## 2 Methodology
### Procedure for Loading the Monitoring Data into the Database
Figure 1 shows an example of how the information from a set of inverters and string current metering devices of one of the PV installations analysed in this work is organised. In this case, the files are stored in a directory and they are identified by means of a code (wb150014229 in Figure 1), which identifies the plant and the inverter group to which the data refer, together with the year, month and day (yyyymmdd, 20220704 in Figure 1), and separated by a hyphen, the time at which the storage of such data took place (hhmmss). These files are zipped, and within them, there are other files, as can be seen in Figure 1. Some are log files, which are not used except in case of problems, and other files are called Mean, which in this case only have in the name allusion to the date and time at which the data they store were recorded. These files are also compressed, and if they are decompressed, an XML format file is obtained containing the information of interest recorded by the inverters and string current sensors. Depending on the group of inverters, it may also contain the measurements of the irradiance and temperature sensors that were recorded in the plant. Figure 1 shows that the Mean files corresponding to 14:45:39 and 14:50:39 were unzipped. Each of these XML files corresponds to the record, in a set of inverters and string current sensors, of all the parameters they monitor in each sampling period, i.e., each XML file saves the data that were recorded in 5 min (the system was configured in such a way that the metering devices are recording information and save a value of each parameter recorded every 5 min). A fragment of the information stored in one of these XML files is shown in Figure 2, which shows, for the inverter model SCC100N7, with identification code 139028664, the recording of the parameters _E-total_, _fac_ and _fahler_, at the time instant 14:45:39. The rest of the XML file contains the rest of the parameters recorded by this inverter, as well as by other inverters located in the same sector of the PV plant, and by string current sensors on the same sector, whose data are stored together in the same file. In these XML files the data are enclosed in _MeanPublic_ tags, where _Key_ includes the inverter and parameter information, separated by a colon. In addition, the file itself also includes the time at which the data were recorded, in the _TimeStamp_ tag, which is very important when storing and processing the data. Since this file corresponds to a PV plant with 17 inverters, similar files with data from other inverters and string current sensors in the plant will be found in another directory. However, as already mentioned, only in some of these files is the information corresponding to the meteorological parameter records stored. In the case of a small PV plant with few inverters, all the plant's inverter data are grouped in a single directory and will generate only one XML file every 5 min. Figure 1: Organisation and format of the files corresponding to the monitoring of a sector of a PV plant during some hours of a specific day. In general, it can be said that, for each day, 288 useful files will be available for each plant or set of inverters, in which information is recorded every 5 min throughout the day. Such disaggregation of the information makes it very difficult to process, so the tool developed in this work allows the automated loading of all this information and to have access to it in a much more orderly, selective and practical way. However, not all inverters generate the information with this structure. There are cases of PV plants in which the metering devices directly generate the measured data in CSV format files. Moreover, in this case, the CSV files are not compressed and the structure of the directories that contain them is different, as is the structure inside the file (Figures 3 and 4).