## 1 Introduction
The growth of this technology is explained by the significant increase in the market on all continents, led by countries such as China, which held 31% of the global market, the United States, which installed 26.9 GW in 2021, India, with an estimated annual installed capacity of 13 GW in 2021, Japan with 6.5 GW, Brazil with 5.5 GW, Germany with 5.3 GW, Spain with 4.9 GW, Australia with 4.6 GW, South Korea with 4.2 GW and France with 3.4 GW [5]. The opportunities for improvement in this sector are based on development at the level of installed capacity. However, there are also a series of challenges that must be addressed, among which the achievement of technological improvements must be highlighted, which undoubtedly seek to increase generation capacity, cost reduction and better integration into the grid. Improving the competitiveness of PV installations compared to other electricity generation technologies must be a priority for this sector, and to this end, it is essential to improve the efficiency and production of its elements and to have the least possible impact on the electricity grid. In terms of increasing efficiency, research is focused on improving both the production processes and the long-term stability of cells and modules. On the one hand, the aim is to increase the theoretical performance of the PV plant's generation components by improving both the semiconductor materials currently used to manufacture PV modules, such as silicon or thin-film panels, and by making use of emerging panel technologies based on organic cells [13; 14; 15]. It is also possible to improve the configuration and internal structure of the panels, as well as to make progress in the encapsulating or coating materials of the modules [16; 17; 18; 19]. Work is also being done to optimise the mode of operation of the inverters in order to extract as much power as possible from the generator panels [20; 21; 22]. It is also important, especially considering the increasing growth of this sector, to optimise the lifetime of the panels by analysing the causes of their degradation [23; 24; 25], and, once this lifetime is over, to ensure that their impact is reduced as much as possible [26; 27; 28; 29]. Regarding the operation of PV plants, once a certain technology has been installed, two important aspects to consider are the optimisation of their operation and the optimal integration of their production into the grid, if they are connected to it. PV systems may have significant fluctuations in operation due to cloud cover, unplanned outages, dust, soiling, or temporary events such as failures and damages, or operation and maintenance (O&M) issues [30]. Therefore, the implementation of means to assist in the diagnosis, monitoring and detection of these variations in production will allow easier performance of maintenance of the plant. The characterisation of the real margins in which a given PV installation operates allows preventive and predictive maintenance to be carried out, enabling a more active action instead of reactive fixes [31]. This will result in a higher number of operating hours and, therefore, an increase in profitability. In this sense, an efficient O&M service is essential to achieve the best technical and economic performance of any PV system during its entire life cycle [27; 32; 33; 34]. To improve this service, which can be extremely complex and time-consuming [27], further innovations and developments are needed to provide a range of technological solutions or advanced services such as tools for automated fault or deviation detection [35; 36; 37; 38], including even the use of digital twins [27; 39], intelligent monitoring of modules by drones [40; 41], proposed anti-dirt solutions [41; 42] or systems to provide cooling [43; 44; 45; 46] to optimise production [47; 48].