This ancillary service consists of mutual assistance between the TSOs of two synchronously interconnected transmission systems one of which asks for ESA and the other offers to provide the required ESA; the provider who puts forward the most favourable offer which, at the same time, fulfils the criteria set by the enquiring TSO is ultimately selected. The respective agreement is signed by ČEPS and a natural or legal person which guarantees that the power requested by ČEPS is actually delivered. ESA is utilised primarily if an unexpected operational situation occurs in the Czech power system, such as interconnector overload, power lack/surplus within the power system, non-fulfilment of the N-1 criterion etc.
ESA is activated through the ČEPS Control Centre which notifies certified providers of the power volume required (in MW), the start date and time and the duration of required ESA provision. Providers are obliged to submit their offers by a set time. Offers are subsequently evaluated and the most favourable in terms of ČEPS’s needs is then selected. If two offers contain identical terms, the first offer received is selected.
The power supplied is considered either as the provision of positive regulation energy (representing electricity import for the power system which requires AnS activation) or the provision of negative regulation energy (electricity export for the power system which requires AnS activation).
If this ancillary service is utilised, the regulation energy price equals the selected offer price and is entered into the balancing and settlement mechanism. ESA costs are covered by settlement entities within the balancing and settlement mechanism.