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Hydrogen sources

Hydrogen and decarbonization

Hydrogen is the most abundant element in the universe. Its combustion reaction with oxygen produces high temperatures and relases heat, whilst only emitting water vapor. For decarbonization, it is an ideal fuel because:

  • it is a clean alternative to methane 
  • a useful energy vector that can be used to store, convert and release energy
  • it has the potential to be used as a fuel for power and transportation
  • it can be produced using several technologies
  • it does not generate any greenhouse gases (GHGs) when used 
  • it offers the potential for zero carbon footprint when produced using renewable energy. 

These advantages make hydrogen an important solution in the global clean energy transition process for achieving decarbonization.

Usages of Hydrogen

Industry: oil refining, ammonia production, methanol production and steel production are sectors in which important amounts of hydrogen supplied from fossil fuels is used, this represents a significant potential for emissions reductions from clean hydrogen.


Transportation: Powering fuel cell vehicles but their competitiveness depends on fuel cell costs and refueling stations while for trucks the priority is to reduce the delivered price of hydrogen. Shipping and aviation have limited low-carbon fuel options available and represent an opportunity for hydrogen-based fuels.


Buildings: hydrogen could be mixed into existing natural gas networks, with the highest potential in multifamily and commercial buildings, particularly in dense cities while longer-term prospects could include the direct use of hydrogen in hydrogen boilers or fuel cells.

Power generation: hydrogen is one of the leading options for storing renewable energy, and hydrogen and ammonia can be used in gas turbines to increase power system flexibility.

Types of hydrogen

Even though hydrogen is a colorless gas, its different types are named using color designations, in order to  refer to and differentiate bewteen the technologies used to produce each type. It must be stressed that these different colors only refer to the production means, not the hydrogen produced.

This video illustrates the different production routes to make hydrogen.

The following table summarizes the different hydrogen processes routes: green, blue, grey, black and brown and grey hydrogen.
The following figure summarizes the three most important routes (source:
The basic colours of hydrogen (source: taken from
Grey hydrogen Grey hydrogen is produced inexpensively using coal, natural gas or methane without capturing the GHG generated in the process; thus, it has a significant carbon footprint. The majority of the grey hydrogen manufactured today is made by a process called steam methane reforming (SMR), that requires combining steam with fossil fuels, and heating them to around 800°C. For each kilogram of hydrogen produced, this process generates between 9 kilograms and 12 kilograms of carbon dioxide. According to the International Energy Agency, 96% of hydrogen produced worldwide is grey hydrogen. When most of the carbon emissions generated are captured, Grey hydrogen becomes “Blue hydrogen”. Blue hydrogen Blue hydrogen is produced using the same reforming process that is used for producing grey hydrogen, exept that the CO₂ that would ordinarily be released is captured and stored underground via industrial carbon capture and storage (CSS), but around 10-20% of the generated CO₂ cannot be captured. Hydrogen production from fossil fuels with carbon capture, utilization and storage (CCUS). CCUS means that the carbon emissions are captured from the combustion processes and either re-used or stored underground. CCUS is important in the production of low-carbon hydrogen from fossil fuels for two reasons:
  • It enables a reduction in emissions from already existing hydrogen plants in both chemical and refining fields, that account for 2.5% of global emissions.
  • It is a low-cost option to scale up production for new hydrogen demand in countries where the conditions are favorable.
The following figure, gives an idea on hydrogen production with CCUS projects in-use and in development (IEA).
A recent article released by Cornell and Stanford Universities ( claims that blue hydrogen may actually produce more greenhouse gases as shown in the figure below. This work states that carbon capture will not effectively stop fugitive methane and upstream emissions of carbon dioxide from escaping and argues that blue hydrogen’s carbon footprint could be 20% larger than using either natural gas or coal directly for heat, or about 60% greater than using diesel oil for heat. Comparison of carbon dioxide equivalent emissions from gray hydrogen, blue hydrogen with carbon dioxide capture from the SMR process but not from the exhaust flue gases created from burning natural gas to run the SMR equipment, blue hydrogen with carbon dioxide capture from both the SMR process and from the exhaust flue gases, natural gas burned for heat generation, diesel oil burned for heat, and coal burned for heat. Carbon dioxide emissions, including emissions from developing, processing, and transporting the fuels, are shown in orange. Carbon dioxide equivalent emissions of fugitive, unburned methane are shown in red. The methane leakage rate is 3.5%. Source:

Green hydrogen 

Green hydrogen is produced from carbon-free sources. The associated carbon emissions during Green H2 production come from the manufaturing equipment (for example the PV panels or the wind turbines) and the (potential) emissions due to transportation, storage etc.

Several European countries have included green hydrogen in their energy transition plans and published hydrogen strategies with ambitious targets. For instance, Netherlands targets 3-4 GW electrolysers, Germany targets 3-5 GW electrolysers (source: and global European electrolyzer project targets scaling up to 6 GW of capacity by 2024, which would produce up to 1 million Mt/year of renewable hydrogen (source: as shown in the following figure.


Green hydrogen is produced through a process called electrolysis, which separates water into hydrogen and oxygen, using electricity generated from renewable sources, as shown in the below figure.
Green hydrogen production process (source:
Electricity production using Hydrogen is achieved by carrying out the inverse reaction used to obtain green hydrogen as shown below.
Electricity production using Hydrogen (source:

The current green hydrogen production accounts for just 0,1% of the global hydrogen production, but is expected to increase highly due to its importance in maintaining of a sustainable development.

The following figure, shows the expected world-wide hydrogen demand from 2019 to 2070 by sector.

Forecast hydrogen demand worldwide in a sustainable development scenario from 2019 to 2070, by sector. (Source:

Hydrogen cost

Today the Levelized Costs of Hydrogen (LCOH) for green hydrogen are still much higher than those for grey hydrogen, but it is expected that green hydrogen will become competitive in 2030 due to the declining costs of both renewable electricity (accounting for ~70% of the cost of producing hydrogen) and electrolysis technology.

The following figure (source: gives levelized hydrogen costs by 2050 from different institutions.

By lining up the analyses of various research and consultancy firms, we arrive at a price trend as shown in the graph below.

Hydrogen price trend (source:

In its 2021 Report on Hydrogen, the IEA has envisaged a Net Zero Emissions Scenario in Year 2050. The following charts, show respectively the source of hydrogen production in the NZE 2020-2050 that will be mainly based on electricity in order to maintain sustainable and clean development and the cumulative emissions reduction in the NZE 2021-2050 in which hydrogen has a share of 6%.

Acknowledgment : This Section was prepared from Internet Sources by Nassima MOUMNI (Ingénieur Polytechnique Alger).