Andreas ZÜTTEL ^1* Christoph Nützenadel C) ² Louis Schlapbach ³ Paul W. Gilgen ⁴

• ¹ Swiss Federal Institute of Technology Lausanne, Lausanne, Switzerland
• ² Independent researcher, Zürich, Switzerland
• ³ ETH Zürich, Zurich, Switzerland
• ⁴ Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland

An analysis of the technical opportunities and economic consequences of the transition from fossil fuels to renewable energy in Switzerland is presented. The technically realized efficiencies showed that complete electrification leads to the most efficient energy system and cheapest electricity. The electricity demand is expected to almost double, and the overall energy cost will increase by 20% compared to 2019. However, the technical challenges of seasonal electricity storage, without any reserves and redundancy, amounts to 20 TWh. Hydropower and PV without storage produce the cheapest electricity. Future nuclear fission technologies, e.g. molten salt Thorium breading reactor -currently still in an experimental stage -might become the most economical and least environmental impact solution for CO2 neutral continuous electricity production. The opportunities for a massive increase of hydroelectric production are limited, already shifting the use of water (9 TWh) from summer to winter is a great challenge. PV and hydrogen production in Switzerland have the advantage to provide approximately 75% of the electricity without seasonal storage leading to significantly lower electricity cost than from imported hydrogen or synthetic hydrocarbons. The most economical solution for aviation and reserves is imported bio-oil converted to synthetic Kerosene, for which large storages already exist.• Renewable energy on demand is essential for replacing fossil fuels and can be realized by combining intermittent energy supplies like photovoltaic and wind with battery and seasonal storage in a power plant unit. • Importing renewable energy carriers requires a storage capacity similar to the seasonal storage for domestic production of renewable energy.• Renewable energy production in Switzerland with seasonal storage and importing renewable energy carriers is a technical and economic challenge, respectively.• The fuel for aviation and the energy reserves for the power plant units can be realized with synthetic oil produced by hydriding bio-oil, avoiding the need for new large and expensive storage systems and CO2 capture from the atmosphere.• Thermal power plants fueled with renewable energy carriers provide equal amounts of electricity and heat. Both forms of energy are of high value in the wintertime.