(Invited) The Role of Electrolysis in a Renewable Energy Economy

Abstract

The United Nations Framework Convention on Climate Change (COP21) in Paris last year has underlined the urgency of a fast and consequent transformation of the various energy systems from a fossil based energy feedstock towards renewable energies like photovoltaics, wind- and hydropower, in order to drastically decrease the greenhouse gas emissions (GHG). Such a transformation requires a thorough restructuring of the energy systems with all energy carriers and consumer sectors including its intersectoral dependencies, grid structures and energy storage needs. At Fraunhofer ISE we performed time-resolved studies on how to reach the main goal of the German energy transformation to decrease its GHG emissions by at least 80% until 2050 and thus, to widely decarbonize all energy related sectors. Potential transformation pathways based on various scenarios were studied and the required costs were modelled for each scenario. The results of this modelling made very obvious that the ambitious GHG reduction targets can only be fulfilled by a strong rise in electricity generation by fluctuating renewable energies and on the other hand by the installation of large plants for producing synthetic energy carriers from renewable energies. The most versatile energy carrier for such large amounts of energy is hydrogen produced from water electrolysis. Hydrogen can be stored in large amounts in gas tube fields or salt caverns and can be used directly either in fuel cell cars and buses as a fuel or in stationary combined heat and power fuel cell systems. Furthermore the hydrogen can be used in order to hydrogenate CO2 and thus to generate green liquid fuels such as oxymehylenether (OME) or other chemicals in order to replace oil based products. The conversion of electricity into hydrogen is called Power-to-Gas, the further processing of the hydrogen and CO2 towards liquid energy carriers and chemicals is called Power-to-Liquid. With the advent of various Power-to-Gas demonstration projects it becomes clear how important this technology will be in the future energy system. Distributed water electrolyzers in the Megawatt power range will stabilize the grid frequency and voltage or will deliver other ancillary services and thus, will contribute to the secondary balancing market. Alkaline water electrolyzers are applied for more than 100 years in industrial applications and are nowadays complemented by proton exchange membrane (PEM) electrolysers in order to cover the needs for a highly dynamic load in the grid. However, main challenges of the PEM technology are high costs associated with expensive materials and the durability of cells and stacks. With ongoing technological development it is expected that PEM electrolysis systems become a competitive alternative to alkaline systems in the next years. In this talk, the technological base of water electrolyzers will be described and the related performance data, life-time expectation and cost reduction potential will be discussed. Furthermore the impact of distributed water electrolyzers in the Megawatt power range as part of an increasingly renewable energy system in terms of Power-to-Gas modelling scenarios will be given. Figure 1