Black-start capability refers to the ability of a power generation facility to restart on its own, without any external power supply, following a complete power outage. It is one of the key prerequisites for restoring the power grid after a major outage and is becoming increasingly important with the growing role of battery storage systems is increasingly coming into focus.
How does the power grid recover after a blackout?
A power plant is considered capable of black start if, after being completely shut down, it can restart on its own without any external power supply and generate the necessary voltage and frequency itself. The energy generated in this process is then used to gradually bring online other generation units that are not capable of black start.
The Process of Restoring the Network
Following a major outage, the transmission system operators assume responsibility for coordinating what is known as grid restoration. This is carried out in close coordination with the distribution system operators based on predefined grid restoration plans:
- Systems capable of black start initially bring a small, stable sub-grid (island grid) online
- This subnetwork is being expanded in stages
- Additional power plants and consumers will be gradually synchronized and brought online
Black Start Capability in Germany Today
According to regulatory monitoring under Section 35 of the Energy Industry Act (EnWG), there are currently 174 plants in Germany capable of black start with a rated capacity of at least 10 MW, primarily hydroelectric and gas-fired power plants. However, only 26 of these plants actually have a contractual agreement with the transmission system operators for system-wide grid restoration.
Legal Framework and Market-Based Procurement
Since January 2024, transmission system operators have been required under Section 12h of the Energy Industry Act (EnWG) to issue calls for bids for black-start capability as a non-frequency-related system service in a technology-neutral and market-based manner. This means that, in principle, battery storage systems can also participate as providers on an equal footing with traditional power plants.
Battery storage systems capable of black start
To be capable of black start, a battery storage system requires grid-forming inverters that can independently set voltage and frequency, as well as a properly designed energy management system. Compared to conventional power plants, battery storage systems offer several technical advantages:
- significantly faster availability, often within seconds rather than minutes or hours
- More precise control of frequency and voltage through power electronics
- Zero-emission startup without diesel generators or gas turbines
- Decentralized deployment at strategically important network nodes
Why Is Black Start Capability Important for Companies?
For operators of battery storage systems, market-based procurement opens up another potential application option, provided the system is designed with grid-forming technology as early as the planning phase—retrofitting is generally much more costly.
Distinction from related terms
Not to be confused with:
- (Market-based procurement of instantaneous reserve): This is also a market-based, non-frequency-related system service, but it pertains to ongoing grid stabilization rather than restoration following a total outage.
- Redispatch 2.0: A measure to prevent grid congestion during normal operation, not for restoring power after a blackout
- Energy Management Systems (EMS): a technical prerequisite for implementing black start capability in battery storage systems from a control engineering perspective
Summary
Black-start capability is a key feature for restoring the power grid after a major outage. With grid-forming inverters and a suitable energy management system, battery storage systems can also perform this task—often faster, more precisely, and with zero emissions compared to conventional power plants.
