## 1 Introduction
The performance of PCMs coupled with PV panels has also been investigated numerically, to understand the working mechanism of the heat transfer and the parametric optimization [19]. These studies are divided into one-dimension (1D) [20], two-dimensions (2D) [21] and three-dimensions (3D) model analyses [22]. Phase change materials suffer from a low thermal conductivity, and this represents an obstacle to the heat transfer rate. For instance, a paraffin wax has a thermal conductivity of around 0.2 W/m K. Over the years, many strategies have been tested with the aim of increasing this parameter [23]. One of these consists of adding high thermal conductive nanoparticles in the PCM matrix, as they work as a \"thermal bridge\" for the heat flow. Studies focused on the quantification of the conductivity enhancement, on the thermal stability, on chemical compatibility and on the optimization of the arrangement of the particles in the PCM matrix. [PERSON] et [PERSON] [24] proved that the thermal conductivity of a PCM increase with the percentage content of graphene. [PERSON] et al. [25] introduced expanded graphite in a paraffin wax and obtained an improvement of the conductivity up to 12 W/m K with a mass percentage of graphite of 20%wt. For other percentages, 2%wt, 5%wt, 10%wt and 15%wt, the thermal conductivity resulted in 2.1, 4.0, 13.6 and 20.4 times higher than pure paraffin. Other nanoparticles have been tested with the same aim. The most promising are TiO\({}_{2}\) with a thermal conductivity increased by 47% with a mass ratio of 3%wt [26], SiO\({}_{2}\) with time saved during the melting process of 25% obtained with a mass content of 1%wt [27], carbon nanotubes [28] and Al\({}_{2}\)O\({}_{3}\)[29]. [PERSON] et al. [30] infiltrated the PCM to a PS-CNT (polystyrene-carbon nanotube) foam, finding a good increase in PCM conductivity. Alternatively, many studies have been conducted on the effect of metallic fins as a medium for heat transfer from the PV module to the PCM [31; 32]. Fins allow to increase the contact surface between the panel and PCM and are usually metallic with high thermal conductivity. [PERSON] et al. [33] obtained an improvement of 5% with the introduction of fins compared to traditional phase change materials. This paper investigates the energy performance of a PV panel cooled by an innovative hybrid graphene/fins/phase change materials technology. The innovation consists of combining different strategies, aiming at optimizing the melting process. Aluminum fins work as a thermal bridge between the back of the FV panel and the PCM, while the presence of graphene nanoparticles increases the thermal conductivity of PCM. The procedure for preparing samples is widely presented in the paper. Initially, the proposed solution is tested under a solar simulator with controllable parameters (such as radiation and ambient temperature). The enhanced panel is compared to the reference case, namely, the pure panel, under the same conditions. The aim is to obtain a minor frontal temperature in the PV panel cooled by the hybrid system. This way the conversion yield increases, and the panel produces a greater amount of energy with an equal incident radiation. Later, the two configurations are tested simultaneously outdoors, to investigate the performances under natural atmospheric conditions. The system is analyzed continuously for three days, both during the day and night, to study the performances (melting and solidification cycles of PCM) under external conditions. The paper is organized as follows: in Section 2, a detailed description is provided as regards to the materials utilized and the design phase, results are discussed in Section 3 and, in Section 4, the conclusions are listed.