Grey, Blue, Green the color shades of Hydrogen.

Hydrogen has stepped with force in the debate for low carbon energies with a promising future on multiple applications, from heavy industries to mobility. We can resume the current H2 situation with the words of Cedric Philibert (IAE expert), “Before becoming the clean energy vector of the future, Hydrogen is today part of the dirty ones.”

Let’s review the spectrum of H2 colors and analyze what it takes to give it a chance within the decarbonation race.

From Grey to Green

Dihydrogen (H2), made of first Mendeleev table element needs to be produced as it does not exist “as is” on Earth (tied to Oxygen in water -H2O- or to Carbon in natural gas -CH4-).

The vast majority of today’s H2 is either producedfrom coal gasification or steam methane reforming (SMR). Both methods are energy intensive and release a significant amount of carbon dioxyde (0,9 Gt in 2020 worldwide, see ref 1). This is the so called “Grey H2” with an overall Carbon emission factor of 11, 1 kgCO2 / kgH2 (ref 2)

Capturing CO2 during production of “Grey H2” turns it into “Blue H2”. A recent study (ref 3) done onthat process concludes to a poor ultimate 9 to 12% Carbon reduction emission considering the overall energy and powerplant life cycle. “Greyed” blue is the true color of blue Hydrogen.

When produced out of water electrolysis and powered from renewable electrical source (solar, wind or hydraulic), H2 gets its green color label.

The below chart is providing a comparison of theH2 production carbon footprint depending on the process & electrical source involved.

Source ADEME (except for Blue H2 where source is ref 3)

In addition to its low carbon content, the excitement around green H2 stands in the possibility to stock the surplus of electricity produced from renewable sources during offer peaks. Smart at first look.. but does this answer volume and cost demand ?

How expensive is green H2 ?

The cost driver for green H2 directly comes from the electricity price, electrolyzer cost and its load factor. A low electricity prices associated to an high electrolyzer usage factor will get the cheapest green H2 as shown in below chart.

Source IRENA(International Renewable ENergy Agency)

To be competitive over production made out from fossil fuels (at current barrel price & carbon tax levels), a 200US$/kW H2 electrolyzer shall run a minimum of 4000 hours per year (equivalent 6 months full time) and be powered by electricity under 15 US$/MWh. While we can expect a decrease of the cost of electricity produced out of Wind power plant, its intermittency will remain incompatible with a high electrolyzer load factor. This applies to other renewable electrical sources by the way.

On a broader scale, none of the low carbon electricity sources have achieved that 15 US$ floor price anywhere in the world in 2020. (see below IEA chart).

Levelized price of 1 MWh of electricity per source and region (IEA source – 2020)

This obvious lack of H2 electrolyzer competitiveness along with a slow deployment rate explains why Grey H2 remains highly prevalent today.

This situation has driven the IEA to publish a report on Oct 4th 2021 calling governments for an accelerated deployment of H2 electrolyzers.



“Currently, global production of low-carbon hydrogen is minimal, its cost is not yet competitive, and its use in promising sectors such as industry and transport remains limited 

“Investments and focused policies are needed to close the price gap between low-carbon hydrogen and emissions-intensive hydrogen produced from fossil fuels


Applications for Green H2

The applications for green H2 are vast as summarized in below

Source IRENA (International Renewable ENergy Agency)

One must not forget that H2 transport from production plants to end user is a significant carbon emissions driver potentially ruining the decarbonation efforts made out of green H2. (Or decreasing its yield if H2 used to transport “itself” to customers)

As such, green H2 shall optimally be produced where it is needed and in priority for nitrogen fertilizers (50% of today’s H2 applications) and for high intensive energy and carbon emission productions such as  iron-ore reduction to steel.

A further post will be focussing on the yield of H2 when used in mobility (aviation and road transportation)


Let’s take the road mobility example. Replacing a fleet of 30 millions vehicles (estimate of all cars, trucks, buses etc in France) powered by fuel with hydrolyzed H2 fuel cell vehicles would require to multiply the French electrical production by a 2,5 factor.

In the USA, the current electrical power capacity would have to be multiplied by 9 to convert the whole vehicle park (350 millions) to H2 fuel cells models.

Nuclear power plant is certainly the most indicated mean to ensure a low carbon content, high electrolyzer load factor and consequent volume of H2 production all along with a minimum landscape foot print.

This is particularly true when considering the predictable massive rise of the electricity demand resulting from all the others sectors to be decarbonized.


Many projects are being launched to use H2 as a master piece of the low carbon transition with some promising perspectives. H2 will obviously not substitute all fossil fuels application but can be part of the solutions. In addition to its current applications & future role within energy intensives industries, one can foresee H2 to be well positioned whenever the energy density of batteries is to weak (high payload transports for ex).

But above all, best is to not put the cart before the horse.

Today’s priority is to scale and ensure competitiveness of H2 produced out of low carbon sources before promoting it usage. 

Otherwise Hydrogen will  remain forever the clean energy vector of the future.


Ref 1: IEA Global Hydrogen Review 2021

Ref2: ADEME Carbon database, H2 emission factor from cradle to gate (excluding transportation to end users)

Ref 3: How green is blue Hydrogen. Robert W.Howarth1 & Mark Z.Jacobson paper (

Ref 4: World electricity prices:


2 thoughts on “Grey, Blue, Green the color shades of Hydrogen.”

  1. While cost of gaz is increasing, LCOE of photovoltaic is decreasing that means good opportunities. The point is before decarbonize mobility, the priority should be decarbonize the industry and replace the existing grey H2

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