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The inductive power transfer for photovoltaic modules was elaborated in the detailed scientific studies in order to develop a completely new and innovative PV system, which does not require a large number of traditional electrical connectors. Different variants and concepts are discussed. The most promising and expedient PV system solution has been designed in depth taking into account the close linkage of the power electronics topology based on the newest semiconductor devices with the intrinsic capacitances of the solar cells and with the magnetic circuit determined analytically as well as by electromagnetic field simulations. A classical development process would not have led to this goal. The functional principle, which was finally verified by measurements in the laboratory, is based on the fact that the DC current generated in the solar cells is converted into an AC current via a resonance converter and that it is fed through a primary planar coil. The converter and the coil will be integrated in the laminated area of the PV module. The AC voltage at the primary coil induces a voltage in the secondary coil that is located outside the PV module directly above the primary coil. The wirelessly transmitted energy is fed into parallel-connected string via a rectifier. The goal is to develop a PV system that does not require connectors, makes planning more efficient, requires less electrical expertise on site during the installation, reduces installation and maintenance costs, increases plant safety, eliminates the potential induced degradation of typical crystalline silicon PV modules and reduces cable losses or the amount of copper used, respectively. To achieve this goal, it was investigated whether required input capacitor of the converter can be substituted by the intrinsic capacitance of the solar cells. Furthermore, the design of the resonant converter was combined with an analytical coil design in order to establish their ideal geometry and in order to optimally determine other important parameters e.g. power losses, resonant frequency, switching topology, output voltage, solar cell matrix configuration. The inductive power transfer was verified by electromagnetic field simulation before the coils were manufactured, coupled by ferrite cores and connected with the resonant capacitor. This setup could be measured in the laboratory and an efficiency of 97.9% ±0.83% (k=1) was achieved. The loss models of the full-bridge LLC resonant converter, the inductive power transfer and the rectifier used during the design phase were combined with the PV performance model in order to calculate the efficiencies at different temperature and irradiance conditions. It could be shown that the wireless PV module could reach European and Californian efficiencies of 94.3% and 95.5 %, respectively. This means that this new PV system solution could have a chance on the market in the long-term due to its advantages. The potential is there to reduce the levelised cost of electricity of PV systems based on this completely new PV system approach by implementing parts of the power electronics in the solar module and wireless power transmission in the power plant. Die induktive Leistungsübertragung für Photovoltaikmodule ist in den wissenschaftlichen Detailstudien erarbeitet worden, um ein komplett neues und innovatives PV-system zu entwickeln, welches keine Vielzahl von traditionellen elektrischen Steckern benötigt. Verschiedenste Varianten und Konzepte werden diskutiert, wobei die vielversprechendste und zielführendste PV-Systemlösung in der Tiefe entworfen wurde unter Berücksichtigung der engen Verkettung von der Topologie der Leistungselektronik mit neuesten Halbleiterbauelementen mit den intrinsischen Kapazitäten der Solarzellen und mit dem Magnetkreis, bestimmt durch analytische Lösungen bzw. durch Magnetfeldsimulation. Ein klassischer Entwicklungsprozess hätte nicht zum Ziel geführt. Das Funktionsprinzip, welches schlussendlich messtechnisch im Labor überprüft werden konnte, beruht darauf, dass der in den Solarzellen produzierte Gleichstrom über einen Resonanzwandler in einen Wechselstrom umgewandelt und durch eine planare Primärspule geführt wird. Der Wandler und die Spule werden sich im laminierten Bereich des Solarmoduls befinden. Die Wechselspannung über der Primärspule induziert eine Spannung in der Sekundärspule, die ausserhalb des PV-Moduls direkt über der Primärspule angebracht wird. Die somit drahtlos übertragene Energie wird über einen Gleichrichter in einen parallel geschalteten String eingespeist. Das Ziel ist ein PV-System zu entwickeln, dass ohne Stecker auskommt, die Planung effizienter gestaltet, weniger elektrische Expertise während der Installation benötigt, den Installation- und Wartungssaufwand reduziert, die Anlagensicherheit erhöht, potenzial induzierte Degradation von klassischen kristallinen Silizium Solarmodulen eliminiert und Kabelverluste bzw. den Kupfereinsatz verringert. Um dieses Ziel zu erreichen, wurde untersucht, ob der nötige Kondensator am Eingang des Wandlers durch die intrinsischen Kapazitäten der Solarzellen substituiert werden kann. Weiter wurde das Resonanzwandlerdesign an die analytische Auslegung des Spulensystem gekoppelt, um deren ideale Geometrie und weitere wichtige Parameter wie z.B. Verlustleistungen, Resonanzfrequenz, Schaltungstopologie, Ausgangspannung, Konfiguration der Zellmatrix optimal zu bestimmen. Die induktive Leistungsübertragung wurde mittels elektromagnetischen Feldsimulationen verifiziert, bevor die Spulen gewickelt, mittels Ferritkerne gekoppelt und mit dem Resonanzkondensator verbunden wurden. Dieser Aufbau konnte im Labor vermessen und dessen Wirkungsgrad mit 97.9% ±0.83% (k=1) quantifiziert werden. Die während der Designphase angewandten Verlustleistungsmodelle des LLC Resonanzwandlers mit Vollbrückenansteuerung, der induktiven Leistungsübertragung und des Gleichrichters wurden mit einem PV-Performancemodell kombiniert, um die Effizienzen bei verschiedenen Temperaturen und Einstrahlungsbedingungen zu berechnen. Es konnte aufgezeigt werden, dass der Euro-Wirkungsgrad und der CEC-Wirkungsgrad des kabellosen PV-Moduls bei 94.3% bzw. 95.5% liegt. Somit hat diese neue PVSystemlösung langfristig durchaus Chancen am Markt mit den gegebenen Vorteilen. Durch die Umsetzung von Teilen der Leistungselektronik im Solarmodulaufbau und der drahtlosen Leistungsübertragung im Kraftwerk ist das Potenzial da, um zukünftig die Gestehungskosten von PV-Systemen mit diesem vollständig neuem Photovoltaik Systemansatz zu senken.

PV systems using bifacial modules have gained a lot of interest in recent years. Due to the bifacialty of the modules the energy yield of the systems can be enhanced compared to monofacial ones depending on the installation conditions. While bifaciality enables a larger variety of promising installation options, it is difficult to simulate or to predict the output with sufficient accuracy and a realization of test fields is an extensive task. In this work, we use a miniaturized test rig as an alternative approach for the appraisal of specific installation situations. The small size allows a quick realization of layouts and comparative outdoor power measurements at identical irradiance conditions. By means of this tool, we analyze the performance of PV systems using vertically installed, east/west-orientated, bifacial modules in combination with different grounds in comparison to state-of-the-art, east/west oriented, monofacial PV systems with low tilt angles by means of simulations and measurements. Special emphasis is given to east/west-oriented modules in combination with highly reflecting foils with and without the use of ground sculptures that lead to a weak light concentration effect.

38th European Photovoltaic Solar Energy Conference and Exhibition; 1565-1568, PV carports are an ideal solution to produce electricity locally and sustainably, while taking advantage of the dual use of the space. On average, large carports have a power output of 0.17 kWp/m2. The average costs amount to 2'100 CHF/kWp. The price per kWp decreases slightly when the power clearly increases. The costs of the PV modules are lower than the costs for the carport's foundation and supporting structure, which represent generally between 30 % and 60 % of the total costs. The amount of steel is estimated to 155 kg/kWp and the quantity of concrete required is approximately 650 kg/kWp. The specificities of the terrain naturally have an impact on these values. A carport parking space emits 690 kgCO2-eq during the construction phase and an electric vehicle (EV) 11.2 kg-Co2-eq/100 km on average. Innovative projects include retractable roofs to offers the potential to reduce the amount of material used in the mounting structure, due to storing the PV modules in a safety box during heavy wind or snow load. The use of wood instead of metal, and screws anchor instead of concrete, as well as the addition of greenery, greatly reduces total CO2 emissions.

38th European Photovoltaic Solar Energy Conference and Exhibition; 1187-1192, Several mono- and bifacial mc-Si PV modules were installed at a location 2500 m above sea level in the Alps and grouped in six segments with different inclinations 30°, 70° and 90°. The PV modules and the meteorological conditions are monitored minutely and compared to a 30° tilted PV module installed in the urban region of Zurich. During the analysis period between October 2018 and September 2020, the yield loss due to snow coverage was minimal. The highest loss was 2.3 % (2018/19) and 3.6 % (2019/20) for the 30° inclined PV modules evaluated by the introduced snow coverage model based on electrical and weather data. The two segments with a 30° inclination showed a 20.9 % to 27.2 % higher yield than the PV module installed in the urban region, mostly produced in the winter season. The bifacial alpine energy yield is about twice as high as that of the urban PV module from November to May. The highest yields of 1800 Wh/Wp in 2018/19 and 1696 Wh/Wp in 2019/20 was measured at the 70° tilted bifacial PV module without losses due to row shading as it is expected in PV plants.

Grid codes around the world are requiring grid-support functions (GSFs) and standardized interoperability interfaces for distributed energy resources (DERs) to address the rapid increase of renewable energy. However, these new GSFs need to be assessed to ensure the desired power and communication capabilities exist in the field. The IEEE 1547.1 standard outlines the conformance test procedures for DER devices and is currently undergoing a major revision to align it with IEEE 1547–2018. Once it is published (anticipated in mid-2020), GSFs in commercial PV inverters in USA and Canada will be certified to the IEEE 1547.1 conformance test procedures. Several international research laboratories are collaborating to develop a versatile open-source DER testing platform that performs automated testing of DER devices. This community of laboratories is developing open-source IEEE Std. 1547.1 test scripts to lower barriers to DER vendor internal equipment evaluations, ease product compliance testing at certification laboratories, and provide research institutions a tool to study DER behaviors. In this work, test scripts were used for test verification of GSFs, including limit active power, constant reactive power, active power-reactive power (watt-var), and prioritization of GSF response for several DER devices. Sample test results for these DER GSFs and test protocol recommendations are presented in this paper.

37th European Photovoltaic Solar Energy Conference and Exhibition; 1188-1194, In the last decade, very few papers with outdoor measurement test results were published, which demonstrated a benefit of module-level power electronics (MLPE) higher than the measurement uncertainty. Due to the expected small difference in efficiency between conventional string-inverter based and MLPE systems, indoor measurements are required to exclude natural variation of solar irradiance in outdoor tests. Therefore, indoor efficiency measurements were performed on MLPE. Afterwards, the indoor measured efficiency of the single PV module DC/DC power optimizers were multiplied with the DC/AC inverter measurements. The final system efficiency with the maximum average value resulted in 94.78 % and with the power weighted efficiency in 94.37 %. Accordingly, if mismatches are neglected, the analysed MLPE system is expected to yield approximately 2.82% less energy than a comparable stringinverter based system in unshaded conditions. However, in the case of shading, the tested system with heavy-shading orthogonal to the cell strings was estimated to yield approximately 3.5 % more energy on a clear-sky day in March in Winterthur, Switzerland. The performances determined in the tests are significantly lower than the efficiencies provided by the datasheet of the power optimizers (around -2.29 %). However, they are still presumed to provide significant additional yields for PV systems with medium- and heavy-shading conditions.

36th European Photovoltaic Solar Energy Conference and Exhibition; 1209-1211, A first wireless PV module prototype is presented. The energy transfer from the solar cells to the string cable is done using the inductive power transfer technology. A half-bridge LLC resonant converter is designed for the DC/AC conversion. The wireless module consists of 60 half-cells and an integrated planar coil. The resonant converter is not yet integrated into the module, but it can be connected externally to the planar coil. The energy is transferred from the primary coil to the secondary planar coil placed outside of the PV module on top of the primary coil. An active rectifier is connected to the secondary coil and it feeds the DC system cable. The first measurements yielded in an efficiency of 88.2 % including the resonant converter, the inductive power transmission and the active rectifier efficiencies. The corresponding output was 207 W.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1720-1725, High penetration of PV plants or numerous electric vehicle (EV) charging station stations connected to the low voltage distribution grids (LVDG) may cause a voltage rise or voltage decrease respectively. There are several measures of maintaining the voltage stability such as grid reinforcement, battery energy storage, line voltage regulator, etc., although they vary in effectiveness and economic viability. This paper focuses on using decentralised voltagedependent active and reactive power (PQ(V)) control of PV inverters to stabilise the voltage in the grid. Using two grid models in Southern Germany and Switzerland the best PQ(V) control strategy is evaluated using load flow calculations. The weakest node in the first grid exhibits a maximum voltage of 1.072 pu on a sunny day. Due to the implementation of the PQ(V) control the maximum voltage is reduced to 1.024 pu at the same node. Costs considered for PQ(V) control are the PV yield loss and the additional reactive power compensation, which amount to roughly CHF 2’600.- per year. The future installation of EV charging stations may positively interact with PV feed-in. The voltage decrease can further be limited using PQ(V) control. Further grids and means for voltage stabilisation will be analysed in the future.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1504-1509, A combination of PV and green roof is an ideal fusion in terms of ecology. The green roof improves the water retention in the city, whereas the PV system produces electric power at the place where it is consumed. Flat tilted modules in south or east west direction on green roofs generally require intensive maintenance to prevent them from being shaded by plants and often cover the roof area to a large extent. Because of the space requirement conflict between PV on the roof and green roofs, it is essential to combine these two systems in a smart way. Vertically mounted bifacial modules can be an option to combine PV and green roof and to also allow a cost-effective maintenance. In this paper we report about the layout and the performance of a corresponding system, subdivided into two groups with differing albedo. Custom made bifacial modules with 20 cells were produced to reduce the wind load and to improve the general appearance. This 9.09 kWp bifacial plant achieved a specific yield of 942 kWh/kWp in one year (11.08.2017 to 10.08.2018). High quality DC power measurement systems are installed to monitor two modules in each bifacial test field and a reference south-facing module. This allows an energy yield comparison between the vertical bifacial test system with east-west orientation and the monofacial south-facing reference over four months of outdoor measurements. The use of plants with good reflective properties, which are also well suited two the ambient conditions on flat roofs, resulted in a yield increase of 17 % compared to a standard green roof planting. The vertically installed bifacial modules obtained an almost identical specific yield (-1.4 %) compared to a stand-alone monofacial southfacing reference module. Due to the increased yield in the mornings and afternoons, the vertical bifacial modules can achieve higher self-consumption depending on the load profile.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 2007-2012, Nominal power measurements of individual PV modules are needed to quantify the critical modules of PV plants offering lower energy production than expected. Today’s state of the art procedure of shipping a small number of modules to a laboratory is time- and cost intensive and it bears the chance of accidental damage. The Portable LED Flasher (PLF) was developed to require no dismounting of the modules. The quality of the PLF was tested on three PV plants in Switzerland. Additionally, ten PV modules of each plant were measured in the certified indoor laboratory of SUPSI, resulting in a maximum deviation of 3% of the STC values. Furthermore, a round robin test on a single crystalline silicon reference module at 25°C was performed at the JRC’s ESTI laboratory, the Swiss Mobile Flasher Bus and SUPSI resulting in a maximum deviation of the mean values below 1% compared to the PLF. A throughput of up to 150 modules or 500 modules respectively per day is expected and the total measurement costs are estimated to be about a tenth of the costs compared to an indoor laboratory. Module temperature measurement is crucial for a low total uncertainty. Thus, methods such as pre-shadowing of the module and approximation of cell temperature are the current focus of further improvement of the PLF measurement method.

The low-voltage distribution grid in Dettighofen, Germany was analysed regarding load flows and the voltage behaviour because of decentralised photovoltaic (PV) power generation. High load flow fluctuations of 400kW within 25 min were observed in the more critical western part of the grid. During the night, the average base and the peak load obtained from the medium voltage grid was 55.8 and 150 kW, respectively. On certain days, the transformer (400 kVA) fed with rated power into the medium-voltage grid. The relative voltage rise on the transformer was between 2% and 3%. A critical situation was found at a distribution box with two long stubs and a total PV installation power of 99.3 kWp. The load flows caused a relative voltage rise of 4.5% on a day with clear sky, and there was a voltage peak slightly above 110% on a day with high fluctuating irradiance. In a second step, load flow simulations with NEPLAN were performed to analyse three different voltage reducing measures. The relative voltage rise could be reduced by 3% with an active power curtailment ratio of 70% together with reactive power control (cosφ of 0.95 and cosφ of 0.9 at p>13.8kW). Peak shifting with battery storage leads to the same reduction if the power that exceeds 40% of the rated PV power is shifted. The average costs of limiting the active power to 70% are 1.45 ct/kWh compared with €3.11/kWh for peak shifting with commercial available lead-acid batteries. This is due to the low number of storage cycles resulting in high costs.

Cable based mounting of bifacial modules in a vertical or in a horizontal orientation is demonstrated, also on top of carports. Yield gains of 8% on a clear sky day for fixed vertically mounted bifacial modules were measured, together with higher yield at lower irradiance levels, by the use of the new fast module tracker. First results of applying the commercial tool PVSYST lead to annual additional electricity production in Switzerland of about 15% if the bifacial modules are tracked at two fixed positions relative to fixed mounted 30° tilted south oriented modules. These simulation show relevant deviations to the measured daily power production characteristics and will be improved in a future.

28th European Photovoltaic Solar Energy Conference and Exhibition; 2897-2901, Innovations on all aspects of BOS and solar cell integration into the module are essential to further reducing the costs of PV electricity and substantial progress has been made in the past years. One other important aspect is the availability of space for PV power production, especially in densely occupied urban areas. Roof space is limited or only partially useable. A promising other application for PV power production in urban areas today are PV carports on parking lots, which require massive structures and foundations. The approach presented here is a newly developed PV plant which automatically stores the PV modules in a protection box in case of bad weather conditions. Avoiding bad weather conditions implies that only a fraction of the mechanical load is present on the PV modules and the structure, enabling light weight structural design. The newly developed PV plant is folding the PV generator into a protection box and will pull out the PV generator, carried on two supporting cables for operation during good weather conditions. An innovative autonomous control system was developed based on local meteo sensors and regional weather information. The PV modules of the Urban Plant are mounted six meters above a parking lot with the benefit of full double use of the land below. Thus a PV system has been built with currently 52 kW nominal power, 16 meter wide, with a folding roof of PV modules expanding 24 meters in one direction. The system can be extended to 104 kWp with a second folding roof expanding into the other direction. As special PV system design was developed with a light weight PV generator using module laminates with special mounting elements. Moreover the system comprises innovative string wiring and inverters that can be also integrated into the safety box. A first 250kW commercial system is scheduled to be set into operation in Jan 2014 in Southern Germany.