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.
Seems like it would still annihilate the payload/range.
- 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
2. https://cleantechnica.com/2021/03/25/groundbreaking-h3x-moto...
3. https://www.globalair.com/aircraft-for-sale/specifications?s...
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.
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.
Ha! Well put.
Silly as it sounds just thinking :)
Perfectly agree with everything, but 1.5hr may be very short if you need to have 30 minutes of reserve at landing. On the saving side, you don’t have to have an alternator to transform ICE energy into energy for the dashboard instruments. On the downside, you now need to heat the cabin manually, rather than reusing the ICE heat.
Interestingly, the Boeing 787 has already dispensed with bleed air. It uses compressors for heat and electric pumps for hydraulics.
Most modern airliners do not use bleed air for climate control in the cabin anymore.
Electric aircraft of the future will have half the drag or less. High aspect ratios, flush fairings, streamlined cockpits etc.
https://en.wikipedia.org/wiki/Pipistrel_Alpha_Trainer#Alpha_...
324 nmi range for the regular variant. Around 65 nmi for the electric version.
This is with older batteries, probably with very bad pack-level energy density. The battery pack can even be swapped. Great to avoid having to wait for charging, but probably terrible for weight.
If you design the aircraft for electric flight from the ground up (see Maxwell X-57 for how you could do that), with a structural battery pack, and with 300-500wh/kg batteries, I'm willing to bet a 2-5 times increase in range is viable.
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.
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-sna...
We may also see a return to more of a hub-and-spoke model. Fly from a smaller, local airport close to you. Fly to some hub near the half-way point, switch to a plane that takes you to a small airport close to your destination. If planes are smaller maybe security can be relaxed too. Total time spent travelling could be comparable to taking a direct flight with a large international airport further from your origin and destination. Then the aircraft doesn't need to be very long range.
OTOH, security costs and airport fees could be cut I guess?
https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio...
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:
"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
But. Turbine engine is actually very reliable and doesn't need overhaul for 20,000 flight hours.
Recharging multiple airliners will take a nuclear reactor at the airport.
The challenge would be getting the right amount at the right time, like now with quick charging. Like there, you'd probably have buffer storage at the airport so that it consumes electricity when available (e.g. during the day from solar) and dispenses it to aircrafts when needed. Luckily, most airports in the world have nearly all take offs and landings during the day, so there's a big overlap. Dubai would be an example where likely all would come from solar but a lot is needed over night (if we ever get electric long-haul flights).
So overall I don't think that this would be the limiting factor. But I guess larger airliners are more likely to run on synthetic fuels than electricity for a long time. And I guess that's fine, we have a lot of areas where cheap and/or dense batteries can help us much more in the short term (grid storage, cars, trucks).
Those are pipe dreams :-)))
Solar recharging for electric cars is not realistic, let alone for electric planes.
Wind charger... maybe there's something there, but the fact that nobody has tried it probably means it's not good enough.
https://www.arenaev.com/why_solar_panels_on_cars_are_beyond_...
> So under optimal conditions the Hyundai solar roof would yield 280kWh *yearly*. In London you'd get 164kWh.
Wind charging is more of a pipe dream, but there's no reason a plane couldn't glide for a period of time to get some energy back, similar to regenerative breaking.
There have been experiments in both areas, and while it's certainly unfeasible today for any large aircraft, the technology and efficiency will only improve. It would be wrong to discard these as an impossibility.
And the energy they require for flying is an order of magnitude than that required to drive stuff on the ground.
Take off requires a lot of resources, but maintaining altitude and speed are likely minimal additional energy.
The extra weight and structural challenges imposed by solar panels on aircraft don't seem worth it. The math on (174 sqft) * ideal theoretical power (250 W /m2) yields an optimistic ideal 4000 Watts. A conservative 75% power usage of a 172 engine is around 100kW. 4% under ideal circumstances.
Solar and wind are in many areas a) only available during certain hours b) expensive.
To ensure you have a stable power cost, and stable power availability, you as a large consumer (In the EU) make PPA agreements with power producers for specific KW rates, for specific KWh amounts, for specific times. These are complicated agreements.
A few panels on some warehouses and hangers close to an airport could keep the lights and the A/C on in the terminal, but that's about it. No one is putting up wind turbines anywhere close to an airport.
You can also do this on regular flights just to save weight. It's SpaceX style reusability but on a commercial aviation scale.
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.
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/Aurora_XV-24_LightningStrike, and 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.)
90% likely doesn't include the efficieny of the prop?
[1] https://www.alexander-schleicher.de/en/flugzeuge/as-34-me/
[2] https://www.lange-aviation.com/antares-serie/antares-21e/
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.
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.
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).
The third expensive component is staffing. Pilots are expensive and for complex aircraft they need lots of training. So, simple electrical airplanes lower the training cost and make it easier to train and find new pilots. And complexity is also a reason you often need two pilots. Smaller/simpler airplanes can be one pilot operations. And of course replacing pilots entirely when these things become autonomous brings further cost savings. The flip side is that lots of small planes require more pilots.
Finally, big airports are expensive. You have to pay landing fees in lots of places. And service fees. And missing your assigned slot because of delays is expensive. That too goes away if you start flying from less busy/cheaper airports.
So, there a few additional savings here beyond fuel. But that is the biggest one.
IMHO this is going to be a repeat of the EV revolution a decade ago. But minus a lot of the emotional bickering about range anxiety, etc. Most planes are operated by for profit businesses. The second something cheap becomes available, they'll be all over it. In the same way using electrical vans vs. ice vans is not a topic of debate in the industry. You get the electrical van if you can. They are cheaper to operate. There's zero uncertainty on that front so you see essentially all large fleets transitioning to electrical vans as soon as they can get it done.
With electrical flight, a lot of this stuff is bottle necked on product development (happening), certification (starting to happen), and volume production (not happening yet). Better batteries increase the demand further. But without volume production, demand is not the issue. Supply is. This is and will be supply constrained for a long time.
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.
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.
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.
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_ai...
(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.)