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8th World Conference on Photovoltaic Energy Conversion; 488-491, BIPV (Building Integrated Photovoltaics) systems play an important role in generating electricity for net-zero energy buildings. Since BIPV modules and systems are fully integrated into the building envelope, their rear side is exposed to no or low ventilation, leading to increased operating temperature. Therefore, the performance of the modules – which decreases with increasing temperatures – is reduced, and the durability of the module – and its components (e.g. encapsulant, backsheet etc.) – may be impacted. Over the years, three different BIPV mock-ups have been installed at SUPSI (in Southern Switzerland) in different configurations: open-rack, BIPV-ventilated (partial ventilation) and BIPV-insulated (no ventilation) to investigate the impact of the operating temperature on the long-term performance of different BIPV modules. In this work, first, we show that since larger thermal stress accelerates UVinduced degradation of EVA (discoloration), there could be loss in Isc in BIPV configurations. Secondly, due to larger thermo-mechanical stress, there could be damaged cells and metallization, which causes loss in FF. Additionally, operating in a BIPV configuration does not mean that there will be faster degradation. There could be faster degradation only if there are larger thermal and-or thermo-mechanical stresses.

8th World Conference on Photovoltaic Energy Conversion; 95-97, We present passivating contacts for silicon solar cells using an interfacial layer of SiO2 grown by immersion in hot HNO3 and in-situ doped layers of both polarities grown by plasma enhanced chemical vapor deposition (PECVD). The doped layers are crystallized and their dopants are activated by rapid thermal processing (RTP) with a temperature profile similar to the firing of screen-printed metallization pastes, hence we call them fired passivating contacts (FPCs). After RTP, we apply hydrogenation to passivate defects, using thermal release of hydrogen from a SiNx reservoir layer during hot plate annealing at 450°C. We find that the kinetics of the hydrogenation process is characterized by a fast process associated to the passivation of defect states at the Si/SiO2 interface and a slower process likely related to the hydrogenation of bulk defects that are formed during RTP in the floating zone wafers used in this experiment. Despite the issue with bulk defects, we test the suitability of the FPCs for solar cells by depositing n- and p-type layers on the textured front and on the flat rear of single-side textured wafers, respectively. After co-processing in a single RTP step, we apply the optimum hydrogenation conditions identified above. Using an ITO/Ag metallization made at low temperature to fabricate proof-ofconcept solar cells, we obtain efficiencies up 20.5%.

8th World Conference on Photovoltaic Energy Conversion; 902-906, Aesthetics plays a major role in the development of BIPV products. Several BIPV module manufacturers attempt to mask the reflective metallic interconnects to obtain uniformly colored modules. This is achieved using expensive manufacturing steps, such as colored stripes with manual positioning. Inks could be an alternative to perform this process automatically. However, inks used in BIPV products must be extremely stable and do not alter their visual appearance over time. In this work, we propose a screening protocol to assess the long-term stability of seven commercial black colored inks used to mask ribbons. We apply it to coupons mimicking the structure of conventional glass/glass (G/G) and glass/backsheet (G/Bs) structures encapsulated with EVA and POE, and to one-cell modules with ink-coated ribbons with the help of an in-house developed ribbon coating equipment. The protocol includes three different test sequences. Sequence A involves 250 h of DH (85°C, 85%RH) followed by to 60 kWh/m2 of UV light exposure, sequence B the UV test only, and sequence C adhesion tests. The results show no degradation after the DH test and yellowing with unstable inks after the UV exposure. The electrical performance of modules coated with UV unstable inks, is only slightly affected (~-1%).

8th World Conference on Photovoltaic Energy Conversion; 1285-1288, PV systems' short- and long-term performances are often analyzed using satellite-derived insolation data. Despite the fact that higher uncertainties are associated with satellite-derived insolation data, no studies have been conducted to quantify the impact on the assessment of the PV plant's performance ratio (PR), used to judge the overall health status of a plant. In order to evaluate the performance of a PV system accurately, the uncertainty contribution needs to be carefully computed. In this work, we quantify: (1) the accuracy of two satellite-derived insolation data-set (opensource and paid service) with respect to the irradiance ground measurement obtained by properly maintained sensors; and (2) their effect on the uncertainty of the plant’s PR computed using satellite-derived insolation with different temporal resolutions. The uncertainty of PR computed using insolation data from a well-maintained and regularly recalibrated pyranometer computed as 3.6% (k=2), and it assumed constant for all temporal resolutions (daily, monthly and yearly) as a conservative assumption. The statistical evaluation shows that monthly and yearly PR values, which have an uncertainty of less than 5%, can be obtained using satellite-derived insolation data without having to deal with regular calibration and maintenance of an on-site pyranometer. We showed that depending on the quality of satellite-derived data and temporal resolution, uncertainty of PR differs. The PR computed using paid-service satellite-derived data has approximately a 1.7% lower uncertainty (k=2) than the PR computed using open-source satellite-derived data for the temporal resolutions considered (day and month), with the exception of the yearly resolution (for which this value is 0.6% lower).

8th World Conference on Photovoltaic Energy Conversion; 636-641, Silicon heterojunction (SHJ) solar cells and bifacial modules are expected to rapidly grow in the PV market, with their high power conversion efficiency, good performance at low irradiation and better temperature coefficients (TCs) allowing for improved energy yields. It is therefore increasingly relevant to have comparative analyses with conventional monofacial modules and market leading PERC cells. The aim of this contribution is to assess the performance of five PV modules on a rooftop monitoring station in Neuchâtel: two bifacial SHJ, two monofacial SHJ and one benchmark monofacial PERC. These three module types allow for detailed comparisons of performance enhancing factors both on the module structure and solar cell technology levels, allowing to decouple individual performance effects. After almost two years of monitoring, results show that bifacial modules yield 7.2% energy gains over both monofacial technologies, and 5% improved performance ratio (PR). For the corrected PR, current bifacial corrections may not fully describe the angular, optical and seasonal effects, as a 2.2% bifacial gain is still observed after temperature and rear irradiance corrections, leaving room for improvement in the current bifacial PR definition. In terms of temperature dependence, field-based TCs are found to be better for SHJ cells than PERC (-0.16%/°C vs. -0.31%/°C at STC, respectively), although performance gains also vary with irradiance conditions.

38th European Photovoltaic Solar Energy Conference and Exhibition; 749-753, Corrosion is one main lifetime limiting degradation modes of photovoltaic (PV) modules. The process is usually gradual and it can take decades to become a factor that significantly affects performance because of the slow accumulation of moisture and acetic acid (from encapsulant degradation). In this work accelerated corrosion tests were performed on modules with Al-back surface field (BSF) and silicon heterojunction (SHJ) solar cells by immersion in water or acetic acid baths. After lamination the top encapsulant/glass were removed so that only the front size of the cells was exposed. During the tests to failure three factors were varied: acid concentration, temperature, and electrical bias. SHJ solar cells were found to be more resistant to degradation than Al-BSF cells. For all factors studied the presence of acid accelerated degradation compared to the control tests with water. Elevated temperatures accelerated the rate of degradation by several times. Application of electrical bias led to an initial drop in current, but these modules eventually outperformed the non-biased modules. Lead oxides were the primary degradation products detected, found to accumulate mostly along the printed metallization in proximity to the busbar. The accelerated corrosion test methodology is being optimized to match characteristics observed in field modules with corrosion, and can readily be applied to other solar cell, metallization, and interconnection technologies to assess their long-term durability.

38th European Photovoltaic Solar Energy Conference and Exhibition; 1388-1393, Building integrated photovoltaic (BIPV) systems often operate under elevated temperatures and recurrent shading, which can accelerate performance loss. However, to date there are few reports on long-term performance of BIPV systems, as distinct from building applied PV (BAPV). This work reports the performance loss rates (PLR) after 5 to 10 years of operation of 55 rooftop BIPV systems in Switzerland. Median PLR was calculated to be 0.06% per year, indicating essentially no degradation, though there was a large spread of rates. Some systems were noted to be shaded at times, so a fault detection and diagnosis algorithm (FDDA) was developed to quantify shading severity. The FDDA used DC voltage and current and meteorological data as inputs and classified faults according to pre-defined thresholds. Faults caused by shading were grouped to determine the shading factor of each system. Shading factor showed a weak correlation to PLR, but delineated an upper limit, indicating it limits maximum achievable performance. Shading factor was found to increase in newer systems, and decrease with system capacity. Through innovative BIPV module and system design, the effect of shading and corresponding performance losses can be mitigated.

38th European Photovoltaic Solar Energy Conference and Exhibition; 1037-1041, Accurate assessment of the long-term performance of photovoltaic (PV) systems is critical for manufacturers, investors, plant owners and O&M companies. M any PV systems, especially residential and some commercial/industrial systems, are not equipped with meteorological monitoring systems such as irradiance and temperature sensors. Whereas to calculate the performance ratio (PR), a common performance measure, the plane of array irradiance (GPOA) is an input parameter. The irradiance data is the largest contribution to uncertainty in PR. Therefore, in this study, we first evaluate satellite-based irradiance and compare to ground-based irradiance data. Next, we investigate the accuracy of using the satellite-based meteorological data in long-term performance analysis of three test modules in the absence of ground-based data. We use (1) ground-based and (2) satellite-based data separately as input irradiance. We calculate 60 PR time series and performance loss rates (PLR) for each irradiance data using different filtering methods and performance metrics. As a representative PLR value, we used the mean value (excluding outliers) of the various PLR values obtained as suggested by IEA PVPS Task 13. For the first module, this method gave almost identical PLR values (-0.5% error) when ground- and satellite-based data are used. For the other two modules, the values are not identical, but standard deviations largely overlap. We show that when the mean of PLR values is used, it is possible to accurately evaluate the long-term performance using satellite-based meteorological data.

38th European Photovoltaic Solar Energy Conference and Exhibition; 1608-1611, In order to minimize unnecessary land exploitation and to allow PV to play a major role in the decarbonization of Europe, a massive deployment of PV in Europe should occur through the integration of PV in buildings and infrastructures, including the integration of PV on surfaces with a sub-optimal orientation. To assess the meaningfulness of installing PV on surfaces with sub-optimal orientations, we consider firstly the carbon intensity balances for PV. We show that for several cities (Milan, Frankfurt, La Valletta, …), it becomes obvious that a carbon intensity balance is largely in favor of PV not only for the optimal orientations, but also for less favorable ones: i.e. all the facades, including north-facing ones. For other cities/countries with a very low carbon footprint for the local electricity mixes (e.g. Oslo), the installation of PV may in principle not always be justifiable exclusively from a carbon balance point of view. We should however point out that in countries massively relying on nuclear power for their electricity supply – or planning nuclear phase-outs - other elements should be considered simultaneously. We also highlight the fact that installations in surfaces with less optimal orientations (e.g. north-facing facades) should possibly not be incentivized in the first place, but not expressly “prohibited” (or abandoned), as we have demonstrated that, in several countries, they are fully justifiable from the point of view of a carbon footprint balance. In addition, this may still help in promoting and creating “PV-awareness” among citizens and help architects in preserving building harmony/aesthetics.

The aim of this work is to propose a BIPV module design that is contemporarily lightweight, rigid and resistant to the relevant climatic and mechanical stresses (e.g. exposure to DH, UV, hail impacts, etc), supporting structure and reliability at the same time. Encapsulants represent a key part in the PV structure, acting as the bonding layer between the front or back sheet and the PV cell. Therefore, they need to provide excellent adhesion between these components, which is achieved via lamination. They also have to be transparent and provide outstanding electrical insulation and impact resistance to the module. All these properties must be retained after years of exposure to the UV from the sun or other severe weather conditions. With this work, we want to provide a “recipe” to define and qualify the optimum front sheet encapsulant for the proposed lightweight composite PV modules. Keywords: lightweight PV modules, encapsulants, frontsheet, hail resistance

37th European Photovoltaic Solar Energy Conference and Exhibition; 256-260, A premium photovoltaic module technology with high efficiency, high reliability, and low LCOE has been industrialized in Europe by Enel Green Power in the framework of the H2020 funded project AMPERE, acronym for Automated photovoltaic cell and Module industrial Production to regain and secure European Renewable Energy market.. An innovative full-scale automated 200MWp/y production line of innovative silicon heterojunction technology (HJT) PV bifacial cells and modules has been started up in 2019 in Catania (Italy). In this paper we report the main outcome of this successful project. All the processes, methods, techniques, automation systems developed in the project and used in production represent an innovation with respect to the market mainstream technologies and with respect to the current practice in PV industry. The manufacturing plant is actually representing a technological leap that revolutionizes the production of the system allowing a new line of European latest-generation bifacial photovoltaic HJT modules.

37th European Photovoltaic Solar Energy Conference and Exhibition; 1108-1111, For some PV applications, the weight of c-Si PV modules is a crucial aspect that needs to be addressed. Commercial and industrial buildings sometimes cannot be designed for conventional rooftop solar installations, especially without costly structural improvement. Also particular PV systems, such as, PV elements for foldable parking roofs or greenhouses need lightweight modules to enable cost effective mounting structures. Often, when old buildings undergo renovation, excessive loads are often not well tolerated by roofs or other architectural structures (e.g. facades). The adoption of conventional PV in these contexts could represent a crucial limit. The use of Lightweight modules appear very attractive, especially for the building-integration of photovoltaics (BIPV), Building Applied Photovoltaic systems (BAPV) as for Vehicles integrated PV (VIPV), due to their reduced weight and strong improvements in durability. One of the great advantages of using a lightweight module structure stands in the possibility to develop a cheap and practical mounting system solution. This is currently becoming a relevant topic, as the share of costs for mounting structures has significantly increased in the last years. Considering the option of “frameless lightweight modules” may also have a dramatic effect in lowering the transport costs. With this work, an alternative installation for lightweight (6 kg/m2) photovoltaic module is proposed. Modules with a composite sandwich backsheet and a polymeric frontsheet structure were manufactured with a new mounting system based on the use of Velcro (Hook-and-Loop). We demonstrate how this alternative mounting system allows a fast and easier mounting that comply with the static mechanical load test present in the IEC 61215.

37th European Photovoltaic Solar Energy Conference and Exhibition; 704-705, We present a process sequence for electrodeposition of copper on solar cells with aluminum zinc oxide (AZO) on the surface. The process has been originally developed for silicon heterojunction cells with indium tin oxide and comprises a sputtered seed layer and patterning by hotmelt inkjet printing. High efficiency of 24.7% has been achieved on industrial heterojunction cell precursors and excellent module stability confirmed in extended aging tests. This process has been adapted for cells having an aluminum zinc oxide electrode. Since AZO is chemically very sensitive the chemical composition of required processing solutions, and in particular for the etch-back of the seed layer, had to be modified to avoid AZO dissolution. Well adherent narrow copper lines have been realized on CIGS-AZO-surface and the fabrication of mini modules with copper electroplated grid is ongoing.

37th European Photovoltaic Solar Energy Conference and Exhibition; 228-232, For the current PV production about 2000 tons of silver are consumed per year. This is already 10% of the entire world annual silver supply. The PV production is expected to grow significantly in the next decades in order to enable the energy transition to 100% renewables. Annual production volumes in the terawatt range are predicted already for 2030 and this may lead to higher silver price and put more pressure on the industry to replace silver by copper. With the currently available processes the cost advantage of copper plating over screen printing is relatively small and the implementation of plating in production is slowed down by the high up-front investment for equipment. The highest cost share of the process sequence has the patterning and research activities focus on new, i.e. more cost competitive patterning techniques. Within the Ameliz project several approaches are investigated: firstly, patterning by printing a metal seed grid with a dielectric layer as plating mask and secondly masking by a monolayer of self-assembling molecules. These molecules consist of a phosphonic acid group and a hydrocarbon chain. They are bonded to the ITO surface and form a monolayer of well-ordered, densely packed hydrophobic chains, which protects the ITO surface against plating solutions. Furthermore, methods for selective formation of a copper seed layer by electrografting and for improved adhesion by ITO reduction are being investigated.

37th European Photovoltaic Solar Energy Conference and Exhibition; 784-788, Double glass PV modules are expected to be more durable on the long term with respect to modules in a conventional glass/back-sheet configuration. The combination of a rear and front glass cover can in fact delay or completely prevent moisture ingress into the module structure. However, water can be absorbed from the environment by the virgin encapsulant so that storage conditions can be relevant in ensuring the long-time performance of the encapsulant and the PV module. Additionally, in a glass/glass configuration products formed during the aging of the polymeric encapsulant will remain trapped inside the module, affecting the long-term performance of the module. The encapsulant choice is then an important aspect to consider for the encapsulation scheme of bifacial modules. In this work, we investigate the effect of non-optimal storage conditions of EVA and its impact on long-term UV aging. After a total UV dose of 165 kWh/m2 (corresponding to an outdoor exposure of ~2.2 years in a temperate climate the performance of 1-cell mini-modules does not vary. However, preliminary signs of chemical degradation are detectable by means of Raman and FTIR spectroscopy for the non-properly-stored polymer , suggesting that carefully controlling the storage conditions of the polymer may be critical if EVA is used in double glass structures.

37th European Photovoltaic Solar Energy Conference and Exhibition; 890-893, A premium photovoltaic module technology with high efficiency, high reliability, and low LCOE has been industrialized in Europe by Enel Green Power through the AMPERE project. An innovative full-scale automated 200MWp/y production line of SHJ bifacial cells and modules has been started up in 2019 at the Enel Green Power 3SUN Fab in Catania (Italy). In this paper, we report the investigations performed on two low interconnection solutions meeting the low temperature requirements of HJT technology that have been investigated in terms of performance, production costs and reliability: the BusBar/ribbons interconnection technology with Electrical Conductive Adhesive (ECA) and the SmartWire Contacting Technology (SWCT) developed by Meyer Burger. First, the cell metallization and the interconnection designs have been optimized. Then results have then been validated for full-size (72 cells) modules by IEC61215 certification and extended Damp Heat (DH, 85°C, 85%RH) and Thermal Cycling (TC, -40°C + 85°C) tests, leading to complete certifications of both approaches.

37th European Photovoltaic Solar Energy Conference and Exhibition; 206-207, We present a firing-through metallisation approach for n-type passivating rear contacts that consist of a tunnelling oxide and an n-doped bilayer of a-SiOx and μc-Si. We find implied Voc up to 738 mV and contact resistivities as low as 20 mΩcm2. Implemented into 6-inch solar cells with a B-diffused emitter on the front, the best cell showed a Voc of 687 mV, FF 79.4 % and an overall efficiency of 22.2 %, proving the compatibility with metallisation by a conventional firing-through process. In view of the higher iVoc of the passivating μc-Si(n) contact, higher cell efficiencies are expected through improvements of the front side.