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>It's interesting how further up someone accused people of opposing nuclear energy for ideological reasons and then read proposals like this, which are complete

by krasin 5y ago

>It's interesting how further up someone accused people of opposing nuclear energy for ideological reasons and then read proposals like this, which are completely removed from reality. Let's see. There are two variables here in regards to power subsystem: power and energy capacity. Let's start with the power: >A container can weigh up to 28 tonnes, there was exactly one helicopter that could carry this kind of load the Mil Mi-12 and that looked really more like a plane. According to ([1]), we need around 0.28 kW/kg of thrust. Assuming that the drone weights twice more than a container, we need to have a lift of around 84 tonnes-force minimum, and ~100 tonnes-force in reality. That translates to 0.28 * 10^5 kW = 28 MW. This is close to what Mi-12 had (19.2 MW). LTO batteries from Toshiba ([2]) advertise 3.5 kW/kg of energy density, which gives us 28 MW/3.5 kW/kg = 800 kg of batteries. Reasonable, given that our budget for drone dry weight is 56 tonnes. Let's consider the energy capacity. To transfer a container from one ship to another standing 200 meters apart moving at 10 km/h, we would need 144 seconds for roundtrip. Let's make it 300 seconds for redundancy. 28 MW * 300 seconds = 2333 kWh. At 84 Wh/kg ([2]), we get 27.8 tonnes of batteries. Not great, but within out weight budget of 56 tonnes. The gotcha here that I see is the longevity of these batteries (they are rated for 8000 cycles). Do you see any other issues? I mean, basic physics seems to allow for such drones (not saying it's trivial to make). 1. https://store.tmotor.com/goods.php?id=974 https://store.tmotor.com/goods.php?id=974 2. https://www.electrive.com/2022/01/12/toshiba-presents-new-20-ah-lto-cell/ https://www.electrive.com/2022/01/12/toshiba-presents-new-20...

adgjlsfhk1 5y ago
Issue number 1 is cost. At $100 per kwh, each of these drones will cost a quarter million dollars (just for the batteries). Also, since each trip will require recharge, if we assume that the batteries can charge at 500kw (which is really high), it will take about 5 hours to transfer 1 container. That seems pretty much untenable.
- krasin 5y ago
  Cost on its own is rarely an issue. The thing that matters is payback time. If one container move generates $10, and the drone moves 12 containers per hour, 12 hours a day, it will only take 6 months to earn the quarter of million mentioned. Also, it might actually sound like a very cheap option compared to the ship-to-shore container cranes, which cost $20M-$40M each: https://www.freightcourse.com/port-cranes/ https://www.freightcourse.com/port-cranes/ As for recharging: if our power train is 28 MW, why not charging it at the same speed as we discharge it? Why settle on 500 kW, which is really low? For comparison, Tesla supercharger is up to 300 kW, and a car is a much smaller EV.
  - adgjlsfhk1 5y ago
    25 MW charging sounds great, but that does restrict you to 4 drones charging at a time per nuclear reactor (comparing to reactors used on carriers), which might be a little bit limiting (not to mention that making a battery that can be charged this quickly without overheating would be a triumph of engineering). Also your example of 12 containers per hour 12 hours a day for 6 months would be 26000 recharges, which is roughly 3x as long as the battery will last given current battery technology. In other words, this workload would require spending somewhere around $1M per year in batteries for a drone that takes roughly 12 minutes to unload a container. For comparison, a port crane, can unload 30 to 50 containers an hour, and will use far less electricity since it is lifting 1/3rd the weight (and isn't hovering).
    - krasin 5y ago
      Yes, the battery lifespan is the big issue (as pointed out in my original post). As for charging at 28 MW: might work, given that the battery is physically larger, so there's more space to dissipate heat. I agree that it's not proven by the napkin math that it's doable. What I really suspect is that if Los Angeles refuses to accept nuclear container ships, Mexico would let them in, and then the regular railway will be used to move them to the US. A much simpler solution. :)
cycomanic 5y ago
I know this has been a couple of days ago, but still meant to reply. Regarding your numbers, not that that ~3.5 kW of _power_ density is for 10s when the charge is _at least 50%_. Moving back and forth between two ships is also likely more than 300s, they can't just let the containers drop, they have to be carefully placed. A bigger issue is that you can't just scale the numbers of a 500g battery up to 800kg, I mean just getting the heat away will require significant effort. There is a reason the Tesla battery is ~500kg. But the biggest issue is is recharge, you can't recharge every 5 min. I mean how many of those drones are you going to employ? I mean a panamax class ship has 5000 containers. So either you need 5000 of those drones (good luck with them managing the off-onloading in 5 min) or some small subfraction, which then need to be recharged. Even if we assume we need to only move 500 containers (and use 500 drones), That means we either need to recharge 500 2333kWh batteries in 300s, how are you going to do that out on the ocean, or more likely you have 5 drones operating which need to work for 100 times as long, which increases you weight by 100. It just doesn't add up.

by krasin 5y ago

adgjlsfhk1 5y ago

Issue number 1 is cost. At $100 per kwh, each of these drones will cost a quarter million dollars (just for the batteries). Also, since each trip will require recharge, if we assume that the batteries can charge at 500kw (which is really high), it will take about 5 hours to transfer 1 container. That seems pretty much untenable.

krasin 5y ago
Cost on its own is rarely an issue. The thing that matters is payback time. If one container move generates $10, and the drone moves 12 containers per hour, 12 hours a day, it will only take 6 months to earn the quarter of million mentioned. Also, it might actually sound like a very cheap option compared to the ship-to-shore container cranes, which cost $20M-$40M each: https://www.freightcourse.com/port-cranes/ https://www.freightcourse.com/port-cranes/ As for recharging: if our power train is 28 MW, why not charging it at the same speed as we discharge it? Why settle on 500 kW, which is really low? For comparison, Tesla supercharger is up to 300 kW, and a car is a much smaller EV.
- adgjlsfhk1 5y ago
  25 MW charging sounds great, but that does restrict you to 4 drones charging at a time per nuclear reactor (comparing to reactors used on carriers), which might be a little bit limiting (not to mention that making a battery that can be charged this quickly without overheating would be a triumph of engineering). Also your example of 12 containers per hour 12 hours a day for 6 months would be 26000 recharges, which is roughly 3x as long as the battery will last given current battery technology. In other words, this workload would require spending somewhere around $1M per year in batteries for a drone that takes roughly 12 minutes to unload a container. For comparison, a port crane, can unload 30 to 50 containers an hour, and will use far less electricity since it is lifting 1/3rd the weight (and isn't hovering).
  - krasin 5y ago
    Yes, the battery lifespan is the big issue (as pointed out in my original post). As for charging at 28 MW: might work, given that the battery is physically larger, so there's more space to dissipate heat. I agree that it's not proven by the napkin math that it's doable. What I really suspect is that if Los Angeles refuses to accept nuclear container ships, Mexico would let them in, and then the regular railway will be used to move them to the US. A much simpler solution. :)

cycomanic 5y ago

I know this has been a couple of days ago, but still meant to reply. Regarding your numbers, not that that ~3.5 kW of _power_ density is for 10s when the charge is _at least 50%_. Moving back and forth between two ships is also likely more than 300s, they can't just let the containers drop, they have to be carefully placed. A bigger issue is that you can't just scale the numbers of a 500g battery up to 800kg, I mean just getting the heat away will require significant effort. There is a reason the Tesla battery is ~500kg. But the biggest issue is is recharge, you can't recharge every 5 min. I mean how many of those drones are you going to employ? I mean a panamax class ship has 5000 containers. So either you need 5000 of those drones (good luck with them managing the off-onloading in 5 min) or some small subfraction, which then need to be recharged. Even if we assume we need to only move 500 containers (and use 500 drones), That means we either need to recharge 500 2333kWh batteries in 300s, how are you going to do that out on the ocean, or more likely you have 5 drones operating which need to work for 100 times as long, which increases you weight by 100. It just doesn't add up.