Green Hydrogen for Sustainable Environment

Abstract

Green hydrogen, produced through renewable-powered electrolysis or biomass pathways, is emerging as a key enabler of India’s energy independence and net-zero ambitions. Advances in electrolyser technologies, storage systems, and modular plants are accelerating large-scale, low-carbon hydrogen adoption across industry, mobility, and energy sectors.

Introduction
India has announced a target of energy independence by 2047 and a net-zero by 2070. Green Hydrogen is expected to play a substantial role towards achieving these goals. Green Hydrogen, is produced by the process of electrolysis, where water is split into hydrogen and oxygen using electricity generated from renewable sources like solar, wind, or hydropower. This process results in a clean and emission-free fuel that has immense potential to replace fossil fuels and reduce carbon emissions. Another method of producing Green Hydrogen is from biomass, which involves the gasification of biomass to produce hydrogen. Both these production methods are clean and sustainable, making Green Hydrogen an attractive option for the transition to a low-carbon future.

Need for Green Hydrogen

The need for Green Hydrogen is rapidly increasing due to its potential to decarbonize several sectors, including transportation, shipping, fertilisers and steel among others. Green hydrogen can replace traditional fossil fuels in transportation, which contributes significantly to greenhouse gas emissions. It can also be used in industry for the production of ammonia, methanol, and steel, which are currently heavily reliant on fossil fuels. Additionally, Green Hydrogen can be used as a backup energy source for renewable energy plants, providing a constant and reliable source of energy.

Green hydrogen has numerous applications and can be used in fuel cells to power vehicles and provide electricity. It can also be used in heating systems and in the production of chemicals and fertilizers. Hydrogen fuel cells have a high energy density and are more efficient than traditional combustion engines, making them an attractive option for powering vehicles. Furthermore, Green Hydrogen can be used in microgrids, providing electricity to remote areas and enabling energy independence.

National Green Hydrogen Mission

India has launched the National Green Hydrogen Mission with an outlay of Rs. 19,744 crores¹ with a target of 5MMT production capacity of Green Hydrogen per annum.

What is Green Hydrogen

Hydrogen can be termed as green, only if the non-biogenic greenhouse gas emissions arising from water treatment, electrolysis, gas purification and drying and compression of hydrogen shall not be greater than 2 kilogram of carbon dioxide equivalent per kilogram of Hydrogen (kg CO₂ eq./kg Hydrogen), taken as an average over last 12-month period¹.

Classification of Hydrogen

Hydrogen is classified into different “colors” based on how it is produced and the environmental impact of its production. Green hydrogen is the cleanest form, generated by using renewable energy sources such as solar, wind, or hydro power to split water through electrolysis. Since no fossil fuels are involved, it has zero carbon emissions. Blue hydrogen is produced from natural gas through processes like steam methane reforming (SMR) or auto thermal reforming (ATR), but the carbon dioxide generated is captured and stored using carbon capture and storage (CCS). This makes it lower-carbon but still dependent on fossil fuels. Grey hydrogen is also produced from natural gas using (Steam Methane reforming) SMR, but without capturing the CO₂ emissions, making it carbon-intensive. Brown hydrogen (or black hydrogen) comes from gasification of coal or lignite and has the highest carbon footprint.

Another emerging category is pink hydrogen, produced using electrolysis powered by nuclear energy. Turquoise hydrogen is created through methane pyrolysis, producing solid carbon instead of CO₂, which can be easier to store or use. Yellow hydrogen is made using grid electricity, which can be a mix of renewable and non-renewable energy sources. White/Gold hydrogen is the hydrogen found in nature.

Technologies Involved

Currently, several advanced water electrolysis technologies are available in the market for green hydrogen production these include Proton Exchange Membrane (PEM) Electrolysers, Alkaline Electrolysers, Anion Exchange Membrane (AEM) Electrolysers, and Solid Oxide Electrolysers.

Process Technology – Green Hydrogen: Electrolysis³ is a promising option for carbon-free hydrogen production from renewable and nuclear resources. Electrolysis is the process of using electricity to split water into hydrogen and oxygen. This reaction takes place in a unit called an electrolyser. Electrolyser can range in size from small, appliance-size equipment that is well-suited for small-scale distributed hydrogen production to large-scale, central production facilities that could be tied directly to renewable or other non-greenhouse-gas-emitting forms of electricity production.

 Figure: 1: Hydrogen Cell

Like fuel cells, electrolyser consist of an anode and a cathode separated by an electrolyte. Different electrolyser function in different ways, mainly due to the different type of electrolyte material involved and the ionic species it conducts.

Currently, several technologies are available in the market for producing green hydrogen. The main technologies include:

1. PEM Electrolyser Technology (Proton Exchange Membrane type)
2. Alkaline Electrolysers – Both pressurized and non-pressurized
3. Solid Oxide Electrolysers
4. AEM Electrolysers (Anion Exchange Membrane type)

Proton Exchange Membrane (PEM) Electrolyser: In a proton exchange membrane (PEM) electrolyser, the electrolyte is a solid specialty plastic material. Water reacts at the anode to form oxygen and positively charged hydrogen ions (protons). The electrons flow through an external circuit and the hydrogen ions selectively move across the PEM to the cathode. At the cathode, hydrogen ions combine with electrons from the external circuit to form hydrogen gas. Anode Reaction: 2H₂O → O₂ + 4H⁺ + 4e^– Cathode Reaction: 4H⁺ + 4e^– → 2H₂

 Alkaline Electrolyser: Alkaline electrolyser operate via transport of hydroxide ions (OH^–) through the electrolyte from the cathode to the anode with hydrogen being generated on the cathode side. Electrolyser using a liquid alkaline solution of sodium or potassium hydroxide as the electrolyte have been commercially available for many years. Newer approaches using solid alkaline exchange membranes (AEM) as the electrolyte are showing promise on the lab scale.

Solid Oxide Electrolyser: Solid oxide electrolyser, which use a solid ceramic material as the electrolyte that selectively conducts negatively charged oxygen ions (O^2-) at elevated temperatures, generate hydrogen in a slightly different way. Steam at the cathode combines with electrons from the external circuit to form hydrogen gas and negatively charged oxygen ions. The oxygen ions pass through the solid ceramic membrane and react at the anode to form oxygen gas and generate electrons for the external circuit.

Solid oxide electrolyser must operate at temperatures high enough for the solid oxide membranes to function properly (about 700°–800°C, compared to PEM electrolyser, which operate at 70°–90°C, and commercial alkaline electrolyser, which typically operate at less than 100°C). Advanced lab-scale solid oxide electrolyser based on proton-conducting ceramic electrolytes are showing promise for lowering the operating temperature to 500°–600°C. The solid oxide electrolyzers can effectively use heat available at these elevated temperatures (from various sources, including nuclear energy) to decrease the amount of electrical energy needed to produce hydrogen from water.

 Given the rapid advancements in green hydrogen technologies and the increasing number of plants under construction worldwide, it is important to incorporate the latest trends and learnings from global installations to ensure a robust and future-ready setup.

Green Hydrogen Plants

Green hydrogen plants are often supplied in modular, skid-mounted formats, making installation and commissioning faster and more efficient. The major utility systems that will be required for a green hydrogen plant include:

• A cooling tower
• A DM water treatment plant
• An instrument air compressor package
• A hydrogen compression and cascade storage system

A typical block diagram of a green hydrogen plant is shown in Figure 2 below.

Figure 2: Block Diagram

Compared to the long service life of civil structures, foundations, and other mechanical equipment in a typical process plant, an electrolytic cell generally has a lifespan of only about 10 years. As a result, the electrolyser will require replacement after this period, leading to an additional capital expenditure. Unlike conventional plants, a significant portion of the capital cost in a green hydrogen facility is associated with the electrolyser module and its periodic replacement.

In terms of operating cost, the major contributors are power and water consumption. Producing 1 ton of green hydrogen requires approximately 2 to 2.5 MW of power and 12 to 15 m³ of water. Owing to the modular, robust, and user-friendly design of modern electrolysers, the manpower required to operate a green hydrogen plant is lower compared to that of a traditional process plant.

Hydrogen Storage: Hydrogen can be stored as a gas at 350 to 700 kg/cm2 .

Hydrogen can be stored as a liquid at a temperature of  -253 0C .

Hydrogen gas storage cascades are high-pressure systems comprising multiple interconnected gas cylinders, designed to store and deliver hydrogen efficiently. For industrial applications, such as green ammonia production or metallurgical processes, these cascades typically operate at pressure about 500 barg. The storage cylinders² are generally constructed from steel (Type-I) or partially composite-wrapped (Type-II) materials and are arranged in low, medium, and high-pressure banks to facilitate efficient cascade filling and reduce compressor load. These systems usually operate at ambient temperatures and can be either stationary or skid-mounted for flexibility and ease of transport.

In contrast, hydrogen cascades for automotive fuel applications are tailored to meet the requirements of Hydrogen Refuelling Stations (HRS) for vehicles such as cars, buses, and trucks. These systems operate at significantly higher pressures. For instance, to refuel heavy-duty vehicles like buses and trucks at 350 bar, the cascade storage must be rated at around 500 bar. Similarly, for light-duty vehicles such as cars, which require 700 bar filling pressure, the cascade storage would need to be rated up to 900 bar—such high-pressure storage systems are still under development and not widely available in the market.

These automotive systems use advanced composite cylinders (Type-III or Type-IV) capable of withstanding ultra-high pressures and are equipped with pre-cooling systems (typically down to -40°C) to mitigate heat generated during fast refuelling. The cascades are also designed for sequential discharge from high to low-pressure banks, ensuring efficient delivery and reduced compressor cycling. Compliance with international safety and refuelling standards such as ISO 19880 and NFPA 2 is essential in these applications.

“$1, 1KG, 1 DECADE ($1,1,1): Electrolysis is a leading hydrogen production pathway to achieve the Hydrogen Energy Earth shot goal of reducing the cost of clean hydrogen by 80% to $1 per 1 kilogram in 1 decade (“1 1 1”). Hydrogen produced via electrolysis can result in zero greenhouse gas emissions, depending on the source of the electricity used. The source of the required electricity—including its cost and efficiency, as well as emissions resulting from electricity generation—must be considered when evaluating the benefits and economic viability of hydrogen production via electrolysis.

 In many regions of the country, today’s power grid is not ideal for providing the electricity required for electrolysis because of the greenhouse gases released and the amount of fuel required due to the low efficiency of the electricity generation process. Hydrogen production via electrolysis is being pursued for renewable (wind, solar, hydro, geothermal) and nuclear energy options. These hydrogen production pathways result in virtually zero greenhouse gas and criteria pollutant emissions; however, the production cost needs to be decreased significantly to be competitive with more mature carbon-based pathways such as natural gas reforming.

Benefits / Advantages: Green Hydrogen will have the following advantages:

1. Green hydrogen production generates minimal to no greenhouse gas emissions, helping combat climate change.
2. It uses renewable energy sources like wind, solar, or hydroelectric power, promoting a sustainable energy system.
3. It can be used in various sectors, including transportation, industry, and heating, enhancing energy flexibility.
4. Promotes energy independence by decreasing dependence on imported fossil fuels, enhancing energy security.
5. Countries with abundant renewable resources can produce and export green hydrogen, creating new trade opportunities.

References:

• National Green Hydrogen Mission, 2023
• EIGA Doc 15/21 Gaseous hydrogen Installations
• ISO 22734
• US Department of Energy Website & MNRE Website
• Wang, T., Cao, X., & Jiao, L. (2022). PEM water electrolysis for hydrogen production: fundamentals, advances, and prospects. Carbon Neutrality
• Bernat, R., Milewski, J., Dybinski, O., Martsinchyk, A., & Shuhayeu, P. (2024). Review of AEM Electrolysis Research from the Perspective of Developing a Reliable Model. Energies
• Afroze, S., Sofri, A. N. S. B., Reza, M. S., et al. (2023). Solar-Powered Water Electrolysis Using Hybrid Solid Oxide Electrolyzer Cell (SOEC) for Green Hydrogen
• Green Hydrogen Production by Water Electrolysis: Very technical; covers PEM, AEM, SOEC, electrochemistry, materials, mechanics. Editors: Junbo Hou & Min Yang.

Authors:

Aswathy Mohan A

Aswathy Mohan A, is currently working as Deputy Manager (Process), FACT Engineering And Design Organisation (FEDO), FACT Udyogamandal is B.Tech in Chemical Engineering from Government Engineering College , Thrissur. Joined FACT in 2017 and has eight years of experience in the areas of Petrochemical & Fertiliser Process Optimization, Process Design, Energy Audit, Consultancy, HAZOP Studies, Process Simulations.

Sri Tittu Alagu A

Sri Tittu Alagu A, is currently working as AGM(Process), FACT Engineering And Design Organisation (FEDO), FACT Udyogamandal, is B.Tech in Chemical Engineering from Bharathidasan University   Trichy, Tamilnadu. Joined FACT in 2011 he has fourteen years of experience in the areas of Petrochemical & Fertiliser Process Optimization, Process Design, Process Simulations, Energy Audit, Consultancy, HAZOP Studies, Process Simulations.

Sri Koya Venkata Reddy

Sri Koya Venkata Reddy, currently working as Deputy General Manager (Process), FACT Engineering And Design Organisation (FEDO), FACT Udyogamandal is B.Tech in Chemical Engineering from College of Engineering, Andhra University, Visakhapatnam. He has done his Master of Business Administration (MBA) in Finance from IGNOU, New Delhi and M.Tech in Project Management from Cochin University of Science and Technology (CUSAT), Kochi.

Joined FACT in 1991 and has three decades of experience in the areas of Petrochemical & Fertiliser Process plant operations, Trouble shooting and Optimization, Process Design, Revamping of chemical plants, Process Simulations, Energy Audit, Consultancy, HAZOP Studies etc. He has worked in Kingdom of Saudi Arabia and Oman for two years in Oil & Gas sector working for clients like Saudi Aramco and PDO. He can be contacted at koyareddy@yahoo.com and +91-9446435451.