ANCILLARY SERVICES
Non-frequency-related ancillary services
BACKGROUND AND PROCUREMENT
Inertia
Frequency deviations can occur in the event of imbalances between the electrical energy supplied and that consumed in a given area. These deviations can occur almost immediately and, depending on the cause, at different locations, for example in the event of a system split. With such rapid changes, inertia is required to immediately and effectively cushion rapidly occurring power imbalances until the primary control system stabilises the grid frequency and secondary control restores it to 50 Hz.
At present, the available inertia is mainly determined by the number and size of the available synchronous generators. In the course of the energy transition, however, these capacities will decrease and power generation based on renewables and battery systems will increase. These latter resources will increasingly have to provide the ability to provide inertia electronically in order to meet demand.
With determination BK6-23-010, the Federal Network Agency has published a procurement framework requiring the German transmission system operators to procure inertia (Momentanreserve) on a market-based framework from 22 January 2026 onwards. In addition, VDE FNN has issued technical specifications defining the system-related control requirements for the provision of inertia and setting out the corresponding technical criteria for the product.
TransnetBW has implemented the legal and regulatory requirements and, since 22 January 2026, has been contracting inertia in accordance with the established procurement framework. TransnetBW procures all defined products, with the control area serving as the designated procurement region. The required volumes amount to 19.8 GWs of positive inertia and 14.6 GWs of negative inertia. The model contract, current price sheet, and further information and documentation are available on www.netztransparenz.de under the following link:
Interested providers may contact momentanreserve@transnetbw.de for further information.
BACKGROUND AND PROCUREMENT
Black start capability
As the transmission system operator responsible for the control area, TransnetBW maintains restoration and recovery plans to restart parts of the power grid in case of a blackout. These plans describe how the transmission system can be gradually restored to power after a large-scale power outage. This requires power generators that can generate power without an external supply of power and thereby restore power to sub-grids.
With resolutions BK6-21-023 and BK6-18-249, the Federal Network Agency specified framework conditions for the transmission system operators' procurement procedures for contracting these black start system services.
Tender
TransnetBW is currently planning two tenders with the aim of contractually securing the necessary black start capability in future: A first tender is planned in January 2024 for the TransnetBW West region, another tender at the beginning of 2026 for the TransnetBW East region.
Information on tender participation can be found here:
An overview of the tenders planned throughout Germany and further information can be found under "Marktgestützte Beschaffung Schwarzstartfähigkeit" at netztransparenz.de.
BACKGROUND AND PROCUREMENT
Reactive power
In order to ensure the undisturbed flow of electricity in the grid, TransnetBW must ensure a constant voltage in its network. This requires, among other things, the use of reactive power. This reactive power is provided by network components such as coils (inductors) and capacitor banks (further information about reactive power in general and TransnetBW activities in particular is portrayed (only in German) here: STATCOM-Anlagen - Innovation - Porträt - Unternehmen - TransnetBW), and from third-party systems such as power plant generators, power converters or battery storage systems.
The Federal Network Agency has defined a procurement concept under number BK6-23-072, which describes the specifications and technical requirements for the future market procurement of reactive power (Federal Network Agency - Determination of Procurement of Reactive Power, in German). TransnetBW will initiate a first procurement round for one initial procurement region by June 25, 2025 at the latest.
TransnetBW considers the following procurement regions for the procurement of reactive power (outlined in colour):
According to the Federal Network Agency procurement concept, only offers of reactive power that go beyond the level required by the TAR/TAB valid at the time of publication can be considered for the market-based procurement.
Exact information on the required products, the participation requirements, the required delivery periods and further details will be published by TransnetBW and made accessible via this page. This further information and information on offer submission will be made available by June 25, 2025 at the latest, analogous to the procedure for procuring black start capability (see above).