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(...)( 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.

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(...)( 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.

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

Possible problem

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?

General principlesGeneral principles

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.

Estimate #1

Suppose,

• that all of today's energy demand were to be met using hydrogen gas
• that all hydrogen gas is produced using wind power (or something with the same capacity factor as wind)

This section has not been filled in yet.

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.