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Hydrogen gas: Difference between revisions
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: <small>''Not to be confused with [[nuclear fusion]] of hydrogen atoms.''</small> | |||
[[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. | |||
<!-- TALK: Maybe this is wrong if NOx emissions can be emitted too? {{qn}} If so, how to rephrase while maintaining simplicity? --> | |||
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}}. | |||
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]].''''' | |||
{{considerations}} | |||
=== | ==Use-cases== | ||
===Production=== | |||
* Storing energy from [[wind]] power, as the windy seasons and non-windy seasons both tend to last for months at a time. | |||
* 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. | |||
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=== | |||
{{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 or hydrogen sulfide}}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. | |||
===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=== | |||
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. | |||
==Considerations== | |||
===Platinum-group metals=== | |||
{{sum|Possible problem}} | |||
{{empty}} | |||
<!-- 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.}} }} | |||
--> | |||
==Color terminology== | |||
Hydrogen is a colorless gas, but people 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.<!-- TODO: cite that article I found awhile ago --> | |||
* "Pink hydrogen" is made from electrolysis using [[nuclear]] energy. | |||
* "Green hydrogen" is made from electrolysis using renewable energy. | |||
<!-- | |||
SCRAP: Not sure where to put this... it continues from "compared to status quo" but doesn't quite fit in that section... | |||
===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. | ||
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> → C + 2 H<sub>2</sub>   (endothermic: 75 kJ/mol)<br />2 H<sub>2</sub> + O<sub>2</sub> → 2 H<sub>2</sub>O (exothermic: 572 kJ/mol)}} | {{p|Chemistry equations:<br />CH<sub>4</sub> → C + 2 H<sub>2</sub>   (endothermic: 75 kJ/mol)<br />2 H<sub>2</sub> + O<sub>2</sub> → 2 H<sub>2</sub>O (exothermic: 572 kJ/mol)}} | ||
==Usage== | ==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: | 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. | * Hydrogen gas can be burned. | ||
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*** "electricity → hydrogen gas → 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.}}. | *** "electricity → hydrogen gas → 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]]. | 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]]. | ||
--> | |||
<!-- TALK: maybe refactor the page to start with a section called "basics" that explains fuel cells, electrolysis, steam reforming and methane cracking? --> | |||