RWE plans to offer a system-stabilising secondary reserve, also known as automatic frequency restoration reserve, for the German power grid via its offshore wind farm, Amrumbank West. The transmission system operator TenneT recently granted the necessary pre-qualification for a capacity of 60 megawatts (MW).
The secondary reserve complements the primary and minute reserves to maintain the grid frequency at a stable 50 Hertz, preventing potential grid failures. To participate in the secondary reserve auctions, a participant's bid power - in this case, the 60 MW reduction in wind farm capacity - must be able to be fully activated within five minutes.
Starting in the first quarter of 2025, RWE will market this secondary reserve through daily balancing energy auctions. From then on, the offshore wind farm off the German North Sea coast will not only supply green electricity but will also actively contribute to the stability of the German power grid. Located approximately 37 kilometres west of the North Frisian island of Amrum, the Amrumbank West wind farm has 80 turbines with a total capacity of 302 MW.
RWE has many years of experience in marketing and providing balancing reserve for grid stabilisation from various types of assets (e.g. by means of pumped storage, gas-fired power plants and, more recently, batteries). With the provision of balancing reserve from wind, the company is now entering a new area. Market participants are remunerated by the transmission system operator for the provision of secondary reserve as well as for the actual supply.
Aside from Amrumbank West, RWE Supply & Trading plans to qualify additional RWE wind and solar farms for the automatic frequency restoration reserve and will also provide this service for external clients, as the marketing of balancing power opens up additional sources of income for renewable energy plant operators.
Transmission system operators embrace balancing reserve from wind farms
Transmission system operators have extended their requirements and included additional conditions for wind assets to enable them to participate in the secondary reserve. After all, a wind farm must be able to follow the grid operator’s target values precisely, even if the wind speed changes. In practice, this means that the offshore wind farm Amrumbank West must be able to reduce its output within seconds; this is done by changing the position of the rotor blades and thus turning them out of the wind with pinpoint accuracy. This requires appropriate processes and suitable technology for the wind farm control systems that can respond ad hoc to short-term wind fluctuations and at the same time take current wind forecasts into account. For this reason, RWE has developed a highly automated and scalable infrastructure for balancing power from wind; this includes the control system of the partner Generac Energy Services
The role of balancing power
Electricity production and consumption must always remain balanced to ensure the target grid frequency of 50 Hertz. When frequency fluctuations occur anywhere in the grid area, the respective transmission system operator calls in balancing power to counteract and then correct the imbalance. The capacity required for this is auctioned daily by the transmission system operator.