The P2G® (Power-to-Gas) concept, which was largely developed at ZSW in collaboration with Fraunhofer IWES and a private company, seeks to convert “excess” electricity into hydrogen by means of electrolysis and then in a subsequent synthesis step to convert the hydrogen into methane (methanisation) by combining it with CO2. Converting electricity into gas allows for the use of the existing underground storage systems in the natural gas grid that have a capacity of more than 200 TWh. The REG research department has carried out the basic engineering for the P2G® plants and their adaptation to specific requirement profiles. In 2011, container-integrated systems went into operation at various sites using different types of CO2 sources. As part of the “Power-to-Gas” project (0325275A) funded by the German Federal Ministry for the Environment, a further test plant at ZSW commenced operation at the end of 2012. This plant is ten times larger and has a capacity of 250 kWel.
A further obstacle to achieving the marketability of P2G® technology was overcome on the completion of this 250-kW research plant. ZSW inaugurated its new plant on 30 October 2012. With a potential methane production of up to 300 cm3 per day, it was the largest plant of its kind in the world at the time. The aims of the test operation were to optimise the process in terms of the achievable gas quality and the costs. The 250-kW plant comprises an alkaline pressure electrolyser, a methanisation unit and a process control system, which regulates the plant. The research plant works dynamically and intermittently. In contrast to the first plant, it can react flexibly to fluctuating energy supplies from the wind and sun and it can also react to sudden interruptions. The control and regulation technology is the same as the technology to be used in future large-scale industrial plants.