Uncertainties in the German energy transition: detecting robust solutions under shock events in long-term transformation pathways

Energy system models are used worldwide in political decision-making processes for the energy transition. As they project into an uncertain future, there is a growing focus on addressing their inherent uncertainties. In addition, the robustness of model results against changing conditions and uncertainties is becoming increasingly important. In this paper, a Global Sensitivity Analysis (GSA) is applied for the first time to a German sector-coupled energy system model. This allows examination of uncertainties in the energy system model REMod and derivation of more robust solutions for the energy transition. While many input assumptions, such as projected investment costs of technologies and prices of imported hydrogen and synthetic fuels, have a low influence on the model results, there are a few parameters with high influence, namely demand-related assumptions, the carbon budget, the discount rate and expansion limits of wind power and photovoltaics. Based on the GSA and potential societal and geopolitical developments, five shock events have been modeled to occur between 2036 and 2040: limited expansion of photovoltaics, onshore and offshore wind, increasing electricity demand and restricted hydrogen imports. A quantitative scenario analysis is used to evaluate the robustness of the model results against a combination of these shock events. The results show that an accelerated expansion of photovoltaics, electrolysis and hydrogen storage before 2035 in line with an early decarbonization, increases the robustness of the energy transition, leading to additional costs of a maximum of (180 +/- 30) billion € relative to the optimal path until 2045.