Control energy: How does the market work and which power plants does Vattenfall use?
The electricity grid must be kept stable at a grid frequency of 50 Hertz at all times. The transmission system operators ensure that this stability is maintained despite fluctuations in electricity generation and consumption. When you consider how many fluctuations the grid is constantly exposed to, it seems like a masterstroke.
When stabilising the electricity grid, the transmission system operators (TSOs) can rely on the expertise of the balancing group managers, who balance their virtual energy accounts, the balancing groups, in the best possible way. They also compensate for unforeseeable deviations by calling up balancing energy in a matter of seconds.
The TSOs utilise the so-called balancing energy market in Germany for this purpose. This is an essential component of electricity grid operation. The TSOs can procure the necessary capacities via this market so that sufficient energy is available to adjust generation and consumption at very short notice.
Primary, secondary and tertiary control power
The primary control power (PRL) - or frequency containment reserve (FCR) - must be fully available within just 30 seconds of being requested. This power is activated automatically based on the grid frequency. A large proportion of the FCR required in Germany is already provided symmetrically by battery energy storage systems (BESS).
The grid is then stabilised by the secondary control reserve (SRL) - automatic Frequency Restoration Reserve (aFRR). This control power must react after 30 seconds and be fully activated within five minutes. When electricity is fed into the grid, this is referred to as positive control power; when electricity is withdrawn, it is referred to as negative control power. The secondary control power is asymmetrical. This means that either only positive or negative balancing capacity or both directions can be offered simultaneously with the same or different bid levels.
If the provision of secondary control power is still not sufficient to stabilise the grid, it is replaced by tertiary control power, also known as minute reserve power (MRL). This is known as manual Frequency Restoration Reserve (mFRR). Here, the TSO activates the power via the merit order list server (MOLS) communication procedure and the power must be fully activated within 12.5 minutes. This capacity is also asymmetrical, meaning that the same bidding rules apply for suppliers as for the secondary reserve.
Time sequence of balancing energy marketing
Trading on the balancing energy and balancing power market
The marketing of balancing energy has changed significantly over the past few years. In particular, the tradable products have been further developed, especially with the introduction of the balancing energy market (RAM). Here, the procurement of balancing capacity on the balancing capacity market (RLM) and balancing energy on the balancing energy market have been separated.
Calendar day tenders take place on the balancing market. Here, the transmission system operators procure the balancing capacity in three successive auctions on the previous day (D-1) for primary control reserve (FCR), secondary control reserve (aFRR) and tertiary control or minute reserve (mFRR). These tenders ensure that sufficient capacity is available for control energy.
In addition, there are quarter-hourly labour price tenders in which the labour prices (energy prices) can be corrected until shortly before delivery.
Spotlight: Which plants does Vattenfall use to provide control energy?
The demand for secondary reserve is determined every four seconds (‘control cycle’) and called up continuously - suppliers must then provide the required power within five minutes. In Germany, a large proportion is provided by pumped storage power plants, as these are particularly well suited to the rapid response and high requirements.
As a pre-qualified power plant operator, Vattenfall has been making some of its power plant capacities available to stabilise the grid since market liberalisation. In the past, conventional plants were also used for this purpose; today, seven pumped storage power plants (PSP) in particular are actively involved in the control reserve.
Vattenfall's aggregated pumped storage capacity of almost 2,700 megawatts in Germany is already making an important contribution to grid stability. In addition, thanks to its black start capability - the ability to start up independently without external voltage - it could also make it possible to restore the energy supply in the German extra-high voltage grid in the event of a large-scale grid failure (blackout).
Conclusion
Our hydropower plants make a key contribution to grid security. At the same time, we are working hard to open up this possibility for other plants. For this reason, more of our plants are already being prequalified for the provision of balancing energy in the short to medium term. Large batteries and offshore wind farms (OPWs) are available for this purpose.
Do you have questions about the balancing energy market? Please feel free to contact us!
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