People expect electricity supply to be secure and reliable. But end users tend not to notice that this requires continuous corrections during ongoing operations – the term used here is “ancillary services”. They run in the background, exerting a controlling influence by monitoring, balancing and repairing the energy infrastructure. Ancillary services also restore factors such as voltage and frequency to their normal ranges when disturbances occur. Until now, conventional power stations have provided important parts of these services. In future, though, producers of renewable energy sources will have to contribute to grid stability as well. Smooth coordination between the grid and system operators is also necessary.
Focussing on 4 areas: the dena Ancillary Services Study 2030
The dena Ancillary Services Study 2030 has shown that in principle, adequate technological solutions already exist for all types of ancillary services, and that they can maintain the current level of stability, reliability and quality in electricity supply. Nonetheless, improvements will be necessary in the four core areas – frequency and voltage control, provision of supply and system control – and that the technological solutions must interact efficiently when in use.
On the issue of voltage and frequency control: to ensure stable operation of the electricity supply system, the capacity introduced to the grid must correspond with electricity consumption in the grid at all times. The reserve is an important factor here, in additional to the balancing mechanisms of electricity trading and sales. In terms of frequency control, system operators can use loads which can be connected or disconnected as required in the event of risks or faults, in addition to increasing or throttling generation capacities.
The study indicates that so far, the necessary reserve has not increased sufficiently to meet future challenges. The situation with voltage control is similar. The correct grid voltage must be provided in normal operations and during malfunctions in order to ensure maximum security of the electric power system. Here, static voltage control is achieved using voltage controllers and transformer tapping, also by the provision of reactive power, i.e. unused energy. The increasing transport distances and the introduction of renewable energy sources fed into the system mean that the reactive power requirements will rise exponentially by 2030. Accordingly, the dena study recommends the increasing use of alternative solutions. The technological resources are available in principle, for instance the use of reactive power from decentralised power generation units or the ramping up of individual power stations to maintain voltage control (redispatch).
The study does see room for improvement in the area of system restoration und system control. Concerning the first point: in the event of a full or widespread power failure in the European integrated grid, system restoration is achieved by ramping up large-scale power stations with black start capabilities – meaning independent of the electricity grid – in the transmission grid, which would then each provide insular grids. Large hydroelectric power stations (pump storage) and gas turbines are examples here. They could also be ramped up using batteries or emergency power generators in the event of a black start situation. Within the scenario framework described in the study, there will still be sufficient pump storage and gas power stations in 2030 to implement the concept of central system restoration. In contrast, the alternative method for decentralised system restoration involves significant technological effort and therefore high investment costs, and is therefore not recommended. The requirements for system control are rising in all electricity grids due to the larger integration of volatile renewable energy sources, the greater provision of ancillary services in the distribution grid, the planned hybrid structure of the transmission grid comprising three-phase current and direct current, and the increasingly multi-regional exchange of energy in the European electricity market. The study shows that grid stability by means of ancillary services can be guaranteed for 2030 based on the current and planned operating resources, combined with utilisation of renewable energy sources and more flexible industry loads.
The sequence and content of the recommended measures to improve ancillary services are presented in the Ancillary Services 2030 Roadmap. You will find additional information and details on ancillary service here: http://www.plattform-systemdienstleistungen.de/