With the transformation of the German energy system, the physical basis of grid stability is fundamentally changing. Previously, such system services, which serve to stabilize frequencies, were provided as a by-product of large thermal power plants. In the future, inverter-based generation units, renewable energy systems and battery storage systems will also take on this task.
System services can generally be divided into frequency or voltage-stabilizing measures. The current reserve is one of the frequency-stabilizing services and aims to limit the rate of change in the network frequency. It thus ensures that frequency deviations in the AC grid are slower and more controlled — a decisive contribution to system security in an increasingly renewable energy system.
On April 22, 2025, the Federal Network Agency (BNetzA) defined the final procurement concept to ensure security of supply in an energy system with low mass inertia through rotating generators. Following the expiry of the nine-month implementation period, it has now been possible to procure current reserves on a market-based basis since January 22, 2026. Particularly exciting: For the first time, inverter-based systems such as battery storage systems can also participate in this market. This creates a new framework for ensuring frequency maintenance in the renewable energy system.
The instantaneous reserve is understood to mean the immediate response to an imbalance of active power. Its primary purpose is to limit the frequency gradient and thus prevent the violation of critical frequency maintenance limits before downstream control services take effect. Until now, the current reserve has been provided as a by-product of large thermal power plants. Their rotating generators provided the necessary physical inertia to generate electrical energy. The phase-out of coal and the changing operation of gas-fired power plants are creating a supply gap that will have to be filled in the future by new market players and innovative technological solutions.
The current reserve is purchased using a fixed price system, whose level of remuneration is largely determined by the procurement region and availability in the billing period. The market design distinguishes between four product categories, which consist of the direction of action (positive/negative) and the degree of availability (basic/premium):
• Basic product: Requires a minimum availability of 30% over the billing period
• Premium product: Requires an availability of at least 90%
In the first preview period 2026/2027, the procurement region corresponds to the existing control areas of German transmission system operators. In the future, however, it is planned to dynamically adjust the layout of the regions to the dependence of residual requirements.
Current reserves are paid exclusively on the basis of the availability provided, not on the actual use in network operation. Prequalified investments are contracted at fixed administratively fixed prices, which remain unchanged over the entire contract period of two to ten years. Tenders can be submitted continuously, as there are no traditional tendering deadlines.
Large-scale battery storage systems act as an ideal addition to fill the system-critical gap of outgoing large thermal power plants. Thanks to their ability to absorb and deliver energy without delay, they can react immediately to grid fluctuations and precisely provide the necessary synthetic mass inertia through short-term active power adjustments.
As part of the last publish Draft network development plan The role of large battery storage systems for security of supply is emphasized. Battery storage systems are highlighted as an important component for cost-effective and resilient system management. In addition to clarifying technical requirements, the introduction of transparent market mechanisms for system services such as instant reserves is an important step towards integrating battery storage as an active part of supply security.
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