• Energy Research

Abstract Photovoltaic modules were manufactured by vacuum resin infusion process using glass reinforced epoxy composite as encapsulant where the cells are embedded. Incorporation of ultraviolet absorber (UVA) and hindered amine light stabilizer (HALS) additives to the epoxy resin was studied, given their potential to enhance the performance stability of the modules under ultraviolet (UV) radiation exposure. Photovoltaic and aging performance were examined through the evolution of external quantum efficiency (EQE) spectra, short-circuit current values and colour change. Decrease in the initial photovoltaic performance of the modules was observed, as evidenced in the short-circuit losses when additives are incorporated. Regarding the performance stability, increasing the content of both, UVA and HALS, leaded to improved results with lower short-circuit current loss and yellowness observed due to UV radiation. The most stable module, with cells embedded in 1% UVA and 1% HALS containing composite, showed a 2.8% short-circuit current loss after an UV exposure of 15.4 KWh/m2. UV protection enhancement was obtained in trade-off with initial photovoltaic performance, which should be considered when defining the additives and the amount to be used.

Abstract The front cover glass required for photovoltaic (PV) module insulation is the first surface in receiving irradiation towards solar cell, and the first surface in limiting the photon flux impinging it due to optical losses, which can be counteracted by means of antireflective (AR) coatings. The soiling adherence inherently disrupts the intended function of the AR coatings, thus reducing the power output of the PV plants. In this work, hydrophobicity of highly antireflective layer stacks was pursued to deal against soiling adherence. Whereas antireflection property has a direct effect on the minimization of cell-to-module losses, antisoiling property reduces maintenance expenditures, both contributing to the reduction of levelized cost of energy. Properties of methyl-silylated silica and polyfluoroalkyl-silica mono- and bi-layer stacks were compared to achieve the most rational AR design based on a proper trade-off between cost-efficiency, processability, optical properties, mechanical properties and reliability during real life operation. Nanoindentation permitted to compare hardness of different coatings; cohesion and adhesion were studied by nanoscratch, both related to cleaning resistance studied by reciprocating wear test. Effect of AR layer stacks on electrical response of monocrystalline silicon cells was assessed during outdoor exposure as well as the effect of environmental relative humidity on the optical properties. Methyl-silylated silica mono-layer and polyfluoroalkyl-silica bi-layer both prepared in two-steps were the more rational designs based on adhesion, mechanical properties and abrasion resistance to cleaning process. They showed an equivalent overgeneration of 2% when applied on cover glass of PV mono-modules compared to uncoated ones along one-year exposure.

A simple analytical calculation based on a transfer matrix method for incoherent optics, allowing the prediction of photovoltaic module efficiencies in different encapsulation conditions is presented. This approach is used for the experimental validation of the main features of the optical model for multilayer glazing systems considered, through the relation between the external quantum efficiency of the module and its optical modeling. The theoretical procedure avoids the need to manufacture and characterize by solar simulator or external quantum efficiency measurements all the variety of photovoltaic module configurations, which is of interest at research and manufacturing levels, especially for building-integrated photovoltaics. The absorptivity of encapsulated solar cells is not directly accessible from direct air-bare cell or air-encapsulated cell optical measurements, and therefore analytical or numerical methods are generally needed. The calculations presented in this work provide closed analytical expressions for the layer-by-layer absorption of the different components of a photovoltaic module. From a small set of experimental measurements of a particular encapsulation configuration, and the theoretical expressions for spectral absorptivities, the short-circuit current of a module can be predicted for any other encapsulation scheme. It will be proved that the method accurately matches short-circuit current density of the modules as obtained from experimental measurements. Results will be presented for crystalline silicon and CIGS thin film cell technologies with several glass and encapsulation material combinations. This work has received funding from the European Union’s Seventh Programme for research, technological development and demonstration under Grant Agreement No 609788.

Abstract The present work aims encapsulating photovoltaic cells in glass reinforced epoxy composite by vacuum resin infusion, incorporating additives directed to enhance the performance stability of the manufactured photovoltaic modules under ultraviolet (UV) exposure. UV absorber (UVA) and hindered amine light stabilizer (HALS) additives were incorporated in the resin system in different content. Photovoltaic performance and stability under UV radiation exposure were studied through external quantum efficiency (EQE) spectra, chromatic coordinates and short-circuit current values. Decrease in current values and increase in yellowness were observed in the presence of UVA and HALS. However, an enhanced performance stability was observed when additives are incorporated, improving the stability when increasing the additive amount. The most stable module, with cells embedded in 2% additive containing composite, showed a 2.7% short-circuit current loss after UV aging exposure.