Hydrogen gas
- Not to be confused with nuclear fusion of hydrogen atoms.
Hydrogen gas (H2) is a combustible fuel that leaves behind nothing but water vapor (H2O) when burned.
There are no natural resources of hydrogen gas
This page is about how hydrogen gas could be used with renewable energy.
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 (H2O) into hydrogen gas (H2) and oxygen gas (O2). This process is called electrolysis.
Transport
Research needed for this section
- Is it viable to repurpose natural gas pipelines? Or would it leak too much since H2 molecules are much smaller than methane? [RESEARCH needed]
- How about pressurized storage tanks on trains? [RESEARCH needed]
Usage
Combustion
- for cooking (much like natural gas stoves)
- for heating homes / buildings
Fuel cells
- for vehicles
- for home electricity, in some cases[ELABORATION needed]
(...)( waste heat could also be used to heat the home )
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
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%
(...)( 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
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.
How much would be needed, if hydrogen were scaled up?
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.
Last updated in 2023
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https://www.heraeus.com/media/media/hpm/doc_hpm/precious_metal_update/en_6/20181031_PGM_Market_Analysis.pdf
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
Source: USGS Mineral Commodity Summaries 2021
Source: USGS Mineral Commodity Summaries 2021
Platinum-group metal reserves worldwide by country 2021
Statista - https://www.statista.com › statistics › platinum-me...
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).
https://css.umich.edu/factsheets/wind-energy-factsheet
- 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
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
Suppose,
- 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.
We'd have to start mining a lot faster, and find some way to do it without exploitative labor. [ELABORATION needed]
Calculations: PGMs needed for hydrogen production: (calculation loading)
PGMs needed for hydrogen-based electricity consumption: (calculation loading)
PGMs recoverable from catalytic converters of old gas cars:Old semi trucks (not counted here) could also provide a bit more (calculation loading)
Compared to mineral reserves: (calculation loading)
Compared to current production rate: (calculation loading)
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,
- 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.
In any case, producing that much wind power is maybe reasonable if most farmland were to be covered in wind turbines. (calculation loading)
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.
- 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).
- If electric semi trucks use fuel cells too, we'd need more PGMs than this estimate.
- 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).
- 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 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.
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.
- "Pink hydrogen" is made from electrolysis using nuclear energy.
- "Green hydrogen" is made from electrolysis using renewable energy.