## 1 Introduction
### Literature Review
For this reason, energy management systems are being developed in which BM plays an important role in stabilising the electricity grid when there is a large PV installation [51]. Similarly, in [52], an optimisation of a PV- and BM-based system is carried out, where it is determined that although it can supply the proposed demand, the system performance is only 40%. On the other hand, due to the distribution of sunny hours, BM has a great weight to ensure the necessary power during the winter months in solar plants where energy is stored in the form of heat [53]. Moreover, the combination of these technologies is interesting for the domestic self-consumption of single-family homes [54]. In this work it is demonstrated that with low-power systems (1 kW of PV, a 1 kW BG generator, a small 1 kW wind turbine, and a battery system) it is possible to not depend on the electrical grid. If we analyse the particular case of Spain, it has a great potential for the installation of these renewable resources. Specifically, in [55], a replicable, multi-criteria spatial approach based on a geographical information system to estimate the potential of solar PV, wind, and BM energy technologies that could be implemented in the short-term in a given territory is shown. The results of this work show that the combination of these resources could generate 3.8 times the current electricity consumption of the municipality and would only require 1.5% of the total area of the municipality. However, due to administrative barriers,it is not possible to implement this in the short term. On the other hand, reference [56] presents a methodology to optimise a grid-connected hybrid renewable energy system that hybridises photovoltaic, wind, and forest BM energy sources, considering the cost and environmental impact criteria from a life-cycle perspective. It is concluded that because those renewable systems with the least climate impact are the most expensive, renewable resources are still not presented as a great alternative for massive electricity generation. On a smaller scale of electricity generation, in [57] a method is shown for managing a solar thermal plant, using BG as an energy support system, with the aim of improving the profitability of the installation. Therefore, after analysing all the studies carried out considering large-scale plants, the combination of PV and BM is not yet profitable in Spain. However, for the supply of buildings, it is interesting if the necessary surface is available. For example, in [58], self-consumption for a slaughterhouse is sought through both systems. For this, there are 79 kWe of BG and 225 kWe of PVs, obtaining a payback of 9 years and an internal rate of return (IRR) of 9%. On the other hand, in [59], an existing near Zero Energy Building (nZEB) and zero carbon emissions building on a university campus are analysed. In this case, BM is described as helping to reduce the carbon footprint of buildings under new European regulations. However, in urban environments, the implementation of BM is not easy or economically attractive. In [60], the combination of BM and PVs is proposed to supply electricity to educational buildings. Although the results show that for these urban buildings PVs are more convenient, the limitation of the available surfaces makes it necessary to use other renewable resources to increase the percentage of renewable energy used. In this case, BM is a possible solution, but it has a high current cost. Table 1 summarises the studied works, classifying them according to the size of the installations, whether they improve the electricity supply, and how economically attractive these systems are, which provides some insights to the advantages and disadvantages of each proposed solution.