• Energy Research

AbstractIn the field of hybrid photovoltaic cell technology, the present work aims studying titanium dioxide layers with ordered nanostructure and poly-3-methylthiophene (P3MT) films in-situ electropolymerized onto them. Nanotube arrays were synthesized by anodization technique using a wide range of process conditions, and the dimensions and morphology of the obtained nanotubes were thoroughly analyzed. This study allowed tailoring the nanotube dimensions as requested by the final application. In this case, arrays with low thickness and large pore diameter, obtained in the acidic water based electrolyte, were selected to carry out further electropolymerization onto them. The nanotube pore diameter was identified as the dominant parameter influencing the P3MT layer thickness. The P3MT layers with the lowest thickness were obtained onto the less porous morphologies with low nanopore diameter values.

Photovoltaic modules consisting of one back-contact cell were manufactured by vacuum resin infusion process using glass reinforced epoxy composite as encapsulant where the cells are embedded. Incorporation of three coatings onto the composite surface was studied with the aim to improve the electrical performance stability of the modules under ultraviolet (UV), thermal cycling and damp-heat environmental weathering. Photovoltaic and aging performance were examined through the short-circuit current density values and colour change of the composite. Decrease in the initial photovoltaic performance of the modules was caused by the coating deposition. The highest drop in the initial values was observed for the varnish type coating, showing a decrease of 2.6% in short-circuit current. Regarding the performance stability, the decrease was more pronounced in the damp-heat test, presenting the varnish type coating the minimum loss of 1.4% in short-circuit current and a variation of 87% in b* chromatic parameter after 1000 h exposure at 85 °C and 85% relative humidity. The study concluded that the protective coating should be selected to provide the composite modules with an optimal trade-off between the initial electrical performance and the desired stability, with further research work targeted to improve moisture barrier properties. This work was supported by Eurostars Programme (Grant Agreement E12409) and Basque Government Elkartek 2021 Programme (Grant Agreement KK-2021/00066).

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.

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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.

The electrical ageing of photovoltaic modules during extended damp-heat tests at different stress levels is investigated for three types of crystalline silicon photovoltaic modules with different backsheets, encapsulants and cell types. Deploying different stress levels allows determination of an equivalent stress dose function, which is a first step towards a lifetime prediction of devices. The derived humidity dose is used to characterise the degradation of power as well as that of the solar cell's equivalent circuit parameters calculated from measured current–voltage characteristics. An application of this to the samples demonstrates different modes in the degradation and thus enables better understanding of the module's underlying ageing mechanisms. The analysis of changes in the solar cell equivalent circuit parameters identified the primary contributors to the power degradation and distinguished the potential ageing mechanism for each types of module investigated in this paper. © 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd. © 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd. This work was supported in part by the European Commission under FP7 grant N° 262533 SOPHIA (INFRA-2010- 1.1.22_CP-CSA-Infra) and by the Research Councils UK (RCUK) under project ‘Stability and Performance of Photovoltaics (STAPP)’ (contract no: EP/H040331/1).

Abstract An efficient and environment-friendly process, consisting of acid-catalyzed sol-gel process combined with evaporation induced self-assembly, was conducted to build antireflective (AR) layer stacks for concentrated solar applications. Considering the external factors that may alter the optical properties of the system when operating outdoors, such as soiling, harsh climate conditions and alkali ions diffusion from glass, several stack configurations were proposed. Particularly, the effect of a methyl-silylating post-treatment, the presence of the inner layer and the optimization of sintering temperature have been devised in order to minimize soiling adherence and alkali diffusion from the glass substrate and to assure the required robustness to comply with the durability requirements. The assessment consisted of (i) an analysis of the optical transmittance, reflectance and refractive index and (ii) hydrophobicity and effect of water absorption on the external porous coatings in relation to the results of accelerated aging tests following photovoltaics standards. The main goal was to achieve the most rational design, based on a proper trade-off between cost efficiency, processability, optical properties and reliability during real life operation.

This paper studies a new innovative concrete with phase change materials (PCM) on thermal aspects. The final objective is to develop a product which would achieve important energy savings in buildings. The work here presented is the construction and experimental installation of two real size concrete cubicles to study the effect of the inclusion of a PCM with a melting point of 26 °C. The cubicles were constructed in the locality of Puigverd of Lleida (Spain). The results of this study show the energy storage in the walls by encapsulating PCMs and the comparison with conventional concrete without PCMs leading to an improved thermal inertia as well as lower inner temperatures.