Common Grid Model Alignment (CGMA) process is one of the additional RSC services, which can be defined as a set of procedures by which the initial estimates of net positions are revised such that the resulting set of net positions is balanced. Net position represents the netted sum of electricity exports and imports for each market time unit for a bidding zone.
When no market schedules are available, TSOs will typically base their Individual Grid Model (IGM) on an estimate of the net position which, in the first instance, they are free to determine by themselves. However, TSOs collectively have to respect a critical consistency requirement – all net positions within an interconnected system have to sum to zero because the sum of exports has to be equal to the sum of imports. When this consistency requirement is met, the net positions are referred to as "balanced" and the IGMs are said to be "aligned". Unless this condition is fulfilled, it is not possible to merge the IGMs from all TSOs into the Common Grid Model (CGM).
Establishing balanced net positions is, in principle, straightforward for those timeframes for which schedule data are available (i.e. day-ahead and intraday). However, for timeframes for which schedules are not available (from two-days ahead up to year-ahead), balanced net positions have to be established using CGMA process. The CGMA process can be divided into three phases:
- Pre-processing phase,
- Processing phase and
- Post-processing phase.
During the pre-processing phase each TSO provides its Pre-Processing Data (PPD) to the CGMA IT platform which is operated by one or more Alignment Agents. The Alignment Agents, which are in practice Regional Security Coordinators (RSCs), are responsible for completing a number of tasks related to the CGMA process on behalf of the TSOs. The PPD consists of:
- the preliminary net positions (PNPs);
- the feasibility range (FR) for the adjustment of the preliminary net positions;
- preliminary flows on DC lines;
- maximum import and maximum export flows on DC lines.
The PPD should correspond to the TSO's best forecast. During the processing phase, the CGMA algorithm redistributes the PNPs across all bidding zones, until they sum up to zero. Basically, in this phase PPDs are used for the computation of variables of interest, namely:
- balanced net positions;
- balanced flows on DC lines.
During the post-processing phase the balanced net positions and the balanced flows on DC lines should be used for creation of IGMs by TSOs, and subsequently as target values in total adjustment process by RSCs.
As Alignment Agent for its service users, SCC is performing the role of mediator between TSOs and ENTSO-E CGMA platform, including submission of input data, delivery of aligned exchange programs, as the final result of CGMA process, and some additional operations using CGMA platform.