Italy has witnessed a very massive penetration of photovoltaic and wind generation in the recent years.
The largest share of wind plants is connected to the transmission grid and the total power installed exceeded 8.5 GW at the end of 2013. Photovoltaic plants are generally connected to the distribution grid and at the end of year 2013 the total power installed in Italy reached almost 18.5 GW. In such a context, the energy produced from non-programmable RES (or Variable Renewable Energy – VRE) plants has reached a considerable amount. In particular, in the southern regions of Italy the “green generation” covers an increasing share of the electricity demand. On the other hand, due to the recent economic downturn the national electric consumption has not followed the increase in generation. In fact, during the last years the electricity demand has experienced a worrying decrease and as consequence the new VRE capacity available is gradually replacing part of the power coming from thermal plants. Furthermore, a number of thermal power plants must always run over a certain system security threshold in order to ensure the proper regulation capability, high service standards and ancillary services required by the power system operation.
The security requirements above mentioned represent a constraint for the full dispatching of the available renewable generation. Thus, it may happen that the Italian power system in certain low load conditions is characterized by surplus in generation, which is not balanceable with the local or national electricity demand. Consequently, such operational conditions do not allow the complete integration of photovoltaic and wind generation. Besides, PV generation is installed in a large percentage (more than 90%) in MV and LV networks and, as such, this form of generation is not directly controllable by the TSOs.
The paper aims to investigate on the “over-generation” (OG) phenomena in the Italian power system highlighting how the power markets framework evolution affects the OG.