Control energy


Control energy is understood to mean electrical energy or power, which is needed in a control area to compensate for unforeseen fluctuations in supply and demand, which could otherwise jeopardize the stability of the electricity grid.
In order to permanently stabilize the power grid, the German transmission system operators (TSOs) have the responsibility to keep the frequency of the German power grid constant at 50 Hz. The TÖNBs monitor and operate the high-voltage and high-voltage lines for transporting electricity over long distances.

If fluctuations have to be compensated for, electricity can be fed into the grid as well as withdrawn from the grid through the use of control energy. More power supply, to compensate for an excessively low network frequency, is called positive control energy referred to. With Feed-in throttling To reduce the network frequency, it is negative control energy.

In order to keep the grid frequency stable at all times, there are 3 types of control energy, which can be used for various scenarios. These are shown in the following infographic.

If there is a fluctuation, the primary control system therefore takes effect first and balances the network frequency. This works automatically and without communication with power plant operators.
If the primary control power is not sufficient to compensate for the fluctuation, the secondary control is activated.
The minute reserve is effective for fluctuations in the network frequency that occur over somewhat longer periods of time.

How is control energy retrieved?

A provider of Primary control power must be guaranteed to be able to provide the agreed service within 30 seconds, for a maximum of 15 minutes from the start of the control process. Thanks to your fast response time and ability to provide positive and negative control power, a Large-scale battery storage particularly suitable for providing primary control power.

So what happens to the memory when the primary control power is called up?

When the grid frequency drops below 50 Hz, the memory feeds into the grid. Depending on the level of the variance, only a portion of the memory's power is used. As can be seen in the diagram below, when there is a deviation of 49.8 Hz, the full marketed performance of the memory is called up.
When the grid frequency is higher than 50 Hz, the large battery storage system absorbs power from the grid. Here, too, the power retrieved depends on the amount of fluctuation. From a deviation of 50.2 Hz, the memory stores at full power.

Who is allowed to participate in the control energy market?

In order to participate in the PRL market, the systems must be prequalified by the responsible transmission system operator. To do this, the system passes through certain load profiles to ensure that it meets the control energy requirements. For example, the system completes the so-called double hump curve and must feed into the network twice in a positive direction and twice in a negative direction (PQ drive) in order to complete the prequalification process vis-à-vis the TSO.

How big is the market for PRL?

The call for tenders for primary control power runs over 4 hours. For these four-hour periods, 1450 MW of primary control power for the ENTSO-E network (Association of European Transmission System Operators) will be tendered. Within Germany, it is 650 MW.
450 MW battery storage systems are currently prequalified for primary control power in Germany. As a result of the further expansion of large battery storage systems, they will dominate the control energy market in the future. In addition to control energy, large battery storage systems can also be used for a whole range of other applications. As part of a well-coordinated multi-use strategy, large battery storage systems can optimally develop their full potential.

How is the price for balancing energy set?

The PRL prices are calculated using the merit order process. Merit order describes the order in which electricity-producing power plants are used on the electricity trading venue. In the merit order, power plants are arranged according to their marginal costs/opportunity costs. The marginal costs describe the variable costs of an additional unit produced and are therefore independent of the fixed costs of a power generation technology. In conventional power plants, these are exactly the costs of the energy source used. Opportunity costs are the revenue that could be generated from the investment in other electricity markets.
Power plants with higher marginal costs will be awarded the contract until demand of the current 1450 MW is met. The most expensive power plant called up then determines the market price for all control energy. This motivates operators to build plants with the lowest possible marginal costs in order to obtain a larger margin.

What are the marginal costs of storage power plants (e.g. large battery storage)?

Storage power plants have the lowest marginal prices of all market participants, which is why the marginal costs/opportunity costs of storage power plants will form the market in the future. Severe price fluctuations offer flexible systems (especially storage power plants) alternative revenue paths and thus raise opportunity costs in PRL.

What effect does the coal and nuclear phase-out and the energy revolution have on balancing energy?

The phase-out of nuclear energy (2022) and coal (by 2038 at the latest) is shortening the supply of prequalified power. At the same time, this increases opportunity costs in the electricity market for remaining capacity, as these power plants in reserve are technically and legally unable to provide balancing power.
Both have a positive effect on the development of contribution margins under primary legislation.