The trend, which has been in progress for several years now, whereby generation from renewable energy sources is replacing large fossil-fuelled generation plants, means that the regulation capacity and mechanical inertia of the power system is being increasingly reduced. Therefore, to ensure safe operation of the system, proposals are being pursued by transmission system operators to allow renewable plants to participate in frequency containment in the event of a generation/load imbalance.

In this report, a control strategy is suggested to enable photovoltaic plants to provide power support during under-frequency disturbances. This strategy allows the plant to operate at a point where the power output is not the maximum possible according to the weather conditions of radiation and temperature, but such that, through voltage control, the possibility of rapidly increasing the generated power is guaranteed (deloading).

This mode of control allows the plant to participate in upward frequency regulation even without a supporting storage system. Obviously, remuneration mechanisms are required to compensate for the loss of revenue due to the reduction of power delivered to the grid.

Simulation results for a scenario concerning the Sardinian power system in 2030 show that the performance of the upward regulation carried out by photovoltaic systems is comparable to that achieved by wind power plants or by battery storage systems enabled to perform “ultra-rapid” frequency regulation. Furthermore, the regulation carried out by photovoltaic systems does not entail problems related to the restoration of pre-perturbation operating conditions, as could be the case with regulation carried out by wind turbines not operated in deloading.

The Report is available on the Italian site