Grid integration of large-scale PV plants: dealing with powerfluctuations

The power grid comprises three distinct activities: generation, transmission, and distribution. Given the fact that electricity cannot be stored, there needs to be a constant balance between demand and generation, making it necessary to forecast energy consumption and to maintain sufficient power generation reserves in order to be in a position to address possible contingencies or changes in either power generation or demand. With regard to the European electricity system, the organisation responsible for this activity is the ENTSO-E, the European Network of Transmission System Operators represents 41 electricity transmission system operators (TSOs) from 34 countries across Europe [1]. The geographical area covered by ENTSO-E's member TSOs is divided into seven different synchronous areas (groups of countries that are connected via their respective power systems) and the system frequency, 50 Hz, is synchronous within each area. Its value is the direct consequence of the balance between the active powers generated and consumed. Frequency is an essential parameter in the quality of the power supply and must remain within a very tight range around the reference frequency, 50 ± 1 Hz. Outside this range, there is a risk that the system could collapse. If the power imbalance is significant, then the frequency moves out of the allowable range, which in turn leads to the automatic disconnection of other generating equipment, causing a chain reaction that could collapse the system. In order to avoid these situations and to guarantee stability, there are three different regulation systems available to the system operator: primary, secondary, and tertiary regulation.