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Power-to-Gas (PtG) as a key technology in a green hydrogen roadmap? Green Hydrogen – Hope for the energy transition.

Power-to-Gas (PtG) as a key technology in a green hydrogen roadmap?
Alexander Kirch

After all, hydrogen as an energy source brings with it high hopes of using renewable energy to begin supplying sectors whose main source of supply is currently fossil fuels.

This applies, for example, to shipping and the production of hydrogen for industrial purposes. In order to avoid future emissions and steer these sectors towards climate neutrality, ‘green hydrogen’ – which is generated from renewable energy sources – should be used. One of the techniques with which this can be achieved is known as ‘Power-to-Gas’ (PtG).

In the Power-to-Gas process, electrical energy, which in the case of ‘green hydrogen’ is obtained from renewable energy, is converted into gas. Water is split into its components – oxygen and hydrogen – by means of an electrolyser and electric current. The gas obtained from the process, as well as partial use of downstream methanation, can now be stored and used as an energy source for a wide variety of purposes.

What the colour of hydrogen reveals about the colourless energy source  

Hydrogen (H2) is the most abundant element in the universe. But it does not occur in an unbound form either in space or on earth. Instead, hydrogen forms a variety of bonds. For example, it combines with oxygen (O2) to create water (H2O). It occurs in the earth’s atmosphere in the form of water vapour. It is found in plant remains as a hydrocarbon and can therefore also be extracted from crude oil and natural gas. The problem is that this generates emissions that are harmful to the climate.

In contrast to green hydrogen, the hydrogen produced from crude oil and natural gas is called ‘grey hydrogen’ – even though hydrogen itself is colourless and therefore invisible. Producing one ton of grey hydrogen generates around 10 ton of carbon dioxide (CO2). The hydrogen colour-coding system provides information about the gas’s emissions content.

In addition to grey and green hydrogen, there are also blue and turquoise hydrogen. These also cause emissions during production. However, in the case of blue hydrogen, which is obtained from natural gas, the undesired by-product carbon dioxide is thought to be permanently stored in rock formations. Methane is used for turquoise hydrogen. Instead of gaseous CO2, methane pyrolysis produces solid carbon, which must also be permanently bound to ensure that there are no harmful consequences for the climate.

Range of manufacturing processes for the production of hydrogen

Power-to-Gas is a form of Power-to-X. In these terms the X denotes the form of energy into which ‘power’, understood as electrical energy, is converted. But power-to-gas processes are not the only way of producing hydrogen. In many chemical processes, hydrogen is produced as a by-product, for example in chlor-alkali electrolysis or in crude oil refining processes.

Processes that can be used here include steam reforming, partial oxidation or small reformers. Hydrogen can also be obtained from biomass, for example via biomass gasification, fermentation of biomass or biological hydrogen production. Some of these processes are still in the early stages of research.

However, the process of electrolysis is more advanced. There are also different variants for this. These include alkaline water electrolysis, PEM water electrolysis and high-temperature electrolysis. For hydrogen to be labelled ‘green’ and thus CO2-free, the electrolysis process is not particularly significant. The decisive factor here is where the energy used to produce it is sourced. Only if the electricity used is 100% renewable can hydrogen be produced as 100% emission-free. 

Today’s dilemma for the green hydrogen economy

This results in a dilemma. In order to generate vast amounts of green hydrogen by means of Power-to-X in general and Power-to-Gas in particular, you need more than just an appropriate infrastructure for producing the hydrogen, such as gas networks or Power-to-Gas systems. What your really need is appropriate generation capacities from renewable energy sources.

This is far less trivial than it appears at first glance. Renewable energy sources, used today across all sectors, aim to contribute to the decarbonisation of all economic sectors. Green electricity is required both in the transport sector for electromobility and in the building sector for energy, heating and cooling. It is needed for greater self-sufficiency in trade and industry as well as for accelerated digitisation, not to mention the replacement of nuclear power plants that have been switched off or coal-fired power plants that are scheduled for removal from the grid.

Sooner or later, all of these areas will have to be supplied with renewable energy. So it is not surprising that there are increasing doubts about the feasibility of a green hydrogen economy. It is also becoming clear that there can be no green hydrogen economy without a rapid expansion of renewable energy – in this country or abroad. Because it does not matter whether it is imported or produced here locally. It only matters that it comes from clean, emission-free sources in order to live up to its name as ‘green hydrogen’. Only if this is ensured will the technology contribute to the energy transition and to compliance with the constitutionally Paris Agreement’s binding target of 1.5 degrees. However, there are also advocates of blue hydrogen as a temporary solution. Without extensive investments in renewable energy, infrastructure and modern technology, there will be no green hydrogen economy.

A start has been made...

The German ‘National Hydrogen Strategy’ (NdWS), launched in mid-2020, is a start. The German government has thus agreed to support the expansion of green hydrogen technologies with a seven billion euro funding programme in the coming years. But it’s a long journey towards a green hydrogen economy.

With the NWS, the wheels have at least been set in motion and a message has been sent to the economy to invest in green hydrogen technologies and to convert them into practical applications. Because even as the first wave of euphoria slowly subsides in public, the first funded projects are starting and announcing a market-oriented implementation.

North German Living Lab in practice

For example, the ‘North German Living Lab’ (NRL) recently received a funding commitment of 52 million euros from the Federal Ministry for Economic Affairs and Energy (BMWi) to directly link the sectors of industry, transport and heat supply on the basis of green hydrogen. In addition to the practical application and testing of the interaction of new technologies under real conditions, the aim is to save large amounts of carbon dioxide.

The target is a saving of around 560,000 tons of CO2 emissions every year. This practical test for the implementation of green hydrogen technologies is also intended to promote the restructuring of the energy industry. The North German Living Lab is spread over five ‘hubs’ distributed in Hamburg, Schleswig-Holstein and Mecklenburg-Western Pomerania. The project will run until the end of March 2006.

Prof. Dr Werner Beba from HAW Hamburg, Head of CC4E Project Coordinator NDRL explains what the project is about in a YouTube video:

About the author

Dr Katja Reisswig is a freelance editor and blogger. She launched the cross-industry B2B portal for the green economy. She writes on topics related to sustainability, the energy transition, green innovations and technologies with a view to companies, start-ups, research institutions and other stakeholders in the green economy.

About Tom Mikus

Profilbild zu: Tom Mikus

I’ve been working as an International Project Manager for the Renewable Energy Hamburg Cluster since 2019. At the cluster, I focus on sharing information about renewable energies beyond Germany's borders. I report on the current developments and activities of the Hamburg cluster and renewable energy hub at an international level.