Primary Control Reserve

AC networks in Europe have a target frequency of 50 Hz. The responsible transmission system operators (TSOs) must guarantee this normal frequency at all times within a narrow bandwidth. Frequency stability is ensured by balancing power generation and consumption. If there are deviations between generation and consumption, a frequency drift occurs and the grid frequency changes. The provision of Primary Control Reserve (PCR) stops this frequency drift and thus stabilizes the grid frequency. The PCR must be fully activatable within 30 seconds and available for at least 15 minutes. In Germany, there are four transmission system operators, each of which ensures a balance between electricity feed-in and withdrawal and the provision of balancing energy in their grid areas and cooperates in the grid control network. The costs for this are refinanced via the network charges. This network has been expanded to include Denmark, Belgium, the Netherlands, Switzerland, France and Austria. As a result of the liberalization of the electricity markets, the four transmission system operators in Germany, which are responsible for grid frequency maintenance and the supply of balancing power, publicly tender the required balancing power on the balancing power market via an Internet platform. For a harmonized European balancing energy market, there has also been a balancing work market in addition to the balancing power market since November 2020. Here, the required quantities of control energy are tendered and remunerated independently of the control energy market.

Benefits:

• Additional revenue stream
• Security of supply

How Primary Control Reserve (PCR) works

The activation of the primary reserve depends on the frequency. The provider of primary reserve independently measures the grid frequency at the point of generation or consumption and responds immediately to the change in the grid frequency. The increase or reduction of the mains power must be proportional to the mains frequency as soon as it falls below or exceeds the range between 49.99 Hertz and 50.01 Hertz. Here, the primary reserve must be fully available within 30 seconds and maintained for up to 15 minutes. In addition, the primary control reserve must be provided symmetrically. Besides large power plants, battery storage systems can also provide PCR.

Activation of control reserve

Secondary Control Reserve

Related to PCR the term Secondary Control Reserve (SCR) is also often used. Transmission system operators use SCR to regulate the frequency back to 50 Hz in the event of deviations. SCR is subordinate to the primary control reserve (PCR) and succeeds it. Primary control power initially stabilizes the grid frequency to a frequency that deviates from the nominal frequency. The secondary control reserve then ensures that the frequency returns to the nominal frequency. The secondary control power must be fully available within 5 minutes for 15 minutes. As a positive SCR, it can supply additional power to the power grid in the event of undersupply, or as a negative SCR, it can draw power from the power grid in the event of oversupply.

Benefits:

• Additional revenue stream
• Security of supply