Green hydrogen: 10 questions and answers

24 January, 2024

Green hydrogen is a clean, versatile energy that has the potential to become a key element for the future of the planet. It will play a major role in the decarbonisation of different sectors of the economy, especially those for which electrification is not a viable option, as well as in guaranteeing the security of supply and energy independence of Europe and other regions.

In this article you will find 10 questions and answers to help you know and understand this energy carrier a little better.

1. What is green hydrogen?

To understand more easily what green hydrogen is, it is first necessary to know that hydrogen is the most abundant chemical element on the planet, present in 75% of matter. One of its attributes is that it is an energy carrier, i.e. it is able to transport and release energy and can therefore be used as an alternative to traditional fuels.

However, hydrogen is not found alone, but is always bound to other elements, as in the case of water (H2O, two atoms of hydrogen and one of oxygen). It is therefore necessary to obtain it through different processes and this is where the colour differentiation arises: if it originates from renewable sources, then it is called green hydrogen.

2. How is green hydrogen produced?

Since hydrogen is not found in its free state, it must be obtained from various compounds. In the specific case of green hydrogen, it is produced by breaking down the water molecule into its two elements – oxygen and hydrogen – through the process of electrolysis, applying a continuous electrical current from renewable energy sources such as wind or solar power.

This means that no pollutant emissions are generated during the production of the resulting hydrogen and it can therefore be considered “green”.

3. What can green hydrogen be used for?

Renewable hydrogen has various applications, the main ones being:

Intensive industry. Its adoption in industry can significantly reduce emissions, as this sector consumes almost 90% of hydrogen globally today, mostly grey (i.e., with CO2 emissions).

Sustainable mobility. Green hydrogen can be essential in the decarbonisation of road, rail, maritime and air transport.

Energy storage. One of the advantages of hydrogen is that, as an energy carrier, it allows energy to be stored and transported for later use in a controlled manner. In this way, surpluses such as those from renewable production can be used to contribute to energy stability.

Households and businesses. It could be used in heating systems, to generate electricity by means of fuel cells and even to heat up domestic water.

4. How is green hydrogen transmitted?

The transmission of renewable hydrogen can be carried out by various means, taking into account factors such as the distance between the place of production and use, the volume to be transmitted, the efficiency of the system, the available infrastructure or the economic implications. These are some of the main alternatives for distribution:

H2 pipelines. These are specific pipelines for the transmission of hydrogen. It is an efficient and competitive alternative for long distances and, while such networks are currently being deployed, it is also possible to take advantage of existing infrastructure used for the transmission of natural gas. According to estimates of the European Hydrogen Backbone, around 70% of the European gas system could be used for hydrogen transmission.

Vessels. The use of carriers (ammonia, methanol or organic carriers) is an alternative that allows transport by sea.

Road transport. Trucks for transporting hydrogen in liquid or gaseous compressed form are a suitable option for short distances. Although it allows access by road to points without access to ports or rail, it does require specific loading and unloading infrastructure.

5. How is green hydrogen stored?

Although there are still technological challenges to maximise its performance, renewable hydrogen can be stored in a variety of ways. For example:

Underground storage. Gaseous hydrogen can be stored in aquifers, old natural gas fields or salt caverns, for example. Research is ongoing and, a priori, salt caverns seem to be the best option, as they allow large volumes of H2 to be confined at moderate pressures and at lower cost. In addition, such salt caverns are particularly interesting because they allow for great flexibility in the storage operation and present a lower technical risk for their construction.

Cryogenic storage. Liquid hydrogen is stored in cryogenic tanks at a low temperature (-253°C) and pressure of around 700 bar, which significantly reduces its volume. The use of such tanks is also common for transporting large quantities of hydrogen in trucks or tankers, for example.

Storage in pressurised tanks. The gaseous hydrogen is stored at high pressure – between 150 and 700 bar – to compress it. It is a suitable method for large-scale and long-term storage. It also offers the advantage of being able to use part of the existing natural gas infrastructure.

6. What differentiates green hydrogen from others labelled as blue, grey, pink or other colours?

The colour associated to hydrogen depends on the form in which it is obtained and the amount of emissions generated during the process. In the case of green hydrogen, this colour is given because it is generated using water and electricity from renewable energies. This means that no CO2 is emitted during production.

The colour associated to hydrogen depends on the form in which it is obtained and the amount of emissions generated during the process

Other colours associated to hydrogen are:

Grey hydrogen: is produced by reforming processes using natural gas or other light hydrocarbons such as methane or liquefied petroleum gases. Currently, 99% of the hydrogen consumed in Spain is of this type.

Blue hydrogen: obtained in a similar way to grey hydrogen, but with the application of Carbon Capture, Utilisation and Storage (CCUS) techniques, which reduces CO2 emissions generated during the process by up to 95%.

Yellow hydrogen: is generated from electricity from the primary grid, using water as a raw material through the process of electrolysis.

Pink hydrogen: produced from electricity from nuclear energy, using water as a raw material and through the process of electrolysis.

Turquoise hydrogen: hydrogen generated from the pyrolysis of methane. Solid carbon is generated during this process, so unlike blue hydrogen, there is no need to capture the resulting carbon.

Black and brown hydrogen: obtained from coal gasification. A large amount of CO2 is generated during production.

White hydrogen: is hydrogen found in nature itself. It forms in isolated environments without the presence of oxygen due to the interaction of water with certain minerals, such as iron-rich ones. It is, for example, underground and offers the possibility of being used without the need for chemical processes, any transformation and without emitting pollutants. Deposits have been discovered in Spain, France, Australia and Finland.

7. What is the role of renewable hydrogen in the energy transition?

Green hydrogen is a renewable energy source with great potential and multiple applications. It is expected to play a key role in the decarbonisation of the economy, mainly in sectors such as industry, transport and those where electrification is not feasible, either because they are energy intensive or due to technological or operational constraints.

Green hydrogen is a renewable energy source with great potential and multiple applications

Thus, renewable hydrogen is another alternative to reduce dependence on fossil fuels and mitigate climate change, helping to build a more sustainable energy system.

The ability to be stored provides an opportunity to support the use of this renewable energy, harnessing it for times of peak demand or transporting it to where it is needed.

8. What are the prospects for green hydrogen in Spain?

Spain is well positioned to become a major producer and exporter of green hydrogen to the rest of Europe. Its main competitive advantages include the use of a large part of the existing gas infrastructure, its geographical location and its renewable energy generation capacity

Spain is well positioned to become a major producer and exporter of green hydrogen to the rest of Europe

According to a theoretical study presented by Enagás at its first Hydrogen Day, the estimated potential for renewable hydrogen production in Spain for 2030 is between 2 and 3 million tonnes and, for 2040, between 3 and 4 million tonnes. In terms of domestic demand, estimates for 2030 are 1.3 million tonnes, while up to 2 million more tonnes are expected to be exported via the maritime connection between Barcelona and Marseille, equivalent to 10% of the total expected demand in Europe.

9. What are Europe's plans for green hydrogen?

Europe aims to be climate neutral by 2050, as expressed in the European Green Deal. To achieve this, in addition to other measures, clean technologies and fuels such as renewable hydrogen are required.

The European Commission adopted a Hydrogen Strategy for the EU in 2020, seeking to promote the development and deployment of renewable hydrogen, especially in sectors that are difficult to decarbonise. The strategy aims to install at least 6 GW of electrolysers by 2024 and to reach 40 GW by 2030. The REPowerEU plan, which aims to guarantee security of supply and independence in the region, also includes this renewable gas as a key factor of the strategy.

In addition, the EU’s list of Projects of Common Interest includes cross-border renewable hydrogen energy infrastructures, reflecting the region’s interest in this energy carrier. One example is the H2Med hydrogen corridor. 

10. What are the challenges of green hydrogen production?

Making renewable hydrogen a viable large-scale alternative to fossil fuels means making it more economically competitive and energy efficient. This is a path that is already being travelled through different initiatives and projects.

Infrastructure development. Creating and adapting facilities to drive uptake and expansion of the sector. For example, the construction of H2 pipelines connecting production and demand centres.

Integration of large-scale projects. Cooperating in the development of large projects and infrastructures that facilitate the creation of economies of scale, such as hydrogen corridors between countries.

Technological advances. Increasing the efficiency of processes and materials used to produce, store, transport and use renewable hydrogen.

Research. Promoting knowledge around renewable hydrogen to, for example, identify energy efficiency and safety standards.