Procurement of control power and energy in Germany
1. Control power market in Germany
The German transmission system operators (TSOs) are required to maintain a permanent balance between power generation and demand in their control area, and provide balancing energy to the balancing groups (electricity producers and consumers) from the secondary control power and minutes reserve kept available. The close cooperation among the German TSOs enables the overall amount of control power required to be minimized.
Since 2001, the German TSOs have procured their primary control, secondary control and minutes reserve in an open, transparent and non-discriminatory control power market in accordance with the provisions of the Federal Cartel Office. The total control power demand of all German TSOs amounts to approximately 7,400 MW. Primary control and secondary control power are procured in a monthly cycle; minutes reserve is daily called for tender. For tenders, the shared IT-platform www.regelleistung.net has been installed by the German TSOs. They have developed market-based solutions which also meet the requirements of a secure and stable system operation.
Procurement is ensured through competitive bidding on a tender basis in the German control power market where a large number of suppliers (generators as well as consumers) participate, especially for minutes reserve. Via pooling also small suppliers can participate in the call for tenders. Almost 90 percent of all generating plants capable of providing control energy are qualified for participation at the TSOs. Since 2004, suppliers from the Austrian control areas of TIWAG Netz and VKW have also participated in the German market for minutes reserve.
For the information of market participants, the results of the call for tender (e.g. volumes and prices) are published on the web sites.
2. Tariff system for the settlement of imbalances
The tariff system for the settlement of imbalances of a balancing responsible party is a single price system showing the following characteristics:
- prices for balancing group deviations are calculated on a 15 min basis;
- they are determined on the basis of the TSO’s payments for or revenues from the secondary control and minutes reserve energy used;
- single price per 15 min, i.e. no price spread between positive and negative balancing group deviations;
- balance responsible parties showing a surplus get paid the price for balancing group deviations;
- balance responsible parties showing a deficit have to pay the price for balancing group deviations;
- prices for balancing group deviations are published on the TSOs’ websites accessible to all market participants;
- costs for the provision of primary and secondary control power and minutes reserve (power prices) are part of the network tariffs.
3. Technical aspects
The permanent balance between generation and consumption of electricity is an important prerequisite for stable and reliable system operation. In order to guarantee to consumers a sufficiently reliable electricity supply, TSOs keep control power available.
A demand for control energy arises if the sum of actual generation differs from the actual load. Differences can arise from the load side (e.g. meteorological influences, daily load forecast error) as well as from the generation side (e.g. power station failures).
According to the requirements of the European interconnected power system of UCTE (Union for the Co-ordination of Transmission of Electricity) the German TSOs procure the following types of control power:
a) primary control:
- provided in a way of solidarity by all synchronously connected TSOs inside the UCTE area
- to be activated within 30 sec
- time period per single incident 0 < t < 15 min
b) secondary control:
- direct and automatic activation by the affected TSO
- to be activated within 5 min
- time period per single incident 30 s < t < 15 min
c) minutes reserve (tertiary control):
- telephonic and schedule-based request of the affected TSO at the respective suppliers
- time period per single incident t < 15 min up to 4 quarter hours or up to several hours in the event of several disturbances
- manually activated according to the 15 min schedule time frame or rather within 15 min.
The time frame of control energy usage is shown hereafter:
The chart above shows that according to the German market rules, TSOs are responsible for the provision of reserves only within the first 4 quarter hours after occurrence of a power imbalance, e.g. after a power station failure. To this end, the primary control power of all TSOs automatically stabilizes the system frequency according to the impact on the power balance within the UCTE. The TSO concerned commits the products of primary control, secondary control and minutes reserve with a relevant graduation in time. At the beginning of the 5th quarter hour (i.e. after 60 minutes, at the latest) after the occurrence of a power imbalance, the balance responsible party concerned must take care of the compensation.
4. Necessary volume of primary control, secondary control and minutes reserve
According to the UCTE rules, the German TSOs participate in the provision of primary control power that is required within the entire synchronous area of the UCTE.
Each TSO is responsible for the provision of secondary control and minutes reserve power in its own control area. By means of a mathematical approach, the German TSOs determine the necessary volume of secondary control and minutes reserve power for their control areas in such a way that the defined residual risk probability of a power surplus or deficit that cannot be balanced is not exceeded. This scientific approach was developed in cooperation with the University of Aachen to determine the necessary volume of secondary control power and minutes reserve on the basis of a probabilistic calculation.