## 2 Methodology
### Characterisation and Modelling of the System Whose Information Is to Be Managed  
In this paper, the tool developed to carry out the management of the data monitored in the PV plants will consist first in a Relational Database Management System (RDBMS) that allows storage in an orderly, accessible, fast way and without space limitations of all the information corresponding to the real PV systems to be studied, including the specifications of each and every one of its components or equipment, its configuration, and all the data that are recorded by the different measurement elements. The transcription of a real system to an RDBMS first needs to be modelled by defining a logical and conceptual model of all the elements that compose it, for which it is essential to have correctly characterised the complete real system. Subsequently, an RDBMS must be designed to allow the model of the real system to be transferred to it and to represent the real system as faithfully as possible. This will allow the efficient management of all the information. The conceptual model in this case corresponds to the description of the configuration of the different elements that constitute the various PV facilities to be analysed, and of the existing relationships between these elements, some of which will be involved in the generation of the information to be organised and analysed in the data storage system that has been developed. This conceptual model must be independent of the RDBMS to be used. In this case, the RDBMS must include the real entities shown in Table 1.  
It is also necessary to consider the inverters in each of the plants, their technical specifications, and how this equipment is associated with the set of modules from which they receive the generated energy. If there are measurement sensors in the PV plant that record additional parameters to those measured by the inverters, such as meteorological parameters that affect the production of the plant, or the current generated in each string of PV modules (\(I_{grid}\)), the configuration of these sensors must also be considered in the RDBMS. In addition to the different pieces of equipment that are part of the PV installations, it is necessary to characterise the data that are measured by the inverters or additional sensors in each one of them, the notation they use and their units. It is also necessary to consider how the measured data are configured and organised after monitoring, as their structure will condition how the automated migration of their content to the information storage system can be carried out. If we focus on the data measured by the inverters of the plants, these depend on the specific inverter model. An example of the parameters that can be measured by these devices is shown in Table 2, which corresponds to some inverter models from the SMA company, which are the ones analysed in this work. However, not all inverters measure the same parameters, nor do they use the same notation or measurement units, and there may even exist differences between the different models of the same manufacturer. With respect to the monitored meteorological data, these may include horizontal and/or in-plane solar irradiance, ambient and module temperatures and, in some cases, wind velocity and relative humidity. The values of these parameters may be usually recorded at the same frequency as the data logged by inverters and saved in the same or different files. In the case of the PV plants analysed in this work, the data from meteorological sensors are sent, as well as the data from inverters, to a communication centre, such that all the information is collected and stored together in daily files or data files every 5 min. However, in the case of PV installations with a larger number of inverters, data from all inverters may not be collected in the same file but may be divided into different files corresponding to data from different groups of inverters.