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37th European Photovoltaic Solar Energy Conference and Exhibition; 792-795, The recent trend to increase the PV system voltage from 1000 V to 1500 V implies a higher PID stress level for the PV modules. This raises the question whether the modules might face PID problems caused by 1500 V system voltage during long-term field operation. Particularly, the IEC TS 62804-1 PID test does not provide a correlation between accelerated chamber testing and outdoor field operation. In this work, we follow the principle established for thin film modules according to the IEC TS 62804-2, where the transferred charge is the metric for the PID stress load. Furthermore, in order to transfer charge as fast as possible during lab testing, extreme PID testing conditions were applied. Test modules were manufactured combining two types of c-Si cells, “more PID stable” and “less PID stable”, with three types of encapsulation material, EVA1, EVA-2, and POE respectively. Surprisingly the IEC standard test could not differentiate the PID susceptibilities of the test modules. Even prolonged testing did not provoke a further degradation. Dropping leakage currents due to a blocking anode effect are suspected as the root cause for the observed, but misleading PID stability. In contrast to this, a clear differentiation of the module´s PID susceptibility was possible with our extreme test conditions. The transferred Coulombs under real outdoor conditions were measured at the ZSW test field for a whole year. With this information, the PID service life could be predicted. Modules based on POE are predicted to stay free from PID during a service life of 40 years.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1762-1769, The new functional encapsulation layer which is presented in this study, known as conduction path on encapsulant (CPOE), has the potential to interconnect high efficiency IBC solar cells. In our study, single cell demonstrator modules were assembled reaching an efficiency of 19.3% with relative cell to module (CTM) losses below 2%. However, this concept so far requires reduction in the cell area (e.g. one-eighth cell size module design) since significant losses in FF were observed due to the high resistive losses in the CPOE. Accelerated environmental indoor tests reveal that the module based on CPOE technology passes the precondition ultra-violet (UV) degradation and damp heat (DH) exposure test for 1250 hrs. without any signs of degradation in the module packaging materials or electrically power losses. However, thermo-cycling for 200 cycles reveal relative Pmpp losses higher than 5%. Additionally, power degradation after applying a PID test at +1000V at 85°C was observed. Finally, outdoor energy yield studies of the CPOE modules compared with Zebra and p-type cell modules with soldered ribbons as references reveal higher energy yield (Ya) and performance ratio (PR) of CPOE and Zebra reference than p-type full cell module. In addition during cloudy days, CPOE modules show better energy performance when compared to Zebra reference modules.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 2570-2576, This work aims to determine the contribution of smart photovoltaic (PV) windows with integrated luminescent solar concentrators (LSCs) to the energy performance of near-zero energy buildings (NZEB). The work focused a case study in Santiago of Chile, taking as a starting point local parameters such as the overall energy requirements, geometrical features and consumption patterns of office buildings in this location. Dynamic simulations were done to assess buildings features for energy efficiency, considering different estimated performances of the smart windows system. For rectangular-shaped buildings with windows mainly facing the sun, and considering daily occupation and the use of energy-efficient appliances together with high performance insulated walls, simulation results highlight a contribution of the smart window up to nearly one-half of the buildings energy demand. In usual office buildings this contribution is somewhat less expressive, but proper construction features can be regulated to meet the energy-efficiency goals stated by many countries, in line with the Paris Agreement for climate action.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 2564-2569, This paper describes the main findings of the WINNER project, focused on the development of an innovative smart window based in the concept of luminescent solar concentrators (LSCs). Different luminophores have been used to realize semitransparent and colorless photovoltaic (PV) windows to convert the energy-passive façades of urban buildings into effective energy and, at the same time, promoting building’s visual and thermal comfort. Here we used inorganic dyes with rare-earth elements such as Eu3+ and Dy3+, and Nd3+/Yb3+ lanthanide couple to down-shift the solar spectrum towards the NIR wavelength range where the solar cells have an optimal response. Experimental results demonstrate an optical power efficiency of 2.2% (inorganic dyes) and 1.3% (lanthanides) under AM1.5G conditions for 3.5x3.5 cm2 tinted and fully transparent (optical transmittance ≈ 90%) LSCs. The design of the smart window was completed following a study of user and architectural requirements as well as market trends. The LSC system integrates not only the PV cells on the window frame but also all the basic electronic components for an autonomous mode of operation, including batteries and miniaturized balance-of-system elements. These results open the way for the realization of visible transparent solar energy harvesting clear glass windows.

31st European Photovoltaic Solar Energy Conference and Exhibition; 149-152, The aim of this work is the development of an innovative module encapsulation technology based on a novel encapsulation foil with intrinsic conductive structures. The system is able to replace traditional interconnection schemes based on ribbon soldering, enabling a highly efficiency module assembly process and therefore increasing productivity and potentially reducing production costs. Conductive encapsulant foils are produced by combining advanced conductive inks with high-throughput roll-to-roll printed electronics technologies for the production of the conductive structures. Special focus is placed on developing printing and ink sintering processes for the intrinsic conductors, which i) maintain the properties of the encapsulant material, ii) meet stringent specifications regarding flexibility and mechanical strength of the conductive network and iii) reach high electrical serial and contact resistance after a typical lamination cycle.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 4253-4256, Reducing the nominal operation cell temperature (NOCT) of a PV module is one way to increase the energy yield and performance ratio of PV systems. We have built a thermal model of the PV module, in order to analyze the influence of different module design and installation parameters on the thermal performance of the system. The impact of building integrated installations on the thermal performance has been investigated. Several PV module samples with different configurations have been built and experimentally monitored in order to verify the model results. Also, the influence of the operating temperature on the energy yield of PV modules has been analyzed through simulations and experimental measurements.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 2705-2708, During the last years, new stringing techniques with low stress have been developed, such as the use of conductive adhesives [1], low temperature solders [2] or laser soldering. The aim of this work is to evaluate the stress introduced in the cells during the soldering process, making a comparison between different techniques and solder materials that exist nowadays in the market. The interconnection technologies under investigation have been: lowtemperature snap-cure conductive adhesives, induction and infrared soldering and laser spot soldering. For the soldering approaches different alloys and materials were evaluated, such as low temperature solders, low CTE alloys and copper ribbons of very low yield strength. Electroluminescence imaging and mechanical tests have been used to quantify the stress experienced by the cells. In addition, the possible propagation of microcracks during thermal cycling has been investigated.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 2986-2988, This paper analyses the electrical and thermal effects that partial shadowing commonly causes in PV modules. After typifying different possible shading configurations we have reproduced them in the laboratory and outdoors and have measured the IV characteristic curve at those different operation conditions. Also outdoors we have taken IR thermographies from the back side of the PV modules in order to evaluate the thermal effects with partial shading. The shadowing pattern and the PV module configuration are determinant of the electrical and thermal effects, although also the irradiance level, the clearness index and the ambience temperature have to be considered. Especially harmful is a shadow over part of all the sub-strings associated to different bypass diodes. In general if a PV module is constituted by series connected PV cells a good design for building integration would be a nearly squared module with a bypass diode every two adjacent columns (around 18 PV cells).

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 2698-2700, One cause of power losses in photovoltaic systems is the accumulated dirt on modules surface, mainly dust but also bird droppings. It is usual to include a loss factor for this cause about 3-4%. The large grid-connect photovoltaic plants include periodic modules cleaning to avoid these losses. In this paper we have quantified the losses caused by accumulated dirt on module surface. The use of textured glasses increases the performance of the modules due to the decrease of reflection losses. We have checked if these losses depend on the structure of the module surface and also if the rain cleans well enough the modules and in which conditions this cleaning happens. The obtained results show that losses due to accumulated dirt in modules can reach values about the 15% for period without rain. We have measure yearly average dirt values of losses about 6% that is greater than the values used in the sizing and design of grid-connected photovoltaic systems. We can conclude that textured glasses do not accumulate more dirt than the non-textured glasses and therefore the maintenance of photovoltaic system with textured glasses does not mean additional expenses.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 2834-2836, This paper presents first results of an experimental work that is being carried out at CIEMAT in collaboration with ISOFOTON, to evaluate mismatch effects of PV devices serially connected. With this purpose, a special module consisting of two 8 cell strings plus four additional special cells has been manufactured. Individual cells can be accessed for measurement, so that module I-V characteristic can be measured at the same time than individual cell voltages. First results of working point of cells for different module operation conditions are presented, together with the effect of substituting string cells by special cells (low Isc and/or FF). The study is complemented by IR characterization of the module.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 346-349, We study the effect of the white rear sheet located around photocells in photovoltaic modules. This white sheet reflects part of the incident light back to the photocell by means of internal reflections, thus increasing the production of electrical current with a low additional cost. We have developed a software program that simulates a simple module with once cell in order to obtain the improvement of electrical current production as a function of the width of the white strip surrounding the cell. We find that the wider the white sheet around the photocell, the greater the increase of electrical current generated in it. These results will help to the optimization of the design of solar panels. We obtain a good agreement when comparing our simulation results with measurements carried out in a real prototype.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 2701-2704, Series resistance characterization and its associated power losses are of great importance in the PV module design process. A general modelling tool has been built, which allows the calculation of the power losses in a PV module due to the series resistance increase during the interconnection process. The model has been used to evaluate recently developed interconnection processes such as conductive adhesives, new interconnecting ribbon materials and new metallization grid designs with three or more busbars. A sensibility analysis of each input parameter has been carried out. The model has been validated by comparison with experimental measurements of the series resistance in cells interconnected with different methods.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 2858-2860, Moisture ingress into a photovoltaic module accelerates the degradation phenomena in different ways [1-3]. Polymeric components of photovoltaic modules are sensitive to moisture, due to hydrolysis reactions which can cause changes in their chemical structure and therefore in their properties. Hydrolysis of EVA leads to the formation of acetic acid, which accelerates the corrosion reactions of metallic parts of the circuit. PET hydrolysis is also an undesirable process caused by the presence of water inside the module. In addition, moisture ingress will reduce the adhesion between glass and EVA. This work is focused on investigating the behaviour in terms of moisture ingress of some new backsheets that have recently appeared in the PV market due to the shortage of Tedlar®. After a market survey, suitable humidity sensors have been selected and used to quantify the humidity content inside the module while it is being exposed to damp heat conditions. Gravimetric measurements have also been carried out to evaluate the water vapour ingress rates at different exposure times to various conditions of temperature and relative humidity.