Colours of `hydrogen`

[l-emele]

Description of the issue

In the current scenarios (and political discussions) more and more often hydrogen is characterised by "colours". Hydrogen has of course not really different colours, but these are catchy names depicting different sources / processes of the hydrogen. Some examples

• green hydrogen: hydrogen from water electrolysis using renewable electricity
• grey hydrogen: hydrogen from steam reforming of fossil fuels
• blue hydrogen: hydrogen from steam reforming of fossil fuels and CCS of the CO2 produced in the steam reforming

Some resouces describing the "colours": 1, 2, 3

Ideas of solution

We already have two subclasses of hydrogen (fossil hydrogen and synthetic hydrogen) that describe hydrogen with different origins. We can add further subclasses, describing the process involved to produces the different kinds involved.

As the "colours" are neither really neutral descriptions nor self-explaning I strongly prefer that we use the "colours" only as alternative terms but find better class labels.

Workflow checklist

• [ ] I discussed the issue with someone else than me before working on a solution
• [ ] I already read the latest version of the workflow for this repository
• [ ] The goal of this ontology is clear to me

I am aware that

• [ ] every entry in the ontology should have a definition
• [ ] classes should arise from concepts rather than from words

[stap-m]

As the "colours" are neither really neutral descriptions nor self-explaning I strongly prefer that we use the "colours" only as alternative terms but find better class labels.

We could make use of the origin sustainable discussed in #872 for green H2 and conventional for blue and grey. Further, we could have subclasses of the latter to distiguish blue and grey.

[l-emele]

Axiomatically we can describe blue hydrogen as physical output of a process hat has both a steam reforming process and a carbon capture and storage process as partial process. We have an energy converting device steam reformer but currently do not have a steam reforming process.

[l-emele]

To move forward with this issue, here some proposals:

• Electrolytic hydrogen is hydrogen that is physical output of a water electrolysis process. Axiom: 'electrolytic hydrogen' EquivalentTo: hydrogen and 'physical output of' some 'water electrolysis process' Axiom: 'electrolytic hydrogen' 'bearer of' some 'renewable energy carrier disposition' Axiom: 'electrolytic hydrogen' has origin some synthetic.
• X hydrogen is hydrogen that is produced with renewable electrical energy. => Alternative label: green hydrogen Axiom: 'X hydrogen' EquivalentTo: hydrogen' and 'physical output of' some ('water electrolysis process' 'has energy input' some ('electrical energy' 'has origin' some renewable)[^1] Axiom: 'X hydrogen' has origin some synthetic.
• Y hydrogen is hydrogen that is physical output of a steam reforming process. Axiom: 'Y hydrogen' EquivalentTo: hydrogen and 'physical output of' some 'steam reforming' Axiom: 'Y hydrogen' has origin some synthetic.
• Fossil Y hydrogen is hydrogen that is produced from a fossil combustion fuel in a steam reforming process which is not followed by a carbon capture and storage process. => Alternative label: grey hydrogen Axiom: 'Z hydrogen' EquivalentTo hydrogen and 'physical output of' some ('steam reforming' 'has physical input' some 'fossil combustion fuel' and not ('causally upstream or within' some 'carbon capture and storage')'. Axiom: 'fossil Y hydrogen' 'bearer of' some 'conventional energy carrier disposition' Axiom: 'fossil Y hydrogen' 'has origin' some fossil. Axiom: 'fossil Y hydrogen' has origin some synthetic.
• Z hydrogen is hydrogen that is output of a steam reforming process which is followed by a carbon capture and storage process. => Alternative label: blue hydrogen. Axiom: 'Z hydrogen' EquivalentTo hydrogen and 'physical output of' some ('steam reforming' 'has physical input' some 'fossil combustion fuel' and ('causally upstream or within' some 'carbon capture and storage'). Axiom: 'fossil Y hydrogen' 'bearer of' some 'conventional energy carrier disposition' Axiom: 'fossil Z hydrogen' 'has origin' some fossil. Axiom: 'Z hydrogen' has origin some synthetic.

This should then produced the following inferred structure:

• hydrogen
  • synthetic hydrogen
  • electrolytic hydrogen
    • X hydrogen = green hydrogen
  • Y hydrogen = hydrogen from steam reforming
    • fossil Y hydrogen = grey hydrogen
    • Z hydrogen = blue hydrogen
  • fossil hydrogen
    • fossil Y hydrogen = grey hydrogen
    • Z hydrogen = blue hydrogen

The multi-hierarchical is intended.

The class synthetic hydrogen has currently the definition; Synthetic hydrogen is hydrogen with synthetic origin. It is usually produced from water applying the water electrolysis process. The second sentence should be deleted, as this is then in the proposed structure a bit misleading.

Proper labels for X, Y and Z are still open for discussion.

[^1]: This is quite a long axiom. This can be shortened if we introduce: Renewable electrical energy is electrical energy with a renewable origin. Axiom: 'renewable electrical energy' EquivalentTo: 'electrical energy' and 'has origin' some renewable. Then the shortened axiom above would reduce to: 'X hydrogen' EquivalentTo: 'electrolytic hydrogen' and 'physical output of' some ('water electrolysis process' 'has energy input' some 'renewable electrical energy'.

[l-emele]

For X hydrogen I propose the label renewable electrolytic hydrogen and for Y hydrogen I propose steam reforming hydrogen. But maybe these labels are too clunky.

[stap-m]

For X hydrogen I propose the label renewable electrolytic hydrogen and for Y hydrogen I propose steam reforming hydrogen. But maybe these labels are too clunky.

Since we add the "colours" as alternative term, I think it is ok. Otherwise, we could switch label and alternative terms to use more common vocabulary?!

[l-emele]

For Z hydrogen I still struggle to find a proper label, something like CCS steam reforming hydrogen or abated steam reforming hydrogen . But I am not happy with any of these.

Seems to be a reason, why the colour names were invented ;)

[l-emele]

No further reaction for the last two months. I'll implement this now with abated steam reforming hydrogen has primary label for blue hydrogen.