Even when the total electricity supply and demand across Germany is balanced, there can still be bottlenecks at specific points in the grid. This is where Redispatch comes into play.
The Bottleneck Problem
Grid congestion occurs when a particular power line or substation does not have enough capacity to carry all the electricity trying to flow through it at that moment. Common causes include:
- Geographic imbalance: Large amounts of wind power generated in northern Germany cannot all be transported south because the transmission lines lack sufficient capacity.
- Unexpected outages: A critical transmission line or substation going offline for maintenance or due to a fault narrows the available capacity.
- High local demand: A sudden surge in electricity use in one specific city or region.
Redispatch: Rerouting the Flow
When grid congestion occurs, TSOs and DSOs must intervene to prevent instability. This intervention is called Redispatch — essentially a directive to change the planned power output of a generation plant or storage system to relieve the bottleneck.
The process works as follows:
- Identify congestion: Grid operators forecast potential bottlenecks based on planned generation and consumption schedules.
- Issue instructions: If a bottleneck is predicted or occurs, the grid operator instructs specific power plants or BESS units to either reduce their output (curtailment) if they are contributing to congestion, or increase their output if they can help meet local demand or push power in from a less congested area.
- Compensation: Operators of affected plants are compensated for the changes to their schedules, so they are not financially disadvantaged by helping the grid.
Redispatch 2.0: Modernising Grid Management
Germany introduced Redispatch 2.0 on 1 October 2021. This was a major update to how congestion management is handled.
- Broader scope: Before this update, Redispatch mostly involved large conventional power plants. Redispatch 2.0 significantly expanded participation to include more renewable energy plants and BESS units larger than 100 kW.
- Better data exchange: It improved data exchange between grid operators and plant operators, making the process more automated and efficient.
- Curtailment priority for BESS: While Redispatch 2.0 aims for better integration of all assets, it is important to understand that renewable energy sources generally have feed-in priority in Germany.
BESS assets can be — and frequently are — subject to curtailment under Redispatch measures before renewable generators. BESS are treated as flexible assets that can be adjusted to manage grid constraints, and they are compensated for these adjustments. This is a real operational consideration for any BESS asset owner.
