Glossary
Certified ancillary services
Ancillary services are contractually provided regulatory services (supply or consumption of balancing energy) delivered by entities certified by the transmission system operator – SEPS. These services are essential for maintaining the frequency, stability, and reliability of the power grid.
Based on the response time required to activate a device providing balancing energy, ancillary services are divided into:
Primary control (Frequency Containment Reserve, FCR): activation within 30 seconds
Secondary control (automatic Frequency Restoration Reserve, aFRR): activation within 300 seconds
Tertiary control (manual Frequency Restoration Reserve, mFRR): activation within 750 seconds
How it works
An entity providing ancillary services enters into a contract to guarantee availability – the ability to activate the energy source during an agreed time window. For both the delivery of regulating energy and the disponsibility itself (even if energy is not actually delivered), the provider receives financial compensation. If the entity fails to meet the contractual conditions or maintain availability, SEPS may impose a penalty.
Who can provide ancillary services
Ancillary services have traditionally been provided by fossil-fuel-based units, such as heating plants and diesel generators. However, the share of low-carbon and renewable solutions is steadily growing – including pumped-storage hydropower plants, biomass-fueled units, and battery storage systems, which, due to their fast response time, are particularly effective in grid stabilization.
Unlike flexibility, which does not require SEPS certification and focuses mainly on optimizing consumption and production according to market conditions, ancillary services are primarily aimed at maintaining grid balance and are subject to strict technical and commercial requirements.