The Liquid Buffer: Multi-Year Storage for Defossilization and Energy Security under Climate Uncertainty

Abstract

The climate-driven uncertainty of renewable generation and electricity demand challenges energy security in net-zero energy systems. By introducing a scalable stochastic model that implicitly accounts for 51'840 climate years, this paper identifies multi-year storage of liquid hydrocarbons as a key option for managing climate uncertainty and ensuring energy security. In Europe, multi-year storage reduces system costs by 4.1%, fossil imports by 86%, and curtailment by 60%. The benefit of multi-year storage is that a renewable surplus in one year is not curtailed but converted to synthetic oil, with hydrogen as an intermediate product, and stored to balance a future deficit. We find that the required energy capacity for liquid hydrocarbons is 525 TWh, a quarter of the European Union's current oil and gas reserves, complemented by 116 TWh for hydrogen storage. Security of supply remains high and unserved energy only amounts to 0.0035 per thousand, well below the common target of 0.02 per thousand.

Figures (23)

• Figure 1: Overview of security options that can manage mismatches of supply and demand lasting longer than multiple days. Incoming arrows to the middle circle indicate additional supply; outgoing edges indicate additional demand. Consequently, storages have two-sided edges. Other edges represent independence between options.
• Figure 2: The bar charts show how multi-year storage reduces system costs in the reference case. The left chart breaks down the system costs without multi-year storage. The chart on the right shows how costs change if multi-year storage is an option.
• Figure 3: Cost reductions from multi-year storage depend on the flexibility of imports. The bar charts in the top row show the composition of system costs without multi-year storage for different sensitivities; the bottom row how costs change with multi-year storage.
• Figure 4: The graphs show the levels of long-term storage with multi-year storage in the left column and without multi-year storage in the right column. The violin plot for multi-year storage shows how levels vary from year to year. The storage levels were simulated 200 times for 100 years to generate the distributions. Each year in the simulation performs a probability weighted random walk through the set of representative months shown in Fig. \ref{['fig:clusterResult']} of the method section. The displayed values on the y-axis give the total energy capacity. Since the plot aggregates across regions, aggregated levels only ever reach the total energy capacity if all regions reach their maximum level simultaneously.
• Figure 5: The diagram shows how yearly energy flows in TWh change with multi-year storage. The bold nodes represent energy carriers, and the other nodes represent technologies. Technologies with increasing generation or decreasing demand enters carrier nodes from the left; vice versa, decreasing generation, or increasing demand exit on the right. All values are expected values across the 51'840 considered climate years. For clarity, the figure aggregates and simplifies the actual flows in the underlying model. For a detailed model description, see the method section. Furthermore, the appendix provides more detailed Sankey diagrams with absolute values.