This is a guest post by Andrea Appel. The guest post reflects the opinion of the author and does not necessarily represent the opinion of the VDE.
Sustainable hydrogen economy: the focus is on the carbon footprint
The seven colours of the rainbow are modest compared to the colour theory of hydrogen, which has eleven nuances – one for almost every type of production process.
This categorization into a spectrum primarily serves to classify the respective carbon footprint of each type of production and to distinguish it from other types of production processes. At present, this categorization is rather broad, as there is still no clarity about the exact emissions in the entire value chain, depending on the production process. Therefore, there may still be shifts and reassessments in the evaluation of production processes in the future.
However, it is generally agreed that the production process with the highest overall efficiency and the lowest emissions will prevail in the long term.
Green hydrogen is preferred
It is no coincidence that the so-called green hydrogen is receiving a lot of attention in discussions on low-emission energy supply: green hydrogen is produced by using only renewable energy sources such as wind-, solar- or hydro-power in combination with electrolysis plants and is considered particularly environmentally friendly.
This, however, does not mean that the process of producing green hydrogen can take place completely carbon neutral or even carbon free. The life cycle (provision of raw materials, construction, recycling) of the renewable energy systems and electrolyzers also generates emissions that need to be taken into account.
Hence, it would be appropriate to classify the production of green hydrogen as a low-carbon production.
Carbon-neutral hydrogen production is an illusion
For all H2 production processes it is for sure that a carbon-neutral hydrogen production is only possible in theory but can hardly be accomplished in practice. But what exactly does carbon-neutral or climate-neutral mean? The definition is that no more greenhouse gases are emitted than can be converted via natural sinks.
This means: the focus shall be on the carbon footprint per kilogram H2 and how it is compensated by natural CO2 sinks. In the ideal case, the entire system boundary will be taken into account – cradle to cradle.
Most of the H2 production processes, which are spuriously classified as being carbon-free, could only be considered carbon-free in operation.
Yellow and red hydrogen: further products of electrolysis
Just like green hydrogen, yellow and red hydrogen are also produced by methods of electrolysis.
The production of yellow hydrogen uses a mix of electricity from renewable and fossil energy sources.
The production of red hydrogen (also referred to as purple or pink hydrogen) uses electricity generated from nuclear power.
Grey, brown, black, blue and turquoise hydrogen are based on fossil fuels
Grey hydrogen is produced from natural gas by steam reforming.
Brown and black hydrogen are produced using hard coal or lignite. They are thus similar to grey hydrogen.
Blue hydrogen is produced just like grey hydrogen. In this case, however, the produced CO2 is captured and stored by means of carbon capture and storage (CCS) or separated for further use by carbon capture and utilization (CCU). Turquoise hydrogen is similar to blue hydrogen, but is obtained by pyrolysis of methane. During the process, solid carbon is produced and CO2 emissions do not occur.
Blue hydrogen is seen as a temporary CO2-free solution for boosting the hydrogen economy. Basically, doubts exist concerning whether H2 production based on fossil fuels contributes to the deceleration of climate change and reduces emissions in the total value chain. Furthermore, it is questionable whether the necessary large investments in this technology are economically reasonable if it is only operated for a period of about ten years. Another objection is the goal of abandoning the use of fossil fuels in the long term.
However, a stagnation of renewable energy capacities can be observed today – with an electrolysis output tending towards zero. The intended market boost can therefore not be accomplished within the envisaged period of time without using blue and turquoise hydrogen.
Orange hydrogen is based on biomass
Orange hydrogen is produced by fermentation or gasification of biomass or by electrolysis using electricity produced in waste-to-energy plants.
Not yet categorized: plasmalysis and the like.
The production processes using plasmalysis of industrial waste-water, plastics or other carbon compounds have not been categorized yet. These technologies are said to be less energy-consuming than production processes using electrolysis.
Hydrogen as a byproduct of processes in the chemical industry also still needs to be categorized. One example for such processes is the chlor-alkali electrolysis.
White hydrogen from geological processes
White hydrogen is produced in natural or geological processes. However, it is still not clear to what extent the exploitation of this type of hydrogen is technically and economically feasible.
Is hydrogen a greenhouse gas?
Discussions about the sustainability of H2 as an energy source also led to the question of whether hydrogen is possibly more harmful to the climate than other greenhouse gases.
In fact, hydrogen shows a global warming potential which is six times higher than that of CO2. The quantity of CO2 emissions compared to the quantity of hydrogen as well as the emission site and the reaction products play a significant role in assessing the relative harmfulness of the hydrogen emissions.
Hydrogen used in fuel cells produces water vapour, which also has a global warming potential. Burning fossil fuels also produces water vapour in combination with various other greenhouse gases. The question now would be, which application produced a higher amount of water vapour. This ratio is of utmost importance.
In summary, it is noted that every gas has an effect on the atmosphere. Consequently, all emissions and their effects must be closely monitored – this also applies to hydrogen.
Up to 800 terawatt-hours until 2050
The German National Hydrogen Council (Nationaler Wasserstoffrat) has commissioned a meta-study. Key statement: current studies estimate a hydrogen demand of 400 to 800 terawatt-hours until 2050 in Germany. But how to produce these enormous amounts of hydrogen?
Although Germany has conducted negotiation, has signed contracts and letters of intent, questions still arise which cannot be answered up to this point, such as questions concerning long-distance transport and associated emissions. Political aspects also need to be taken into account: hydrogen has the potential to change the geopolitical situation – if so, Germany would be less dependent on the current oil supplying countries.
Regionally produced hydrogen would stand for the ideal case. Then, if necessary, the production radius should be extended across Europe. Only in the next step, hydrogen supply from non-European countries, which are much sunnier, will be taken into consideration. At the same time, it would be necessary to avoid that the hydrogen production for Germany will lead to a higher consumption of fossil fuels in these countries due to the export of the renewable energy. The National Hydrogen Strategy also aims to avoid this.
Germany’s position: national and international perception
Which position does Germany take in the international ranking concerning hydrogen? This is very differently evaluated depending on the perspective. Abroad, Germany is considered a pioneer: for example, in the field of filling stations, only Japan and the USA have even better developed hydrogen filling station networks than Germany, and German expertise in the fields of electrolysis and fuel cells is recognized all over the world. Future hydrogen producers such as Australia are planning to purchase their production equipment in Germany. Japan and New Zealand also look at Germany: various joint international research packages are currently being set up.
The German perspective, however, is focussing on the risk of losing the position of the international leader. Low dynamics and a lack of efficiency in research and development are being criticized. Conclusion: Germany must stay in the game.
Author information
Andrea Appel is an expert in the fields of hydrogen and hydrogen economy.
She is a qualified management assistant in traffic services (2007-2009) and an environmental engineer with two degrees from RheinMain University of Applied Sciences (Environmental Engineering B. Eng. and Environmental Management and Urban Planning in Metropolitan Areas M. Eng. 2011-2018). She worked for two and a half years (2018-2020) in the solar, wind and battery storage systems industry before becoming part of the VDE team, where she acts as a project manager concerning hydrogen development issues.
