## 1 Introduction  
Renewable energy sources, which are clean and inexhaustible resources that are used for electricity generation through different technologies, are currently playing a crucial role in the race to achieve some of the Sustainable Development Goals of the United Nations [1], such as Goal 7, which aims to ensure access to affordable, reliable, sustainable and modern energy for all. The target set by the International Renewable Energy Agency (IRENA) is to produce 57% of the world's energy from renewable sources by 2030, up from 26% today, more than doubling the existing share, so this decade is considered to be the one in which renewable energies will drive the global energy transformation [2]. Even more ambitious are the objectives proposed by European countries through the European Green Deal, whose objective, in the fight against the threat of climate change and environmental degradation, is that there will be no net emissions of greenhouse gases by 2050 [3]. Within renewable energies, a wide range of typologies can be found, and the one that currently has the highest growth rate is photovoltaic (PV) energy [4]. In 2019, this was the most installed energy source among both renewables and non-renewable energies, accounting for 40% of new global capacity [4, 5, 6]. Globally, new PV capacity in 2019 was 115 GW, an increase of 12% compared to 2018, giving a cumulative total of 627 GW. Thesefigures were obtained due to the growth that took place on all continents, highlighting the increase in some countries such as China (30 GW), USA (13 GW), India (10 GW) and Japan (7 GW). In the European Union, PV energy saw very significant growth, with 16.7 GW installed, an increase of 104 % compared to 2018 (8.2 GW), the strongest growth since 2010 [4; 7; 8]. This increase in the installed capacity of renewable energies, and in particular the increase in PV power, has allowed around a third of the world's electricity generation to take place without fossil fuels and therefore with zero emissions [4]. With this rate of expansion, PV technology, which has come to be considered the world's fastest growing power generation source and a driving force behind energy transition in some countries, is expected to further increase in installed capacity in the near future [4; 7; 9; 10]. In this regard, renewable energies in general, and PV in particular, have in recent years considerably increased their role in the generation mix of different countries, and their presence has led to changes in grid operation strategies [6]. These policies must continue to evolve in the future so that renewables energies form the basis of electricity generation and of the transition towards greater decarbonisation of sectors such as the demand for building power, air conditioning and transport [3; 11; 12; 13]. Nowadays, the main disadvantage of renewable energy sources is their manageability or dispatchability, as the energy they produce is conditioned by the randomness of the weather, giving rise to rapid variations in their production [14]. If electricity generated from renewable sources cannot be stored at a reasonable cost, its penetration in the grid is limited, and the share of renewable energy in the generation mix will be even more difficult to increase. For a better manageability of solar PV installations, which enables an increase in their penetration in the power grid, it is important to know in advance the electrical energy that is to be produced, in order to be able to predict more accurately how the product can be delivered in the time intervals considered in the daily and intraday energy markets. The need for better forecasting has for years increased interest in various solutions, and different authors have used different techniques [15; 16; 17; 18; 19; 20; 21], such as time series prediction with statistical and learning methods [22], or atmospheric modelling with the analysis of sky satellite images and the study of cloud propagation [23]. All these models are based on meteorological and/or historical production data.