The Colors of Hydrogen
Hydrogen is colorless — but you will hear it called green, blue, grey, and more. The colors are a shorthand for how it is made, and they decide whether it actually helps the climate.
Hydrogen is the same colorless gas no matter how you make it. But you’ll constantly hear it described in color — green, blue, grey, pink, turquoise. Those names are a shorthand for the production route, and that’s what determines whether a kilogram of hydrogen is a climate solution or a climate problem.
A spectrum of production
Splitting water with wind or solar power. Near-zero emissions — the goal of a clean hydrogen economy.
Hydrogen is colourless — the "colours" are shorthand for how it is made. Emissions are approximate, illustrative figures.
The headline: most hydrogen made today is grey — steam-reforming natural gas, emitting roughly ten kilograms of CO₂ for every kilogram of hydrogen. Green hydrogen (electrolysis run on renewables) is the goal, with blue (reforming plus carbon capture) and turquoise (methane pyrolysis to solid carbon) as lower-carbon bridges.
The catch: storing it
Whatever its color, hydrogen shares an awkward physical trait. It packs more energy per kilogram than any other fuel — and almost the least per litre.
Hydrogen carries the most energy per kilogram of any fuel — but among the least per litre. That single fact is why storing useful amounts means handling huge volumes, and why the cheapest place to put it is underground. Illustrative lower-heating-value figures.
That mismatch is the whole reason underground storage exists. You can’t keep meaningful amounts of hydrogen in tanks; you need the volume of a cavern or a reservoir. So the color question — how do we make it cleanly? — leads straight to a storage question — where do we keep it? — which is exactly where the geology of salt and trona comes in.
Sources & further reading
- International Energy Agency (2019) — The Future of Hydrogen.
- IEA — Global Hydrogen Review (annual), on production routes and emissions intensity.
- Tarkowski, R. (2019) — Underground hydrogen storage: Characteristics and prospects, Renewable and Sustainable Energy Reviews.
CO2 intensities and energy-density figures are approximate, illustrative values.