Hydrogen gas: Difference between revisions

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(Refactored page. But the PGMs section still needs redoing.)
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[[Category:Energy storage]]
[[Category:Energy storage]]


'''Hydrogen gas''' (H<sub>2</sub>) is a combustible fuel that leaves behind nothing but water vapor (H<sub>2</sub>O) when burned.
'''Hydrogen gas''' (H<sub>2</sub>) is a combustible fuel that leaves behind water vapor (H<sub>2</sub>O) when burned {{light|(no carbon)}}. <!--
<!-- TALK: Maybe this is wrong if NOx emissions can be emitted too? {{qn}} If so, how to rephrase while maintaining simplicity? -->
'''Hydrogen gas''' (H<sub>2</sub>) is a combustible fuel that leaves behind only water vapor (H<sub>2</sub>O) when burned {{x|when burned in pure oxygen at least. Note that when it's burned in plain air, there are still some nitrogen oxides produced as well - but in any case, no CO<sub>2</sub> is produced from the combustion}}. -->


There are '''no''' natural resources of hydrogen gas{{x|except in rare and extremely small quantities, not a viable way to supply [[energy]] in any meaningful amount}}.
There are basically '''no''' natural resources of hydrogen gas{{x|except in rare and extremely small quantities, not a viable way to supply [[energy]] in any meaningful amount}}. To make hydrogen gas, you need to use some other [[energy]] source. In this way, hydrogen can be understood as a form of '''[[energy storage]]'''.
To make hydrogen gas, you need to use some other [[energy]] source. In this way, hydrogen can be understood as a form of '''[[energy storage]]'''.




'''''This page is about how hydrogen gas could be used with renewable [[energy]].'''''
'''''This page is about how hydrogen gas could be used in an all-renewable [[energy]] scenario.'''''
{{considerations}}
{{considerations}}


Line 38: Line 37:


==Energy sources==
==Energy sources==
'''Main use-case:''' Storing [[wind]] power.<br />
'''Main use-case:''' Storing surplus [[wind power]].<br />
Here's why:
Here's why:
* Wind power is far more intermittent than [[solar]]. Whereas solar follows a day/night cycle, windy and not-so-windy seasons can last for ''months'' at a time.
* Wind power is far more intermittent than [[solar]]. Whereas solar follows a day/night cycle, windy and not-so-windy seasons can last for ''months'' at a time.
Line 52: Line 51:


==Status quo==
==Status quo==
* [[Wind power]] is not in surplus yet {{light|(in most parts of the world)}}.
* Most hydrogen today is '''produced''' from [[fossil fuels]] ([[natural gas]]) via [//wikipedia.org/wiki/Steam_reforming steam reforming]. The carbon emissions are as high as burning the natural gas itself.
* Most hydrogen today is '''produced''' from [[fossil fuels]] ([[natural gas]]) via [//wikipedia.org/wiki/Steam_reforming steam reforming]. The carbon emissions are as high as burning the natural gas itself.
* Most hydrogen today is '''used''' in producing [[fertilizer]].
* Most hydrogen today is '''used''' in producing [[fertilizer]].
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==Platinum-group metals==
==Platinum-group metals==
{{sum|Problem in some cases}}
{{sum|Problem in some cases}}
'''Tl;dr:''' Too many [[fuel cell vehicles]] '''would''' be a problem. Hydrogen production would '''not''' be.


Both '''electrolysis''' and '''fuel cells''' need platinum-group metals (PGMs):
 
Both ''electrolysis'' and ''fuel cells'' need platinum-group metals (PGMs):
* '''[platinum, palladium, rhodium, ruthenium, iridium, osmium]'''
* '''[platinum, palladium, rhodium, ruthenium, iridium, osmium]'''
** Any of these metals will do, but all of them are extremely scarce (even more than gold), with platinum & palladium being the most available.
** Any of these metals will do, but all of them are extremely scarce (even more than gold), with platinum & palladium being the most available.
Line 65: Line 67:
{{minor|Note: It ''is'' possible to build fuel cells and electrolysis systems without PGMs, but the energy-efficiency is much lower.{{qn}} There are scientists trying to overcome this,<sup>[LINKS needed]</sup> but there's no guarantee that it will be viable in the near future.}}
{{minor|Note: It ''is'' possible to build fuel cells and electrolysis systems without PGMs, but the energy-efficiency is much lower.{{qn}} There are scientists trying to overcome this,<sup>[LINKS needed]</sup> but there's no guarantee that it will be viable in the near future.}}


====How much would be needed, if hydrogen were scaled up?====
The supply of PGMs is limited to what we can mine from the Earth (mineral reserves / resources), so we have to be mindful of how much would be needed.
<tab name="General principles" collapsed>
{{minor|The mass of PGMs needed is proportional to ''peak power'':}}
* For electrolysis systems, the maximum '''rate of hydrogen production''' {{light|is limited by the amount of PGMs}}.
* For fuel cell vehicles, the '''horsepower''' {{light|is limited by the amount of PGMs}}.
** {{minor|But the vehicle can still achieve ''short bursts'' of higher horsepower if there's a battery or supercapacitor in parallel with the fuel cell.}}
</tab>


===How much would be needed, if hydrogen were scaled up?===
<!-- --- DATA POINTS --- -->
<!-- --- DATA POINTS --- -->
{{dp
{{dp
Line 128: Line 125:
}}
}}
{{dp
{{dp
|<nowiki>pgm.mine_production</nowiki>
|<nowiki>pgm.status_quo_mining_production</nowiki>
|<nowiki>platinum.mine_production + palladium.mine_production</nowiki>
|<nowiki>platinum.mine_production + palladium.mine_production</nowiki>
|<nowiki>Global production of platinum-group metals (PGMs) from mining</nowiki>
|<nowiki>Global production of platinum-group metals (PGMs) from mining (status quo)</nowiki>
|<nowiki>Assumption: that the other PGMs (iridium, rhodium, osmium, ruthenium) are in such small quantities that it's ok that they aren't counted here (because data is unavailable)</nowiki>
|<nowiki>Assumption: that the other PGMs (iridium, rhodium, osmium, ruthenium) are in such small quantities that it's ok that they aren't counted here (because data is unavailable)</nowiki>
}}
}}
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|<nowiki>pgm.reserves</nowiki>
|<nowiki>pgm.reserves</nowiki>
|<nowiki>70000 tonnes</nowiki>
|<nowiki>70000 tonnes</nowiki>
|<nowiki>Global reserves of platinum-group metals</nowiki>
|<nowiki>Global mineral reserves of platinum-group metals</nowiki>
|<nowiki>Includes platinum, palladium, ruthenium, rhodium, osmium, iridium.</nowiki><br /><nowiki>
|<nowiki>Includes platinum, palladium, ruthenium, rhodium, osmium, iridium.</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
Line 204: Line 201:
}}
}}
{{dp
{{dp
|<nowiki>fossil_fuels.energy</nowiki>
|<nowiki>fossil_fuels.consumption</nowiki>
|<nowiki>11596.92 Mtoe/year</nowiki>
|<nowiki>11596.92 Mtoe/year</nowiki>
|<nowiki>Total consumption of coal, oil, and natural gas (worldwide)</nowiki>
|<nowiki>Total consumption of coal, oil, and natural gas (worldwide) (energy units)</nowiki>
|<nowiki>Key World Energy Statistics 2020 (IEA report)</nowiki><br /><nowiki>
|<nowiki>Key World Energy Statistics 2020 (IEA report)</nowiki><br /><nowiki>
- page 47: World energy balance, 2018</nowiki><br /><nowiki>
- page 47: World energy balance, 2018</nowiki><br /><nowiki>
Line 222: Line 219:
|2
|2
|
|
|Without this, we'd be calculating for just personal vehicles. But we also need to factor in commercial vehicles such as buses and trucks. These vary widely in size, and data is hard to find, so for simplicity sake, we just assume that they'd add up to about the same as personal vehicles - thus doubling total energy storage needed. This assumption is based on the fact that freight trucks are a somewhat smaller share of [[energy demand]] than passenger vehicles, but the trucks probably need a longer range.
|Without this, we'd be calculating for just personal vehicles. But we also need to factor in commercial vehicles such as buses and trucks. These vary widely in size, and data is hard to find, so for simplicity sake, we just assume that they'd add up to about the same as personal vehicles - thus doubling total energy storage needed. This assumption is based on the fact that freight trucks are a somewhat smaller share of [[energy demand]] than passenger vehicles, but the trucks need far more horsepower and probably a longer range.
}}
}}
<!-- --- END OF DATA POINTS --- -->
<!-- --- END OF DATA POINTS ---


<tabs><tab name="Estimate #1">
-->
Suppose,
'''Scenario 1:''' If hydrogen gas (from wind power) were to directly replace all fossil fuels (this implies that people would drive [[hydrogen combustion vehicles]]):
* that all of today's [[energy demand]] were to be met using hydrogen gas
* that all hydrogen gas were to be produced using [[wind]] power (or something with the same [[capacity factor]] as wind)
* that all PGMs can forever be recovered and recycled


'''Tl;dr: There ''are'' enough PGM minerals in the Earth, but today's mining rates would be ''far too slow''.'''<br />
<tab name="SEE MATHS" collapsed>
<small>We'd have to start mining a lot faster, and find some way to do it '''without''' exploitative [[labor]]. {{en}}</small>
 
'''Calculations:'''
{{calc
{{calc
|energy.tfc / wind.capacity_factor * electrolysis.pgm_by_power
|electrolysis.pgm_by_power / electrolysis.efficiency / wind.capacity_factor * fossil_fuels.consumption
|grams per capita * world.population
|% pgm.reserves
|production_pgm
|...
|PGMs needed for hydrogen production:
}}
}}
{{calc
{{calc
|world.cars * toyota_mirai.pgm
|...
|grams per capita * world.population
|years pgm.status_quo_mining_production
|consumption_pgm
|||'''PGMs needed for hydrogen gas production.'''
|PGMs needed for hydrogen-based electricity consumption:
}}
}}
</tab>
* The amount of PGMs needed is pretty reasonable '''(16% of mineral reserves)'''. We'd still have to mine for PGMs a lot faster than the status-quo (and do it ''without'' exploitative [[labor]]). {{npn}}
{{minor|To prevent NOx emissions ([[#NOx emissions|see section below]]), hydrogen combustion vehicles need ''catalytic converters'', just like gasoline or diesel vehicles do. Catalytic converters ''also'' contain some PGMs, which could be obtained by recycling old catalytic converters from fossil-fuel vehicles.}}


{{calc
'''Scenario 2:''' If all vehicles were hydrogen [[fuel cell vehicles]] instead:
|world.cars * catalytic_converter.pgm
|grams per capita * world.population
|recyclable_pgm
|PGMs recoverable from catalytic converters of old gas cars:{{minor|Old semi trucks (not counted here) could also provide a bit more}}</small>
}}


<tab name="SEE MATHS" collapsed>
{{calc
{{calc
|production_pgm + consumption_pgm - recyclable_pgm
|(toyota_mirai.pgm - catalytic_converter.pgm) * world.cars * commercial_factor
|% pgm.reserves
|% pgm.reserves
|
|...
|Compared to mineral reserves:
}}
}}
{{calc
{{calc
|production_pgm + consumption_pgm - recyclable_pgm
|...
|years pgm.mine_production
|years pgm.status_quo_mining_production
|
|||'''PGMs needed to make the fuel-cell vehicles.'''{{minor|Fuel-cell vehicles don't have catalytic converters, but a fuel cell contains far more PGMs than a catalytic converter.}}
|Compared to current production rate:
}}
}}
</tab>
<!-- TALK:
Maybe I should refactor [[template:calc]] to allow for presenting one calculation in multiple units? This would involve some design decisions.
-->


This estimate is imperfect and oversimplified, but probably reasonable in a scenario where some vehicles use hydrogen combustion and some use fuel cells. In general,
* One benefit of fuel cell vehicles is that they're more energy-efficient than combustion vehicles (i.e. less hydrogen used per kilometer driven).
* If more vehicles use hydrogen combustion, we'd need more wind power but less PGM.
 
* If more vehicles use fuel cells, we'd need less wind power but more PGM.
* The problem is, the fuel cells alone would need '''7 times more''' PGMs mined than Scenario 1 (estimated). Perhaps too much to be scalable. And this is true ''even though'' we factored in the recycling of old catalytic converters.


In any case, producing that much wind power is maybe reasonable if most farmland were to be covered in wind turbines.
{{calc
|energy.tfc / wind.capacity_factor * wind.rq_land
|% crop_land
}}


<div style="font-size:70%;color:#333;margin:1em;border:1px dashed #CCC">
<tab name="General principles" collapsed>
{{minor|The mass of PGMs needed is proportional to ''peak power'':}}
* For electrolysis systems, the maximum '''rate of hydrogen production''' {{light|is limited by the amount of PGMs}}.
* For fuel cell vehicles, the '''horsepower''' {{light|is limited by the amount of PGMs}}.
** {{minor|But the vehicle can still achieve ''short bursts'' of higher horsepower if there's a battery or supercapacitor in parallel with the fuel cell.}}
</tab>
<tab name="More notes on these estimates" collapsed>
More musings about the calculations above:
More musings about the calculations above:
* Hydrogen ''combustion'' vehicles are about as energy-efficient as gasoline combustion vehicles. But hydrogen ''fuel cell'' vehicles are more efficient. We'd need '''less''' hydrogen than this estimate calls for.
* All of this assumes that electrolyzers and fuel cells can be completely recycled at their end-of-life, with all PGMs recovered. If they can't, we're kind of screwed in the long run (at least for hydrogen).
* Home electricity would be done with fuel cells too. We'd need '''more''' PGMs than this estimate. We'd need '''more''' hydrogen than this estimate, to make up for the losses in fuel cells (although those losses could be used as [[heating]] in some cases).
* Hydrogen ''combustion'' vehicles are about as energy-efficient as gasoline combustion vehicles. Hence we can assume that the Scenario 1 estimate is accurate enough.
* If electric [[semi trucks]] use fuel cells too, we'd need '''more''' PGMs than this estimate.
* Home electricity can also be done with fuel cells - this would of course need more PGMs (and more hydrogen to make up for the losses in fuel cells (although those losses could be used as [[heating]] in some cases)).
* Or if a large enough percent of all vehicles use combustion instead of fuel cells, then we'd need '''less''' PGM than this estimate.
* We didn't count the hydrogen needed in the vehicles that transport the hydrogen (hopefully would be minor, like with fossil fuel transport).
* We didn't count the hydrogen needed in the vehicles that transport the hydrogen (hopefully would be minor, like with fossil fuel transport).</small>
* All this is based on status-quo energy demand, which unfortunately relies on the fact that most of the world currently lives in poverty. If all nations were developed, more resources would be needed.
* All this is based on status-quo energy demand, which relies on the fact that most of the world currently lives in poverty. If all nations were developed, a lot more resources would be needed.
* Wind power land estimates are based on status-quo installations which are likely on windier-than-average land. In which case, maybe crop land wouldn't be enough - but then again, there's also pasture and barren land that could be used.
* But in any case, we probably wouldn't actually use wind/hydrogen for everything anyway. [[Rooftop solar]] combined with [[the great battery challenge|batteries]] could probably be a better way to provide electricity whenever hydrogen need not be involved.
* But in any case, we probably wouldn't actually use wind/hydrogen for everything anyway. [[Rooftop solar]] combined with [[the great battery challenge|batteries]] could probably be a better way to provide electricity whenever hydrogen need not be involved.
* Since vehicle fuel cells use the biggest share of PGMs in this estimate, this is yet another reason to advocate for [[public transit]] and [[walkability]].
* Since vehicle fuel cells use the biggest share of PGMs in this estimate, this is yet another reason to advocate for [[public transit]] and [[walkability]].
</div></tab></tabs>
</tab>


===Verdict===
* If we're going to have hydrogen-powered vehicles, most of them will probably have to be combustion only (or some sort of hybrid with just a very small fuel cell).
* At least PGMs are not a limiting factor for wind-based hydrogen ''production''.


<!-- TODO: Uncomment this when done writing about PGMs above (a more immediate and important mention that should be on here first)
==Atmospheric losses==
{{sum|Probably minor}}
The concern would be that when hydrogen gas leaks to the atmosphere, it's so light that it ends up being lost into outer space via [//wikipedia.org/wiki/Jeans_escape Jeans escape]. At what point would this permanent loss of hydrogen affect ecosystems? Would it be on the scale of billions of years or millions of years or thousands? Per unit of energy, I bet there would actually be hydrogen loss than with [[nuclear fusion]]. {{rn}} {{pn|TODO: Estimate using the status-quo gas leak rate of natural gas.}} }}
-->


==Energy losses==
==Energy losses==
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*** Note however: For vehicles, this is outweighed by the fact that [[hydrogen combustion vehicles]] are less fuel-efficient than [[fuel cell vehicles]].
*** Note however: For vehicles, this is outweighed by the fact that [[hydrogen combustion vehicles]] are less fuel-efficient than [[fuel cell vehicles]].


{{pn|TODO: add calculation: knowing the losses, is there still enough [[land]] for wind-generated hydrogen gas were to directly replace all fossil fuels, in principle?}}
{{pn|TODO: Add calculation: Knowing the losses, is there still enough [[land]] for wind-generated hydrogen gas were to directly replace all fossil fuels, in principle?}}


{{dp
|<nowiki>hydrogen_gas.specific_energy</nowiki>
|<nowiki>120 MJ/kg</nowiki>
|<nowiki></nowiki>
|<nowiki>"By contrast, hydrogen has an energy density of approximately 120 MJ/kg , almost three times more than diesel or gasoline. In electrical terms, the energy density of hydrogen is equal to 33.6 kWh of usable energy per kg, versus diesel which only holds about 12–14 kWh per kg."</nowiki><br /><nowiki>
Oct 2, 2019</nowiki><br /><nowiki>
Run on Less with Hydrogen Fuel Cells - RMI</nowiki><br /><nowiki>
rmi.org › Blog </nowiki>
}}
{{dp
|<nowiki>water.hydrogen_by_mass</nowiki>
|<nowiki>hydrogen*2 / (hydrogen*2 + oxygen)</nowiki>
|<nowiki>What percent of water's mass is hydrogen atoms</nowiki>
|<nowiki>It's about 11%. Expressed using the calculator's built-in chemistry constants (atomic masses).</nowiki>
}}
{{dp
|<nowiki>electrolysis.efficiency</nowiki>
|<nowiki>80%</nowiki>
|<nowiki>Energy efficiency of producing hydrogen & oxygen gases from water</nowiki>
|<nowiki>Hydrogen made by the electrolysis of water is now cost-competitive ...</nowiki><br /><nowiki>
www.carboncommentary.com › blog › hydrogen-made-by-the-electrolysis... </nowiki>
}}
In cases where electrolysis is done in weather below 0&deg;C, such as beside wind turbines in cold parts of the world during winter, losses may be somewhat worse. {{x|The water has to be liquid (not frozen) while it's being electrolyzed to become hydrogen and oxygen. Heating takes energy; then again, maybe the waste heat of electrolysis would already be enough to keep the water liquid. In theory it can: For any amount of H<sub>2</sub>O electrolyzed, the waste heat is 8 times more than what it takes to melt that amount of ice: {{p2|'''[See calculation]'''|{{calc|hydrogen_gas.specific_energy * water.hydrogen_by_mass * (100% - electrolysis.efficiency)|water_fusion_heat}} {{pn|Maybe this belongs on a separate page called "hydrogen gas production in winter weather"?}} }}. For this to work, the hydrogen production system would have to be well-insulated from the weather. }} {{npn}}


==Shelf life==
==Shelf life==
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* Just like natural gas, hydrogen gas is non-toxic and odorless but highly flammable. For safety in consumer applications, small quantities of some non-toxic but smelly gas{{x|such as methyl mercaptan, hydrogen sulfide, or ethyl isobutyrate (Wikipedia has a page "Hydrogen odorant")}}should be added to it, so that people would know if there's a gas leak.
* Just like natural gas, hydrogen gas is non-toxic and odorless but highly flammable. For safety in consumer applications, small quantities of some non-toxic but smelly gas{{x|such as methyl mercaptan, hydrogen sulfide, or ethyl isobutyrate (Wikipedia has a page "Hydrogen odorant")}}should be added to it, so that people would know if there's a gas leak.
* {{pn|This section needs more safety-related info.}}
* {{pn|This section needs more safety-related info.}}
==NOx emissions==
{{sum|Manageable}}
Burning hydrogen gas in air produces nitrogen oxides (NOx) in the same amount as burning gasoline or any other fuel. This happens because air is 78% nitrogen gas and 21% oxygen gas - any high temperature will cause some of the nitrogen to react with the oxygen. NOx gases contribute to [[climate change]]. {{qn}}
For [[hydrogen combustion vehicles]], this problem can be solved the same way it is for gasoline or diesel combustion: The vehicle has a ''catalytic converter'' to convert these gases into harmless substances. This requires some platinum-group metals ([[#Platinum-group metals|see section above]]).
==Atmospheric losses==
{{sum|Very minor}}
'''Concern:''' When hydrogen gas leaks into the atmosphere, it's so light that it ends up being lost forever into outer space via [//wikipedia.org/wiki/Jeans_escape Jeans escape]. If this goes on for ''long enough'', could Earth lose enough hydrogen that this would harm ecosystems or deplete the global water supply? How long would that take exactly?
'''Answer:''' If we assume:
* that hydrogen gas leaks would happen at about the '''same rate''' as natural gas,
* that losing '''0.1%''' of the world's oceans would be enough to be a problem,
* that hydrogen gas would be replacing '''all''' fossil fuels, by energy,
Then it would take more than a '''million''' years to have even a minor effect on the ecosystems:
<tab name="(see maths)">
{{dp
|natural_gas.leak_rate
|1.4%
|Percent of natural gas that is lost to leaks
|[https://www.bloomberg.com/features/2022-methane-leaks-natural-gas-energy-emissions-data/ As Natural Gas Booms, Methane Leaks Spark Climate Alarm - Bloomberg]
}}
{{dp
|water.hydrogen_by_mass
|(hydrogen*2)/(hydrogen*2+oxygen)
|How much of water's mass is hydrogen
|About 11%. Calculated using chemistry constants built into the calculator.
}}
{{dp
|oceans.volume
|1.35 billion km^3
|Total volume of all oceans on Earth
|https://hypertextbook.com/facts/2001/SyedQadri.shtml
}}
{{dp
|hydrogen_gas.energy_by_mass
|120 MJ/kg
|The ''specific energy'' of hydrogen gas
|"...hydrogen has an energy density of approximately 120 MJ/kg , almost three times more than diesel or gasoline. In electrical terms, the energy density of hydrogen is equal to 33.6 kWh of usable energy per kg, versus diesel which only holds about 12–14 kWh per kg." - Oct 2, 2019 - Run on Less with Hydrogen Fuel Cells - RMI - rmi.org › Blog
}}
{{calc
|0.1% oceans.volume * waterdensity * water.hydrogen_by_mass
|million years (natural_gas.leak_rate / hydrogen_gas.energy_by_mass * fossil_fuels.consumption)
}}
{{minor|Side note: For the same amount of energy, this is still a lot more hydrogen loss than [[nuclear fusion]] of hydrogen atoms.}}
</tab>
<!--
TODO: compare the hydrogen losses to the hydrogen the earth gains from solar winds
TODO: add new heading:
==Climate effects of leaks==
Hydrogen is not directly a greenhouse gas, but it slows the breakdown of atmospheric methane (which ''is'' a greenhouse gas). Therefore hydrogen gas leaks do have ''some'' effect on warming the climate. {{qn}}
-->




Line 334: Line 402:
* "Pink hydrogen" is made from electrolysis using [[nuclear]] energy.
* "Pink hydrogen" is made from electrolysis using [[nuclear]] energy.
* "Green hydrogen" is made from electrolysis using renewable energy.
* "Green hydrogen" is made from electrolysis using renewable energy.
* "White hydrogen" is naturally-occuring hydrogen (very rare).
<!-- TODO: mention white hydrogen discovered in france (september 2023), 46 Mt resource which is nothing compared to global energy demand of 9938 Mtoe/year -->


<!--
<!--
Line 346: Line 416:
==See also==
==See also==
* [[Methane cracking]] {{light|- another way to produce hydrogen gas. Not worthwhile currently, but ''in theory'' the right tech could maybe change that.}}
* [[Methane cracking]] {{light|- another way to produce hydrogen gas. Not worthwhile currently, but ''in theory'' the right tech could maybe change that.}}
* [[Energy storage]]

Revision as of 18:57, 22 March 2024

Not to be confused with nuclear fusion of hydrogen atoms.

Hydrogen gas (H2) is a combustible fuel that leaves behind water vapor (H2O) when burned (no carbon).

There are basically no natural resources of hydrogen gas(...)( except in rare and extremely small quantities, not a viable way to supply energy in any meaningful amount ). To make hydrogen gas, you need to use some other energy source. In this way, hydrogen can be understood as a form of energy storage.


This page is about how hydrogen gas could be used in an all-renewable energy scenario.


Energy storage basics

For energy storage of renewable electricity:

  • Hydrogen gas would be produced via electrolysis:
    • Electricity is used to convert water (H2O) into hydrogen gas and oxygen gas.
  • Hydrogen gas would be consumed via...
    • Burning it as fuel, producing heat.
    • Using it in fuel cells, producing electricity (and still some heat).
    • In both cases, the hydrogen reacts with oxygen in the air to form H2O again (water vapor).


This process has more energy losses than charging/discharging a battery, but hydrogen gas is far better suited for long-term energy storage. Hydrogen can be stockpiled in pressurized tanks (if designed properly). It can also be shipped long distances, just like any other fuel. This could help in cases where renewable energy sources are geographically far away from where energy is needed.


The intent would be for hydrogen gas to be used in place of fossil fuels:

  • Cars, trucks, etc. would be:
  • Homes & buildings:
    • For heating: Hydrogen gas could be burned instead of natural gas.
    • For cooking food: Hydrogen gas could probably work with gas stoves. [RESEARCH needed]
  • Factories:
    • Most of the energy used in manufacturing is in the form of high heat needed for processing materials. Factories could burn hydrogen gas instead of burning coal or natural gas.


Energy sources

Main use-case: Storing surplus wind power.
Here's why:

  • Wind power is far more intermittent than solar. Whereas solar follows a day/night cycle, windy and not-so-windy seasons can last for months at a time.
  • Wind turbines tend to be geographically far away from where electricity is needed, on average. Wind power is more spread out in terms of land, compared to the same amount of energy from local rooftop solar. Hydrogen could be transported long distances that can't be reached with power lines.

Other use-case: Since solar panels produce more energy in the summer, it would still be worthwhile to store some of that energy via hydrogen gas, to be used during the winter. Note, however: Batteries are a better choice for smoothing out the day/night cycle of solar power.

Other use-case: Storing energy from hydroelectricity during long periods of low demand.


Status quo


Platinum-group metals

Problem in some cases

Tl;dr: Too many fuel cell vehicles would be a problem. Hydrogen production would not be.


Both electrolysis and fuel cells need platinum-group metals (PGMs):

  • [platinum, palladium, rhodium, ruthenium, iridium, osmium]
    • Any of these metals will do, but all of them are extremely scarce (even more than gold), with platinum & palladium being the most available.
    • These metals serve as catalysts in the reactions. They are not used up, but they need to be there, in a thin layer plated onto the electrodes.

Note: It is possible to build fuel cells and electrolysis systems without PGMs, but the energy-efficiency is much lower.[QUANTIFICATION needed] There are scientists trying to overcome this,[LINKS needed] but there's no guarantee that it will be viable in the near future.

The supply of PGMs is limited to what we can mine from the Earth (mineral reserves / resources), so we have to be mindful of how much would be needed.

How much would be needed, if hydrogen were scaled up?

world.population
8 billion
Number of people alive today, globally
https://www.unfpa.org/data/world-population-dashboard
Last updated in 2023
world.cars
1.446 billion
Number of cars in the world
Last updated in 2022
www.carsguide.com.au › car-advice › how-many-cars-are-there-in-the-wor...
hedgescompany.com › blog › 2021/06 › how-many-cars-are-there-in-the-...
toyota_mirai.pgm
30 grams
Amount of platinum-group metals (PGMs) in a Toyota Mirai (fuel cell vehicle)
The Toyota Mirai is a common example of a hydrogen-powered vehicle.

https://www.heraeus.com/media/media/hpm/doc_hpm/precious_metal_update/en_6/20181031_PGM_Market_Analysis.pdf
catalytic_converter.pgm
2 grams
Platinum-group metals (PGMs) in a catalytic converter of a car
Countless automotive forums say 3 to 7 grams for a typical car.

But ThermoFisher (which is more reputable, perhaps) says "The recoverable amounts of Pt, Pd, and Rh in each [vehicle] can range from 1-2 grams for a small car to 12-15 grams for a big truck in the US." - Are There Precious Metals in Catalytic Converters? https://www.thermofisher.com/blog/metals/platinum-group-metal-recovery-from-spent-catalytic-converters-using-xrf/

I assume they mean 1-2 grams ''total'', not 1-2 grams ''of each'' Pt Pd Rh, right? That would make sense considering they also mention that the ratios vary as metal prices/availability change over time.

1 to 2 grams total recoverable is also consistent with the following study: Yakoumis et al 2018 IOP Conf. Ser.: Mater. Sci. Eng. 329 012009 - Real life experimental determination of platinum group metals content in automotive catalytic converters - https://iopscience.iop.org/article/10.1088/1757-899X/329/1/012009/pdf

Still no word on what percentage this ''recoverable'' is of total PGMs - how efficient is the recycling process? Unknown
platinum.mine_production
186000 kg/year
Global production of new platinum from mining
Using data from 2019.

Source: USGS Mineral Commodity Summaries 2021
palladium.mine_production
227000 kg/year
Global production of new palladium from mining
Using data from 2019.

Source: USGS Mineral Commodity Summaries 2021
pgm.status_quo_mining_production
platinum.mine_production + palladium.mine_production
Global production of platinum-group metals (PGMs) from mining (status quo)
Assumption: that the other PGMs (iridium, rhodium, osmium, ruthenium) are in such small quantities that it's ok that they aren't counted here (because data is unavailable)
pgm.reserves
70000 tonnes
Global mineral reserves of platinum-group metals
Includes platinum, palladium, ruthenium, rhodium, osmium, iridium.

Platinum-group metal reserves worldwide by country 2021
Statista - https://www.statista.com › statistics › platinum-me...
crop_land
15000000 km^2
Agricultural land used for growing crops - global total
https://ourworldindata.org/land-use
electrolysis.pgm_by_power
0.209 grams per kilowatt
Quantity of platinum-group metals (PGMs) in an electrolyzer
Electrolyzers make hydrogen gas from water & electricity. Platinum and/or similar metals are needed as catalytic plating.

Data source:
Manufacturing Cost Analysis for Proton Exchange Membrane Water Electrolyzers
August 2019 Technical Report NREL/TP-6A20-72740
https://www.nrel.gov/docs/fy19osti/72740.pdf
Pages 4 and 5: Table 1:
Cell plate area: CCM coated area: 748 cm^2
Platinum loading (anode): 7 g/m^2
Platinum-iridium loading (cathode): 4 g/m^2
Single cell power: 1965 W
From this we can calculate:
(7 g/m^2 + 4 g/m^2)/2 * 748 cm^2 / 1965 W = 0.20936387 g/kW
Sucks that the article doesn't directly specify this 'g/kW' value for us to confirm whether my calculations are correct. Still this is the best data source I could find. The article does also provide a lot of specs on total costs (ranging from $561/kW all the way down to $69/kW for some proposed systems with advanced techniques and economies of scale).
wind.capacity_factor
35%
Wind power: ratio: average output / peak power capacity
"The capacity factor of a wind turbine is its average power output divided by its maximum power capability. On land, capacity factors range from 0.26 to 0.52. The average 2019 capacity factor for projects built between 2014 and 2018 was 41%. In the U.S., the fleetwide average capacity factor was 35%."
https://css.umich.edu/factsheets/wind-energy-factsheet
wind.rq_land
34.5 hectares/MW
Land requirements of wind power
Important:
- This is per megawatt capacity (peak), not per average output.
- Stats can vary tremendously based on how windy the location is.
- This stat is based on 172 different wind projects scattered throughout the USA.
- Consider variance: (34.5 +/- 22.4) hectares/MW
- This is the total land use, including the spacing between turbines in a wind farm.
- This is much bigger than [wind.rq_land_disturbed] which is just the land directly impacted by constructing the turbine itself.

Citation:
Land-Use Requirements Of Modern Wind Power Plants In The United States
(Paul Denholm, Maureen Hand, Maddalena Jackson, and Sean Ong)
Page 16
energy.tfc
9937.70 Mtoe/year
Global energy usage - total final consumption (TFC)
Includes: fuel (80.7%) + electricity (19.3%) AFTER it is generated.

Does not include the fuel used in generating electricity. See [energy.tes] for that.

Citation: "Key World Energy Statistics 2020" IEA
- Page 47 - Simplified energy balance table - World energy balance, 2018
fossil_fuels.consumption
11596.92 Mtoe/year
Total consumption of coal, oil, and natural gas (worldwide) (energy units)
Key World Energy Statistics 2020 (IEA report)
- page 47: World energy balance, 2018
- - Total Energy Supply (TES), first 4 columns combined
electrolysis.efficiency
80%
Energy efficiency of producing hydrogen & oxygen gases from water
Hydrogen made by the electrolysis of water is now cost-competitive ...
www.carboncommentary.com › blog › hydrogen-made-by-the-electrolysis...
commercial_factor
2
Without this, we'd be calculating for just personal vehicles. But we also need to factor in commercial vehicles such as buses and trucks. These vary widely in size, and data is hard to find, so for simplicity sake, we just assume that they'd add up to about the same as personal vehicles - thus doubling total energy storage needed. This assumption is based on the fact that freight trucks are a somewhat smaller share of energy demand than passenger vehicles, but the trucks need far more horsepower and probably a longer range.

Scenario 1: If hydrogen gas (from wind power) were to directly replace all fossil fuels (this implies that people would drive hydrogen combustion vehicles):

electrolysis.pgm_by_power / electrolysis.efficiency / wind.capacity_factor * fossil_fuels.consumption % pgm.reserves ... (calculation loading) ... years pgm.status_quo_mining_production (calculation loading) PGMs needed for hydrogen gas production.

  • The amount of PGMs needed is pretty reasonable (16% of mineral reserves). We'd still have to mine for PGMs a lot faster than the status-quo (and do it without exploitative labor). [new page needed]

To prevent NOx emissions (see section below), hydrogen combustion vehicles need catalytic converters, just like gasoline or diesel vehicles do. Catalytic converters also contain some PGMs, which could be obtained by recycling old catalytic converters from fossil-fuel vehicles.


Scenario 2: If all vehicles were hydrogen fuel cell vehicles instead:

(toyota_mirai.pgm - catalytic_converter.pgm) * world.cars * commercial_factor % pgm.reserves ... (calculation loading) ... years pgm.status_quo_mining_production (calculation loading) PGMs needed to make the fuel-cell vehicles.Fuel-cell vehicles don't have catalytic converters, but a fuel cell contains far more PGMs than a catalytic converter.

  • One benefit of fuel cell vehicles is that they're more energy-efficient than combustion vehicles (i.e. less hydrogen used per kilometer driven).
  • The problem is, the fuel cells alone would need 7 times more PGMs mined than Scenario 1 (estimated). Perhaps too much to be scalable. And this is true even though we factored in the recycling of old catalytic converters.


The mass of PGMs needed is proportional to peak power:

  • For electrolysis systems, the maximum rate of hydrogen production is limited by the amount of PGMs.
  • For fuel cell vehicles, the horsepower is limited by the amount of PGMs.
    • But the vehicle can still achieve short bursts of higher horsepower if there's a battery or supercapacitor in parallel with the fuel cell.

More musings about the calculations above:

  • All of this assumes that electrolyzers and fuel cells can be completely recycled at their end-of-life, with all PGMs recovered. If they can't, we're kind of screwed in the long run (at least for hydrogen).
  • Hydrogen combustion vehicles are about as energy-efficient as gasoline combustion vehicles. Hence we can assume that the Scenario 1 estimate is accurate enough.
  • Home electricity can also be done with fuel cells - this would of course need more PGMs (and more hydrogen to make up for the losses in fuel cells (although those losses could be used as heating in some cases)).
  • We didn't count the hydrogen needed in the vehicles that transport the hydrogen (hopefully would be minor, like with fossil fuel transport).
  • All this is based on status-quo energy demand, which unfortunately relies on the fact that most of the world currently lives in poverty. If all nations were developed, more resources would be needed.
  • But in any case, we probably wouldn't actually use wind/hydrogen for everything anyway. Rooftop solar combined with batteries could probably be a better way to provide electricity whenever hydrogen need not be involved.
  • Since vehicle fuel cells use the biggest share of PGMs in this estimate, this is yet another reason to advocate for public transit and walkability.

Verdict

  • If we're going to have hydrogen-powered vehicles, most of them will probably have to be combustion only (or some sort of hybrid with just a very small fuel cell).
  • At least PGMs are not a limiting factor for wind-based hydrogen production.


Energy losses

Lossy but manageable
  • Electrolysis is at most 80% efficient.
  • Fuel cells are at most 60% efficient.
  • Thus, best-case electricity recovery is only 48%(...)( in other words, 60% of 80% ). Far less than most batteries which have a charge-discharge efficiency of 80% to 90%.
    • But for things that just need heat, then the energy recovery is still a good 80%. For example, wind power to produce hydrogen gas to burn for heating homes.

TODO: Add calculation: Knowing the losses, is there still enough land for wind-generated hydrogen gas were to directly replace all fossil fuels, in principle?

hydrogen_gas.specific_energy
120 MJ/kg
"By contrast, hydrogen has an energy density of approximately 120 MJ/kg , almost three times more than diesel or gasoline. In electrical terms, the energy density of hydrogen is equal to 33.6 kWh of usable energy per kg, versus diesel which only holds about 12–14 kWh per kg."
Oct 2, 2019
Run on Less with Hydrogen Fuel Cells - RMI
rmi.org › Blog
water.hydrogen_by_mass
hydrogen*2 / (hydrogen*2 + oxygen)
What percent of water's mass is hydrogen atoms
It's about 11%. Expressed using the calculator's built-in chemistry constants (atomic masses).
electrolysis.efficiency
80%
Energy efficiency of producing hydrogen & oxygen gases from water
Hydrogen made by the electrolysis of water is now cost-competitive ...
www.carboncommentary.com › blog › hydrogen-made-by-the-electrolysis...

In cases where electrolysis is done in weather below 0°C, such as beside wind turbines in cold parts of the world during winter, losses may be somewhat worse. (...)( The water has to be liquid (not frozen) while it's being electrolyzed to become hydrogen and oxygen. Heating takes energy; then again, maybe the waste heat of electrolysis would already be enough to keep the water liquid. In theory it can: For any amount of H2O electrolyzed, the waste heat is 8 times more than what it takes to melt that amount of ice: [See calculation] hydrogen_gas.specific_energy * water.hydrogen_by_mass * (100% - electrolysis.efficiency)water_fusion_heat(calculation loading) Maybe this belongs on a separate page called "hydrogen gas production in winter weather"? . For this to work, the hydrogen production system would have to be well-insulated from the weather. ) [new page needed]

Shelf life

[RESEARCH needed]

Chemically, hydrogen is the lightest gas (smallest molecules). This makes it harder to store than other gases, but there are still ways. [ELABORATION needed]


Pipelines

[RESEARCH needed]

Could existing natural gas pipelines be used for transporting hydrogen gas? Or would it cause too much leakage/corrosion? [RESEARCH needed]


Safety

Manageable
  • Just like natural gas, hydrogen gas is non-toxic and odorless but highly flammable. For safety in consumer applications, small quantities of some non-toxic but smelly gas(...)( such as methyl mercaptan, hydrogen sulfide, or ethyl isobutyrate (Wikipedia has a page "Hydrogen odorant") )should be added to it, so that people would know if there's a gas leak.
  • This section needs more safety-related info.


NOx emissions

Manageable

Burning hydrogen gas in air produces nitrogen oxides (NOx) in the same amount as burning gasoline or any other fuel. This happens because air is 78% nitrogen gas and 21% oxygen gas - any high temperature will cause some of the nitrogen to react with the oxygen. NOx gases contribute to climate change. [QUANTIFICATION needed]

For hydrogen combustion vehicles, this problem can be solved the same way it is for gasoline or diesel combustion: The vehicle has a catalytic converter to convert these gases into harmless substances. This requires some platinum-group metals (see section above).


Atmospheric losses

Very minor

Concern: When hydrogen gas leaks into the atmosphere, it's so light that it ends up being lost forever into outer space via Jeans escape. If this goes on for long enough, could Earth lose enough hydrogen that this would harm ecosystems or deplete the global water supply? How long would that take exactly?

Answer: If we assume:

  • that hydrogen gas leaks would happen at about the same rate as natural gas,
  • that losing 0.1% of the world's oceans would be enough to be a problem,
  • that hydrogen gas would be replacing all fossil fuels, by energy,

Then it would take more than a million years to have even a minor effect on the ecosystems:

natural_gas.leak_rate
1.4%
Percent of natural gas that is lost to leaks
As Natural Gas Booms, Methane Leaks Spark Climate Alarm - Bloomberg
water.hydrogen_by_mass
(hydrogen*2)/(hydrogen*2+oxygen)
How much of water's mass is hydrogen
About 11%. Calculated using chemistry constants built into the calculator.
oceans.volume
1.35 billion km^3
Total volume of all oceans on Earth
https://hypertextbook.com/facts/2001/SyedQadri.shtml
hydrogen_gas.energy_by_mass
120 MJ/kg
The specific energy of hydrogen gas
"...hydrogen has an energy density of approximately 120 MJ/kg , almost three times more than diesel or gasoline. In electrical terms, the energy density of hydrogen is equal to 33.6 kWh of usable energy per kg, versus diesel which only holds about 12–14 kWh per kg." - Oct 2, 2019 - Run on Less with Hydrogen Fuel Cells - RMI - rmi.org › Blog

0.1% oceans.volume * waterdensity * water.hydrogen_by_mass million years (natural_gas.leak_rate / hydrogen_gas.energy_by_mass * fossil_fuels.consumption) (calculation loading) Side note: For the same amount of energy, this is still a lot more hydrogen loss than nuclear fusion of hydrogen atoms.


Color terminology

Hydrogen is a colorless gas, but researchers sometimes name it with colors to indicate how it was produced:

  • "Grey hydrogen" is made from natural gas (steam reforming) - high greenhouse gas emissions. Currently the vast majority of hydrogen is produced this way.
  • "Blue hydrogen" is made from natural gas the same way, but with carbon capture. This is supposed to reduce emissions, but in practice it doesn't help much.
  • "Pink hydrogen" is made from electrolysis using nuclear energy.
  • "Green hydrogen" is made from electrolysis using renewable energy.
  • "White hydrogen" is naturally-occuring hydrogen (very rare).


See also

  • Methane cracking - another way to produce hydrogen gas. Not worthwhile currently, but in theory the right tech could maybe change that.
  • Energy storage
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