Green Hydrogen Production Paths: A Glimpse of a Zero Emission and Clean Future

What is Green Hydrogen and how is it affecting our march towards a low carbon future? In this article, we will explore hydrogen as a fuel of the future. Let’s start with Hydrogen as an element. Hydrogen is the simplest element on earth. It consists of only one proton and one electron. Hydrogen can be stored and delivered usable energy, but it doesn’t typically exist by itself in nature and must be produced from compounds that contain it. 

Hydrogen is versatile in both energy capacity and power capacity. The energy density of hydrogen per unit mass is so high that one kilograms of hydrogen carries as much energy as three kilograms of gasoline, making hydrogen a convenient energy carrier and energy storage medium. At times of peak demand, when electricity is usually at its highest prices, the stored hydrogen can be reconverted into electricity.

Hydrogen can be used in fuel cells to generate power using a chemical reaction rather than combustion, producing only water and heat as byproducts. It can be used in cars, in houses, for portable power, and in many more applications.

Different Types of Hydrogen, based on Production Method

The crux of emissions from this method, however, lies in the method in which the electricity is produced.Hydrogen is often associated with a color, whether it’s grey, blue, or green. These colors represent key distinctions in the emissions profiles for the various ways hydrogen is produced:

Grey Hydrogen:

  • Grey hydrogen is typically produced from natural gas in a process called methane reformation while brown hydrogen is produced from coal gasification.
  • These are the most dominant and cheap method of hydrogen production, but account for the “highest CO2 emissions”.

Blue Hydrogen:

  • Blue hydrogen is usually produced using fossil fuels but is usually dealt with by using CCS(Carbon Capture Storage).
  • Blue hydrogen can be a stepping stone of sorts to move away form ‘Grey and Brown Hydrogen and move towards a green hydrogen economy.

Green Hydrogen:

  • Green hydrogen is produced using renewable sources such as solar and wind via electrolysis of water.
  • The process is clean but currently expensive. But the costs of renewable energy sources have plummeted in recent years, Solar PV in particular
  • The costs associated with this are a function of electrolyser costs and cost of energy source.

As of today, only 4% of Hydrogen produced is through electrolysis (Green Hydrogen).

Fig 1: Sources of Hydrogen Production
Fig 1: Sources of Hydrogen Production

Green Hydrogen & Production Methods

There are different Green Hydrogen Production methods as elaborated in the figure below.

Fig 2: Pathways for Green Hydrogen Production
Fig 2: Pathways for Green Hydrogen Production

Direct Water Splitting:

  • In this process, the solar radiation is directly used to split water into hydrogen and oxygen molecules. This process is also known as Photoelectrochemical (PEC) water splitting.
  • The PEC water splitting process uses semiconductor materials to convert solar energy directly to chemical energy in the form of hydrogen.
  • The semiconductor materials used in the PEC process are similar to those used in photovoltaic solar electricity generation, but for PEC applications the semiconductor is immersed in a water-based electrolyte, where sunlight energizes the water-splitting process.
Fig 3: PEC Water Splitting using Solar Thermal Energy
Fig 3: PEC Water Splitting using Solar Thermal Energy

Biomass Gasification:

  • Biomass gasification is a technology pathway that uses a controlled process involving heat, steam, and oxygen to convert biomass to hydrogen and other products, without combustion. 
  • Because growing biomass removes carbon dioxide from the atmosphere, the net carbon emissions of this method can be low, especially if coupled with carbon capture, utilization, and storage in the long term.
  • Gasification is a process that converts organic or fossil-based carbonaceous materials at high temperatures (>700°C), without combustion, with a controlled amount of oxygen and/or steam into carbon monoxide, hydrogen, and carbon dioxide. 
  • The carbon monoxide then reacts with water to form carbon dioxide and more hydrogen via a water-gas shift reaction. Adsorbers or special membranes can separate the hydrogen from this gas stream.
Fig 4: Hydrogen Production from Biomass
Fig 4: Hydrogen Production from Biomass


  • Technology for grid-scale hydrogen energy storage is a regenerative fuel cell. A regenerative hydrogen fuel cell system consists of a water electrolyzer, compressed hydrogen gas storage tanks, and a fuel cell.
  • The system uses electricity to generate hydrogen from water in an electrolyzer. The hydrogen is stored in high-pressure tanks, and dispatched to the hydrogen fuel cell to generate electricity when desired.
  • Energy in the form of electricity is used in an ‘Electrolyser’ which splits water in hydrogen and oxygen. Hydrogen is under pressure in storage tanks. The oxygen too is stored as it is required in the fuel cell process to electricity again. It is important to note that hydrogen is not an energy source, but is an energy carrier.
  • Regenerative Hydrogen Fuel Cells offer an environmentally friendly method to store excess power from solar panels and wind turbines. The fuel cells convert excess electricity from the solar panels and wind turbines into hydrogen that is stored on-site.
Fig 5: Hydrogen Production using Electrolysis
Fig 5: Hydrogen Production using Electrolysis

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Keyword: Hydrogen, Renewable Energy, Biomass, Hydrogen Production, Solar, Wind, Geothermal, Green Hydrogen

Reference: Pellow, Matthew & Emmott, Christopher & Barnhart, Charles & Benson, S.. (2015). “Hydrogen or batteries for grid storage? A net energy analysis.” Energy Environ. Sci.. 8. 10.1039/C4EE04041D.