## 1 Introduction
### Literature Review  
The use of PV energy and biomass (BM) is highly advanced and has been thoroughly studied separately on a worldwide level. On the one hand, PV energy is the most widely used renewable resource due to the large number of solar resources available on the planet [40]. On the other hand, while BM has been widely used on a small scale in developing countries, in recent years it has gained great importance as an energy vector for sustainable development [41]. In this literature review, we will not address the studies carried out on these types of installations on their own, but rather the works that analyse the combination of both technologies. In developing countries, the hybridisation of PV systems with BG digesters has been widely embraced, particularly on a small scale. The main reason for this is the high number of sunny hours, the abundance of organic waste for processing, and the widespread electrical supply issues in these regions, as demonstrated in [42]. In [43], a small hybridisation of 1 kW of PV and 3.5 kVA of BG is carried out to study the amortisation of the system based on Indian regulations. The tests carried out show that the amortisation of these systems ranges from 6.45 to 17 years, in addition to improving the reliability of the electrical supply. On the other hand, the work carried out in [44] proposes the simulation of a 3.0 kW integrated PV/BG power generation model (2.84 kW solar system and 4.0 Nm\({}^{3}\) BG system), with the aim of providing a stable source of power for a house in a remote area or village. While the proposed system significantly improves the electrical supply, it still largely depends on the general electrical grid. That is why the authors of [45] use an on-grid PV/BG/diesel system for the electrification of a small village in Iran. In this study, the production ratio of each technology is sought, with the aim of minimising the cost of energy production. With this system, there is a reduced dependence on the general electrical grid, as there is a diesel generator that can act in emergency cases. If we analyse the studies carried out to seek self-consumption of small homes/municipalities, [46] analyses the feasibility of a 12.9 kWp off-grid mini-grid power system with a 1 kW BG generator to supply a remote area in Bangladesh. Due to the conditions of the country itself, the amortisation of this system is estimated at 6.9 years, reducing CO2 emissions and allowing for more economical and reliable energy. Finally, the application of PVs and BM is also interesting in agriculture and livestock farming, due to the great availability of organic matter for the BM digester. In [47], it is analysed how BM alone is not as economically or energetically profitable for a stable, requiring the hybridisation with a PV system to obtain better economic results. While in [48], the technical and economic feasibility for the electrification of an apple farm is analysed, through the modelling of a system of 25 PV modules, 2 BM generators, and a battery. Therefore, in developing countries, the hybridisation of PV and BG systems is very interesting for self-consumption in rural areas. This is due to their short amortisation period and the improvement in the reliability of the electrical supply, as analysed in [49], which considering 20 different installations. In this study, BM digesters between 2.4 and 4.8 Nm\({}^{3}\) and PV installations between 40 and 85 kWp are analysed to obtain the payback. This work concludes that these systems have a payback of less than 5 years. However, this combination of renewable resources is also starting to be considered as an energy solution for electric vehicle charging [50]. For this, different solar PV systems (3 kW, 4.5 kW, 6 kW, and 9 kW) are available, where the most efficient is the 4.5 kW since it is amortised in 12 years. Two 5 kW BG generators are used as support in the hours when there is no solar generation. In Europe, new regulations are leading to energy communities that combine PV and BM.