## 2 Methodology
### Characterisation and Modelling of the System Whose Information Is to Be Managed
In this case, if there is only a single meteorological data record in the PV plant, these weather data will be stored in the files corresponding to the data register by one group of inverters, and in the data files \begin{table}
\begin{tabular}{c} \hline
**Real Entities Included in RDBMS** \\ \hline PV installations and their configuration and features. \\ PV modules and their technical specifications. \\ Inverters and their technical specifications. \\ Meteorological sensors \\ Other measuring devices, such as those that measure the current generated in strings of \\ PV modules. \\ Monitored meteorological data. \\ Data from inverters. \\ Instantaneous parameters calculated using the parameters from monitoring. \\ Aggregated and averaged parameters, calculated from monitored and calculated parameters. \\ \hline \end{tabular}
\end{table} 
Table 1: Real entities included in the Relational Data Base Management System (RDBMS) implemented in this paper for the analysis of PV installations. corresponding to the rest of the inverters in the plant these weather measurements will not appear. However, once stored in the databases, the meteorological data measured in each installation must be available in such a way that, for example, if calculating the yields of PV modules associated with all the inverters of the plant is desired, it is necessary to have access to both the power production data of each inverter and the irradiance data. It is important to take these issues into account in order to be able to organise the information correctly. Returning to Table 1, the last item listed refers to the parameters to be determined by calculation from the monitored data, which allows characterisation of the behaviour of the PV plant elements. These are those recommended by the standard IEC 61724, Photovoltaic system performance--Part 1: Monitoring, which indicates a series of parameters that must be calculated in order to perform an adequate analysis of the performance of the plant elements according to the type of PV installation [60]. All of these parameters are listed in a previous publication [80]. To calculate these parameters, in addition to the monitored data, it is necessary to know the specifications of the modules and their configuration in the plant, information which, as mentioned above, must be stored in the database system, and which would have to be accessed to proceed with the calculation. In order to create a complete model of the real system that allows its transcription to the databases that comprise the RDBMS, it is necessary, in addition to knowing the entities that compose and configure the system, to establish the existing relationships between them, which, in the case of the PV plants analysed in this work, are those shown in Table 3. \begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Notation** \\ \hline DC current from PV modules & \(I_{DC}\) \\ Inverter input DC voltage from PV modules & \(V_{DC}\) \\ Inverter input DC power from the generator & \(P_{DC}\) \\ Inverter output AC power & \(P_{AC}\) \\ Inverter output total energy & \(E_{AC}\) \\ AC current injected into the grid & \(I_{AC}\) \\ Grid current & \(I_{grid}\) \\ Grid AC voltage in phase 1 & \(V_{AC\_1}\) \\ Grid AC voltage in phase 2 & \(V_{AC\_2}\) \\ Grid AC voltage in phase 3 & \(V_{AC\_3}\) \\ Grid frequency & \(E_{ac}\) \\ Grid impedance & \(Z_{grid}\) \\ Inverter operating status & Status \\ Error code (where appropriate) & _Error_ \\ Number of times that the inverter finds the MPP & \(n_{MPP}\) \\ Inverter working total hours & \(I_{lon}\) \\ Grid injecting total hours & \(h_{an\_grid}\) \\ Total connections to the grid & \(n_{an\_grid}\) \\ Installation boot-up number & \(n_{b}\) \\ \multicolumn{2}{c}{Boot-up time} & \(h_{b}\) \\ Inverter operating temperature & \(T_{int}\) \\ Isolation resistance & \(R_{isol}\) \\ \hline \end{tabular}
\end{table} 
Table 2: Parameters generally measured by inverters.