The Hydrogen Rainbow

  • Adam Kay
  • As more companies launch hydrogen pilots, the conversation around hydrogen’s role in the energy mix is only accelerating.  National Grid Chief Strategy and External Affairs Officer, Ben Wilson, in a recent interview with S&P Global Commodity Insights, stated that analysis shows that carbon neutral green hydrogen will be cost-competitive with natural gas by 2030. Currently, natural gas is half to a third the cost of other energy sources including electricity and is projected by the EIA to remain the most affordable source of energy through at least 2050. This fuel emits only water when combusted. There are currently many different approaches to producing it, each with varying degrees of carbon intensity – some of which even have net-negative emissions profiles. The discussion of hydrogen is only going to ramp up – however, the terms used to describe different types of hydrogen can be perplexing. If you want to learn more about the different types of hydrogen, this is the post for you.

    At the molecular level, all hydrogen is the same. The end uses are interchangeable across all types, as are the properties of the hydrogen itself. A color-coding system is used to describe how hydrogen is produced. Let’s dive in!

    Green hydrogen is currently the most discussed type of hydrogen. This type of hydrogen is produced via a process called electrolysis, in which water molecules are split into oxygen and hydrogen in a process that must be powered by renewable energy. Green hydrogen is carbon neutral, and eligible for production tax credits passed as part of the Inflation Reduction Act. Green hydrogen produced specifically through solar energy is also sometimes referred to as yellow hydrogen.

    Grey hydrogen is produced via a process called steam reformation using natural gas as the basic feedstock. The natural gas is heated in the presence of a catalytic material, splitting it into hydrogen and CO2.

    Blue hydrogen is produced with the same method as grey hydrogen using natural gas as a feedstock. The difference is that the CO2 is captured in gaseous form and stored, making it a low emissions type of hydrogen, and is eligible for some types of IRA tax credits.

    Turquoise hydrogen is produced from natural gas like blue hydrogen. However, rather than steam reformation, it makes use of a process called pyrolysis, in which the carbon is cooked out in solid form as synthetic graphite which can also be sold for various industrial applications. Turquoise hydrogen is carbon-neutral and eligible for all IRA tax credits. The cost of production can be so low that, with tax credits included, production costs can be negative in some parts of the country, even before the hydrogen and synthetic graphite are sold.

    Gold hydrogen has a particularly unique production method. This type of hydrogen is extracted from depleted oil wells. These wells contain residual oil hydrocarbons that cannot be profitably extracted in their current form. To produce gold hydrogen, proprietary mixes of nutrients and bacteria are pumped into the depleted wells. The bacteria then break the oil residue down into hydrogen and CO2. This process can bring new life to wells with existing infrastructure. However, ensuring that the CO2 is captured from the wells is a priority in order to ensure this type of hydrogen is carbon neutral.

    Pink hydrogen, sometimes also called purple or red hydrogen, is produced through electrolysis like green hydrogen. The difference is the energy source – pink hydrogen makes use of nuclear energy, potentially including small modular reactors (SMRs) to store excess energy as hydrogen, rather than renewable energy. Because the energy used is nuclear, this is carbon neutral and potentially eligible for inflation reduction tax credits.

    Black or brown hydrogen is produced by gasifying coal. Black hydrogen refers to the use of bituminous (black) coal, while brown hydrogen is produced from a lignite (brown) coal feedstock. Lignite coal is higher in water content and emissions than bituminous coal, although both types have relatively high carbon emissions.

    White hydrogen is naturally occurring, typically within iron-rich geological formations by oxidation-reduction between the iron and water. Combustion of it does not create carbon emissions. However, white hydrogen rarely occurs in nature and is not a significant source of hydrogen fuel.

    Orange hydrogen combines hydrogen generation with CO2 sequestration by creating a chemical reaction in iron-rich geological formations. Water, including saltwater, is charged with CO2 and injected into the target formation where it reacts with the iron ore, leaving the CO2 behind and enriching the material with hydrogen that can then be extracted. This is, in effect, artificially creating the conditions for white hydrogen development, all while sequestering CO2, giving it a net-negative emissions profile.

    The pace of change for hydrogen is swift, as pioneering companies come up with new and exciting methods of producing hydrogen affordably and cleanly. Stay tuned for additional innovations in hydrogen production coming soon!