Operating reserve

The control power, also known as standby power or imprecise as balancing power, ensures the supply of electricity customers with exactly the electrical power required for unforeseen events in the power grid. These short-term performance adjustments during regular -fired power plants can be performed quickly incipient power plants started or pumped storage power plants are used (eg gas turbine power plants). Alternatively, certain current customers can be separated with load control in the short term from the mains.

Control power is part of the compensation required under the provision of energy to cover losses and to compensate for differences between input and off (§ 3 of the Energy Act ). Frequently, the term control energy is also used for energy, the shopping, the transmission system operators for the provision of ancillary services. In this sense, then balancing energy is a part of the system services that provide the transmission system operator, the underlying network operators.

Moreover, disconnect from the mains power plants or assign target values ​​of the transmission system operator in special operating conditions to maintain system security, automatically or by switching instruction loads. This allows the supply network stabilize and prevent that it comes in the extreme case of load shedding, thus causing a smaller regionally limited power outages or a territorially large power outage.

• 4.1 Germany
• 4.2 Switzerland and Austria

• 5.1 Procurement in the German system control network
• 5.2 Procurement in Austria
• 5.3 Procurement in Switzerland

Necessity of regulation

By means of power plant management is trying to keep gained in power plants performance and power draw including transport losses in the balance. If the expected power demand does not match the expected value, the deviation must be compensated. This follows from the physical need for electric power grids can not store energy and therefore at any time the power fed to the sum must correspond out of removed power and the power loss due to transport. Deviations from this result in AC systems in a change of the network frequency, which is available in the AC mains uniform (synchronous): With a glut of power, there is a deviation of the grid frequency above the nominal frequency at a lower offer to a so-called under-frequency.

The deviation may be caused by both the side of the providers and the beneficiaries. These performance differences between production and consumption can therefore lead to a positive or a negative deviation, which must be compensated by a corresponding power reserve. To regulate, among other things, the power demand of all consumers is predicted so that an appropriate range of services is available. Control power is then needed to compensate when the actual current power requirement is not of the expected services. Deviations from the actual services for forecasting occur, for example at power plant outages, non-compliance with reference profiles by large consumers, forecast errors in the output of wind turbines or photovoltaic systems as well as power supply failures ( loss of consumers) on. There is a power deficit, so additional power is required to bring the system frequency back to the nominal frequency, it is called a positive system performance. This additional power can be obtained by adding further production capacity and / or speed regulation of consumers. In the opposite case one speaks of a negative system performance that can be provided by speed regulation of generation capacity and / or additional power consumption. The larger a control area is, the smaller the relative demand for balancing energy, since the causes of the variations are mostly independent of each other and therefore partially compensate each other.

Fluctuations in the mains voltage and deviation from the nominal value of the mains voltage, however, are strongly influenced by the regional consumption and the offer and be compensated for example by technical equipment such as tap changers for power transformers, which are housed in substations, in certain areas. This ensures that the consumers connected to the network, an electrical voltage within a tolerance range around the nominal voltage can obtain the load flow is nearly independent.

Control Energy and Renewables

With increased use of wind energy theoretically increases the required control performance; it rises in particular the need for negative control power (absorbance of peak production ). Although renewable energy can provide control power potential, the current legislation is different: The Renewable Energy Act prohibits the technically obvious solution, at wind speeds over-production at the source, by shutting down the power output of the wind turbines, Crudely legislating away; Rather, the law requires that the entire wind power available is fed into the grid and paid. A speed regulation according to § 11 EEG is currently allowed only in case of power shortages.

In reality, however, has shown that the provided control power in recent years has remained the same or even decreased slightly. The actual need for more control energy is to quantify by superposition with the normal control energy supply difficulties precisely because the accuracy of the prediction systems has improved, inter alia, for the wind energy supply in recent years.

The photovoltaics with its power peak during the lunch time can have a dampening effect depending on solar irradiation on the demand for energy from medium-load and expensive peak load power plants and therefore secondary to the control performance, which is especially needed in the middle of the day. For the supply of photovoltaic also forecast programs are developed due to the increasing total installed capacity since 2010 /2011. In addition, the medium-voltage Directive has been amended and in July 2011 with the transition to the beginning of 2012 the policy for production systems in the low voltage network in order to make the potential of photovoltaic systems for grid control gradually usable.

A further problem arises in Germany from the strong construction of new generating facilities with power converters, especially of photovoltaic systems: In the past, solar inverters have been designed due to valid standards so that they are at a grid frequency of 50.2 Hz ( the upper limit of what can be covered by the primary control power ) automatically disconnect from the grid. These standards dated back to times when photovoltaic systems had only a marginal share of electricity generation. This leads today but to the fact that when it reaches the grid frequency of 50.2 Hz - abruptly separates much of the generated power from the grid - that can be achieved with a larger network fault entirely. At least for new plants that were built after April 1, 2011 and will, this problem could be solved: The manufacturer of solar inverters now have the cut-off equally distributed between 50.2 Hz and 51.5 Hz, adjust or implement a frequency-dependent active power reduction.

Technical structure of frequency control

The UCTE is responsible for coordinating the operation and expansion of the interconnected European grid. Members of this Union are transmission system operators ( TSOs) from 24 countries ( UCTE).

A safe and smooth network operation requires maintaining the balance between energy input and loss. A disturbance of this balance will inevitably draw grid frequency changes by itself. Since, given a tolerance range, constant power frequency is the basis of a secure energy supply, in case of failure, the use of coordinated mechanisms for frequency stability is required.

The objective of the frequency stability is divided into different stages of regulation:

• Primary control, the active power balance, primarily via the speed control to the electric generators of the power plants involved.
• Secondary control serves to maintain the frequency stability. In interconnected networks, such as the UTCE also for load flow control and load balancing
• Tertiary control, also referred to as minute reserve, economic optimization is used in operating
• Quartärregelung to compensate the transition error which is caused by accumulated deviations of the mains frequency for prolonged periods

Primary control

The primary control is used to compensate for imbalances between physical power supply and demand, with the aim of restoring a stable grid frequency. The available control power for the primary control is dependent on the size of the power network and the network topology. In the European grid system ( UCTE ) is about ± 3000 MW primary control capacity is needed. This held before the entire UCTE primary control power is allocated according to the net electricity in the different control zones, Germany accounts for this approximately ± 700 MW and Austria about ± 70 MW. In the European UCTE interconnected system frequency gradient of the control power is about 20 GW per Hz deviation of the grid frequency.

Each network operator within the interconnected system must provide within 30 seconds two percent of its current production as a primary control reserve. In this case, not every power plant involved in primary control (eg wind farms, photovoltaic systems, etc.). It does not matter what area of ​​the European power system, a variation occurs because the current grid frequency changes throughout the network area due to load fluctuations. This is compared to the proportional primary regulator of participating in primary control power plants with the desired frequency. If there is a difference, that primary control is activated in each of the participating power plant ( mostly all the power plants of over 100 MW ) according to the controller characteristic and the frequency as supported ( at sudden load increase ) or a further increase in frequency (with load decrease ) prevented.

Participating in the primary control power plants must be able to provide all of the primary control power at a quasi-stationary frequency deviation of ± 200 mHz within 30 seconds, ie increase the power output or decrease linearly and keep this performance up to 15 minutes. The available while standing primary control power, the so-called primary control band, should be identical to at least 2% of the rated power of the system. If the deviation is less than 10 mHz, takes place depends on the primary control provision used no activation of primary control.

Advantageous for the primary control is the frequency dependence of specific burdens. So is the case in an induction motor the relationship. While the engine so at a frequency increase in a higher power abfordert from the network, and this effect occurs with the opposite sign at lower frequency.

Secondary control

The secondary control has the task to restore the balance between the physical electricity supply and demand for the occurrence of a difference again. In contrast to the primary control only the situation in the respective control area including the electricity exchange is observed with other control areas. For this, the planned and actual power flows are compared to other control areas and corrected. It must be ensured that the secondary and primary control are always working in the same direction, which is ensured by monitoring the mains frequency. Primary and secondary control can start at the same time, the secondary control process should have replaced the primary control process according to the requirements of the UCTE for more than 15 minutes so that the primary control is available again.

The amount of benefit secondarily provided depends firstly on the code and the frequency deviation, on the other, of the difference between the actual exchange services to neighboring networks and declared as a roadmap exchange services. The retrieval of the secondary control is automated, to the corresponding process control- forming units are connected to the transmission system operator. Generator units, which provide secondary control power, must meet special requirements. The entire control power must be provided within a maximum of 5 minutes, the load change rate must be at least 2% of the rated power per minute amount. To use this come as pumped storage power plants or conventional combined cycle or coal-fired power plants.

Tertiary control ( minute reserve )

Also in the tertiary control ( minute reserve ), a distinction between negative and positive control energy, it is primarily used for economic optimization. The minute reserve is requested by telephone by the TSO to the supplier. The reproached minutes reserve capacity must be provided in full within 15 minutes, used here come conventional power plants or other generation units and controllable loads. The main controllable loads are used in steel mills or night storage heaters as electric arc furnace.

For the negative minute reserve, two options are available:

• When frequency increases, additional loads in the form of pumped storage power stations, night storage heaters, etc. are activated in the network.
• Another way to represent negative balancing energy, is the partial or complete shutdown of power plants. In addition to the reduction of large power plants can have negative control performance are provided in the form of a virtual power plant by collective disconnection of cogeneration plants ( CHP plants ). In this case, such CHP plants are particularly suited to their heat supply does not have to be continuously guaranteed. However, the injected current must not be remunerated under the EEG, because a parallel marketing is currently the EEG contrary.

Quartärregelung

The Quartärregelung is not absolutely necessary for the technical operation of an interconnection network, but is also present in interconnected networks, such as the European interconnected grid. The Quartärregelung serves to compensate for transient errors of the mains frequency over extended periods of time. Response errors are caused by grid frequency deviations that accumulate over a longer period and may result in synchronous clocks to a transition error in the range of minutes to hours. When Quartärregelung of response errors is determined by comparison to a time standard such as Coordinated Universal Time ( UTC) and reduced when exceeding ± 20 seconds of the nominal value of the mains frequency (nominal mains frequency) at pretriggered network time by 10 mHz to 49.99 Hz to at lagging power time 10 mHz increased to 50.01 Hz. In Europe, Swiss Grid acquired on behalf of the current network UCTE deviations and coordinates the corrections to the nominal frequency in the context of Quartärregelung.

Control area

Germany

The US-led Amprion system control network of the Federal Republic of Germany is divided into four control areas, in each of which a transmission system operator is responsible for the balance of entries and exits in the power grid. In Germany, a total of 7,000 megawatts of positive control power ( extra power for the bottleneck case ), and held 5,500 megawatts negative control power ( reduction in production or artificial increase of consumption). The cost is about 40 percent of the entire transmission network fee.

(: TransnetBW earlier), TenneT TSO (formerly E.ON Netz ): On 1 May 2010, the existing to date system control network of the three TSOs 50 Hertz Transmission have been ordered by the Federal Network Agency in Germany (formerly Vattenfall Europe Transmission ), EnBW to the fourth control area from Amprion ( formerly RWE transport power ) extended so that it was effectively a unified Germany -wide system control network. This is to prevent a so-called conflict rules, is used in the different control zones simultaneously both positive and negative balancing power. Through the control network less control power must be maintained and less control energy are used because compensate Performance surpluses and requirements of the four control zones partially. This should lead to savings of hundreds of millions according to the Federal Network Agency.

The Agency concludes a future even more intensive cooperation of transmission system operators is not sufficient. Also, the control network could be extended in the direction of neighboring European countries.

Switzerland and Austria

In Switzerland, there were up to the year 2008/2009, a total of eight zones. These were brought together under the Swiss Grid.

Austria was divided to 31 December 2011 in two zones: Vorarlberg belonged to the control area Vhf Transmission Ltd. (which in turn was part of the German control block zone ), the remaining states belong to the control zone Austrian Power Grid ( APG). Until 31 December 2010 the Tyrol was part of the control zone TIWAG network, but this was incorporated on 1 January 2011 in the APG control area; in the same way has been integrated into the APG network on 1 January 2012 Vorarlberg.

Procurement of balancing power

The procurement of control power is carried out by the operators of transmission networks.

Procurement in the German system control network

In Germany this is, as in most European countries a tender procedure carried out, which must be non-discriminatory and transparent ( § 22 para 2 of the Energy Act ). The German transmission system operators have set up an internet platform for the procurement of control energy, over which a joint call control power types is handled. Since 1 December 2006, the daily tendering of minute reserve ( tertiary control ) is performed on a common Internet platform and, since 1 December 2007, the common monthly tender for the primary and secondary control. Since May 2010, the four German transmission system operators are members of the Optimized system control network. Took place on 27 June 2011 for the primary and secondary control a switch from monthly to weekly tender tenders. The need for secondary control and minutes reserve is thereby regularly reviewed and adjusted according to the tender; in Germany, this is done on a quarterly basis.

The composite controls in all network areas uniform sizing and the actual procurement, as well as use and billing of control power. Since then applies the so-called " control area -wide uniform price for balance energy " ( reBAP ) for all zones. At the same time situations are avoided, previously considered simultaneously positive ( energy intake) and negative control performance (reduction of power plant feed ) was used in neighboring control areas.

Potential suppliers of control power must pre-qualify for one of the four TSOs at first, that is, they must demonstrate that they can really meet the technical requirements for the provision of one or more species control power also. In June 2013 43 vendors were pre-qualified, 14 of them for primary control, secondary control power for 20 and 36 minutes for the provision of balancing power. The provider offering includes power plant operators and public utilities and large industrial plants.

Procurement in Austria

In Austria, the tender of control performance by Austrian Power Grid through regular tenders takes place. The tender of primary power regulation is in § 68 and provides for the cost allocation in § 67, and the tender and cost allocation of secondary control in § 66.

Procurement in Switzerland

In Switzerland, Swiss Grid procured since 2009, the required control performance through regular tenders on balancing power market. The tenders were initially monthly, in 2012 they were replaced by weekly and daily calls.

Costs for balancing power

The cost of control performance can be significant, since it is covered by (often in less than a minute hochfahrbare ) peak-load power plants, whose production costs are comparatively high. Depending on the supply situation in the electricity grid, up to 1.50 euros per kilowatt hour - six times more pay than Consumer - are calculated by the energy suppliers. In general, the average balancing energy price but at the level of the stock market price of electricity, as covered under control zones will be paid by covered.

The necessary by the expansion of renewable energies increased demand for balancing power cost about 300 to 600 million euros in 2006.