5 ms·

The energy density of gasoline does not matter at all. Batteries are good enough for some applications, like short distance flights. And the operating costs for

The energy density of gasoline does not matter at all. Batteries are good enough for some applications, like short distance flights. And the operating costs for use cases where batteries work strongly favour batteries. Power density has not been a problem for a while. We are not anywhere near the theoretical limits of battery energy density. So as soon as there are some commercial applications for battery powered flight, there will be a strong economic incentive to get closer to the theoretical limits. Current jet engines are absolute engineering miracles that go very close to the physical limits to get maximum efficiency. But it took several decades to get there.

whatshisface 4y ago
There is already a lot of economic incentive for lighter batteries.
- rklaehn 4y ago
  Yes, and they are improving by a few percent every year. No major breakthroughs, but compounding improvements year over year, which do add up. Batteries have improved incredibly in my lifetime. As a kid I had an electric RC plane that barely made it off the ground. Now you can get pretty cheap aerobatic RC planes that easily compete with gasoline powered models. Battery powered screwdrivers used to be incredibly underpowered. Now I have a very decent battery powered rotary hammer... https://cdn.arstechnica.net/wp-content/uploads/2021/05/bnef_e_density-1440x810.jpg https://cdn.arstechnica.net/wp-content/uploads/2021/05/bnef_...
robonerd 4y ago
> The energy density of gasoline does not matter at all. Well if we're talking about commercial aviation, we're talking about jet fuel not gasoline. Regardless, it obviously matters a lot. A fully loaded 747 freighter has somewhere around 200 tons of jet fuel and a max payload of about 130 tons. They already need more fuel than cargo, and that's with the excellent energy density of jet fuel. Furthermore, traditional planes get lighter the longer they fly as they burn off their substantial fuel loads. The last 20% of the fuel goes a lot further than the first 20%. Batteries don't get this advantage at all. (Dropping batteries from the plane with parachutes is a terrible idea, but I've lost count of the number of times I've seen it proposed..) > We are not anywhere near the theoretical limits of battery energy density. This doesn't jive with what I've read. It's my understanding that we're already near the limits of what electrochemistry can give us, and future advancements are likely to come from improved electrode designs, with maybe 2-3x better performance possible if we're lucky.
- rklaehn 4y ago
  > Well if we're talking about commercial aviation, we're talking about jet fuel not gasoline. Regardless, it obviously matters a lot. A fully loaded 747 freighter has somewhere around 200 tons of jet fuel and a max payload of about 130 tons. You only need giant quantities of kerosene for transoceanic or transcontinental travel. The lilium business model requires a range of a few 100 km, which is possible with today's batteries. Very long distance air travel is impossible with today's commercially available batteries, but is possible with exotic chemistries (see below) or with hydrogen fuel cells. > This doesn't jive with what I've read. It's my understanding that we're already near the limits of what electrochemistry can give us, and future advancements are likely to come from improved electrode designs, with maybe 2-3x better performance possible if we're lucky. There are several battery chemistries such as lithium sulfur or lithium air that have extremely high energy densities. But cycle life remains very low, which makes them uneconomical. There has been decent progress made in improving cycle life, but it is still too low to be economical. There are military applications where a low cycle life is acceptable.
  - robonerd 4y ago
    > a range of a few 100 km, which is possible with today's batteries. Not with a meaningful amount of cargo it isn't; look up the electric planes that are actually flying today (and it's certainly not for want of trying, this is a very trendy field.) I can think of only a few niches where very light but expensive cargo needs to go somewhere close-by, but faster than is possible with a truck. Organs for transplant, and rich people.
    - FullyFunctional 4y ago
      The cargo here is humans
      - robonerd 4y ago
        But can you carry enough of them to make the whole thing worth it?

whatshisface 4y ago

There is already a lot of economic incentive for lighter batteries.

rklaehn 4y ago
Yes, and they are improving by a few percent every year. No major breakthroughs, but compounding improvements year over year, which do add up. Batteries have improved incredibly in my lifetime. As a kid I had an electric RC plane that barely made it off the ground. Now you can get pretty cheap aerobatic RC planes that easily compete with gasoline powered models. Battery powered screwdrivers used to be incredibly underpowered. Now I have a very decent battery powered rotary hammer... https://cdn.arstechnica.net/wp-content/uploads/2021/05/bnef_e_density-1440x810.jpg https://cdn.arstechnica.net/wp-content/uploads/2021/05/bnef_...

robonerd 4y ago

> The energy density of gasoline does not matter at all. Well if we're talking about commercial aviation, we're talking about jet fuel not gasoline. Regardless, it obviously matters a lot. A fully loaded 747 freighter has somewhere around 200 tons of jet fuel and a max payload of about 130 tons. They already need more fuel than cargo, and that's with the excellent energy density of jet fuel. Furthermore, traditional planes get lighter the longer they fly as they burn off their substantial fuel loads. The last 20% of the fuel goes a lot further than the first 20%. Batteries don't get this advantage at all. (Dropping batteries from the plane with parachutes is a terrible idea, but I've lost count of the number of times I've seen it proposed..) > We are not anywhere near the theoretical limits of battery energy density. This doesn't jive with what I've read. It's my understanding that we're already near the limits of what electrochemistry can give us, and future advancements are likely to come from improved electrode designs, with maybe 2-3x better performance possible if we're lucky.

rklaehn 4y ago
> Well if we're talking about commercial aviation, we're talking about jet fuel not gasoline. Regardless, it obviously matters a lot. A fully loaded 747 freighter has somewhere around 200 tons of jet fuel and a max payload of about 130 tons. You only need giant quantities of kerosene for transoceanic or transcontinental travel. The lilium business model requires a range of a few 100 km, which is possible with today's batteries. Very long distance air travel is impossible with today's commercially available batteries, but is possible with exotic chemistries (see below) or with hydrogen fuel cells. > This doesn't jive with what I've read. It's my understanding that we're already near the limits of what electrochemistry can give us, and future advancements are likely to come from improved electrode designs, with maybe 2-3x better performance possible if we're lucky. There are several battery chemistries such as lithium sulfur or lithium air that have extremely high energy densities. But cycle life remains very low, which makes them uneconomical. There has been decent progress made in improving cycle life, but it is still too low to be economical. There are military applications where a low cycle life is acceptable.
- robonerd 4y ago
  > a range of a few 100 km, which is possible with today's batteries. Not with a meaningful amount of cargo it isn't; look up the electric planes that are actually flying today (and it's certainly not for want of trying, this is a very trendy field.) I can think of only a few niches where very light but expensive cargo needs to go somewhere close-by, but faster than is possible with a truck. Organs for transplant, and rich people.
  - FullyFunctional 4y ago
    The cargo here is humans
    - robonerd 4y ago
      But can you carry enough of them to make the whole thing worth it?