Green Hydrogen and PtX

Germany must move away from fossil fuels such as coal, oil, and gas if we want to meet the 1.5–2 degree target set out in the Paris Agreement. And this is urgently needed if we want to do our part to slow down climate change. In addition, issues of supply security in the energy sector are becoming increasingly important, calling for a move away from energy sources such as gas.

It is essential that the transition from fossil fuels to renewable energy sources is accelerated. The generation of electricity from wind, solar, and hydro energy is already making an important initial contribution here. In addition to the expansion of renewable energies, energy storage systems are essential to guarantee a continuous and secure electricity supply from volatile sources.  Green hydrogen as an energy source can fill this gap, as it enables the storage and transport of energy from renewable sources.

In addition, the energy transition must be driven forward beyond the electricity sector. Green hydrogen can play a key role here:

• Hydrogen can be used in industry. If green hydrogen is used, processes such as steel production can be made climate-neutral without the use of fossil fuels.
• In mobility, hydrogen is seen as particularly important for heavy-duty transport by trucks, trains, planes, and ships—as a supplement to battery technologies.

To produce green hydrogen, electricity from renewable energies such as water or wind is used to generate hydrogen by means of electrolysis. This forces a redox reaction that splits water into hydrogen and oxygen. This technology converts electrical energy into chemical energy, known as power-to-gas. This process makes it possible, for example, to store surplus green electricity with an efficiency of over 70%.

The different colors of hydrogen describe how the hydrogen is produced or extracted.

In the production of green hydrogen, electricity from renewable energies is used in the electrolysis of water. This makes green hydrogen particularly climate-friendly.

Gray hydrogen is produced using steam reforming. This process involves generating hydrogen from carbon-based energy sources such as natural gas and water. It produces approximately 10 tons of CO2 per ton of hydrogen, which is released into the atmosphere. If the energy sources are coal, a distinction is also made between brown (lignite) and black (hard coal) hydrogen.

Blue hydrogen, like gray hydrogen, uses the steam reforming process, but up to 90% of the CO2 is captured and stored underground (carbon capture and storage, CCS).

Turquoise hydrogen is produced by methane pyrolysis, i.e., the splitting of methane. Instead of CO2, solid carbon is formed as a by-product. This process is still under development.

White hydrogen refers to the natural occurrence of molecular hydrogen in certain regions, such as France or the USA, which is extracted using various methods, such as fracking technologies.

Already today, hydrogen can be fed into the existing gas grid in limited quantities of up to 10%. The hydrogen is burned like natural gas, producing only water vapor, which is released into the environment. Another option is to use fuel cells to generate heat and electricity from the hydrogen.

However, the way in which hydrogen is used for heat supply is still controversial, as the boundary conditions of the studies vary. For example, the results of the Kopernikus Ariadne project show that, at least as far as the building heating sector is concerned, there are already more efficient alternatives available today, such as heat pumps.  

More Information: 

• Copernicus Project Ariadne: Hydrogen in the building sector
• Fraunhofer IEE: Hydrogen in the energy system – focus on building heating (GER)
• Agora Energiewende: The value of efficiency in the building sector