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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}}


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==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.
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==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.
** 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.
** 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.
{{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.}}
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?===
===How much would be needed, if hydrogen were scaled up?===
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}}
}}
{{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 (status quo)</nowiki>
|<nowiki>Global production of platinum-group metals (PGMs) from mining (status quo)</nowiki>
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}}
}}
<!-- --- END OF DATA POINTS ---
<!-- --- END OF DATA POINTS ---
-->
-->
<tab name="General principles" collapsed>
'''Scenario 1:''' If hydrogen gas (from wind power) were to directly replace all fossil fuels (this implies that people would drive [[hydrogen combustion vehicles]]):
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.


{{minor|The mass of PGMs needed is proportional to ''peak power'':}}
<tab name="SEE MATHS" collapsed>
* 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>
 
 
'''Scenario 1:''' If hydrogen gas (from wind power) were to directly replace all fossil fuels (this implies that people would drive [[hydrogen combustion vehicles]]):
<tab name="(see maths)">
{{calc
{{calc
|electrolysis.pgm_by_power / electrolysis.efficiency / wind.capacity_factor * fossil_fuels.consumption
|electrolysis.pgm_by_power / electrolysis.efficiency / wind.capacity_factor * fossil_fuels.consumption
|% pgm.reserves
|% pgm.reserves
|a
|...
}}
}}
{{calc
{{calc
|a
|...
|years pgm.mine_production
|years pgm.status_quo_mining_production
|||'''PGMs needed for hydrogen gas production.'''
}}
}}
</tab>
</tab>


In other words, the amount of PGMs needed is pretty reasonable - but we'd have to start mining a lot faster than the status quo (and find some way to do it '''without''' exploitative [[labor]]).{{npn}}
* 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}}


And in fact, some{{x|about half, if calculated from the same datapoints used on this page}} of this mining could be avoided, as we could also recycle existing catalytic converters{{x|which also contain ''some'' PGMs, though nowhere near as much as fuel cell vehicles}} from the gasoline cars and diesel trucks that would no-longer be used.
{{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.}}




'''Scenario 2:''' If all vehicles were hydrogen [[fuel cell vehicles]] instead:
'''Scenario 2:''' If all vehicles were hydrogen [[fuel cell vehicles]] instead:
<tab name="(see maths)">
 
<tab name="SEE MATHS" collapsed>
{{calc
{{calc
|(toyota_mirai.pgm - catalytic_converter.pgm) * world.cars * commercial_factor
|(toyota_mirai.pgm - catalytic_converter.pgm) * world.cars * commercial_factor
|% pgm.reserves
|% pgm.reserves
|b
|...
}}
}}
{{calc
{{calc
|b
|...
|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.}}
}}
}}
</tab>
</tab>
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  Maybe I should refactor [[template:calc]] to allow for presenting one calculation in multiple units? This would involve some design decisions.
  Maybe I should refactor [[template:calc]] to allow for presenting one calculation in multiple units? This would involve some design decisions.
-->
-->
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, fuel cells would need 7 times the PGMs of Scenario 1 {{light|(estimated)}}. Perhaps too much to be scalable. And this is true even though we factored in the recycling of old catalytic converters this time (which have less than 1/10th the PGMs of a hydrogen fuel cell vehicle, on average).
* 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.


'''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''.


<tab name="More discussion / research needed">
<tab name="General principles" collapsed>
<div style="font-size:70%;color:#333;margin:1em;border:1px dashed #CCC">
{{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:
* 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).
* 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).
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* 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>
</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 / storage==
{{sum|{{rn}} }}
{{sum|{{rn}} }}
Chemically, hydrogen is the lightest gas (smallest molecules). This makes it harder to store than other gases, but there are still ways. {{en}}
Chemically, hydrogen is the lightest gas (smallest molecules). This makes it harder to store than other gases, but there are still ways. {{en}}


{{pn-block|
read later: some relevant info might be found in: https://europe.autonews.com/suppliers/faurecia-gets-213m-euros-eu-french-hydrogen-project
<br />basic question: can pressurized hydrogen be stored in (perhaps modified) steel tanks, or will it corrode all but the most expensive materials?
}}


==Pipelines==
==Pipelines==
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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}}
-->




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* "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 -->


<!--
<!--
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==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]]
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