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Hydrogen fuel cells are not a source of energy, since hydrogen (H2) is not naturally found on Earth. All H2 must be generated in a process which consumes either

Hydrogen fuel cells are not a source of energy, since hydrogen (H2) is not naturally found on Earth. All H2 must be generated in a process which consumes either natural gas or eletricity. Therefore H2 fuel cells are more aptly described as an energy storage system than as an energy source. Therefore the relevant comparison is between H2 fuel cells and Li ion batteries. Batteries have much higher full cycle efficiency (energy input -> storage -> energy output), but they are large and heavy. H2 can be stored in less volume and less weight, but it is less efficient. In my opinion, batteries will be a technically and economicly superior solution for all uses other than where weight is extremely critical such as in aircraft.

nsonha 6y ago
But current battery technologies need elements that require mining and other environmentally taxing processes. Recycling batteries can be energy consuming too. With hydrogen the cost structure of the whole fuel lifecycle is much clearer. Hydrogen also depletes along the trip unlike battery which will be massive dead weight for planes & ships.
- _ph_ 6y ago
  Yes, the cost structure is very visibly more expensive. The problem is the huge amount of additional energy needed to generate the hydrogen. Hydrogen storage is also very expensive. The weight reduction is pretty neglectible, as hydrogen is the lightest element in the universe.
  - kube-system 6y ago
    For anyone wondering what kind of numbers we're talking about in practice -- the Toyota Mirai holds about 5kg of Hydrogen.
    - bryanlarsen 6y ago
      In a pair of tanks that weigh 87.5 kg.
      - wmf 6y ago
        That ratio looks depressing, but what would equivalent batteries weigh? 500 kg? 1,000 kg?
        bryanlarsen 6y ago
        A Tesla battery pack of comparable range is about 500kg.
        bodhiandpysics1 6y ago
        Note that the mirai also needs the fuel cells, which adds another 70 kg, so the difference isn't as stark
        bryanlarsen 6y ago
        Once we start that game, we can also add the weight of the Mirai's 1.6kWh NiMH battery and other esoterica. The proof is in the pudding: the curb weight of a Mirai is more than that of the larger and more capable Model 3.
        8note 6y ago
        How important is weight in their designs though? They're cars, so they don't have to hold themselves up, and they probably both have regenerative braking
        _ph_ 6y ago
        You are right, weight isn't extremely important, especially with regenerative braking. It is only interesting in the comparison with battery electric cars - if the hydrogen car is even heavier, then there is basically no advantage left for the hydrogen car.
  - wombatmobile 6y ago
    What is the energy came free, from renewables? What would the cost structure for hydrogen be in that case?
    - cmrdporcupine 6y ago
      You'd still have to compare it to the equivalent usage of the same energy into a LiOn battery, and in many cases it wouldn't fare well. Maybe there's a future world in which we can do it all in orbit -- harvest comets, produce hydrogen in space using solar power or nuclear, and efficiently drop it down to earth in some safe way. That would definitely alter the equation. But by the time we figure that out, it'll probably be too late.
      - nsonha 6y ago
        If we're talking about space mining is Lithium abundant too? It's number 3 so should be everywhere in the universe?
    - _ph_ 6y ago
      There is no free energy from renewables. Renewables are cheap, but not free. And we are very far from even having a 100% renewable grid.
      - VBprogrammer 6y ago
        When the spot price for energy can go negative due to renewable over production it's fair to say that energy can be free or even better.
        _ph_ 6y ago
        Yes, in those rather short time periods, energy prices are free. But for those periods, batteries are the better storage solution, as the total amount of "free" energy is rather small. Electrolysis plants would have to run basically 24/7 to be viable. More battery electric cars on the roads also mean a lot of storage for excess electricity. Just use the top 10 to 20 percent of the capacity to absorb production peaks.
- cmrdporcupine 6y ago
  FWIW I upvoted you just because the question is reasonable, but I think you're wrong in balance. Last I looked all the current processes for making hydrogen are in fact more environmentally taxing (and worse, CO2 emitting) than the one-time cost of mining lithium. A LiOn battery is good for many many cycles, and can then be recycled. Hydrogen must be produced and then consumed, and is usually produced from natural gas, itself a greenhouse gas that is on the main a byproduct of the oil industry.
  - hughw 6y ago
    CO2 emitting but it's point source so straightforward capture and sequestration.
  - Hypx 6y ago
    Green hydrogen is the long-term option, which makes hydrogen the much less resource demanding option. People who keep on repeating the 'hydrogen = fossil fuel" argument is just the same kind of argument leveled against battery powered cars such as "coal powered cars."
- outworlder 6y ago
  > But current battery technologies need elements that require mining and other environmentally taxing processes But hydrogen requires production, either from fossil fuels, or electrolysis, both can be environmentally taxing. It requires transport. It requires either liquefaction or compression. It require mining to manufacture suitable storage tanks - which will become brittle and have to be replaced pretty often. > Hydrogen also depletes along the trip unlike battery which will be massive dead weight for planes & ships. This is indeed a major difference. Frankly, if you want to burn hydrogen, you're better off synthesizing something like methane. It's a far more effective storage mechanism. After all, if you are willing to spend the massive amount of resources required to do large-scale electrolysis, you might as well go the extra step and setup some sabatier reactors. You'll recapture the CO2 too.
- nickik 6y ago
  I think its not as bad as you make it out to be. Any battery that will be used in flight might have nickel in it but that's about the only thing that's problematic. The anode will likely be silicon. Pretty much all battery research is targeting materials that are common. The DoD made a large bet on Lithium-Sulfer batteries. Battery recycling can be energy intensive if you go for the full metallurgical extraction. But pretty much all car manufacturing plants want to just 'disassemble' the battery and use other far less energy intensive processes to get battery grade materials out. Also, at least in the west, these factories are generally located in location where there is cheap green energy or at least there is the potential. That is both Tesla/Panasonic and Northvolt (Europe) plan. With batteries you can reload the battery from your gravitational energy. That is actually quite a significant range extender but it might be a regulatory issue.
jeffreyrogers 6y ago
> In my opinion, batteries will be a technically and economicly superior solution for all uses other than where weight is extremely critical such as in aircraft. I was excited about the use of hydrogen in aircraft for a while but the more I looked into it the less likely it seems. I think the advantages of liquid fuels are too great and that even if there were no oil production it would still make more sense to synthesize jet fuel or some other liquid fuel for use in aviation. This has nothing to do with feasibility (the Soviet Union had an airliner that ran on hydrogen, so hydrogen aircraft are absolutely feasible), just with lock-in effects and ease of use.
- TylerE 6y ago
  It's not just liquid vs gas. Hydrogen has a couple of "unique" properties that make it especially disadvantageous. Namely: It'll diffuse through just about anything on a fairly short time scale if it isn't kept as a liquid at cryogenic temperatures, and it causes almost all metals to become brittle. I think hydrogen is basically a dead-end as energy storage, except in a few niche applications where it's produced as a byproduct and can be consumed immediately.
  - _ph_ 6y ago
    Steel production, where the hydrogen is a chemical reagent, might be one of the few exceptions where hydrogen is really the best choice.
  - cultus 6y ago
    Not to mention liquid H2 has quite a bit lower energy density than liquid fossil fuels. Many rockets have used kerosene in their first stages for this reason. Not the end of the world for aircraft, but certainly another major disadvantage.
    - funcDropShadow 6y ago
      But the energy density per mass is still better than Li-ion batteries.
landemva 6y ago
Right. Hydrogen can be used to store energy. Unlike flowing water which may turn a generator, hydrogen isn't a continuing source of generating power.
Der_Einzige 6y ago
That's why Astroid Mining and inter-steller mining technologies can't come soon enough. I can't believe that we went to the moon in the 1960's and now we cannot get support 60 years later for trying to economically exploit space.
- jeffreyrogers 6y ago
  What can we mine in space that we can't mine more cheaply on Earth?
  - manishsharan 6y ago
    Unobtanium
  - cellis 6y ago
    It’s environmentally friendly to mine asteroids, so in a way, it will always be “cheaper” to pollute an unlivable rock rather than our only sustainable habitat.
    - nsonha 6y ago
      It'll take like 100 year to get to that point. That's 100 yeard of space engineering simply polluting Earth and then maybe another 100 years to break even?
  - shrimp_emoji 6y ago
    Yes, when the space infrastructure is there. Once in orbit, it takes very little energy to go to an asteroid and to launch that asteroid to a parking orbit compared to dredging mountains of soil and rock on Earth. The yields would be extremely high; there's more gold and platinum in some Inner Belt asteroids than we've ever mined on Earth so far, and it's just floating there for you to grab and bite chunks out of.
    - giantrobot 6y ago
      > Once in orbit, it takes very little energy to go to an asteroid and to launch that asteroid to a parking orbit compared to dredging mountains of soil and rock on Earth. The yields would be extremely high; there's more gold and platinum in some Inner Belt asteroids than we've ever mined on Earth so far, and it's just floating there for you to grab and bite chunks out of. This is not true at all. This is laughably absurd. Getting from Earth's surface to LEO takes about 9.8km/s of delta-v but then getting from LEO to another destination requires more delta-v. To get to the Moon requires another 6km/s of delta-v on top of the 9.8km/s you needed to get from the ground into orbit. There's a reason the Saturn V was a giant rocket with a teeny tiny capsule mounted on top. Getting places in space requires a lot of propellant. Here's a nice list of NEAs and the delta-v required to reach them (one way) from LEO[0]. The list is very helpfully sorted by delta-v requirements. You'll notice that the easiest NEA (2018 AV2) requires an additional 3.758km/s of delta-v. The easiest to reach NEA on the least requires more than half the delta-v that it would take to land on the Moon. Once you rendezvous with an asteroid you need to come home which requires yet more delta-v (thus more propellant). Moving an asteroid to orbit Earth is not in any way as simple as you might think from reading science fiction. So there's nothing "very little" about the energy required to land on an asteroid let alone land on one, mine anything useful, and then return it to Earth. There's also the complexity of the vehicle needed to do the mining. Platinum (pure platinum mind you) goes for up to $37k per kg. Even if we pretended that all of the technology existed and was donated and we just paid for a Falcon Heavy launch (about $150m to get about 17t of payload to an asteroid) we would need to ship back 4t of pure platinum to Earth just to break even. Even if you assumed that in the best case platinum was a thousand times more abundant in an asteroid than Earth's crust[1] that's still only 5ppm! You'd need your asteroid miner to process about eight million tons of ore (if my math is right) to get that 4t. If our asteroid miner is 17t or so how long do you think it will take to process that much ore? The loan for the Falcon Heavy would have defaulted long before it would be even close to finished. There's just nothing asteroids have that ends up being worth the cost to mine them instead of mining them on Earth. Don't forget besides raw ore Earth also has lots of landfills literally filled with stuff than can be recycled and valuable materials extracted. Materials in space are only really useful to an entirely space-based industry and the only way to bootstrap a space-based industry is to launch it from Earth which is basically just lighting money on fire. [0] https://echo.jpl.nasa.gov/~lance/delta_v/delta_v.rendezvous.html https://echo.jpl.nasa.gov/~lance/delta_v/delta_v.rendezvous.... [1] https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth...
takeda 6y ago
I'm a total noob in that area, but I always thought that hydrogen was super efficient when converting it from water + oxygen and then back. Why battery is better?
- kube-system 6y ago
  Bear in mind -- a fueling infrastructure includes a lot of potential points of inefficiency outside of the chemical conversions that are taking place during generation and consumption. Your fuel of choice also must be transmitted from the point of generation to the point of consumption. For electricity, this is easy, you can run it down a wire. For gasoline, you need a tank that can hold liquid. For hydrogen, you need to cool it to −253°C and compress it in a cryogenic tank.
  - giantg2 6y ago
    And water scarcity is expected to be a growing issue for many parts of the world. I guess we could use sea water, but then the shipping you mention comes into play. Just a side note, you could ship it in hydride tanks.
- _ph_ 6y ago
  Elektrolysis isn't very efficient, neither are fuel cells, when you compare it to batteries. On top of that you have the energy usage for transporting and most of all compressing the hydrogen for storage.
- deleted 6y ago
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- shawndrost 6y ago
  Roundtrip efficiency for batteries are 70-95% vs 47% for H2. https://www.sciencedirect.com/topics/engineering/round-trip-efficiency https://www.sciencedirect.com/topics/engineering/round-trip-... Roundtrip efficiency is not the reason to use hydrogen for anything.
  - tomp 6y ago
dumbfoundded 6y ago
The weight factor also makes it easier to transport. In off-grid use-cases, it could make a lot of sense to get hydrogen delivered instead of setting up solar/wind + battery.
- samatman 6y ago
  Not really. Again, it's kind of stuck in the middle: energy density by volume sucks compared to hydrocarbons, and if it isn't cryogenic, it really sucks, and cryo is expensive. Transporting fuel by truck is volume limited, not weight limited. If we're comparing to batteries, then... ok, but you kinda only have to move the batteries once, and then you can either recharge on site with solar or connect to grid. With hydrogen, you have to keep bringing it, and you may as well have hydrocarbons at that point. The lack of carbon emissions on-site is what makes it tempting, but it's just easier to work around this problem in various ways than it is to pay the hydrogen penalty on an ongoing basis. To a first approximation, all commercial hydrogen is cracked off of methane anyway, and electrolysis is a pretty inefficient way to use renewable electricity, so even that just displaces emissions to fossil fuel plants unless none of those exist anymore.
deleted 6y ago
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plat12 6y ago
Even in rockets, where weight is extremely critical, SpaceX chose to use kerosene/methane due to the problems of working with LH2 (very low density, very cold temperatures, hydrogen embrittlement). Depending on energy density and power density requirements, I think a combination of batteries and traditional fossil fuels will win in the short term. In the long term, when we have stopped burning fossil fuels for electricity, then we can use electricity to manufacture them. Under this path, hydrogen will have limited importance.
- elcritch 6y ago
  Preventing explosions in the event of H2 leaks is difficult too. H2 has one of the lowest ignition energy curves of any gas. Electronics used in areas with H2 must follow very strict regulations (worse than medical requirements in many ways).
  - upofadown 6y ago
    The explosion happens when you cross the ignition energy threshold. So having a low ignition energy threshold can actually be an advantage as then much less fuel is available to drive the explosion. Agreed that doing intrinsic safety for H2 is hell. I did once design a LED sidelight for the relevant class with significant current (redundant electronic energy regulation). So it is possible to do stuff, it just takes more work. The tendency for modern electronics to be very low voltage helps a lot.
    - dredmorbius 6y ago
      More likely: A small amount of the leaked hydrogen encounters an ignition point, igniting the primary mass. The ignition zone is larger, risk is higher.
      - Retric 6y ago
        Pure hydrogen can’t burn without oxygen, so you generally get a tiny flare and then a flame based the size of the crack. It’s really about the same risks as using gasoline which almost never causes a significant detonation.
simonebrunozzi 6y ago
> Hydrogen fuel cells are not a source of energy, since hydrogen (H2) is not naturally found on Earth. All H2 must be generated in a process which consumes either natural gas or eletricity. Therefore H2 fuel cells are more aptly described as an energy storage system than as an energy source. 100% this. IMHO, this is by far the biggest misconception about hydrogen among people.
- Hypx 6y ago
  Not actually true. H2 is found naturally, although we don't have an good assessment how much exists or whether there are significant deposits.
  - deleted 6y ago
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  - testermelon 6y ago
    To my understanding, natural discoverability of H2 gas on earth surface is very low due to the gas being very light and buoy itself up the atmosphere, possibly escape the planet entirely.
    - Hypx 6y ago
      Hydrogen is being created and consumed on a vast scale on Earth. The possibility that there are huge pockets of hydrogen gas trapped under impermeable rock layers cannot be ruled out. For one thing, natural gas pretty often contains hydrogen as a constituent.
tinus_hn 6y ago
In theory you can also transport hydrogen through the pipes used for gas. I personally think you’ll run into problems with leaks really quickly but who knows.
- chupasaurus 6y ago
  Hydrogen gas has the smallest size of a molecule which is why only pyromaniacs might try that.
teawrecks 6y ago
Does "less efficient" mean less energy dense, or our current methods for converting its energy to electricity aren't good? If the former, then what does "H2 can be stored in less volume and less weight" mean? I would assume you would want to compare the mass required to store the same amount of energy, in which case it sounds like H2 takes up more space and weight than Li-ion? If the latter, then isn't it just a matter of improving our technologies? Or is there some law of nature that makes efficient conversion to electricity impractical?
- tonyarkles 6y ago
  It’s admittedly been a while since I’ve looked at it, but I recall that the creation of H2 using existing processes takes quite a bit more energy than you ultimately extract back from it. For example, electrolysis of H2O to H2 is a pretty lossy process (I think around 60-70% of the input power is used to break the H2O bond and the other 30-40% is released as heat).
afrojack123 6y ago
Not quite. Usage wise: Batteries have lower gravimetric density than h2 tanks. Batteries have about the same gravimetric density than h2. Economic wise: Batteries have cobalt which is more scarce than oil/nat. gas from which h2 is made.
g3orge 6y ago
do you have a book recommendation for these kinds of things maybe?

nsonha 6y ago

But current battery technologies need elements that require mining and other environmentally taxing processes. Recycling batteries can be energy consuming too. With hydrogen the cost structure of the whole fuel lifecycle is much clearer. Hydrogen also depletes along the trip unlike battery which will be massive dead weight for planes & ships.

_ph_ 6y ago
Yes, the cost structure is very visibly more expensive. The problem is the huge amount of additional energy needed to generate the hydrogen. Hydrogen storage is also very expensive. The weight reduction is pretty neglectible, as hydrogen is the lightest element in the universe.
- kube-system 6y ago
  For anyone wondering what kind of numbers we're talking about in practice -- the Toyota Mirai holds about 5kg of Hydrogen.
  - bryanlarsen 6y ago
    In a pair of tanks that weigh 87.5 kg.
    - wmf 6y ago
      That ratio looks depressing, but what would equivalent batteries weigh? 500 kg? 1,000 kg?
      - bryanlarsen 6y ago
        A Tesla battery pack of comparable range is about 500kg.
        bodhiandpysics1 6y ago
        Note that the mirai also needs the fuel cells, which adds another 70 kg, so the difference isn't as stark
        bryanlarsen 6y ago
        Once we start that game, we can also add the weight of the Mirai's 1.6kWh NiMH battery and other esoterica. The proof is in the pudding: the curb weight of a Mirai is more than that of the larger and more capable Model 3.
        8note 6y ago
        How important is weight in their designs though? They're cars, so they don't have to hold themselves up, and they probably both have regenerative braking
        _ph_ 6y ago
        You are right, weight isn't extremely important, especially with regenerative braking. It is only interesting in the comparison with battery electric cars - if the hydrogen car is even heavier, then there is basically no advantage left for the hydrogen car.
- wombatmobile 6y ago
  What is the energy came free, from renewables? What would the cost structure for hydrogen be in that case?
  - cmrdporcupine 6y ago
    You'd still have to compare it to the equivalent usage of the same energy into a LiOn battery, and in many cases it wouldn't fare well. Maybe there's a future world in which we can do it all in orbit -- harvest comets, produce hydrogen in space using solar power or nuclear, and efficiently drop it down to earth in some safe way. That would definitely alter the equation. But by the time we figure that out, it'll probably be too late.
    - nsonha 6y ago
      If we're talking about space mining is Lithium abundant too? It's number 3 so should be everywhere in the universe?
  - _ph_ 6y ago
    There is no free energy from renewables. Renewables are cheap, but not free. And we are very far from even having a 100% renewable grid.
    - VBprogrammer 6y ago
      When the spot price for energy can go negative due to renewable over production it's fair to say that energy can be free or even better.
      - _ph_ 6y ago
        Yes, in those rather short time periods, energy prices are free. But for those periods, batteries are the better storage solution, as the total amount of "free" energy is rather small. Electrolysis plants would have to run basically 24/7 to be viable. More battery electric cars on the roads also mean a lot of storage for excess electricity. Just use the top 10 to 20 percent of the capacity to absorb production peaks.
cmrdporcupine 6y ago
FWIW I upvoted you just because the question is reasonable, but I think you're wrong in balance. Last I looked all the current processes for making hydrogen are in fact more environmentally taxing (and worse, CO2 emitting) than the one-time cost of mining lithium. A LiOn battery is good for many many cycles, and can then be recycled. Hydrogen must be produced and then consumed, and is usually produced from natural gas, itself a greenhouse gas that is on the main a byproduct of the oil industry.
- hughw 6y ago
  CO2 emitting but it's point source so straightforward capture and sequestration.
- Hypx 6y ago
  Green hydrogen is the long-term option, which makes hydrogen the much less resource demanding option. People who keep on repeating the 'hydrogen = fossil fuel" argument is just the same kind of argument leveled against battery powered cars such as "coal powered cars."
outworlder 6y ago
> But current battery technologies need elements that require mining and other environmentally taxing processes But hydrogen requires production, either from fossil fuels, or electrolysis, both can be environmentally taxing. It requires transport. It requires either liquefaction or compression. It require mining to manufacture suitable storage tanks - which will become brittle and have to be replaced pretty often. > Hydrogen also depletes along the trip unlike battery which will be massive dead weight for planes & ships. This is indeed a major difference. Frankly, if you want to burn hydrogen, you're better off synthesizing something like methane. It's a far more effective storage mechanism. After all, if you are willing to spend the massive amount of resources required to do large-scale electrolysis, you might as well go the extra step and setup some sabatier reactors. You'll recapture the CO2 too.
nickik 6y ago
I think its not as bad as you make it out to be. Any battery that will be used in flight might have nickel in it but that's about the only thing that's problematic. The anode will likely be silicon. Pretty much all battery research is targeting materials that are common. The DoD made a large bet on Lithium-Sulfer batteries. Battery recycling can be energy intensive if you go for the full metallurgical extraction. But pretty much all car manufacturing plants want to just 'disassemble' the battery and use other far less energy intensive processes to get battery grade materials out. Also, at least in the west, these factories are generally located in location where there is cheap green energy or at least there is the potential. That is both Tesla/Panasonic and Northvolt (Europe) plan. With batteries you can reload the battery from your gravitational energy. That is actually quite a significant range extender but it might be a regulatory issue.

jeffreyrogers 6y ago

> In my opinion, batteries will be a technically and economicly superior solution for all uses other than where weight is extremely critical such as in aircraft. I was excited about the use of hydrogen in aircraft for a while but the more I looked into it the less likely it seems. I think the advantages of liquid fuels are too great and that even if there were no oil production it would still make more sense to synthesize jet fuel or some other liquid fuel for use in aviation. This has nothing to do with feasibility (the Soviet Union had an airliner that ran on hydrogen, so hydrogen aircraft are absolutely feasible), just with lock-in effects and ease of use.

TylerE 6y ago
It's not just liquid vs gas. Hydrogen has a couple of "unique" properties that make it especially disadvantageous. Namely: It'll diffuse through just about anything on a fairly short time scale if it isn't kept as a liquid at cryogenic temperatures, and it causes almost all metals to become brittle. I think hydrogen is basically a dead-end as energy storage, except in a few niche applications where it's produced as a byproduct and can be consumed immediately.
- _ph_ 6y ago
  Steel production, where the hydrogen is a chemical reagent, might be one of the few exceptions where hydrogen is really the best choice.
- cultus 6y ago
  Not to mention liquid H2 has quite a bit lower energy density than liquid fossil fuels. Many rockets have used kerosene in their first stages for this reason. Not the end of the world for aircraft, but certainly another major disadvantage.
  - funcDropShadow 6y ago
    But the energy density per mass is still better than Li-ion batteries.

landemva 6y ago

Right. Hydrogen can be used to store energy. Unlike flowing water which may turn a generator, hydrogen isn't a continuing source of generating power.

Der_Einzige 6y ago

That's why Astroid Mining and inter-steller mining technologies can't come soon enough. I can't believe that we went to the moon in the 1960's and now we cannot get support 60 years later for trying to economically exploit space.

jeffreyrogers 6y ago
What can we mine in space that we can't mine more cheaply on Earth?
- manishsharan 6y ago
  Unobtanium
- cellis 6y ago
  It’s environmentally friendly to mine asteroids, so in a way, it will always be “cheaper” to pollute an unlivable rock rather than our only sustainable habitat.
  - nsonha 6y ago
    It'll take like 100 year to get to that point. That's 100 yeard of space engineering simply polluting Earth and then maybe another 100 years to break even?
- shrimp_emoji 6y ago
  Yes, when the space infrastructure is there. Once in orbit, it takes very little energy to go to an asteroid and to launch that asteroid to a parking orbit compared to dredging mountains of soil and rock on Earth. The yields would be extremely high; there's more gold and platinum in some Inner Belt asteroids than we've ever mined on Earth so far, and it's just floating there for you to grab and bite chunks out of.
  - giantrobot 6y ago
    > Once in orbit, it takes very little energy to go to an asteroid and to launch that asteroid to a parking orbit compared to dredging mountains of soil and rock on Earth. The yields would be extremely high; there's more gold and platinum in some Inner Belt asteroids than we've ever mined on Earth so far, and it's just floating there for you to grab and bite chunks out of. This is not true at all. This is laughably absurd. Getting from Earth's surface to LEO takes about 9.8km/s of delta-v but then getting from LEO to another destination requires more delta-v. To get to the Moon requires another 6km/s of delta-v on top of the 9.8km/s you needed to get from the ground into orbit. There's a reason the Saturn V was a giant rocket with a teeny tiny capsule mounted on top. Getting places in space requires a lot of propellant. Here's a nice list of NEAs and the delta-v required to reach them (one way) from LEO[0]. The list is very helpfully sorted by delta-v requirements. You'll notice that the easiest NEA (2018 AV2) requires an additional 3.758km/s of delta-v. The easiest to reach NEA on the least requires more than half the delta-v that it would take to land on the Moon. Once you rendezvous with an asteroid you need to come home which requires yet more delta-v (thus more propellant). Moving an asteroid to orbit Earth is not in any way as simple as you might think from reading science fiction. So there's nothing "very little" about the energy required to land on an asteroid let alone land on one, mine anything useful, and then return it to Earth. There's also the complexity of the vehicle needed to do the mining. Platinum (pure platinum mind you) goes for up to $37k per kg. Even if we pretended that all of the technology existed and was donated and we just paid for a Falcon Heavy launch (about $150m to get about 17t of payload to an asteroid) we would need to ship back 4t of pure platinum to Earth just to break even. Even if you assumed that in the best case platinum was a thousand times more abundant in an asteroid than Earth's crust[1] that's still only 5ppm! You'd need your asteroid miner to process about eight million tons of ore (if my math is right) to get that 4t. If our asteroid miner is 17t or so how long do you think it will take to process that much ore? The loan for the Falcon Heavy would have defaulted long before it would be even close to finished. There's just nothing asteroids have that ends up being worth the cost to mine them instead of mining them on Earth. Don't forget besides raw ore Earth also has lots of landfills literally filled with stuff than can be recycled and valuable materials extracted. Materials in space are only really useful to an entirely space-based industry and the only way to bootstrap a space-based industry is to launch it from Earth which is basically just lighting money on fire. [0] https://echo.jpl.nasa.gov/~lance/delta_v/delta_v.rendezvous.html https://echo.jpl.nasa.gov/~lance/delta_v/delta_v.rendezvous.... [1] https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth...

takeda 6y ago

I'm a total noob in that area, but I always thought that hydrogen was super efficient when converting it from water + oxygen and then back. Why battery is better?

kube-system 6y ago
Bear in mind -- a fueling infrastructure includes a lot of potential points of inefficiency outside of the chemical conversions that are taking place during generation and consumption. Your fuel of choice also must be transmitted from the point of generation to the point of consumption. For electricity, this is easy, you can run it down a wire. For gasoline, you need a tank that can hold liquid. For hydrogen, you need to cool it to −253°C and compress it in a cryogenic tank.
- giantg2 6y ago
  And water scarcity is expected to be a growing issue for many parts of the world. I guess we could use sea water, but then the shipping you mention comes into play. Just a side note, you could ship it in hydride tanks.
_ph_ 6y ago
Elektrolysis isn't very efficient, neither are fuel cells, when you compare it to batteries. On top of that you have the energy usage for transporting and most of all compressing the hydrogen for storage.
deleted 6y ago
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shawndrost 6y ago
Roundtrip efficiency for batteries are 70-95% vs 47% for H2. https://www.sciencedirect.com/topics/engineering/round-trip-efficiency https://www.sciencedirect.com/topics/engineering/round-trip-... Roundtrip efficiency is not the reason to use hydrogen for anything.
- tomp 6y ago

dumbfoundded 6y ago

The weight factor also makes it easier to transport. In off-grid use-cases, it could make a lot of sense to get hydrogen delivered instead of setting up solar/wind + battery.

samatman 6y ago
Not really. Again, it's kind of stuck in the middle: energy density by volume sucks compared to hydrocarbons, and if it isn't cryogenic, it really sucks, and cryo is expensive. Transporting fuel by truck is volume limited, not weight limited. If we're comparing to batteries, then... ok, but you kinda only have to move the batteries once, and then you can either recharge on site with solar or connect to grid. With hydrogen, you have to keep bringing it, and you may as well have hydrocarbons at that point. The lack of carbon emissions on-site is what makes it tempting, but it's just easier to work around this problem in various ways than it is to pay the hydrogen penalty on an ongoing basis. To a first approximation, all commercial hydrogen is cracked off of methane anyway, and electrolysis is a pretty inefficient way to use renewable electricity, so even that just displaces emissions to fossil fuel plants unless none of those exist anymore.

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plat12 6y ago

Even in rockets, where weight is extremely critical, SpaceX chose to use kerosene/methane due to the problems of working with LH2 (very low density, very cold temperatures, hydrogen embrittlement). Depending on energy density and power density requirements, I think a combination of batteries and traditional fossil fuels will win in the short term. In the long term, when we have stopped burning fossil fuels for electricity, then we can use electricity to manufacture them. Under this path, hydrogen will have limited importance.

elcritch 6y ago
Preventing explosions in the event of H2 leaks is difficult too. H2 has one of the lowest ignition energy curves of any gas. Electronics used in areas with H2 must follow very strict regulations (worse than medical requirements in many ways).
- upofadown 6y ago
  The explosion happens when you cross the ignition energy threshold. So having a low ignition energy threshold can actually be an advantage as then much less fuel is available to drive the explosion. Agreed that doing intrinsic safety for H2 is hell. I did once design a LED sidelight for the relevant class with significant current (redundant electronic energy regulation). So it is possible to do stuff, it just takes more work. The tendency for modern electronics to be very low voltage helps a lot.
  - dredmorbius 6y ago
    More likely: A small amount of the leaked hydrogen encounters an ignition point, igniting the primary mass. The ignition zone is larger, risk is higher.
    - Retric 6y ago
      Pure hydrogen can’t burn without oxygen, so you generally get a tiny flare and then a flame based the size of the crack. It’s really about the same risks as using gasoline which almost never causes a significant detonation.

simonebrunozzi 6y ago

> Hydrogen fuel cells are not a source of energy, since hydrogen (H2) is not naturally found on Earth. All H2 must be generated in a process which consumes either natural gas or eletricity. Therefore H2 fuel cells are more aptly described as an energy storage system than as an energy source. 100% this. IMHO, this is by far the biggest misconception about hydrogen among people.

Hypx 6y ago
Not actually true. H2 is found naturally, although we don't have an good assessment how much exists or whether there are significant deposits.
- deleted 6y ago
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- testermelon 6y ago
  To my understanding, natural discoverability of H2 gas on earth surface is very low due to the gas being very light and buoy itself up the atmosphere, possibly escape the planet entirely.
  - Hypx 6y ago
    Hydrogen is being created and consumed on a vast scale on Earth. The possibility that there are huge pockets of hydrogen gas trapped under impermeable rock layers cannot be ruled out. For one thing, natural gas pretty often contains hydrogen as a constituent.

tinus_hn 6y ago

In theory you can also transport hydrogen through the pipes used for gas. I personally think you’ll run into problems with leaks really quickly but who knows.

chupasaurus 6y ago
Hydrogen gas has the smallest size of a molecule which is why only pyromaniacs might try that.

teawrecks 6y ago

Does "less efficient" mean less energy dense, or our current methods for converting its energy to electricity aren't good? If the former, then what does "H2 can be stored in less volume and less weight" mean? I would assume you would want to compare the mass required to store the same amount of energy, in which case it sounds like H2 takes up more space and weight than Li-ion? If the latter, then isn't it just a matter of improving our technologies? Or is there some law of nature that makes efficient conversion to electricity impractical?

tonyarkles 6y ago
It’s admittedly been a while since I’ve looked at it, but I recall that the creation of H2 using existing processes takes quite a bit more energy than you ultimately extract back from it. For example, electrolysis of H2O to H2 is a pretty lossy process (I think around 60-70% of the input power is used to break the H2O bond and the other 30-40% is released as heat).

afrojack123 6y ago

Not quite. Usage wise: Batteries have lower gravimetric density than h2 tanks. Batteries have about the same gravimetric density than h2. Economic wise: Batteries have cobalt which is more scarce than oil/nat. gas from which h2 is made.

g3orge 6y ago

do you have a book recommendation for these kinds of things maybe?