4 ms·

Maybe ships is an even better fit than trucks?

hwillis 6y ago
Trucks are explicitly limited by weight, ships are somewhat limited by volume. Container ships especially need to be loaded way up because the cargo is less dense than eg crude oil. Heavy trucks are also a much bigger issue than international shipping, which is only ~2% of global GHG. 6.7% of US GHG emissions come from medium and heavy duty trucks, or 23% of emissions due to transportation.
dylan604 6y ago
Would it be though? I understand ships are heavy polluters, but the areas they are polluting in are much larger than trucks in traffic in cities. Cities are so much more dense, and you can see that effect in satellite imagery.
Eric_WVGG 6y ago
I was wondering the same thing, from a density perspective. And similarly for airplanes. As planes and boats expend fuel, they get lighter, so less fuel is needed to move the second half of the journey, and less for the last quarter, etc. That “bonus” doesn’t work out with batteries, you need to move all the weight for all the journey. The energy density of batteries, to my understanding, just doesn’t add up correctly for boats or most airplanes. What I would like to know is, wouldn’t a hydrogen-powered boat or plane not only have a similar calculation on how much fuel is needed, but also (in the case of boats) be even cheaper to move because its fuel payload is lighter than water? Water 997kg/m3 vs liquid hydro 71kg/m3, also gasoline 783kg/m3, sounds like a nice bonus for jumbo jets too. (I am NOT a physicist or mechanical engineer) Gasoline-powered sea vessels are terrible polluters, incidentally, accounting for 18% of all air pollution. Between the air pollution benefits and possibility of the vessels being so much more fuel efficient, it seems like hydrogen would be a benefit even if the production isn’t completely clean.
- dredmorbius 6y ago
  with batteries, you need to move all the weight for all the journey For metal-air batteries, one of the more promising areas of research, the problem is actually worse: the cells gain mass as oxygen is reacted with the metal anode, discharging the battery. https://en.wikipedia.org/wiki/Metal–air_electrochemical_cell https://en.wikipedia.org/wiki/Metal–air_electrochemical_cell For marine propulsion, heavy fuels are typically preferred (bunker fuel typically, thogh deisel and petrol engines do exist). Much of the pollution is in the form of particulates and sulfer emissions. You can actually see major shipping routes on atmospheric sensing maps by SO2 emissions: https://earth.nullschool.net/#current/chem/surface/level/overlay=so2smass/orthographic=-257.23,7.16,346 https://earth.nullschool.net/#current/chem/surface/level/ove... As long-term risks these are ... somewhat minor as these contaminants settle out quickly: in days to months rather than centuries to millennia for CO2 and methane. Not great for respiratory health, but not the long-term planetary risk fossil fuel combustion overall is.
  - MayeulC 6y ago
    > For metal-air batteries, one of the more promising areas of research, the problem is actually worse: the cells gain mass as oxygen is reacted with the metal anode, discharging the battery. That's interesting, thank you for the info. Having a different characteristic from the usual one might lead to interesting applications. For instance, airplanes use a lot of fuel for takeoff, as they pay double the price for the weight of their fuel: they need to carry it up, when they have the most. This could actually be a game-changer, I think. That could also be exploited: raise the battery when it is charged, have it gain weight, generate electricity while lowering it. Perpetual motion doesn't exist, of course. But gaining a bit of extra mileage is theoretically possible here :)
    - dredmorbius 6y ago
      More likely, rethinking flight-segment dynamics and design. The bulk of energy expenditure is on takeoff and climb segments of flight. Cruise is relatively low energy, and during approach and landing, aircraft are frequently effectively gliding. Pilots and aviation engineers speak of the amount of energy in the aircraft, exclusive of fuel, represented by its mass, altitude, and velocity. Ideas I've seen suggested include catapult or towed launch, ejectable or jettisonable batteries, and/or hybrid fuel/electric designs, exploiting these factors. The general problems are: - These all increase complexity and failure risks. - They are novel (and hence risky) concepts. - Virtually all have scaling issues, being possibly feasible for smaller (drone, single-passenger, or few-passenger craft), but not heavy or superheavy jumbo jets. (Square-cube relations mean, generally, small aircraft are easier than large ones). - The typical power requirements are violated in emergencies. Fuel-driven aircraft can apply TOGO (take-off/go-around) power on demand, whilst a hybrid or compound design likely could not. And final flight-phase aircraft typically have half their takeoff weight, having burnt the difference in fuel, further expanding performance options. As for "lowering the battery", you'd do better to fly the entire aircraft at a gradually descending flight path, trading lower-drag high altitude for higher-drag lift as the battery gains mass. Current long-haul aircraft (sometimes) practice this in reverse, reching higher flight levels as fuel is consumed, lift requirements reduced, and lower-drag high-elevation flight being possible.
eqvinox 6y ago
Or non-electrified railways. A modern "diesel" engine is actually diesel-electrical anyways, since curiously diesel->electric->movement is more efficient than straight diesel->movement. For a hydrogen-electrical engine you could presumably stick one or two special tanker cars behind it with the necessary tech to keep it cool. The engine could even be dual-mode and use electrification where available (like this one already does for diesel: https://en.wikipedia.org/wiki/Bombardier_ALP-45DP https://en.wikipedia.org/wiki/Bombardier_ALP-45DP ) For comparison, an ES44AC [https://en.wikipedia.org/wiki/GE_Evolution_Series https://en.wikipedia.org/wiki/GE_Evolution_Series] carries 18900l of diesel (weighing 15.7 tons), which at 38.6 MJ/l rounds to 730GJ of energy. Hydrogen seems to have a specific energy of 120-142 MJ/kg, using the conservative 120 that's about 6.1 tons of hydrogen, but now for the volume... https://www.energy.gov/eere/fuelcells/hydrogen-storage https://www.energy.gov/eere/fuelcells/hydrogen-storage lists "0.03kg/l" as a "system target"... so 6.1 tons is 203,333l. That's 2 conventional tank cars (but those don't have any cooling or pressurization systems.) (Of course this assumes the efficiency of diesel->electrical and hydrogen->electrical to be similar, which is not the case.) P.S.: https://en.wikipedia.org/wiki/Hydrail https://en.wikipedia.org/wiki/Hydrail & https://www.bbc.com/future/article/20200227-how-hydrogen-powered-trains-can-tackle-climate-change https://www.bbc.com/future/article/20200227-how-hydrogen-pow...

Trucks are explicitly limited by weight, ships are somewhat limited by volume. Container ships especially need to be loaded way up because the cargo is less dense than eg crude oil. Heavy trucks are also a much bigger issue than international shipping, which is only ~2% of global GHG. 6.7% of US GHG emissions come from medium and heavy duty trucks, or 23% of emissions due to transportation.

dylan604 6y ago

Would it be though? I understand ships are heavy polluters, but the areas they are polluting in are much larger than trucks in traffic in cities. Cities are so much more dense, and you can see that effect in satellite imagery.

Eric_WVGG 6y ago

I was wondering the same thing, from a density perspective. And similarly for airplanes. As planes and boats expend fuel, they get lighter, so less fuel is needed to move the second half of the journey, and less for the last quarter, etc. That “bonus” doesn’t work out with batteries, you need to move all the weight for all the journey. The energy density of batteries, to my understanding, just doesn’t add up correctly for boats or most airplanes. What I would like to know is, wouldn’t a hydrogen-powered boat or plane not only have a similar calculation on how much fuel is needed, but also (in the case of boats) be even cheaper to move because its fuel payload is lighter than water? Water 997kg/m3 vs liquid hydro 71kg/m3, also gasoline 783kg/m3, sounds like a nice bonus for jumbo jets too. (I am NOT a physicist or mechanical engineer) Gasoline-powered sea vessels are terrible polluters, incidentally, accounting for 18% of all air pollution. Between the air pollution benefits and possibility of the vessels being so much more fuel efficient, it seems like hydrogen would be a benefit even if the production isn’t completely clean.

dredmorbius 6y ago
with batteries, you need to move all the weight for all the journey For metal-air batteries, one of the more promising areas of research, the problem is actually worse: the cells gain mass as oxygen is reacted with the metal anode, discharging the battery. https://en.wikipedia.org/wiki/Metal–air_electrochemical_cell https://en.wikipedia.org/wiki/Metal–air_electrochemical_cell For marine propulsion, heavy fuels are typically preferred (bunker fuel typically, thogh deisel and petrol engines do exist). Much of the pollution is in the form of particulates and sulfer emissions. You can actually see major shipping routes on atmospheric sensing maps by SO2 emissions: https://earth.nullschool.net/#current/chem/surface/level/overlay=so2smass/orthographic=-257.23,7.16,346 https://earth.nullschool.net/#current/chem/surface/level/ove... As long-term risks these are ... somewhat minor as these contaminants settle out quickly: in days to months rather than centuries to millennia for CO2 and methane. Not great for respiratory health, but not the long-term planetary risk fossil fuel combustion overall is.
- MayeulC 6y ago
  > For metal-air batteries, one of the more promising areas of research, the problem is actually worse: the cells gain mass as oxygen is reacted with the metal anode, discharging the battery. That's interesting, thank you for the info. Having a different characteristic from the usual one might lead to interesting applications. For instance, airplanes use a lot of fuel for takeoff, as they pay double the price for the weight of their fuel: they need to carry it up, when they have the most. This could actually be a game-changer, I think. That could also be exploited: raise the battery when it is charged, have it gain weight, generate electricity while lowering it. Perpetual motion doesn't exist, of course. But gaining a bit of extra mileage is theoretically possible here :)
  - dredmorbius 6y ago
    More likely, rethinking flight-segment dynamics and design. The bulk of energy expenditure is on takeoff and climb segments of flight. Cruise is relatively low energy, and during approach and landing, aircraft are frequently effectively gliding. Pilots and aviation engineers speak of the amount of energy in the aircraft, exclusive of fuel, represented by its mass, altitude, and velocity. Ideas I've seen suggested include catapult or towed launch, ejectable or jettisonable batteries, and/or hybrid fuel/electric designs, exploiting these factors. The general problems are: - These all increase complexity and failure risks. - They are novel (and hence risky) concepts. - Virtually all have scaling issues, being possibly feasible for smaller (drone, single-passenger, or few-passenger craft), but not heavy or superheavy jumbo jets. (Square-cube relations mean, generally, small aircraft are easier than large ones). - The typical power requirements are violated in emergencies. Fuel-driven aircraft can apply TOGO (take-off/go-around) power on demand, whilst a hybrid or compound design likely could not. And final flight-phase aircraft typically have half their takeoff weight, having burnt the difference in fuel, further expanding performance options. As for "lowering the battery", you'd do better to fly the entire aircraft at a gradually descending flight path, trading lower-drag high altitude for higher-drag lift as the battery gains mass. Current long-haul aircraft (sometimes) practice this in reverse, reching higher flight levels as fuel is consumed, lift requirements reduced, and lower-drag high-elevation flight being possible.

eqvinox 6y ago

Or non-electrified railways. A modern "diesel" engine is actually diesel-electrical anyways, since curiously diesel->electric->movement is more efficient than straight diesel->movement. For a hydrogen-electrical engine you could presumably stick one or two special tanker cars behind it with the necessary tech to keep it cool. The engine could even be dual-mode and use electrification where available (like this one already does for diesel: https://en.wikipedia.org/wiki/Bombardier_ALP-45DP https://en.wikipedia.org/wiki/Bombardier_ALP-45DP ) For comparison, an ES44AC [https://en.wikipedia.org/wiki/GE_Evolution_Series https://en.wikipedia.org/wiki/GE_Evolution_Series] carries 18900l of diesel (weighing 15.7 tons), which at 38.6 MJ/l rounds to 730GJ of energy. Hydrogen seems to have a specific energy of 120-142 MJ/kg, using the conservative 120 that's about 6.1 tons of hydrogen, but now for the volume... https://www.energy.gov/eere/fuelcells/hydrogen-storage https://www.energy.gov/eere/fuelcells/hydrogen-storage lists "0.03kg/l" as a "system target"... so 6.1 tons is 203,333l. That's 2 conventional tank cars (but those don't have any cooling or pressurization systems.) (Of course this assumes the efficiency of diesel->electrical and hydrogen->electrical to be similar, which is not the case.) P.S.: https://en.wikipedia.org/wiki/Hydrail https://en.wikipedia.org/wiki/Hydrail & https://www.bbc.com/future/article/20200227-how-hydrogen-powered-trains-can-tackle-climate-change https://www.bbc.com/future/article/20200227-how-hydrogen-pow...