In the future, hydrogen and other green and climate-neutral gases will become an enabler of the transformation to a climate-neutral energy world. Fossil natural gas will gradually be replaced by biomethane, green as well as initially blue or turquoise hydrogen and synthetic methane. Climate-neutral gases are already helping to reduce greenhouse gas emissions today and will do so much more in the future. Together with the associated infrastructure, they become the ideal partner of renewable electricity by compensating for the weaknesses of electrification.
Biogas refined to biomethane, which is upgraded to “natural gas quality” in special plants, is of particular importance: Naturally obtained by fermenting biowaste, liquid manure, or plant residues, its properties can contribute to reducing greenhouse gas emissions, e.g. in the mobility sector.
Biomethane is a renewable gas produced from biogas by upgrading it to “natural gas quality”. While the methane content of pure biogas is between 40 and 75 percent, it has at least 96 percent after upgrading to so-called biomethane. This means that it can be mixed with natural gas in any quantity. The prefix “bio” stands for the natural-biological production method. Biogas is produced in biogas plants through natural fermentation of biomass. Today, mainly waste and residual materials such as sewage sludge, biowaste, liquid manure, dung, and so-called energy crops are used for this purpose. The emission factor for biogas or biomethane depends on a multitude of influencing factors. Depending on the substrate of production (energy crops, liquid manure, waste, and residual materials), the emission factor for biomethane ranges from 36 to 158 g CO2/kWh. In 2021, Germany had about 9,770 biogas plants with an electrical output of 5,860 MW. This includes 238 biogas upgrading plants for biomethane. These currently feed about 10 TWh into the German gas grid, or about 1 percent of gas sales in Germany.
Since 2007, Germany’s gas suppliers have been offering end customers nationwide supplies of pure biogas or natural gas blended with biogas. Biomethane is also of particular interest to the mobility sector. Thus, biomethane, pure or blended with natural gas and compressed to CNG (Compressed Natural Gas), can be used as a fuel for cars, trucks and buses, making an important contribution to reducing greenhouse gas emissions.
Green hydrogen is a renewable gas and is produced by electrolysis in so-called power-to-gas plants. For this purpose, water is split into hydrogen and oxygen using electrical energy. If the electrical energy comes largely from renewable sources, the hydrogen is called green. Since no CO2 is produced during the conversion process, the emission factor of green hydrogen is 0 g CO2/kWh. There are currently three different variants of the electrolysis process, each with a different degree of technical maturity. These are alkaline electrolysis, proton exchange membrane electrolysis, and high-temperature electrolysis. So far, mainly alkaline electrolysis and proton exchange membrane electrolysis are well established as low-temperature electrolysis and are used commercially. Alkaline electrolysis is the more mature technology, which has been used in various applications for years. High-temperature electrolysis is still in the development phase.
The hydrogen produced by power-to-gas plants (electrolysers) can be converted into synthetic methane in an additional step with the addition of carbon dioxide (Sabatier process). Biogas can serve as a CO2 source, other sources can be industrial processes and sewage treatment plants. In the future, the required CO2 could also be extracted from the air for smaller quantities (direct air capture). The production process of synthetic methane is CO2 neutral. In addition to the Sabatier process, there is also the possibility of biological methanation, but this is not yet available on a large scale.
Since synthetic methane has identical combustion properties to fossil natural gas, it can be fed into the natural gas grid without any quantity limits. There are no other restrictions for the end-use.
Up to now, hydrogen has been produced industrially primarily by steam reforming from fossil natural gas (methane). The resulting product is called grey hydrogen. If the CO2 produced during steam reforming is separated from the exhaust gas stream through carbon capture and storage (CCS) and stored in geological structures and demonstrably does not enter the atmosphere, so-called blue (greenhouse gas-neutral) hydrogen is produced. Blue hydrogen is thus a decarbonised gas.
An alternative to steam reforming in combination with CCS that is still under development is CO2-free hydrogen production from methane through pyrolysis. In the pyrolysis process, the carbon is separated as a solid and can thus be stored comparatively easily or reused as a raw material, which means that the emission factor is also close to zero. The hydrogen produced by pyrolysis is called turquoise hydrogen. However, the process has not yet been established on the market and is only used on a research scale.
Green gas quota are the most economically sensible instrument for market ramp-up
Up to now, there have been no consistent programmes at either EU or federal level to promote renewable gases to ramp up the market for the new technologies. However, there is a consensus that plant costs, especially for electrolysers, need to be reduced by scaling up production to make production for renewable gases economically viable. In particular, a quota for green or decarbonised gases or a time-limited market incentive programme is under discussion.
The FNB Gas has commissioned nymoen|strategieberatung GmbH to analyse the instrument of a green gas quota within the framework of a short study and to compare it with other selected support mechanisms. As a result, the quota is the only instrument that can reliably achieve defined volume targets and thus implicitly CO2 reduction targets. No other instrument, in addition to setting the target value, provides the possibility of setting the speed of expansion in a targeted manner.
If appropriately designed, the quota is also the most effective instrument for a market ramp-up of green gases from an economic point of view. The quota is the only support instrument (apart from CO2 trading) that has a tradable component via guarantees of origin, which ensures the most cost-effective implementation. If it is envisaged that imports can also be used to meet the national quota, there is also a possibility of international expansion.
