# Towards Improving the Durability and Overall Performance of PV-ETICS by Application of a PCM Layer
## 1 Introduction  
Today, a Building Integrated Photovoltaic (BIPV) installation, mounted on roofs and facades, can be considered as one of the most justified on-site renewable electricity generation technologies. Typical systems of photovoltaics integrated with or applied to building materials were widely analysed and described in the context of simulation and monitoring [1]. Most of the currently used BIPV facade systems are an alteration of various rain screen cladding facades [2], curtain walls [3], spandrel panels [4] or shading systems [5]. Such systems are applied mainly in non-residential and public buildings, playing a representative role. In the case of residential buildings, BIPV mainly takes the form of shingles, slate, tiles or standard modules mounted on the roof [6]. For specific geographical localizations and weather conditions, it was proven that electricity from roof-integrated PV can significantly contribute to the improvement of the overall energy performance by reduction of the annual energy consumption in new [7] and retrofitted houses [8]. Nevertheless, thedevelopment of economically viable technology for photovoltaics integrated with external walls is still a challenge [9]. The newly developed PV system integrated with a wall [10] as described and analysed in this article can be considered as a technology for future use in the residential sector, facing the challenges mentioned above. Energy Activated External Thermal Insulation Composite System (En-ActivETIS) is an easy-to-apply, wall-integrated structure based on the well-known ETICS system used for new buildings and building renovations [11]. Unlike typical ETICS, a flexible photovoltaic is applied instead of the existing cement plaster. Single panels can be combined into sections in different arrangements. The proposed technology is an original solution that combines the benefits of a typical well-insulated wall with a photovoltaic built into the building. The limitations in the design of the system include the total area of the walls as well as the size and configuration of the windows. Corresponding to [12], the problem of overheating has been identified as the cause of the decline in energy conversion efficiency [13], mechanical stresses [14], electrical damage [15] and general degradation of the system [16]. The influence of temperature on the production of electricity from photovoltaics was investigated in different applications. As determined by [17], for a multicrystalline silicon photovoltaic module, 1000 h exposure at 85 \({}^{\circ}\)C and 85% relative humidity reduces the average normalized maximum power by 10%. In the case of open-rack panels, such exposure means > 100 years in Munich, 25-50 years in Miami and 6-11 years in Riyadh [18]. Nevertheless, for a poorly ventilated BIPV, the risk of panel overheating is supposed to be significantly higher than in the case of free-standing installations. A subsequent challenge for the insulation layer is the thermal degradation of expanded polystyrene, which is widely used in ETICS. [PERSON] et al. [19] examined various types of expanded polystyrene and noticed that the polymer spheres collapse when exposed to elevated temperatures around 110-120 \({}^{\circ}\)C. Subsequent studies were carried out for expanded graphite polystyrene [20], which is now commonly used in new buildings. It was found that in direct sunlight and temperatures higher than 85 \({}^{\circ}\)C, grey polystyrene is destroyed. As En-ActivETICS is designed as a technological solution without ventilation of the internal surface, there is a high risk of overheating, thermal stresses and mechanical damage in the interstitial joints. One of the main challenges is protection from the possibility of overheating of the external layers (PV panel, adhesive and reinforcing mesh) and the decrease of a large temperature difference between the area covered with standard and activated ETICS. Due to differences in colour and structure of the outer layer, the surfaces may differ significantly in solar absorptivity.