The Blue/Green Discussion
Everyone agrees that hydrogen plays an important role in the energy transition. The reasons are straightforward: hydrogen is nowadays employed on a large scale in a variety of industries such as the steel industry. In some industrial processes hydrogen is simply indispensable. Yet currently some 90% of this hydrogen is produced from fossil fuels (usually natural gas) with the release of green house gases as a result. Hydrogen produced in this way is known as grey hydrogen.
Producing hydrogen in a more sustainable way is thus a way to realize climate goals on global level. Yet it is not immediately clear how to approach the task of giving up hydrogen produced from fossil fuels with release of CO2. Two courses of action have spurred some discussion lately in expert and policy circles.
Blue hydrogen is the hydrogen that is produced in much the same way grey hydrogen is produced but the CO2 (not all) is captured and stored or reused so that it is not released into the atmosphere.
Green hydrogen is the hydrogen that is produced through a process known as 'water electrolysis'. Basically, an electric current is run through water until oxygen and hydrogen are separated. With the exception of heat and some small remnants, this process releases no CO2 into the atmosphere.
In what follows, you will find an overview of the arguments in support of these options, concluding with some loose ends. These arguments are selected from sources we list at the end. Because we want to focus on the blue vs green discussion, we leave out arguments that are advanced for or against the decarbonization of hydrogen production in general. We thus focus on the socio-technical discussion around the choice between blue and green.
At the end you will find a form that you can fill in in order to let us know if there's something we're missing.
Do you feel you need more information about hydrogen and the blue vs. green discussion, please consult this website first. You will find there a lot of information that is useful in preparation for what follows. But if you're all set, please scroll down and enjoy.
- Production costs
Blue hydrogen is cheap
The price of blue hydrogen is around 1- 2,3€/kg, depending on the source of fossil fuel used
Also, captured CO2 can be reused/resold
However, fossil fuel prices are expected to rise in the future.
On the other hand, CCS costs for both technology and infrastructure of carbon capture might need to be incurred anyway in order to decarbonize industry.
Green hydrogen will be increasingly cheaper
The price of green hydrogen is around 2-6€/kg, depending on the electricity price.
Also, the oxygen released can be reused/resold
However, the price of electricity is expected to drop and process efficiency is expected to rise (for instance, through the development of new materials)
On the other hand, by that time, imported green hydrogen from the 'solar belt' might be cheaper than the local one
Sources: , , , 
2. Environmental impact
Blue hydrogen is better than grey hydrogen
By capturing CO2, either pre- or post-combustion, the steam reforming processes for producting hydrogen can be more environmental friendly (from gray to blue)
However, blue hydrogen is still produced by depleting a non-renewable resource (natural gas)
On the other hand, the CO2 reduction from blue hydrogen might be achieved faster, paving the way for green hydrogen
Green hydrogen is emission-free
By using electricity from renewables, hydrogen can be completely environmental friendly
However, by using electricity from renewables, hydrogen production is competing with other direct uses of green electricity
Also: surplus of green energy is not predicted to occur until much later
On the other hand, some industrial processes such as high temperature heating cannot be fully electrified
Sources: , , 
Producing hydrogen from fossil fuels is relatively efficient in terms of energy input and output
Also, the technology is "already here" (high TRL)
However, not all grey hydrogen plants can be simply switched to blue hydrogen, the storage of CO2 also requires energy and not all CO2 is captured
Green hydrogen production shows potential when upscaled (large volumes) and optimized
However, in the meanwhile the production process remains relatively inefficient, which means that green hydrogen requires a lot of green energy
On the other hand, the technology can work with surplus energy and it is 100% CO2-free
Sources: , , 
4. Society & Policy
Blue hydrogen is a good short-term solution for the energy transition
With blue hydrogen, short-term CO2 reductions can be achieved
Also, blue hydrogen receives governmental support for CO2 reduction
However, CCS is not always seen as a viable solution and in the past the technology has been associated with societal & political unrest
On the other hand, caverns for storing CO2 already exist
However, further investment creates lock-in and does not alleviate dependence of fossil fuels
Green hydrogen is good long-term solution for the energy transition
With green hydrogen, long-term CO2 reduction can be achieved
However, the process is slower and it competes with other electron-using, emission-free transitions
On the other hand, green hydrogen enjoys public and political support
However, similar support has occured in the past and it is now labelled as 'hydrogen hypes'
On the other hand, green hydrogen will probably be subsidized as an environmental friendly measure
Sources: , 
5. Illustrative quotes
"Blue hydrogen is a no-brainer for Europe"
Olav Aamlid Syversen is Deputy Head of Equinor EU Affairs Office and Chair of IOGP’s EU Committee.
"Governments are being sold a pup* on blue hydrogen"
Graham Cooley is Chief executive of leading electrolyser manufacturer ITM Power
*British expression meaning, roughly, that one is being sold something that turns out later to be worse than expected
6. The blue-in-green compromise
A solution could be to phase the two: start with blue (for extra speed and certainty) and continue later with green (for sustainability)
However, not all stakeholders are ready to accept the environmental shortages of blue hydrogen
On the other hand, green hydrogen 'later' might lead individuals to wait until the 'good' solution arrive and desist from environmental investments
Also, the details of the blue-in-green transition have not been worked out and it remains just an idea
7. Finally, the question of import
It is yet unclear how the Northen European markets will be affected by a potential boom of low-carbon (blue or green) hydrogen in regions with cheap renewables such as countries with plenty of solar energy (see: 'Sun Belt')
However, import of hydrogen will not affect local markets soon and there are many uncertainties regarding the supply chain
Participate in the discussion
 World Economic Forum (2020) Hydrogen isn't the fuel of the future; it's already here https://www.weforum.org/agenda/2019/06/the-clean-energy-of-the-future-is-already-here/
 CE Delft (2018) Waterstofroutes Nederland: blauw, groen en import https://www.ce.nl/publicaties/2127/waterstofroutes-nederland-blauw-groen-en-import
 Fuel Cells and Hydrogen (2019) Hydrogen Roadmap Europe https://www.hydrogeneurope.eu/news/hydrogen-roadmap-europe-has-been-published
 Hydrogen council - How hydrogen empowers the energy transition https://hydrogencouncil.com/wp-content/uploads/2017/06/Hydrogen-Council-Vision-Document.pdf
 IEA (2019( - The future of Hydrogen https://www.iea.org/reports/the-future-of-hydrogen
 Deltalinqs (2019) - H-Vision: Blue hydrogen as accelerator and pioneer for energy transition in the industry https://www.deltalinqs.nl/h-vision-en
 Hydrogen Council (2020) Path to hydrogen competitiveness: A cost perspective https://hydrogencouncil.com/en/path-to-hydrogen-competitiveness-a-cost-perspective/
 TU Delft - Waterstof: De sleutel voor de energietransitie https://www.tvvl.nl/boeken/waterstof-de-sleutel-voor-de-energietransitie
 Zeeuws Energieakkoord (2019) - De rol van waterstof in de energietransitie https://www.zeeuwsenergieakkoord.nl/ '
 Zohuri, B. (2019). Hydrogen Energy: Challenges and Solutions for a Cleaner Energy. Springer: Dordrecht https://www.springer.com/gp/book/9783319934600