available electric airplanes are flight schools. One plane I looked into has a flight time of 1.5hrs, which is plenty for training. When I last priced out instructor time, 30% of the cost was the fuel. This means that flight schools could cut prices by up to 25% or so. That being said, the plane I looked into was $250k, while a student level ICE plane could be had for $20-50k.
i-dont-remember 4y ago
Video[0] isn't a direct answer, but I found it helpful for understanding the trade offs that come when considering using electric power for a plane vs regular fuel. They show the math in an easy to follow diagram. tl;dr for their small kit aircraft the weight of batteries they would need to match the stored energy of equivalent fuel (even with a battery at 500wh/kg) would be 5-10x heavier, and also not get lighter during the flight. They said for long range it doesn't make sense, but that there are lots of companies iterating in the short range electric space. - [0] https://www.youtube.com/watch?v=LdSnHQtoVTI https://www.youtube.com/watch?v=LdSnHQtoVTI

ralusek 4y ago

I assume it's a limit motivated more by how far you can go rather than the cost of fueling/charging. Like, above a certain weight/energy store ratio, it's either too heavy to fly or would just have an incredibly limited range.

nvy 4y ago

Seems like marketing hype to me. An 8-hour transatlantic flight requires something like 600MWhr of energy. That's about 75MW, which is in small nuclear reactor territory.

kolinko 4y ago
Closer to 200MWh - jet engines are ~30% efficient
rgmerk 4y ago
Not every flight is transatlantic. These batteries, if they deliver on the advertised specs and aren’t too expensive should make short-range electric aviation possible. The electric air taxis that Joby and others are working on suddenly have a lot bigger margin to work with, as do electric regional airliners.
Epa095 4y ago
Replacing transatlantic flights is out of the question (for batteries for now). But there exists shorter routes, and according to this list [1] on Wikipedia, the busiest route in the world is 449km long. That's probably also not doable now, but maybe in some years? For the first years it will probably only be a few wierd, short routes in rich countries like Norway with 110% financial support from the state. But when they can safely fly 5-600km there is a actually quite a number of routes with a lot of passengers out there. 1: https://en.m.wikipedia.org/wiki/List_of_busiest_passenger_air_routes https://en.m.wikipedia.org/wiki/List_of_busiest_passenger_ai...
fwlr 4y ago
The US very nearly built a 60MW nuclear reactor for use in airplanes after their scaled down design at 2.5MW was successfully built, ran, and tested. This was done in the 1950s and, incidentally, required inventing molten salt reactors. https://en.m.wikipedia.org/wiki/Aircraft_Reactor_Experiment https://en.m.wikipedia.org/wiki/Aircraft_Reactor_Experiment (They actually planned to go all the way to 350MW, which could theoretically run a transatlantic passenger jet with 2,000 passengers, assuming it’s even possible to build such an airframe.)

sdenton4 4y ago

ICE engines only manage to turn ~15% of the stored energy in gasoline into actual work. A bit of googling suggests that jet engines are about 35% efficient. Stored electricity is much more efficiently turned into mechanical work... Electric engines have 75-90% efficiency. So, you get a lot more work or unit of stored energy.

jansan 4y ago
That factor 6 already seems to include the efficiency of the engine. Pure chemical energy density of kerosene is 12000 W/kg, 24x the new battery's energy densitiy.
thedrbrian 4y ago
table on wikipedia says the 15% thing might be out of date. https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption?useskin=vector https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio...

kpw94 4y ago

> Why does 500wh/kg make electric aircraft possible? 6x less than kerosene Where did you read that kerosene is at 3000Wh/kg? My googling says 12,000Wh/kg The tweet thread from TFA and its replies just says that for aircraft, weight impact is important. See https://twitter.com/__bdimitrov__/status/1298753593638440960 https://twitter.com/__bdimitrov__/status/1298753593638440960: "260 to 400 Wh/kg should lengthen flight time by 90.8% --- assuming that 100% of the drone weight is from the battery." But going from 400 to 500 Wh/kg adds another 39% on top of that, so 2.6x longer total

DrSAR 4y ago
Yes. 12kWh/kg chemical energy for kerosene, a little more for avgas. But with a 25% efficiency you are only getting 3kWh out of a kg of fuel. Electric motors tend to have higher efficiency -- maybe up to 75% so you might nearly get 500Wh from a kg of battery.
- oblio 4y ago
  Electric motors are over 85%, some reaching 95%, from what I remember.

krasin 4y ago

Let's consider Cessna-172S ([4]). Its characteristics: - 130 kW engine, Lycoming_O-360 that weighs 117 kg. For comparison, an electric motor of this range would weigh 11-13 kg (at 10-12 kW/kg, [2]). That saves 100+ kg weight immediately and we can put 50+ kWh batteries instead. - It carries up to 200 liters of kerosene ([3]), which weighs 164 kg. We can place 82 kWh of batteries instead. - The engine consumes around 30 liters/hour ([1]), which gives us ~6.7 hours of flight time or the equivalent of 6.7*130=871 kWh for an electric-power plane. - The fuel tank weighs about ~14 kg (source: an LLM, sorry) and gives us another 7 kWh. So, we can put 50+82+7=139 kWh. By using modern materials, we can probably increase it to ~180 kWh, which will give us about 1.5 hours of flight time / 300 km range. This is much less than 6.7 hours, but quite practical for recreation and short flights. And it would be much cheaper to run too. That said, still not practical for medium and long flights. 1. https://en.wikipedia.org/wiki/Lycoming_O-360 https://en.wikipedia.org/wiki/Lycoming_O-360 2. https://cleantechnica.com/2021/03/25/groundbreaking-h3x-motor-brings-electric-aircraft-one-step-closer-to-reality/ https://cleantechnica.com/2021/03/25/groundbreaking-h3x-moto... 3. https://www.globalair.com/aircraft-for-sale/specifications?specid=131 https://www.globalair.com/aircraft-for-sale/specifications?s... 4. https://en.wikipedia.org/wiki/Cessna_172 https://en.wikipedia.org/wiki/Cessna_172

Someone 4y ago
The airplane would be a bit heavier at landing, though. I expect that will require a somewhat heavier landing gear. I also think taking out the weight of the tank is unfair if you don’t add weight for the structures for holding the batteries. But yes, for many smaller planes, we’re close to flying electric on shorter flights being economically feasible.
- krasin 4y ago
  Fair points. But the point that CATL makes with this announce is that before this capacity boost, electric planes were a complete joke. Now, they are only somewhat funny. What I am more excited about is that electrically pumped rockets are now a lot more practical. As an example, Electron is such a rocket ([1]). It can now reduce the weight of the battery pack and increase payload. 1. https://en.wikipedia.org/wiki/Rutherford_(rocket_engine) https://en.wikipedia.org/wiki/Rutherford_(rocket_engine)

pcurve 4y ago

Yep. Also... kerosene gets spent. Pilots can also dump fuel in emergency when it's too heavy to land. Battery powered planes can't dump electricity, so I'd imagine some trade offs that have to be made.

thriftwy 4y ago
Electric engines may be much more reliable than kerosene engines.
- Toutouxc 4y ago
  This is more about day to day operations than emergencies. For an electric plane, your MTOW (max takeoff weight) is equal to your MLW (max landing weight). An ICE plane can take off with "bonus" fuel that it can't land with for structural reasons, while an electric plane can't.
- pcurve 4y ago
  I would hope so, considering this is what it looks like inside. https://en.wikipedia.org/wiki/Rolls-Royce_Trent_1000#/media/File:Trent_1000_GoodwinHall_VirginiaTech.jpg https://en.wikipedia.org/wiki/Rolls-Royce_Trent_1000#/media/... But. Turbine engine is actually very reliable and doesn't need overhaul for 20,000 flight hours.
  - thriftwy 4y ago
    The problem here is single-engine planes losing engine on takeoff. Would be almost non-issue with electrics.
jansan 4y ago
That is a very good and often overlooked point. So in average on a flight one has to calculate maybe with 60% weight of kerosene, while the battery keeps 100% of its weight during the entire flight.
- tjmc 4y ago

tormeh 4y ago

We're talking short flights here.

gibolt 4y ago
Not at this density. This is the minimum requirement for medium length large airplanes. Small aircraft are already viable with mass produced batteries. As they scale production of these, hopefully they can get 20% additional improvements at the cell/pack level, reaching potential to replace the most common flights.

jl6 4y ago

I feel that synthetic kerosene via electrolysis is a far more viable path to sustainable aviation than battery-electric engines. The energy-inefficiency doesn’t really matter as long as you can keep the total cost of the flight within consumer reach.

Toutouxc 4y ago
Carbon neutral synthetic fuels might make sense for airliners, because they're already pretty efficient, reliable and incomprehensibly powerful and there's tons of other stuff in them that'd require maintenance even if you took out the engines. They don't make sense for general aviation planes that are usually a fifty year-old engine design that requires expensive overhauls and guzzles expensive fuel wrapped in a bit of aluminum.
- someweirdperson 4y ago
  Compated to jet fuel, avgas is more expensive today because there's almost no market for it. When synthesized, it's probably cheaper to produce than jet fuel.
- dx034 4y ago
  But do we really need to focus on general aviation? I don't have numbers but believe it to be a pretty small part overall. In transportation, it's also fine if we keep some gasoline speciality vehicles for a long time, as long as we're able to convert the vast majority of cars and trucks.

dzhiurgis 4y ago

Well we had electric aircraft for half a century, but thats just toys. The variable is how many passengers can you fit.

jillesvangurp 4y ago
Nope, the variable is cost per passenger. Large jets only exist because fuel is really expensive. The cost per passenger gets astronomical with smaller planes. That's why only rich people can afford that. Big planes are more economical. Because of the fuel. This is simply not true with electrical planes. A mega watt hour of power is about 60-100$. And much cheaper than that with renewables. Not at retail prices of course. But if you consume power by the mwh, you'd be investing in your own generation (solar + storage) pretty soon. A mwh is about what you need to move a small electrical plane a few hundred miles. The kerosene cost for a similar journey in a small jet is going to be hundreds of dollars, even for a small jet. The smallest jets burn 50-100 gallons of fuel per hour (in cruise). Depending where you get your fuel, that ranges from 3-5$ per gallon. That's why small jets are only for rich people. Even a very short flight sets you back hundreds of dollars. A simple propeller plane is cheaper. But we're still talking 5-10 gallons per hour. That's why people talk about 100$ hamburgers. Because that's what it costs to take your tiny plane out to grab a burger somewhere. Big big jets are a bit more economical with fuel than small ones. But they only makes sense if you can distribute fuel cost among many passengers. With electrical, you can use lots of smaller planes cost effectively rather than having to put lots of people in a few bigger ones. For the same reason, you don't need big airports either. Or worry about pollution. And even the noise of small electrical planes is not as much of a problem. And with autonomous flight, we won't even need pilots long term. Small electrical planes are good enough and much nicer for passengers, more flexible to operate, etc.
- Maxion 4y ago
  Nail on the head. Airliners have already moved away from the hub-and-spoke model to a point-to-point model where smaller narrowbodies fly direct from small airport to small airport (E.g. Southwest in the US). They do this specifically because of the increased efficiencies of smaller aircraft. If you can further lower the per passanger cost of small planes, you can make smaller airports more viable, and fly point-to-point from more odd routes. Think Oxford, UK (OXF), to Gothenburg, Sweden (GSE).

jillesvangurp 4y ago

Well, they were already possible and being sold. But with relatively short but usable ranges. Those now more than double with this battery. Which makes those planes usable in a lot more scenarios. Consider the Eviation Alice, one of the 9 passenger prototype electrical planes that is currently undergoing test flights (i.e. it definitely works). The advertised range is 250nm. Not amazing. But far enough for a lot of regional flights. What would happen if you double the battery capacity without increasing the weight? You more than double that range. This is counter intuitive until you realize that you are not going to need more energy for taking off, or reserves. All that extra energy goes into extending cruise range. So you get more than 250nm extra. Basically, it's probably getting closer to 600nm. That's still not amazing but there are a lot of flights every day that are much shorter than that. All of those are now doable with electrical planes. At a fraction of the fuel cost. Most flights are short haul. And they are, well, short. Which means, all of those are in scope for electrical planes. Small planes work well for these too. You don't have to cram hundreds of people in a plane if you eliminate fuel cost as a major cost factor. That's the only reason we do that. It's not like it's pleasant or comfortable. 20 ten passenger planes can do the work of one passenger jet. But it can do it more flexible and cover more destinations too. Electrical planes are not about doing exactly the same things that we do with traditional planes but about doing a lot more than that. Basically, less noise, less pollution, less cost, means that a whole lot of flights that would be considered decadent and obscene right now become perfectly feasible and reasonable. A ten minute hop across town. Why not? Live 70 miles from your office? Not a problem, you commute there in under 15 minutes. For the price of a few cups of coffee.

vidarh 4y ago
> Most flights are short haul. And they are, well, short. Which means, all of those are in scope for electrical planes. Exactly. In the EU, Eurocontrol (European Organisation for the Safety of Air Navigation) says 30.6% of flights in 2020 were 0-500km, roughly within the range of the Eviation Alice currently. A further 43.6% of flights in the EU are between 500 and 1500km. Source [1] > You don't have to cram hundreds of people in a plane if you eliminate fuel cost as a major cost factor. That's the only reason we do that. Not only. Gate capacity and runway capacity is an issue too. But that might also be easier to resolve with smaller electric planes. E.g. there's Liliums approach of vertical takeoff from little more than a helipad-sized platform, but even non VTOL planes capable of taking off from short runways would be helpful. [1] https://www.eurocontrol.int/publication/eurocontrol-data-snapshot-co2-emissions-flight-distance https://www.eurocontrol.int/publication/eurocontrol-data-sna...

fwlr 4y ago

I don’t think Musk has given a writeup of his reasons for thinking 400wh/kg is the magic number, but a lot of research has been done that says similar numbers. This paper https://www.sciencedirect.com/science/article/pii/S2666691X2200032X https://www.sciencedirect.com/science/article/pii/S2666691X2... is a good review; it cites researchers saying 800wh/kg for an electric Airbus A320, NASA saying 400Wh/kg for general aviation and 750Wh/kg for regional aviation, and other researchers saying 600Wh/kg for commercial regional aircraft and 820Wh/kg for commercial narrow-body aircraft. That paper also sketches out the argument for electric flight at close to current battery densities rather than close to kerosene energy densities. It goes: Jet fuel gets roughly 28% final efficiency while electric gets roughly 90%, so divide jet fuel by 3 to get 4,000 effective Wh/kg. Alternate aerodynamic designs and especially distributed propulsion are much more achievable with electric engines. Imagine the difficulty of making a 14-, 24-, or even 36-turbine aircraft, yet all of those have been built and flown with electric engines already (https://en.m.wikipedia.org/wiki/NASA_X-57_Maxwell https://en.m.wikipedia.org/wiki/NASA_X-57_Maxwell, https://en.m.wikipedia.org/wiki/Aurora_XV-24_LightningStrike https://en.m.wikipedia.org/wiki/Aurora_XV-24_LightningStrike, and https://en.m.wikipedia.org/wiki/Lilium_Jet https://en.m.wikipedia.org/wiki/Lilium_Jet respectively). Gains of 3-5x have been observed here and higher is predicted, the conservative mean is 4x, so divide again by 4 to get jet fuel to 1,000 effective Wh/kg. That is getting close to current energy densities of batteries. You only need to find one more ~2x improvement that electric flight can obtain over jet fuel to bring it into the range of 500Wh/kg, which CATL is saying they have in production right now. (Presumably Musk’s magic 400Wh/kg number involved another 2.5x improvement, though I don’t know where specifically he thought it would come from. The internet seems to think he said you can go higher because you don’t need oxidizer from the air to burn jet fuel, but that doesn’t sound right since you still need to push on the air with your fans and you’ll run out of that at high altitude before you run out of oxygen, so it must be coming from somewhere else. Regardless, the point is that jet fuel imposes design constraints that trap you in a local maximum of aircraft efficiency, and electric engines allow you to explore a wider space which may have much much higher maximums.)

someweirdperson 4y ago
> Jet fuel gets roughly 28% final efficiency while electric gets roughly 90% 90% likely doesn't include the efficieny of the prop?

chemmail 4y ago

My house alone makes 12-14kWh of electricity a day. Do that to some land near an airport and it will be almost free.

elihu 4y ago

The point isn't necessarily to equal or beat kerosene in terms of weight and range, but rather to be good enough that electric aircraft are usable for many or most use cases. Planes tend to be very expensive to operate, due to maintenance and fuel costs. Some people would be happy to trade range for dramatically lower operating costs.

fh973 4y ago

Soaring is currently making the switch, not only as sustainers, but also for starting. There are models from major manufacturers, like the Schleicher AS 33/34 me [1] or Antares [2]. [1] https://www.alexander-schleicher.de/en/flugzeuge/as-34-me/ https://www.alexander-schleicher.de/en/flugzeuge/as-34-me/ [2] https://www.lange-aviation.com/antares-serie/antares-21e/ https://www.lange-aviation.com/antares-serie/antares-21e/

ortusdux 4y ago

The best application I've seen for the currently available electric airplanes are flight schools. One plane I looked into has a flight time of 1.5hrs, which is plenty for training. When I last priced out instructor time, 30% of the cost was the fuel. This means that flight schools could cut prices by up to 25% or so. That being said, the plane I looked into was $250k, while a student level ICE plane could be had for $20-50k.

i-dont-remember 4y ago

Video[0] isn't a direct answer, but I found it helpful for understanding the trade offs that come when considering using electric power for a plane vs regular fuel. They show the math in an easy to follow diagram. tl;dr for their small kit aircraft the weight of batteries they would need to match the stored energy of equivalent fuel (even with a battery at 500wh/kg) would be 5-10x heavier, and also not get lighter during the flight. They said for long range it doesn't make sense, but that there are lots of companies iterating in the short range electric space. - [0] https://www.youtube.com/watch?v=LdSnHQtoVTI https://www.youtube.com/watch?v=LdSnHQtoVTI