The generation of the renewable electricity required for the production of green hydrogen is usually exposed to strong fluctuations - especially when primarily wind and solar energy are used. These fluctuations occur both during the course of days (e.g. PV systems do not produce electricity at night) and over the course of months or years (e.g. due to the weather, in Germany wind turbines generate significantly more electricity in the winter half-year than in the summer half-year). Therefore, the storage of green hydrogen is necessary to guarantee a constant delivery of hydrogen to individual consumers and to ensure the general security of renewable energy supply. In this context, long-term storage facilities with a large volume/storage capacity for hydrogen are of special importance when considering future energy systems based entirely on renewable energy sources.
The energy supply of most of the European industrialised countries, and of Germany in particular, is currently highly dependent on the import of fossil fuels. The figure below shows Germany's primary energy consumption in 2019 broken down into the different energy sources. Domestic primary energy sources are lignite and renewables. These two “domestic energy carriers” currently cover only about a quarter of total primary energy consumption.
Germanys's total primary energy demand - Energy sources and share of imports by Fabian Carels and Lisa Karies (CC BY-SA)
In order for Germany to achieve its climate goals (greenhouse gas neutrality by 2045), fossil primary energy sources will have to be almost completely replaced in the coming decades (as explained in Chapter 1.2 and Chapter 1.3). Although a complete replacement of these fossil energy sources with renewable alternatives produced exclusively in Germany is technologically possible, there are several reasons why part of the energy demand will most likely be covered by imported renewable energy carriers. Due to its high population density, Germany has relatively little free land that can be used exclusively for the generation of renewable energy. Land use conflicts, for example with nature conservation or residential development, and resistance from affected local inhabitants (NIMBY-Effect) are already causing considerable delays in the realisation of projects for the construction of wind or solar farms. In the worst case, project plans can even fail completely for the reasons mentioned. Other regions in the world have a significantly higher unused potential for renewable energy generation than Germany. This refers not only to available land, but also in particular to the availability of wind and solar energy as well as hydropower, bioenergy and geothermal energy. For example, a solar module in the south of Algeria generates almost twice the amount of energy compared to an identical solar module in Northern Germany due to the particularly high solar radiation in North Africa.
For the reasons mentioned above, it is likely that a global trade in renewable energy sources will emerge in the future. Densely populated countries with high energy consumption - such as Germany - will probably act as importers in this market. Countries that have a high availability of renewable energy, e.g. wind and solar, and enough space to build large-scale production facilities will be able to export green energy. Gaseous and liquid energy carriers can be transported over long distances much more easily than electricity. Therefore, it is likely that this global trade of renewable energies will be based on green hydrogen and / or its derivatives. In this chapter, you will learn how green hydrogen can first be stored and then transported and what the so-called derivatives are about.
