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Refactored page. But the PGMs section still needs redoing.
(→‎How much would be needed, if hydrogen were scaled up?: Added some more DPs, planning to use them in new estimates in future edits)
(Refactored page. But the PGMs section still needs redoing.)
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==Use-cases==
==Energy storage basics==
===Production===
For [[energy storage]] of renewable electricity:
* Storing energy from [[wind]] power, as the windy seasons and non-windy seasons both tend to last for months at a time.
* Hydrogen gas would be '''produced''' via ''electrolysis'':
* Storing energy from [[geothermal electricity]], which is only available in very specific geographical regions, usually far away from most [[population]] (power lines can't reach). The hydrogen gas can be transported to where people could use it.
** Electricity is used to convert water (H<sub>2</sub>O) 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 {{light|(and still some heat)}}.
** {{light|In both cases, the hydrogen reacts with oxygen in the air to form H<sub>2</sub>O again (water vapor).}}


Hydrogen gas can be produced using electricity to split water molecules (H<sub>2</sub>O) into hydrogen gas (H<sub>2</sub>) and oxygen gas (O<sub>2</sub>). This process is called ''electrolysis''.


===Transport===
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 [[transportation of hydrogen gas|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.
{{pn|Research needed for this section}}
* Is it viable to repurpose natural gas pipelines? Or would it leak too much since H<sub>2</sub> molecules are much smaller than methane? {{rn}}
* How about pressurized storage tanks on trains? {{rn}}


===Usage===
Combustion
* for cooking (much like [[natural gas]] stoves)
* for [[heating]] homes / buildings
Fuel cells
* for [[fuel cell vehicles|vehicles]]
* for home electricity, in ''some'' cases{{en}}{{x|waste heat could also be used to heat the home}}
<small>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 people can smell if there's a gas leak.</small>


Hydrogen fuel cells are the opposite of the electrolysis mentioned above. A fuel cell takes in hydrogen gas (along with oxygen gas from the air), generates electricity, and leaves behind water vapor.
The intent would be for hydrogen gas to be used in place of [[fossil fuels]]:
* Cars, trucks, etc. would be:
** [[Hydrogen combustion vehicles]], or
** [[Hydrogen fuel cell electric vehicles]]
* Homes & buildings:
** For [[heating]]: Hydrogen gas could be burned instead of [[natural gas]].
** For cooking food: Hydrogen gas could probably work with gas stoves. {{rn}}
* 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.


===General===
Compared to batteries,
* Hydrogen is better for ''long-term'' energy storage.
* Hydrogen is better for transporting energy.
* Hydrogen is worse in terms of energy recovery.
** Electrolysis is at most 80% efficient.
** Fuel cells are at most 60% efficient.
** Thus, best-case electricity recovery is only 48%{{x|in other words, 60% of 80%}}. Far less than most batteries which have a charge-discharge efficiency of 80% to 90%.
Batteries may be better for storing [[solar]] energy from the daytime and using it at night.


===Compared to status quo===
==Energy sources==
Most hydrogen gas today is used for making [[fertilizer]], and is produced from natural gas. Fertilizer production can continue with renewables. This is a relatively small amount of hydrogen, compared to a "net zero carbon emissions scenario" involving all the use-cases above.
'''Main use-case:''' Storing [[wind]] power.<br />
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.


==Considerations==
'''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. {{light|Note, however: Batteries are a better choice for smoothing out the ''day/night cycle'' of solar power.}}
===Platinum-group metals===
 
{{sum|Possible problem}}
'''Other use-case:''' Storing energy from [[hydroelectricity]] during long periods of low demand.
 
<!-- TODO: find number to fill this in with:
For renewables & hydrogen to replace all fossil fuels, hydrogen production & consumption would have to scale up by about ___ times the status quo.
-->
 
==Status quo==
* 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]].
 
 
==Platinum-group metals==
{{sum|Problem in some cases}}


Both '''electrolysis''' and '''fuel cells''' need platinum-group metals (PGMs):
Both '''electrolysis''' and '''fuel cells''' need platinum-group metals (PGMs):
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* 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]].
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<!-- TODO: Uncomment this when done writing about PGMs above (a more immediate and important mention that should be on here first)
<!-- TODO: Uncomment this when done writing about PGMs above (a more immediate and important mention that should be on here first)
===Atmospheric losses===
==Atmospheric losses==
{{sum|Probably minor}}
{{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.}} }}
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.}} }}
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==Energy losses==
{{sum|Lossy but manageable}}
* Electrolysis is at most 80% efficient.
* Fuel cells are at most 60% efficient.
* Thus, best-case ''electricity'' recovery is only 48%{{x|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.
*** 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?}}
==Shelf life==
{{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}}
==Pipelines==
{{sum|{{rn}} }}
Could existing natural gas pipelines be used for transporting hydrogen gas? Or would it cause too much leakage/corrosion? {{rn}}
==Safety==
{{sum|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{{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.}}


==Color terminology==
==Color terminology==
Hydrogen is a colorless gas, but people sometimes ''name'' it with colors to indicate ''how it was produced'':
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.
* "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.<!-- TODO: cite that article I found awhile ago -->
* "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.<!-- TODO: cite that article I found awhile ago -->
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SCRAP: Not sure where to put this... it continues from "compared to status quo" but doesn't quite fit in that section...
SCRAP: Not sure where to put this, if anywhere at all:
 
===Production from fossil fuels===
===Production from fossil fuels===
Currently most hydrogen is produced from [[natural gas]] via [//wikipedia.org/wiki/Steam_reforming steam reforming], but this emits just as much CO<sub>2</sub> as burning the natural gas itself.
Currently most hydrogen is produced from [[natural gas]] via [//wikipedia.org/wiki/Steam_reforming steam reforming], but this emits just as much CO<sub>2</sub> as burning the natural gas itself.
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There's another (similar) process called [[methane cracking]] which takes in natural gas, and produces hydrogen gas + solid carbon (not CO<sub>2</sub>). The main problem is that it's a ''net loss'' of energy {{x|it takes a lot more energy than you ultimately get by burning the hydrogen gas}}. In theory, it doesn't have to be.  
There's another (similar) process called [[methane cracking]] which takes in natural gas, and produces hydrogen gas + solid carbon (not CO<sub>2</sub>). The main problem is that it's a ''net loss'' of energy {{x|it takes a lot more energy than you ultimately get by burning the hydrogen gas}}. In theory, it doesn't have to be.  
{{p|Chemistry equations:<br />CH<sub>4</sub> &rarr; C + 2 H<sub>2</sub> &emsp; (endothermic: &nbsp; 75 kJ/mol)<br />2 H<sub>2</sub> + O<sub>2</sub> &rarr; 2 H<sub>2</sub>O (exothermic: &nbsp; 572 kJ/mol)}}
{{p|Chemistry equations:<br />CH<sub>4</sub> &rarr; C + 2 H<sub>2</sub> &emsp; (endothermic: &nbsp; 75 kJ/mol)<br />2 H<sub>2</sub> + O<sub>2</sub> &rarr; 2 H<sub>2</sub>O (exothermic: &nbsp; 572 kJ/mol)}}
==Usage==
Most hydrogen gas today is used in making [[fertilizer]]. However, there are other things that could be done with hydrogen if production was scaled up enough:
* Hydrogen gas can be burned.
** This could be useful for [[heating]] and [[cooking]].
** It ''might'' be possible for some existing ''natural gas'' infrastructure be retrofitted for hydrogen gas.{{rn}}
*** If so, gas stoves could run on hydrogen.
* Hydrogen gas can be used for making electricity, using a ''fuel cell''.
** However, to use this in [[energy storage]] systems is quite '''lossy''':
*** "electricity &rarr; hydrogen gas &rarr; back to electricity" is ''at best'' only 40% to 48% efficient{{x|This is the combined energy-efficiency. The electrolyzers are about 80% efficient, and the fuel cells are about 50% to 60% efficient.}}.
In this way, [[fuel cell vehicles]] are not as efficient as [[battery electric vehicles]]. At least they're still more efficient than [[hydrogen combustion vehicles]].
-->
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<!-- TALK: maybe refactor the page to start with a section called "basics" that explains fuel cells, electrolysis, steam reforming and methane cracking? -->
==See also==
* [[Methane cracking]] {{light|- another way to produce hydrogen gas. Not worthwhile currently, but ''in theory'' the right tech could maybe change that.}}