What types of hydrogen energy are there? A quick guide to hydrogen

Here at The Green List we’ve been hearing a lot more about hydrogen these days. Green, blue, grey… it can be confusing to understand what these different terms actually mean.

Fanatics claim hydrogen is essentially an unlimited and carbon-neutral resource, while critics say it’s neither efficient nor green enough – and too expensive.

The important thing to remember is that not all “colours” of hydrogen are equal – different forms of hydrogen extraction produce different amounts of emissions.

Here’s a quick and basic guide, which we believe are in order of most harmful to least harmful. Keep this on hand the next time someone brings up hydrogen at a dinner party:

  • “Natural gas” (also called fossil gas, fossil fuels, or just gas) is a naturally occurring hydrocarbon gas mixture generally consisting of methane, ethane, and other elements found deep underground. Natural gas can contain hydrogen which would need to be extracted to use. 
  • “Brown hydrogen” is extracted from coal, and emissions are released into the air
  • “Grey hydrogen” is extracted from natural gas, and emissions are released to the air
  • “Blue hydrogen” is extracted from natural gas, and emissions are captured using carbon capture and storage.
  • “Green hydrogen” is extracted through electrolysis splitting the molecules of water into two atoms of hydrogen (H) and one atom of oxygen (O). Electrolysis is achieved by using clean energy (wind or solar). A report from the Australian National University last year estimated that Australia could produce green hydrogen at about $3.18-3.80 a kilogram and at $2 a kg by the end of the decade, making it cost-competitive with fossil fuels. However, it can be expensive to produce, difficult to store, and can use a lot of water
Different forms of hydrogen extraction produce different amounts of emissions.
  • “Geologic hydrogen” is the word we use to refer to hydrogen deposits found deep within the earth. According to Dr Andrew Feitz from Geosciences Australia, rocks like granite contain minerals that undergo radioactive decay. As they undergo radioactive decay, they push out alpha, beta, and gamma rays which interact with water to create hydrogen. This hydrogen gas, which has extremely small molecules, flows up through cracks in the rock until it becomes trapped underneath impermeable rocks, such as rock salts or dolerite.
  • Hydrogen can be produced at depths less than tens of kilometres underground. There are other ways hydrogen can be produced underground, but the radioactive decay pathway is one of the main ones.
  • Back in 2015, geologic hydrogen company Hydroma accidentally discovered a deposit of H2 while drilling for water in Bourakebougou, in Mali. After analysing the well, Bougou-1, the company discovered that the gas had a concentration of 98 per cent pure H2 – making it the purest naturally occurring hydrogen ever discovered. After analysing 12 more wells, they estimated that the size of the hydrogen field was around eight kilometres in diameter. 
  • The accidental discovery has enabled Hydroma to provide enough electricity to power a nearby village “without CO2 emissions”. It has the potential, it’s believed, to last for thousands of years, essentially decarbonising the entire community. 
  • This “geologic” hydrogen has been found in very pure deposits as high as 98 per cent, as in the Mali example, meaning that virtually no GHG emissions are produced. But the “geologic” hydrogen could also be found at low levels of concentration with other gases that could escape or need to undergo capture and storage. What companies are searching for is those high purity concentrations of hydrogen trapped under layers if salt deposits subsurface. 
  • This chemical reaction is natural and ongoing, meaning that it will keep rejuvenating, potentially forever. However, it’s unknown if current deposits exist in commercial quantities and if the rate of replenishment is fast enough to match the rate of extraction. But Australia’s extensive salt deposits are encouraging, exploration companies say.