The energy transition will experience a crucial step with the phase-out of coal-fired units (traditionally suppliers of ancillary services) and require increasingly accurate tools to predictively check the adequacy of the resources needed for the electrical system’s safe operation. This is particularly important for the Sardinian system: as it is potentially subject to high power imbalances, with a view to the year 2030 it will be affected by the phase-out of coal-fired units and by a high growth of non-programmable renewable generation.

In recent RdS periods, the development of tools aimed at 1) analyzing the adequacy of the reserve for conventional frequency regulation and 2) evaluating the optimal “mix” of innovative services such as synthetic inertia and fast primary regulation (“Innovative Services: Automatic Tuning”, SeTA) has been started. The 2019 activity concerned: i) for adequacy, the implementation of the static calculation of the post-imbalance and post-conventional primary regulation steady-state frequency in addition to the discussion of the possible future HVDC “Tyrrhenian Link” route between the Continent, Sicily, and Sardinia, hereinafter referred to as “CO.SI.SA.”; ii) for the SeTA procedure, the consolidation of the method for assessing the optimal “mix” of innovative services through the adoption of new figures of merit, based on the energy exchanged in the event of an impulsive perturbation and/or on the maximum active power necessary to cope with a power step imbalance.

The 2019 developments were tested on a Sardinian scenario for the year 2030. With regard to reserve availability and conventional frequency regulation and in the event that no regulation service was available from new pumping as recommended by the 2017 National Energy Strategy and the National Integrated Energy Climate Plan, in the face of the maximum possible imbalance in deficit and/or surplus, the following emerged: i) the reconstruction of the SA.CO.I., with a capacity of 400 MW and the ability to reverse power, would allow the number of critical hours with insufficient reserve margins to be eliminated but, in the event of overfrequency events due to the loss of export HVDC connections, a quota of hours would remain (8.1% per year) in which the operating frequency is higher than the limit value of the normal/alert operating conditions for Sardinia (50.5 Hz), as indicated by Terna in the network code; ii) the additional implementation of CO.SI.SA., with a capacity of 1,000 MW and the ability to reverse power, would allow frequency deviations to be contained within the acceptable limit.

As regards fast primary regulation and synthetic inertia, the test conducted with the SeTA procedure, considering only the remaking of the SA.CO.I., took into account metrics such as the initial frequency derivative, the maximum transient deviation, and the time in which this is reached. The results for the scenario considered showed that fast services allow avoiding load shedding and the detachment of renewables, especially in the hypothesis in which inertia and regulation services by new pumping were not available.