Hydrogen-driven Power-to-X: State of the art and multicriteria evaluation of a study case

Hydrogen is a versatile energy carrier studied and considered to substitute fossil fuels since the seventies after the first energy crisis. Later, a second hydrogen wave due to another crisis occurred. Currently, the world is discussing the third hydrogen wave, for which, unlike the other two waves, its driving force is not the lack of fossil fuels but the imminent climate change. The hydrogen economy is expected to answer the energy storage challenges created by fluctuating electricity generation from renewable energy sources and provide a solution for the decarbonization of high energy demand sectors and the synthesis of many chemicals. Today, governments around the globe are committed to scale-up the hydrogen economy; more than 30 nations have launched a National Hydrogen Plan or Strategy. The hydrogen economy functions with a Power-to-X (PtX) versatile system. Power-to-X (“X” as an energy carrier) refers to hydrogen produced via a carbon-free process and the further storage of this element either as pure hydrogen or converted to an energy carrier that can easily be stored, transported, and used, such as ammonia, methanol and other liquid organic hydrogen carriers. This paper conducts a literature review of the political commitment regarding the hydrogen economy, the status of PtX technologies, and development worldwide. It also compares four different scenarios for green hydrogen storage using various criteria. Power-to-Ammonia, Power-to-Methanol, Power-to-Hydrogen blended with natural gas, and Power-to-Liquid hydrogen are evaluated. Conclusively, the four concepts have their advantages and disadvantages, depending on the specific application and related scenario. Germany sponsors most of the research associated with PtX and is the country with the most advanced PtX projects. Therefore, Germany was chosen as a study case for multicriteria evaluation of PtX technologies. Power-to-Ammonia appears to be the best solution.