Managing the Mismatch: The Role of Flexibility on the Path to a Carbon-Neutral Energy System

TL;DR

This study quantifies the importance of system flexibility in integrating renewable energy into Germany's energy system, showing how different flexibility technologies impact costs, imports, and system stability towards climate neutrality.

Contribution

It introduces a correlation-based flexibility metric applied to a high-resolution model, providing new insights into technology-specific flexibility contributions and cost implications.

Findings

Daily flexibility needs increase 3.7 times from 2025 to 2045.

Stationary batteries provide 38% of flexibility by 2045.

Higher flexibility reduces system costs, prices, and import dependence.

Abstract

A rapid expansion of system flexibility is essential to integrate increasing shares of renewable energy into future energy systems. However, flexibility needs and technology-specific contributions to flexibility remain poorly quantified in energy system modelling. Existing methods are not widely applied, leaving key questions unanswered: which flexibility technologies are critical for climate neutrality, and what are the cost implications of alternative deployment strategies? To address this gap, we apply a correlation-based flexibility metric to a high-resolution, sector-coupled model of the German energy system, covering its transformation towards climate neutrality. For our default scenario, we find that daily flexibility needs increase by a factor of 3.7 between 2025 and 2045, driven primarily by the expansion of solar PV. By 2045, stationary batteries provide 38% of daily flexibility, while flexible electric vehicle charging contributes 30%. Systems with constrained flexibility increase system costs by 6.9%, electricity prices by 14 EUR/MWh and trigger 47% higher hydrogen and e-fuel imports compared to an unconstrained system in 2045. In contrast, scenarios with high shares of flexible electric vehicle charging, vehicle-to-grid, and industrial demand-side management achieve system cost reductions of 3.3%, while also reducing import dependence. Higher flexibility also reduces electricity price ranges, decreases average electricity prices by 3 EUR/MWh, and reduces backup capacity by 22% (22 GW). Overall, our results highlight the decisive role of specific flexibility technologies in achieving cost-efficient and energy-secure climate-neutral energy systems, providing quantitative guidance for policy and investment decisions.