Between 2022 and 2025, the renewable energy surplus in the German grid has increased fifteenfold.
Residual load analysis reveals what is behind this: The remaining demand after deducting renewable feed-in is increasingly dominated by short-term fluctuations. Each shift between surplus and deficit marks an independent event — and thus a flexibility requirement.
The Driver: Solar and Wind Dominate the Power Mix
The share of solar and wind in the power mix has risen sharply. This increasingly leads to situations where renewable generation exceeds demand.
Short Surplus Phases — The Sweet Spot for Battery Storage
What matters is the duration of these phases. The majority of surplus events last less than 10 hours. These are short-term, recurring patterns within a single day, often driven by solar feed-in.
Battery storage systems are technically and economically designed precisely for these timeframes — they can absorb surpluses and feed them back in just a few hours later when demand exceeds generation.
Longer Deficit Phases Require Different Solutions
In contrast, phases with positive residual load tell a different story. Only a small proportion lasts less than 10 hours. Longer periods with low renewable feed-in — such as calm winter periods with little wind — dominate here and require other forms of flexibility, particularly dispatchable capacity and cross-sector solutions.
Conclusion: Flexibility Becomes the Central Bottleneck
The central bottleneck in the power system is shifting from installed capacity to spatial and temporal flexibility. Short-term imbalances are occurring more frequently and systematically changing price formation — this is precisely the economic sweet spot for battery storage.
At the same time, longer phases with positive residual load remain structurally persistent, making clear: A fully renewable system requires additional flexibility options beyond battery storage.
➡️ For investors and project developers, this means: Market conditions for battery storage are structurally improving. Those who invest in short-term flexibility today are positioning themselves at the core of the future power system.
