Germany’s four transmission system operators (TSOs) have begun procuring inertia services to help stabilise the electric grid as shares of renewable energy grow.
The TSOs, 50Hertz, Amprion, Tennet and Transnet BW, will pay market participants for inertia services under a fixed-price model based on megawatts (MW) registered, with the first period running from the day it launched, 22 January 2026, to 21 January 2028.
The new non-frequency ancillary services, called Momentanreserve (‘Instantaneous Reserve’), are expected to present an opportunity for inverter-based resources, particularly grid-forming battery energy storage systems (BESS), to provide grid inertia.
Grid-forming BESS, along with other technologies such as flywheels and synchronous condensers, could replace the role traditionally played by the large rotating mass of thermal generators in maintaining the grid’s operating frequency within a 0.2Hz deviation from 50Hz.
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As has been extensively covered by Energy-Storage.news, while wind and solar PV can replace thermal generation on the grid with the help of energy storage and other flexibility and capacity resources, variable renewable energy (VRE) still leaves a gap in the provision of system stability services that grid-forming assets can deliver instead.
While other ancillary services, most prominently frequency regulation or frequency response, deliver power to the grid or absorb it to offer correction when supply and demand imbalances occur, inertia is therefore more about maintaining frequency.
This is being addressed in parts of the world with higher shares of renewable energy, such as the UK and Australia, which are respectively creating market mechanisms and mandatory requirements for inertia (and, in some cases, other system stability services, such as Short-Circuit Level).
The launch in Germany comes after the Federal Network Agency (Bundesnetzagentur, or BNetzA) initiated a determination procedure on the procurement of Momentanreserve in September 2023 and then made a final determination on the procurement concept in April last year.
The country’s first large-scale grid-forming BESS went into commercial operation in October.
The new procurement seeks both positive and negative products, and a premium and basic product. Basic products require 30% availability and premium products 90%. Prices range from €888.5/MWs (US$1055.25/MWs) for the top-tier premium product down to €76/MWs for the lowest Basic contract.
As noted last week by optimiser and flexibility provider Entrix on its corporate blog, eligible battery storage projects can qualify for a combination of one positive and one negative product for two to ten years of delivery.
While it opens a new, steady revenue stream for BESS assets, Entrix said that the current prices mean it will not be a main driver of returns but could provide a “stable upside alongside existing revenues.” BESS operators should also choose whether to go for longer contracts that lock in fixed prices for up to ten years or choose shorter contracts.
According to regulator BNetzA’s 2025 System Stability Report, instantaneous reserve requirements in the four TSO service areas for the target year 2030, excluding the 1% of most critical hours, are as follows:
| TSO | Positive requirement | Negative requirement |
| Tennet | 140GW | 259.9GW |
| 50Hertz | 100.4GW | 231.6GW |
| Amprion | 53.8GW | 55.8GW |
| Transnet BW | 19.8GW | 14.6GW |
According to a communication from the official information service of the four TSOs, Netztransparenz, contracted instantaneous reserve figures in megawatts will be published once a year, beginning in Q1 2027.
The prices are as follows, with the higher +1 numbers representing 100% Momentanreserve availability guarantees:
| Product | Direction | Fixed price component | Height [€/MWs/a] |
| Premium | Positive | FP0 | 805 |
| FP0 + FP1 | 888.5 | ||
| Negative | FP0 | 805 | |
| FP0 + FP1 | 888.5 | ||
| Basic | Positive | FB0 | 76 |
| FB0 + FB1 | 109.5 | ||
| Negative | FB0 | 76 | |
| FB0 + FB1 | 109.5 |
In a post to LinkedIn, Carmen Kompatscher, strategy & sales operation manager for Germany at BESS technology provider Fluence noted that while Germany becomes the second country to remunerate inertia provision with contracted revenues after the UK, there are some key differences in the requirements, technical validation and market demands.
Kompatscher also wrote that, to effectively participate, systems must be properly sized to understand which component has the least overload capability and how long it can be held up to the maximum inertia constant of 12.5 seconds.
According to Kompatscher, at the current prices, only the premium product provides a revenue uplift for BESS assets and the >90% availability requirement will be checked retrospectively.
“This is checked retroactively – regardless of if there was a Rate of Change of Frequency (RoCoF) event or not. If you fall below 90%, you lose the full year’s remuneration. So, not much room to play around with contracted capacity,” Kompatscher wrote.
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