Hydrogen production: a challenge for the energy transition

Hydrogen is not a primary energy source like oil or coal, but an energy carrier. That means that, like electricity, it has to be produced using a source of energy.

Dihydrogen (H₂) is present in many molecules on Earth: chiefly in water (H₂O) but also in hydrocarbons such as methane (CH₄). To produce hydrogen, you therefore need to separate the dihydrogen from the other atoms making up the molecule: the oxygen in water and the carbon in methane.

Since hydrogen is the most common element in the universe, it is a valuable renewable energy source to the energy transition. However, its production can be a source of pollution, which is why current policies are to encourage decarbonised methods of hydrogen production.

Today, hydrogen production around the world mostly employs the steam reforming of natural gas. That technique consists in causing a reaction between the methane and the steam at a high temperature. Although it is effective in producing hydrogen from methane, steam reforming has the disadvantage of emitting greenhouse gases.

However, two different ways are now being studied to make steam reforming less polluting:

• Techniques to capture the carbon dioxide (CO₂) and use it: CCUS (Carbon Capture, Utilisation and Storage).

•  The steam reforming of biogas instead of natural gas.

However, these solutions are still not yet being applied on a large scale. That is why, although hydrogen usage can be considered to be clean, its production at present is not.

However, that is about to change. At the end of 2020, the French government presented its national strategy for the development of decarbonised hydrogen. The first aim of the hydrogen plan is to decarbonise industry, which is currently the top hydrogen consumer in France. The second is to decarbonise heavy vehicles (lorries, trains, aircraft etc.) through the use of fuel cells.

Although the cost of decarbonised hydrogen production is higher at the moment, actors in the hydrogen industry are working to reduce the cost of production so they can offer hydrogen at a competitive price. To achieve that, France is focussing on the largescale deployment of a process for manufacturing hydrogen through the electrolysis of water.

Producing hydrogen by electrolysis consists in breaking down the water molecules (H₂O) into dioxygen (O₂) and dihydrogen (H₂) using an electric current. This is currently the solution for producing decarbonised hydrogen that is being encouraged the most.

This technique has a number of advantages:

• Encouraging a more diversified energy mix

Electrolysis uses water and electricity. If the electricity comes from nuclear or renewable sources, that means fossil fuel energy sources can be entirely done away with. With this hydrogen production method, we can look forward to an energy mix that is more diverse, more local and less carbonised.

• Producing decarbonised hydrogen

Unlike methods where hydrogen is produced from methane, electrolysis does not emit any CO₂, and it therefore has less impact on the environment. If the electricity being used comes from a renewable source, the hydrogen produced can then be viewed as clean energy.

• Allowing the control of renewable energy

Renewable energy produced by photovoltaic cells or wind turbines, for example, is a problem when it comes to management. In fact, because it depends on natural elements that cannot be controlled (sunshine and wind), its production cannot be adapted to consumption requirements in real time. To prevent energy wastage in the summer and guarantee supplies in winter, it is therefore necessary to be able to store the excess. The electricity cannot presently be stored in large quantities or long-term.

This is the point where electrolysis offers an attractive solution. By manufacturing hydrogen from solar or wind power, it is possible to exploit that excess electricity, effectively storing it or injecting it into the gas grid. This is a virtuous circle, and we can say that hydrogen production is green in the case of electrolysis. At a later date, it is possible to produce electricity from hydrogen to meet demand during peak consumption periods.

At Teréga, there are a number of study projects under way with partners, looking into the production of hydrogen from photovoltaic electricity. As an infrastructure operator, we are studying the capacity for hydrogen injection into our gas transport grid, alongside storage possibilities. These test phases allow us to control the risks associated with hydrogen and to play our part in the development of a French and European hydrogen grid. We are thus involved in the European Hydrogen Backbone initiative to build that network with other European gas transport infrastructure managers.

Another route is being studied for the production of decarbonised hydrogen: the pyro-gasification of waste. That solution is very attractive in encouraging of a circular economy approach, since it will be applicable to a wide range of waste which is currently not exploited.

• Waste eligible for pyro-gasification

Unlike methanisation, based on the fermentation of organic waste to produce biomethane, pyro-gasification can be applied to waste that is hard to ferment. These two processes for exploiting waste are therefore complementary.

This means it is possible to produce hydrogen from biomass: wood and farming residues, poultry manure, food industry residues etc. Other types of waste can also be used, such as solid recovered fuel (SRF), used tyres, or sewage sludge.

• The method for producing hydrogen by pyro-gasification

Hydrogen production by pyro-gasification consists in heating the waste to a high temperature (over 1000 °C) in the presence of a small quantity of oxygen. The technique allows the waste to be converted into a synthetic gas, or syngas, comprising chiefly carbon monoxide (CO) and hydrogen (H₂). The hydrogen can then be used following purification, or alternatively converted into synthetic methane for injection into the gas grid.