Intermittent non-dispatchable renewable generation and reserve requirements: historical analysis and preliminary evaluations on the Italian electric grid

Intermittent renewable generators, mostly solar photovoltaic (PV) and wind power plants (W), have been growing across the Italian electric grid at an unprecedented rate over the last years. At the beginning of 2013, GSE (state-owned company supporting renewable energy sources) surveyed 16,4 GW of installed PV systems and 8,1 GW of wind farms, covering a significant share of Italian electric demand, which has been ranging between 21 GW and 54 GW over the same year. Such a relevant amount of installed intermittent power generators, fostered by priority dispatch, has already had relevant effects on the electricity market, in both its two components: the energy market (MGP) since the end of 2013 has been steadily lowering its single national purchase price (PUN), even recording zero purchase prices; at the same time, the amount of resources needed to establish reserve margin on the dispatching services market (MDS) has increased, due to a growing amount of intermittent generators penetrating on the grid, at a yearly rate of 5%, as shown from our historical analysis. A preliminary evaluation method of reserve requirements was developed taking into account forecast variability in electric load and intermittent renewable generation. The model was used to evaluate the growth of reserve requirements with an expected larger share of renewable generators. The magnitude of this relevant parameter was assessed, thus estimating the addressable penetration of energy storage systems and virtual power plant needed to overcome renewable intermittency.