Ancillary services: technical specifications, system needs and costs:REserviceS Deliverable D2.2

Ancillary services are grid support services required by the power systems (transmission or distribution system operators TSOs or DSOs) to maintain integrity, stability and power quality or the power system (transmission or distribution system). Ancillary services can be provided by connected generators, controllable loads and/or network devices. Some services are set as requirements in Grid Codes and some services are procured as needed by TSOs and DSOs to keep the frequency and voltage of the power system within operational limits or to recover the system in case of disturbance or failure. It is foreseeable that also variable renewable generators, like wind and solar, will provide ancillary services. This is needed from power system point of view in times of high wind and solar production when conventional generators are at low level. In this report, different ancillary services are described and a table listing main services is presented