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The ZHAW IEFE is involved in the performance research of power optimizer systems, which is funded by the Swiss Federal Office of Energy. The ZHAW PV shading simulation tool was compared to commercial tools, which show forecasts of additional yield by power optimizer systems with percentages in the double digits (PVSyst: 7.2% | PVSol: 14.6 %) relative to the SINV system for the heavy shading case. The reason for this is the use of the manufacturers’ data-sheet values, whereas the effectively measured power optimizer efficiency is generally 1.0 to 2.5% lower in points relevant for real-life operation. Finally, according to the results a list of performance-based recommendations for the application of the different PV systems was formulated.

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.

The IEA PVPS Task 13 group, experts who focus on photovoltaic performance, operation, and reliability from several leading R&D centers, universities, and industrial companies, is developing a framework for the calculation of performance loss rates of a large number of commercial and research photovoltaic (PV) power plants and their related weather data coming across various climatic zones. The general steps to calculate the performance loss rate are (i) input data cleaning and grading; (ii) data filtering; (iii) performance metric selection, corrections, and aggregation; and finally, (iv) application of a statistical modeling method to determine the performance loss rate value. In this study, several high-quality power and irradiance datasets have been shared, and the participants of the study were asked to calculate the performance loss rate of each individual system using their preferred methodologies. The data are used for benchmarking activities and to define capabilities and uncertainties of all the various methods. The combination of data filtering, metrics (performance ratio or power based), and statistical modeling methods are benchmarked in terms of (i) their deviation from the average value and (ii) their uncertainty, standard error, and confidence intervals. It was observed that careful data filtering is an essential foundation for reliable performance loss rate calculations. Furthermore, the selection of the calculation steps filter/metric/statistical method is highly dependent on one another, and the steps should not be assessed individually.

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.

An existing off-grid irrigation system of a 12’000 ha farm in Patagonia today powered by electrical pumps and diesel gensets, will be extended by a PV plant and a battery system to improve ecological ratings of the products and reduce energy costs. An optimal photovoltaic plant and a battery energy storage system had to be designed. The compiled hourly demand profile served as input to a simulation model of a photovoltaic diesel battery hybrid system. With the given assumptions the PV array should be oriented to north at an inclination of 30°. The analysis of electricity cost indicated the optimal system size of 1800 kWp PV nominal power and 500 kWh of battery capacity. With this system 55.2% of the energy used for irrigation will be provided by the photovoltaic plant in the first year. The electricity cost amount to $0.136 per kWh electrical energy compared to the $0.432 per kWh electrical energy currently produced by the diesel-only system. Further analysis showed high dependency of the electricity cost on the time until connection to the utility grid and its electricity price and future diesel price.

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.

Kongressvortrag

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.

29th European Photovoltaic Solar Energy Conference and Exhibition; 2541-2545, A new LED based photovoltaic module flasher is presented to perform nominal power measurements at 1000W/m2 within a flash period of 10ms, together with low light measurements. Additionally performance tests of the typical 3 bypass diodes of a standard 6” crystalline silicon PV module are performed during three flasher periods within totally 2 seconds. Thus the flasher setup (2.2m x 1.5m x 0.1m, weight 50kg, including power electronics) is placed in a distance of a about five centimeters direct onto the PV module, which remains mounted in the same position as it is operated in the outdoor PV plant. The LED flasher is equipped with 2400 single blue LEDs and 1440 IR LEDs. The total flasher area is divided into twenty individually controlled subsections with an area of 0.13m2 each. During one flasher period different values of intensity and color composition are able to be controlled independently. Two LED colors are used at 455nm and 850nm. A standard crystalline module is typically divided in three sub-module areas, protected by one bypass diode for each sub-module. Thus the intensity of these three submodule areas relative to each other is varied. During a single flash up to four different intensity patterns are applied. The complete measurement system was successfully qualified by test sequences performed on standard modules, equipped with different defect bypass diodes. The fast method may also be applied as a new module end test in a production line as well as a new PV field test method performed within a few seconds by the mobile LED flasher.

28th European Photovoltaic Solar Energy Conference and Exhibition; 3532-3535, As the solar spectra are changing during the day, seasons and weather conditions, the accurate annual energy rating has to be based not only on the nominal power at Standard Test Conditions STC but also on the sensitivity of power versus spectrum. The aim of the work is to measure the spectral sensitivity of tandem modules within the current/voltage scan. A standard industrial flasher was used to measure amorphous / microcrystalline (a- Si/uc-Si) tandem modules. This system was equipped with a special developed dynamic LED backlight at ZHAW. Test samples were analyzed using different shapes of dynamic backlight superposing the standard flasher STC spectra. The change of the LED backlight in the millisecond regime according to triangular, rectangular and sinusoidal shapes were applied. The analyzes were manly performed on a-Si/uc-Si tandem modules (1.1m x 1.3m). A triangle backlight characteristic was applied, increasing the IR LED light from 0% to 7% of ISC of the crystalline Silicon reference cell. Immediately after that period of 1.25ms, the IR LEDs are turned off and the blue LED decay from again 7% of ISC to 0% remaining on top of the STC spectra. This analysis shows significantly different spectral sensitivity at this specific time of changing from IR to blue. On the one hand the current of the module at maximum power point (MPP) changes proportionally with the IR intensity increase. On the other hand the tandem module’s short circuit current shows no significant changes at the same IR intensity variation. The same method of analyzes are applied to a-Si/uc-Si tandem modules operating during 4 months and 34 months respectively, under real outdoor conditions. It is evident that this outdoor degraded modules show only marginal changes of the module current at MPP for the same increase of this dynamic IR LED backlight. Thus, a method together with the setup is presented and confirmed to measure the state of degradation of this kind of tandem module during the flasher period of a few milliseconds. The use of the presented dynamic LED backlight has the potential, in the industrial module production process, to improve the output of a standard STC flash during several milliseconds by providing information about the current matching of top and bottom tandem cells on a module scale.

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.

27th European Photovoltaic Solar Energy Conference and Exhibition; 3731-3735, The paper describes recent developments and implementation of a method and a prototype solving the problem of optimal integration of PV-battery energy storage systems into the power grid. The first practical results achieved in cooperation with ABB Switzerland Ltd. using a real-time prototype of the developed advanced battery controller and the largest Li-Ion battery installed in Switzerland at the electric power utility of the canton of Zurich (EKZ) are presented.

26th European Photovoltaic Solar Energy Conference and Exhibition; 3374-3377, The Swiss Mobile Flasher Bus (SMFB) is equipped with a standard high-quality flasher and a very high throughput of up to 200 PV modules per day could be reached direct at customer site. Recently an analysis of the SMFB’s measurement uncertainty budget was presented, resulted in an expanded combined uncertainty of ±3% at a 95% confidence level for standard crystalline Silicon modules. This uncertainty value is about 1% larger than values of the best stationary test labs but enables still very accurate measurements at ambient temperature conditions with the advantage to make more measurements directly on customer’s site. In this paper this uncertainty values were tested by intercomparison of measurement results of the SMFB and the stationary JRC ESTI laboratory on the same PV modules performed within the same hour to reduce uncertainty contributions by instability of the device under test DUT. The largest difference of nominal power measurements was found to be smaller 0.5% for polycrystalline standard modules including the precision measurement at Fraunhofer ISE on the same DUT performed 20 months before. Measurements on standard thin film CIS PV modules resulted in deviations up to 3.7% which are within the calculated SMFB overall uncertainty value of 4%. No light pre-conditioning was performed to the CIS modules and different flasher pulse length was used, 10ms for the SMFB and 1.2ms for the stationary laboratory flasher. In a second intercomparison run the spectral response measurement on module level of SMFB and the JRC ESTI was performed by the use of band pass filters of about 50nm width. The good correlation of the results show that the SMFB spectral response measurement is valuable to calculate the spectral mismatch factor to account for different spectral characteristics of measured PV module, the used monitor cell and the flashers spectra to optimise the overall measurement uncertainty of the SMFB.