---
title: "Tech brief: Hydrogen classification systems"
canonical_url: "https://www.smoltek.com/hydrogen-classification-systems/6529/"
date: 2024-01-16
author: "Thomas Barregren"
featured_image: "https://www.smoltek.com/wp-content/uploads/2024/01/colors-of-hydrogen-jpg.webp"
categories:
  - name: "IR Blog Posts"
    url: "https://www.smoltek.com/category/ir-blog-posts.md"
tags:
  - name: "hydrogen"
    url: "https://www.smoltek.com/topic/hydrogen.md"
  - name: "tech brief"
    url: "https://www.smoltek.com/topic/tech-brief.md"
---

# Tech brief: Hydrogen classification systems

What col­or does hydro­gen have? None at all. It is trans­par­ent and can­not be seen with the naked eye. How­ev­er, hydro­gen is called black, brown, gray, blue, green, and so forth. The col­ors denote the feed­stocks and pro­duc­tion meth­ods used to pro­duce hydro­gen. In this brief, we explain the mean­ing of the dif­fer­ent col­ors and look at an alter­na­tive clas­si­fi­ca­tion of hydro­gen used by the EU.

### Tech brief

This is a tech brief. We craft these to pro­vide tech­ni­cal back­ground infor­ma­tion to help you bet­ter under­stand oth­er blog posts.

## [](https://www.smoltek.com#colors-of-hydrogen)Colors of hydrogen

Let’s start by review­ing the col­or spec­trum used to clas­si­fy hydro­gen based on how it is pro­duced and with which feedstock.

- **Black hydro­gen** is pro­duced by coal gasi­fi­ca­tion of black coal (bitu­mi­nous).
- **Brown hydro­gen** is pro­duced by coal gasi­fi­ca­tion of brown coal (lig­nite) or bio­mass gasification.
- **Grey hydro­gen** is pro­duced by steam methane reform­ing, par­tial oxi­da­tion, or autother­mal reform­ing of nat­ur­al gas and oil.
- **Blue hydro­gen** is pro­duced as black, brown, or grey hydro­gen with the added appli­ca­tion of car­bon cap­ture, uti­liza­tion, and stor­age (CCUS) meth­ods or technologies.
- **Turquoise hydro­gen** is pro­duced by methane pyrolysis.
- **Yel­low hydro­gen** is pro­duced by water elec­trol­y­sis using elec­tric­i­ty from the grid regard­less of how this elec­tric­i­ty has been produced.
- **Pink hydro­gen** is pro­duced by water elec­trol­y­sis using elec­tric­i­ty from nuclear power.
- **Pur­ple hydro­gen** is pro­duced by ther­mo­chem­i­cal water split­ting using ener­gy from nuclear power.
- **Red hydro­gen** is pro­duced by high-tem­per­a­ture cat­alyt­ic split­ting of water using ener­gy from nuclear power.
- **Green hydro­gen** is pro­duced by water elec­trol­y­sis using renew­able ener­gy sources.
- **White hydro­gen** is nat­u­ral­ly occur­ring hydro­gen found as a free gas in lay­ers of con­ti­nen­tal crust, deep in the ocean­ic crust, or in vol­canic gas­es, gey­sers, and hydrother­mal systems.

The list above can be sum­ma­rized in this schemat­ic table illus­trat­ing the rela­tion­ships between the dif­fer­ent col­or class­es used for hydro­gen and the feed­stock and process used to pro­duce it.

| Feed­stock             | Pro­duc­tion method   | Hydro­gen color |                               |                                                                     |
|------------------------|-----------------------|-----------------|-------------------------------|---------------------------------------------------------------------|
| Nat­ur­al gas          | Methane pyrol­y­sis   | Turquoise       |                               |                                                                     |
|                        | Steam reform­ing      | Gray            | Blue (if car­bon is captured) | Yel­low (if used to pro­duce elec­tric­i­ty for water electrolysis) |
| Black coal             | Gas­si­fi­ca­tion     |                 |                               | Black                                                               |
| Brown coal             | Gas­si­fi­ca­tion     |                 |                               | Brown                                                               |
| Bio­mass               |                       |                 |                               |                                                                     |
| Renew­able electricity | Water elec­trol­y­sis | Green           |                               |                                                                     |
| Nuclear elec­tric­i­ty | Water elec­trol­y­sis | Pink            |                               |                                                                     |
|                        | Water split­ting      | Pur­ple         |                               |                                                                     |
|                        | Cat­alyt­ic splitting | Red             |                               |                                                                     |

## [](https://www.smoltek.com#caveat)Caveat

The hydro­gen industry’s col­or clas­si­fi­ca­tion is evolv­ing, and not all terms have uni­ver­sal­ly agreed-upon def­i­n­i­tions. This can lead to vari­a­tions in how terms are used and understood.

Yel­low hydro­gen is an exam­ple that shows vari­a­tion in how terms are used. Above, it’s described as hydro­gen pro­duced by water elec­trol­y­sis, where the elec­tric­i­ty comes from the grid and, there­fore, can be pro­duced by any­thing from coal-fired pow­er sta­tions to wind tur­bines. But quite a few peo­ple have a com­plete­ly dif­fer­ent def­i­n­i­tion: Yel­low hydro­gen is pro­duced by water elec­trol­y­sis using elec­tric­i­ty from solar pow­er plants. This is an entire­ly dif­fer­ent def­i­n­i­tion far from the one used by most inter­na­tion­al orga­ni­za­tions, gov­ern­ments, author­i­ties, and researchers.

Green hydro­gen is an exam­ple that shows vari­a­tion in how terms are under­stood. Above, it’s described as hydro­gen pro­duced by water elec­trol­y­sis, where the elec­tric­i­ty comes from any renew­able source. Bio­mass is an exam­ple of a renew­able source, but it’s not very” green” when used as fuel in pow­er plants. There­fore, the EU Com­mis­sion and Par­lia­ment use a def­i­n­i­tion of green hydro­gen that excludes bio­mass and also requires at least a 70 per­cent reduc­tion in green­house gas emis­sions com­pared to fos­sil fuels.

In addi­tion, some use vio­let instead of pink, and oth­ers con­flate pink, pur­ple, and red hydro­gen and use one of these col­ors to mean all of them.

On top of that, researchers and devel­op­ers slap new col­ors on each nov­el method of cre­at­ing hydro­gen. For exam­ple, *aqua* is used for hydro­gen extract­ed from oil sands and oil fields, and *orange* is used for hydro­gen pro­duced by chem­i­cal reac­tions in iron-rich under­ground formations.

## [](https://www.smoltek.com#eu-classification)EU classification

How­ev­er, as we have seen, there is no con­sen­sus on which col­ors to use and what they stand for. This has prompt­ed the Euro­pean Com­mis­sion to intro­duce its own clas­si­fi­ca­tion in the commission’s [hydro­gen strat­e­gy for a cli­mate-neu­tral Europe](https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX%3A52020DC0301&from=EN):

- **Elec­tric­i­ty-based hydro­gen** is hydro­gen pro­duced through water elec­trol­y­sis regard­less of the elec­tric­i­ty source. (Thus, includes both yel­low and green hydrogen).
- **Renew­able hydro­gen** is hydro­gen pro­duced through water elec­trol­y­sis with elec­tric­i­ty from renew­able sources. (Thus, it’s a large sub­set of green hydrogen).
- **Clean hydro­gen** is anoth­er name for renew­able hydrogen.
- **Fos­sil-based hydro­gen** is hydro­gen pro­duced through var­i­ous process­es using fos­sil fuels as feed­stock. (Thus, this includes black, brown, gray, and blue hydrogen.)
- **Fos­sil-based hydro­gen with car­bon cap­ture** is a sub­part of fos­sil-based hydro­gen, but where green­house gas­es emit­ted as part of the hydro­gen pro­duc­tion process are cap­tured. (Thus, this is equiv­a­lent to blue hydrogen.)
- **Low-car­bon hydro­gen** encom­pass­es fos­sil-based hydro­gen with car­bon cap­ture and elec­tric­i­ty-based hydro­gen, with sig­nif­i­cant­ly reduced full life-cycle green­house gas emis­sions com­pared to exist­ing hydro­gen pro­duc­tion. [As of Feb­ru­ary 7, 2023](https://energy.ec.europa.eu/publications/delegated-regulation-minimum-threshold-ghg-savings-recycled-carbon-fuels-and-annex_en), this means at least a 70% reduc­tion in green­house gas emis­sions com­pared to fos­sil fuels. (Thus, this con­tains a sub­set of blue hydro­gen and a sub­set of yel­low hydrogen.)
- **Hydro­gen-derived syn­thet­ic fuels** refer to var­i­ous gaseous and liq­uid fuels based on hydro­gen and car­bon. (Thus, this has no equiv­a­lent color.)

The table below illus­trates the rela­tion­ships between the Euro­pean Com­mis­sion clas­si­fi­ca­tion and the col­or classification.

| Hydro­gen col­or classification | EU hydro­gen classification                  |
|---------------------------------|----------------------------------------------|
| Black                           | Fos­sil-based hydrogen                       |
| Brown                           |                                              |
| Gray                            |                                              |
| Blue                            | Fos­sil-based hydro­gen with car­bon capture |
|                                 | Low-car­bon hydrogen                         |
| Turquoise                       | Low-car­bon hydrogen                         |
| Red                             |                                              |
| Pur­ple                         |                                              |
| Pink                            | Elec­tric­i­ty-based hydrogen                |
| Yel­low                         |                                              |
| Green                           | Renew­able hydrogen                          |

## [](https://www.smoltek.com#purpose-of-classification)Purpose of classification

The clas­si­fi­ca­tion of hydro­gen helps var­i­ous groups like politi­cians, busi­ness lead­ers, and envi­ron­men­tal­ists to quick­ly iden­ti­fy its pro­duc­tion impact on the envi­ron­ment. This clas­si­fi­ca­tion sep­a­rates hydro­gen with high green­house gas emis­sions (black, brown, and gray) from low-emis­sion (blue) and com­plete­ly fos­sil-free types (pink and green).

## [](https://www.smoltek.com#present-and-future)Present and future

In 2022, almost 95 mil­lion tonnes (Mt) of hydro­gen were pro­duced glob­al­ly, accord­ing to [*Glob­al Hydro­gen Review 2023*](https://www.iea.org/reports/global-hydrogen-review-2023/). 99.3% was fos­sil-based hydro­gen (black, brown, or gray). Only 0.6% was fos­sil-based hydro­gen with car­bon cap­ture (blue). And pity 0.1% was elec­tric­i­ty-based or renew­able hydro­gen (pink, yel­low, or green).

Over the next six years, the Glob­al Hydro­gen Review 2023 pre­dicts a sharp increase in demand. The demand is expect­ed to increase by more than 50%, reach­ing 150 tons of hydro­gen by 2030.

Ana­lysts and experts gen­er­al­ly believe that vir­tu­al­ly all of this increase will con­sist of hydro­gen pro­duced by water elec­trol­y­sis. Data from the [*Hydro­gen Pro­duc­tion and Infra­struc­ture Projects Data­base*](https://www.iea.org/data-and-statistics/data-product/hydrogen-production-and-infrastructure-projects-database) shows that in Octo­ber 2023, there were over 1,500 planned or ongo­ing con­struc­tions of elec­trolyz­er plants to be com­plet­ed by 2030. Togeth­er, they will gen­er­ate 92 Mt of hydro­gen, of which 66 Mt are green, 4 Mt are yel­low, and the rest are unspecified.