**2. Problem Description**

To emphasize the consequences of oversizing the PV array and highlight the effects of clipping, data from a PV plant located in UK with 39% PV array oversizing is presented in Figure 2. This PV plant has an empiric annual plant factor of 15.43%; if oversizing was neglected a yearly plant factor of 11.11% would have been obtained instead. A year of PV power generation from a central inverter grid-tied PV plant is shown in Figure 2a, where the installed capacity of the PV array is 2 MW, while the DC rating of inverter is 1.54 MW. Power measurements were taken at the DC side of the inverter once per minute during a full year, from 1 October 2016 to 30 September 2017. These measurements have been normalized with respect to the inverter rating. The surface presented in Figure 2b (lateral view of Figure 2a) is equivalent to overlapping all daily DC power generation curves, showing the power limitation, hereafter power clipping, caused by the power-oversized PV array reaching the power rating of the inverter. Seasonal behavior is shown in Figure 2c,d, where yearlong dawn, dusk and daily maximum power generation are presented. These characteristics were exploited to propose alternatives to obtain further usage and revenue from the ESS. Autumnal (Autumn) Equinox, Summer Solstice, Vernal (Spring) Equinox and Winter Solstice are identified in Figure 2c,d with the abbreviations AE, SS, VE and WS, respectively.

Irradiance, temperature and DC power measurements are the only data available for the PV plant located in UK. Since the power limitation applied to the system is imposed by the converter rating, power losses caused by clipping are neither estimated nor accounted for. Estimating those losses would result in a mandatory effort to assess clipping effects.

**Figure 2.** PV plant power generation at the DC-side of a central inverter configuration, annual measurements taken every minute (1 October 2016 to 30 September 2017): (**a**) per day and per minute power generation; (**b**) daily power generation and dawn to dusk daily daylight (top view of Figure 2a); (**c**) overlapping of daily power generation (lateral view of Figure 2a); and (**d**) daily maximum generated power (lateral view of Figure 2a).
