Hydrogen is moving from a by- and intermediate product to a key substance with a potential to play a major role in the future picture of energy supply. Strong ambitions can be found at several companies, at a national level and especially in the European Union. A turning point for the development of hydrogen as energy source was the commercial availability of hydrogen produced from water with the help of electrical energy, which is known under the name power- to- gas. The alkaline electrolyser technology takes the forerunner position, as it is most commercialised compared to other competing electrolysis technologies. Besides several advantages of power- to- gas, the utilization of excess energy, the conversion of electricity into a storable gas, and the potential to counteract the volatility of renewable energy sources are the strongest arguments to develop and to push the power- to- gas technology. A consequence of the utilization of energy from a renewable source is, that the produced hydrogen has a potential to be environmental friendlier compared to alternative fossil products with the same intended use as fuel or raw product. In addition, hydrogen can be upgraded with the help of a methanation, in the analysed models by using a catalytic process, and can consume carbon dioxide. Modern environmental policies and business decisions force the regular economic calculations and accounting procedures by considering the impact on the environment. Life cycle assessment (LCA), defined by the ISO 14040:2006 and guided by ISO 14044:2006, is an established tool. A LCA evaluates the environmental burden and assigns it to the phases of the life cycle of a product/product system or a process. The standard specifies four phases which are conducted in the frame of the master thesis. The goal and scope step is built on two Power- to- Gas business models (BM). The assessment excludes the use and disposal phase of the product and service and assumes a negligible impact of the manufacture and disposal of the used plants. The first BM describes the synthesis of a renewable source of energy, more precise the synthesis of hydrogen and methane and a mixture of them, where the targeted hydrogen concentration is assumed with 10 %, and the second BM takes into account the storage of renewable energy in the pore space of an underground reservoir. Both have renewable energy as source of electrical energy. Data of a test bed of the Underground Sun.Storage project are used as source of information for the inventory study, supplemented by the use of data banks, analogies and conceptual design. Selected parameter of the CML method, in conjunction with other parameters, are used to create an environmental profile. To enhance the final required interpretation step, the impact of the source of electrical energy is analysed and compared to non- renewable energy sources. In addition to the contribution analysis, the products of the BM and the process itself are benchmarked against natural gas and hydrogen from fossil sources. Consequently, the environmental burden of the storage process and the synthesis process was accessed, compared and discussed. The assessment can be used as source of information, which supports further improvements of the power- to- gas technology, the establishment of an environmental measurement and indication system, and for decision making.