The Power-to-Gas (P2G®) process uses electrolysis to convert excess electricity from fluctuating sources into hydrogen. It can either be used immediately or turned into methane by using carbon dioxide in a subsequent step. For this purpose, ZSW is currently developing electrolysers and synthesis reactors. Converting electricity to gas allows solar and wind power to be stored in the gas grid for several months. What’s more, hydrogen and methane can be used to power climate-friendly fuel cell vehicles or natural gas vehicles.
The so-called Power-to-Gas (P2G®) process allows the production of hydrogen and methane. While the individual steps in the P2G® electrolysis and methanisation processes have been known for a long time, there are also new developments that include numerous improvements in efficiency during implementation and also the combination of these two processes. In terms of composition, renewable methane produced from wind and solar energy is actually natural gas meaning that it can be fed into the established gas grid and efficiently stored there. The current natural gas infrastructure includes the existing pipelines, gas tanks and underground caverns. All of these storage alternatives already exist and can provide immense storage capacities of more than 200 TWh. Both methane and, to a limited extent, hydrogen can be integrated, distributed and made available for use according to demand. The gases can also be stored without any loss for several months in the locations stated above. Thanks to the P2G® process the electricity grid and the gas network can grow together to create an integrated overall system.
Possible sources of the CO2 that is to be used in the methanisation process could include biogas plants, bioethanol production plants, power plants and the chemical industry. ZSW is conducting research on accessing further sources of CO2. Synthetic natural gas can be used to generate electricity in modern combined cycle power plants or in decentralised CHP plants. It can also be deployed in industry and it can be used as a fuel, e.g., in natural gas vehicles. The hydrogen generated in the P2G® process can also be used for future mobility – as power for fuel cell vehicles.
In particular, its use in future mobility could provide an effective solution for the energy transition in the transport sector, especially as the drive technology for natural gas vehicles is already more advanced than other environment-friendly technologies. The refuelling station network for CNG (compressed natural gas) is also comparatively more highly developed. The commitment of the car manufacturer Audi demonstrates this enormous potential. With ZSW’s scientific support, Audi has constructed the first industrial-scale P2G® plant (6 MWel). The opening of the 6-MWel plant at the end of 2013 was the culmination of many years spent researching, developing and demonstrating P2G® at ZSW. P2G® as a whole also provides a basis to achieve the goals of sustainability in the mobility sector and enables both short and long-distance mobility. The generation of hydrogen and methane is technologically easier, more energy efficient and further developed in comparison to liquid-based, renewable synthetic energy carriers. In addition, the P2G® system will also contribute to securing Germany’s technological lead, reducing its dependence on natural gas imports and lessening its mobility sector’s dependence on petroleum.
The P2G® technology has already taken the first steps on the long and hard path towards commercialisation. Since P2G® technology was developed, ZSW has researched chemical, hydrogen-based energy carriers ranging from methanol using CO2 captured from air to CNG. Some of the research is focused on the basic engineering of P2G® systems and their adaptation to meet specific requirement profiles. Already in 2009, ZSW was able to successfully demonstrate on a container-integrated 25-kWel test plant that the P2G® concept works perfectly. This plant was operated in 2011 at different locations and using different CO2 sources. In autumn 2012, ZSW commenced the operation of a 250-kWel pilot plant with ten times the capacity of the original container-integrated test plant. The successful production of very high quality gas was recorded in the summer of 2013. The gas has a methane content of 99% meaning that the researchers achieved a gas quality that exceeds statutory requirements for gas feed‐in. It was made possible by a membrane technology that was used to process the gas after methanisation. The knowledge and experience gained from this research is currently making a valuable contribution to the project in Werlte in Lower Saxony (6000 kWel).
In summer 2015, ZSW began coordinating the flagship project Power-to-Gas Baden-Württemberg. As part of this project, the newest scientific developments are used to enable the profitable operation of the technology. The goal is to generate renewable hydrogen that is suitable to power cell cars by converting electricity using electrolysis. In doing so it hopes to pave the way for the energy transition in transportation.