## 3 Results and Discussion
### Imbalance of Network Voltage Values between Phases
The different profile of the histograms of the voltage imbalance values of installations 1 and 2 shows that the values of the imbalances do not depend on the operation of the plants but on the previous state of the grid itself, which will be conditioned by the loads that are connected to each of the three phases. Figure 24: Grid voltage imbalance on phase 2, measured by inverter 2 in PV installation 1 (**a**) and the histogram of these grid voltage imbalance values (**b**). Figure 26a shows the voltage imbalance in phase 2 of installation 4, which has single-phase inverters. Initially, this figure shows that there are occasional voltage imbalances between the different phases, especially during the hours when the PV plant's inverters start production and to a lesser extent during their disconnection at the end of the sunshine hours. However, these recorded imbalances are due to the fact that the inverters do not start operating, and therefore measuring, simultaneously on all three phases, but that the inverters connected to one of the phases may start operating a few minutes before those connected to the others. Figure 25: Grid voltage imbalance on phase 3, measured by inverter 1 in PV installation 2 (**a**) and the histogram of these grid voltage imbalance values (**b**). During night-time hours, these inverters are in a disconnected state. They enter this state when the PV voltage is less than 60 V, and the production is too low to connect to the grid and even insufficient to feed the inverter itself. When the voltage coming from the PV field is between 60 and 220 V, the inverter goes into the initialisation state. The power supply from the PV array is sufficient to feed the inverter but there is not yet enough power to connect to the grid. The inverter will perform an automatic test of the electronic components of the equipment and switch to a state where it will monitor the network, taking measurements of the grid voltage, allowing it to verify that the requirements for connection to the grid are met. Therefore, during these initialisation minutes, these inverters are not yet injecting their production, but they are already measuring the grid voltage. Moreover, if the strings of the PV modules connected to each inverter are unevenly shaded, some inverters enter the initialisation state before others. Although in the end, they do inject simultaneously in all three phases, there are moments of time in which the inverters connected to one phase are already initialised and measuring the voltage values, and in other phases, they are still neither connected nor measuring, and therefore in the latter,  
Figure 26: Grid voltage imbalance on phase 2, measured by inverter 2 in PV installation 4 (**a**) and these grid voltage imbalance values detailing smaller deviations (**b**). the voltage value recorded is still zero. Therefore, at this time of day, there is an apparent voltage imbalance between the three phases, whose values are not real, but rather an apparent imbalance only because of some inverters starting to measure before others. This does not happen with three-phase inverters, which, as the same equipment injects into the three phases, the connection will be simultaneous and, in addition to distributing the production equally among the three phases, will generate measurements of the three phases simultaneously at any time of the day. It is also not possible to visualise the values of the grid voltage in the single-phase inverters analysed in this work during night-time hours, when the inverter does not operate and does not record these values. If the data in Figure 26a are represented again but modifying the colour scale so that the imbalances of lesser magnitude can be better seen, the results shown in Figure 26b are obtained.