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36th European Photovoltaic Solar Energy Conference and Exhibition; 1681-1684, Effective utilization of renewable energy is a big motivation to renovate the conventional power systems toward smart energy systems. However, renewable energy is often small scale and intermittent. Hence, the online energy management is necessary to balance between demand and energy production. This paper proposes an online multi-scale optimization framework for smart PV systems in order to reduce the inherent complexity when trying solve the complete problem at a fine-grain time resolution. The proposed framework realizes the effective energy management by solving several optimization problems covering multi time scale. Experimental results shows that the proposed framework can reduce the purchased energy from the utility grid by 19.1% compared with other baseline methods.

36th European Photovoltaic Solar Energy Conference and Exhibition; 1261-1265, Bifacial photovoltaic technology is a promising, new approach to further reducing the Levelized Cost of Electricity of photovoltaic-generated electricity. However, designing and optimizing bifacial photovoltaic plants is a challenging task, which requires new modelling tools. This paper presents a physics-based energy yield simulation approach for bifacial photovoltaic systems, providing accurate yield prediction and insight into the operation of bifacial PV systems. Rear-side, inhomogeneous illumination is modelled using a CAD-assisted, GPU-accelerated ray-tracing-based approach, considering the influence of module build-up and layout, module frame, mounting structure and environment geometry. The non-uniform electrical-thermal operation with geometry-dependent convective and radiative cooling mechanisms and the resulting mismatch effect, which reduces module and system power output is modelled via interconnected electrical and thermal-equivalent circuits, where time-varying thermal resistors are used to model convective and radiative cooling. The combination of high-performance computing techniques, with advanced daylighting and circuit computing algorithms provides high accuracy at low computational costs, ensuring practical applicability to designing photovoltaic power generation system. The presented outdoor validation study confirms that our approach results in high accuracy, since the main mechanisms taking place during photovoltaic energy conversion are modelled on a physics basis. Additionally, physics-based modelling provides insight into the operation, the main loss contributions and mitigation strategies, applicable to bifacial PV systems.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1201-1204, This contribution handles about BIPV modules made with plated bifacial n-PERT cells from imec. For the cell interconnection the advanced smart wire connection technology (SWCT) was used that can reduce silver consumption at cell level considerably. These modules were made for installation in a facade installation of the KU Leuven, with monitoring of module performance, weather conditions and module temperatures. The modules are all glass-glass, both transparent and white. The modules were inspected with EL, and I-V measurements at standard test conditions were performed (also from the back side for the transparent modules). The modules were installed in September 2017, monitoring started one month later. The most important finding was that the bifacial gain when using a white surface behind the module was only considerable when the modules were ventilated. The probable reason is that without ventilation, the extra heat generated by double-sided illumination results in a module temperature that is so high, that the decrease in Voc and FF almost completely compensates for the gain in Isc. The monitoring data still have to be analysed in more detail, including a comparison with energy yield calculations with the imec energy yield software that has been adapted for bifacial modules.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1615-1618, In the future, with costs for PV modules rapidly declining and an expected increase of PV penetration in energy production, the cost for PV installations may be impacted more and more by balancing costs of storage, load management, and curtailment, rather than the currently dominating hardware components (PV modules and BOS components). With a low overall cost in mind, we should consider the interplay of generation (of course also intraday, but in particular seasonal variations are investigated in this work), load (consumption pattern) and storage costs for each location. In this paper we want to raise awareness about the increasing complexity of technology optimization resulting from the evolving cost structure of PV electricity generation. The latter can lead to counter-intuitive outcomes such as: a lower temperature coefficient may not always be the best in the future. First we build some first order analytical model to illustrate the concept and indicate trends. Then we apply our physics-based bottom-up modeling approach, taking into account coupled optical, thermal and electrical effects (and published more in detail elsewhere). This can be used to quantify with high accuracy PV production throughout the year as function of climate data and PV module technical data, in particular the temperature coefficient. Finally, we indicate some locations where the benefits of a higher temperature coefficient may materialize most, and that deserve some further attention.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1478-1482, The purpose of this paper is to compare different cell and module technologies comprising monofacial or bifacial, SmartWire or standard busbar interconnection and white or transparent encapsulant in a real conditions BIPV environment. For bifacial modules, the gain obtained in a BIPV configuration using different wall material with contrasting optical properties was investigated. This paper introduces the experimental set-up, followed by an electrical analysis at STC conditions, an electrical and thermal analysis on a sunny winter day and finally a statistical long-term energy yield analysis. Temperatures were measured each second on the back of each module on several relevant location while IV measurements were acquired every 15 seconds, allowing therefore Voc and Isc comparison between the modules. The electrical measurements have evidenced a power production for transparent encapsulant bifacial modules with SmartWire technology up to 16% higher than mono-facial module with standard busbar interconnection. As for the building integration, the results show an important effect of the wall material on the bifacial modules performances, with Isc up to 0.25A higher for white and aluminum wall material, and on the building temperature, with up to 5°C higher temperature observed for black wall material.

35th European Photovoltaic Solar Energy Conference and Exhibition; 273-277, In this paper, the use of transient thermal measurements inspired by the micro-electronic industry is demonstrated. The transient thermal measurement method entails applying pulsed power through a thermal test chip, with integrated heaters and temperature sensors, laminated on top of a polyolefin elastomer encapsulant layer and a silicon substrate, mimicking the PV module buildup. Measurements of the transient temperature response show that the thermal response variations in the thermally insulating encapsulant material are proportional to the thickness of the material. In addition, introducing direct metal contact the cell surface causes a higher thermal response than only embedding metal in the encapsulant without contact to the cell. Following preliminary transient temperature response measurements of the polyolefin encapsulant, we ran simulations to represent the impact of thermal properties of encapsulant on the overall impact of energy yields in PV modules. Simulation results show that altering encapsulant material from polyolefin to EVA, as well as varying polyolefin thickness within the PV module, have minor impact on the overall energy yields in moderate and desert climates.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1340-1342, Studies that have incorporated both dust and wind have been either review papers [1] or were experimentally performed in outdoor conditions [2][3]. This research paper aims to systematically study the effect that soiling has on the power production of solar cells while exposed to wind in a controlled environment. Dust was homogeneously displaced across a PV module in a dust wind tunnel. Using a dust wind tunnel, the experiments were done in an indoor controlled environment so that the variables tested are isolated and their trends become more visible. Dust densities spanned from 0 to 40 −2 in increments of 5−2. Wind speeds spanned from 0 to 4 −1 in increments of 1−1. Measurements were taken at thermal equilibriums and maximum output power was computed. The results show for 1 −1 the gain in Pmax caused by wind is negatively affected by the amount of soil on the module. Results also show that the gain caused by wind in cells located upwind are negatively affected by soil but that the trend decreases more downwind. This suggests that cooling by wind on a longer module would see a positive cooling effect due to soil.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1182-1185, The energy yield of PV modules depends on solar insolation, wind speed, wind direction, ambient temperature, the mounting structure, the building structure, and the local topography. The interaction of all these factors results in either a heating up or a cooling down of the module. Variations in temperature result in variations in the module’s energy yield. Hence it is imperative to have accurate information on cell and module temperature. State of the art studies already reports on the dependency of module temperature on wind velocity. However, the current literature does not consider fine grain details or assumes a constant heat transfer or an average temperature over the module surface. In this paper, we work on the fine grain details and include volumetric heat generation from the cell and correlate it with the forced convection over PV module surfaces. A test PV setup was mounted on an inclined roof with a 3.5 and 5.5 cm air gap underneath the module. Inlet freestream wind velocities of 3, 4 and 5 ms-1 were considered We only considered forced convection because, for 3, 4 and 5 ms-1 freestream velocities natural convection was negligible. We proposed a feasible method to include the fine details with the thin layer feature of COMSOL inside the module. By doing so, the computational effort was significantly reduced. Results were compared to experimental data collected in a wind tunnel. Overall, there was good agreement between the simulated and the measured results. The mismatches that were observed arose mostly from overestimations in the simulation. The modeling technique can be used in future studies on the effects of wind velocity and wind direction on temperature distributions over PV setups of different configurations.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 2548-2552, The purpose of this paper is to quantitatively compare different façade-integrated BIPV configurations comprising ventilated, unventilated façades and black or white rear encapsulant color. This paper introduces an experimental set-up and analyses the experimental results that were obtained on three representative days: two sunny days with different wind conditions and one cloudy day. Both temperatures and IV characteristics were continuously logged every 15 seconds. The electrical measurements have evidenced a strong impact of rear encapsulant color, with white modules performing up to 3% better. The thermal study has shown a strong cooling effect caused by cavity ventilation, with ventilated modules performing up to 6% better, as well as an important influence of meteorological conditions.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 262-265, In a previous contribution, we presented a multi-wire approach for interconnecting back-contact cells. While a proof-of-concept was clearly demonstrated, some remaining fill factor (FF) losses were not fully explained and initiated the need for a more in-depth analysis. The current abstract therefore reports on this analysis. As a first step, we explain the reasoning towards an optimized theoretical cell-module co-design for multibusbar interdigitated back-contact cells. Indicating the opportunities, we also present the measured results of the fabricated demo modules. Then, looking closely at the remaining FF losses, we determine a hypothesis for this unforeseen pitfall and confirm it through basic circuit simulations. Relying on this hypothesis, the solution is very straightforward and could be implemented at either cell- or interconnect-level. After also experimentally verifying this phenomenon and its solution, we finally present 1-cell laminates to indicate the potential of the technology in terms of Cell-to-Module-performance and compare with previous modeling results on expected FF loss.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1643-1646, A holistic approach for energy yield evaluation of photovoltaic (PV) modules has been developed. The optical, thermal and electrical behaviour of PV modules is integrated into the simulation framework, and as such is based on bottom-up and physics-based models. Incorporating a fine-grain temporal and spatial resolution, the framework enables accuracy and versatility even during highly varying and non-uniform weather conditions. Due to its physics-based nature, the approach can be extrapolated beyond its initial calibration. In contrast to black-box models, it can therefore be safely used for the energy yield exploration of novel PV module technologies and other system-specific (e.g. environmental) conditions. In this paper, an overview of current state-of-the-art energy yield modelling approaches will be discussed. The accuracy of our approach is compared to the other state-of-the-art approaches. Finally, several simulation results are shown where optical, thermal or electrical module characteristics are varied, to demonstrate the physics-based, exploratory simulation capabilities.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1665-1668, The energy yield performance of a novel PV module with 10 strings of 6 cells was investigated. The IV characteristics of each individual 6-cell string were measured and used to determine the monthly energy yield of each sub-string. Differences up to +3.7 % compared to the average value were observed. However, analysis of the daily yield showed variations up to +17.6 %, depending on the wind conditions. These daily yield variations are critical, as the variations may be masked when using longer-term values, such as monthly or yearly yield. As a result, models may give a yearly yield value that is close to the measured value but the daily variation in yield may easily exceed 15%. Cumulatively, this will result in large model errors. Forced convection introduces considerable and often neglected intra-module temperature variations, leading to differences in conversion efficiencies at sub-string level. These temperature variations need to be taken into account for accurate energy yield evaluations. In addition, this insight provides guidelines for novel smart PV module technologies that aim to improve energy yield harvesting.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 61-65, In a reconfigurable PV panel, the connections between groups of cells (cell-strings) can be rearranged in order to increase the overall power output under non-uniform conditions. In a traditional PV panel, current mismatch between the series-connected cells (due to irradiation differences of differential aging) limits the generated power output by either reducing the overall current or by bypassing the substring containing the limiting cells. A reconfigurable panel can respond to such a situation by changing the connections to a more favorable configuration, allowing the majority of the cells to operate at their MPP. This paper elaborates on such a topology and its components (high current switches, wiring). To get a clearer picture of the added value of such a reconfigurable panel, a detailed energy yield analysis was performed which includes the performance of those added components. The simulation model used for this analysis is calibrated with extensive measurement results. A comparison of that model and corresponding measurements will be discussed. The analysis shows that a reconfigurable PV panel can outperform the traditional panels when suboptimal conditions are predominant, as encountered for instance in BIPV. As a demonstration of the principle, a small-scale prototype was created and will be presented in this paper.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1556-1559, The effect of fast-varying weather conditions on (simplified-) models on simulated solar cell temperature and energy yield prediction is investigated. The models have first been calibrated with indoor measurement data. We focus especially on short-term behavior (second to minute level). Frequency response analyses show that the solar cell temperature is mainly influenced by high-frequency illumination conditions, while the effect of highly varying wind on the solar cell temperature is more limited. For a period with highly varying weather, energy yield is calculated to illustrate the effect of the parameters in the model on the overall energy yield outcome.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1216-1218, More complex interconnection schemes of TFPV modules can improve the total efficiency of the module. Also the presence of defects in a thin film photovoltaic (TF PV) module influences the module's behavior. A model is presented to calculate the influence of the interconnection scheme and local defects on the module performance. The proposed modeling tool automatically generates the module netlist through a MATLAB algorithm and runs SPICE simulations, which give I-V and power curves of the module. A methodology is proposed in order to better understand how specific defects of solar cells and how module topologies act on the entire module. Defects are modeled as a variation from the reference solar cells parameters, which typically involves a shunt and/or series resistance variation for cell and/or interconnection structure. The aim of this work is to better understand how to predict and to limit the effects of local defects in a TF PV module.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1997-2000, In this paper we would demonstrate how we developed a model to determine cell-to-module performance starting from available literature. After fabricating 60-cell modules with 2 different types of cells and 2 different stringing configurations, measurements of these modules then allowed us to validate the developed model. In an attempt to demonstrate potential applications for this model, we then show how potential improvements can be quantified and pinpoint which losses are affected. This way, we indicate a potential for improving the fabricated MWT modules with an increase in absolute efficiency up to ~1.7% for the module. On top of that we demonstrate that an additional increase of ~0.1% in absolute efficiency can be obtained by dividing the cells, e.g. into half or third cells.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1552-1555, The ongoing growth of renewable energy installations is slowly shifting the energy mix for grids worldwide. This development is hopeful for a sustainable future, but also imposes additional challenges to grid regulators. In this context, short term solar irradiation forecasting is becoming relevant for both interconnected and isolated grids as a way to balance the energy production and demand. The actual energy yield of a photovoltaic installation though is a function of many parameters and, more importantly, in these short time scales is highly affected by the dynamics of the modules themselves. This work presents the coupling of high temporal-spatial resolution sky imaging forecasts with a detailed electro-thermal PV simulation model, suitable for fine-grain temporal and spatial transient analysis. The final outcome is a forecast of the actual energy yield of the installation for horizons of typically 15 minutes, with detailed information on occurrences of sudden ramps. The proposed method achieves a 5% improvement in RMS error over persistence, for forecast horizons of about 5 minutes.

31st European Photovoltaic Solar Energy Conference and Exhibition; 1942-1945, Current solar simulators only focus on steady-state or pulsed (flasher) irradiance conditions, under standard test condition, to measure peak performance of photovoltaic modules. For realistic scenarios other more dynamic conditions are needed, such as lower irradiance levels that change over time and shading patterns (from clouds and surrounding objects). This work presents a low-cost indoor dynamic illumination setup to test smart PV modules under dynamic conditions of irradiance. It enables the effective evaluation of its performance, allowing temporal and spatial irradiance variation. This setup is be able to simulate conditions close to realistic outdoor patterns enabling. For example, to simulate irradiance conditions in countries such as Belgium with highly variable irradiance which changes constantly in space and time.

29th European Photovoltaic Solar Energy Conference and Exhibition; 2952-2955, This work presents a PV system and financial optimization tool, targeting a holistic design and control approach of real PV systems with the purpose of maximizing the energy yield in synergy with the smart grid. Three typical use cases are shown in this work. For each use case a sensitivity analysis of different design options indicates the potential to reduce Levelized Cost of Energy (LCOE). The first use case targets system developers, comparing the cost-efficiency of different PV module orientations and PV-to-AC dimensioning ratios. The second use case targets inverter developers, comparing the cost-optimization of different inverter dimension limits (DC current, DC voltage and AC power). The last use case targets smart PV module developers, evaluating the gains that can be obtained by the use of by-pass diodes in combination with smart reconfiguration schemes depending on shade conditions. Results show that cost-efficient integration of the different PV system components is reached through holistic cost optimization. The validation of the tool shows that the output results are very close to the real output of operating systems.

29th European Photovoltaic Solar Energy Conference and Exhibition; 2947-2951, Recent developments in silicon photovoltaic (PV) research include smart-PV modules with reconfigurable topologies and short-term prediction of the energy yield of the module for grid regulation purposes. Nevertheless in many cases, traditional simulation models are rendered ineffective both in detail and speed, since extensive transient simulations cannot be covered by simple sets of equations. On top of that, most models do not account for intra-module temperature gradients, or fast non-linear dynamic effects, which can affect the final result. A novel set of Verilog-AMS models is introduced in this paper, enabling transient electro-thermal analysis of a PV module with thermal coupling down to the cell level. These models are based on a validated electro-thermal cell model, extending its capabilities to include shading and wind effects. A speed-up of 3600x is achieved versus finite element method (FEM) solvers, while maintaining accuracy in applicable levels. Moreover, a parameterizable, behavioral maximum power point (MPP) tracker is presented, allowing the exploration of interesting dynamic situations and estimation of long-term energy yield with speed-ups of 500x versus real-time.

29th European Photovoltaic Solar Energy Conference and Exhibition; 3292-3296, An optical-thermal-electrical model of a photovoltaic (PV) module is presented, suitable for energy loss analyses and short- and long-term energy yield calculations as a function of ambient conditions (temperature, wind and irradiance). This bottom-up model consists of a thermal and electrical equivalent sub-circuit. The thermal equivalent circuit incorporates the conduction, convection and radiation of heat within and from the PV module. Finite element modelling (FEM) computational fluid dynamics (CFD) models and wind tunnel tests were used to calibrate the thermal model, both for spatial and temporal effects. Thermal capacitance and resistance values were extracted from measurement and FEM models and the full thermal model was validate by indoor and outdoor measurements. The 1- diode model was used for the electrical circuit of the cell. The parameters of the electrical model were extracted from flash and steady-state I-V measurements. The thermal sub-circuit was used to calculate the temperature of each cell in the module, and this temperature is then further used to calculate the electrical characteristics of every individual cell. A full model of a Phoenix-Solar-PHX-160 module was constructed and the model was used for energy yield simulations. The result was successfully compared to outdoor measurements.

28th European Photovoltaic Solar Energy Conference and Exhibition; 3291-3295, An optical-thermal-electrical model of a photovoltaic (PV) module was developed in SPICE. The mixed-signal model consists of two coupled sub-circuits, one sub-circuit to describe the thermal response and one to incorporate electrical characteristics of the PV module. In this paper, various types of thermal equivalent RCnetworks and the extraction procedure of parameters for the thermal sub-circuit are explained in detail. The thermal sub-circuit is used to simulate module temperatures as a function of illumination level, ambient temperature, wind conditions, electrical load (by coupling the thermal sub-circuit to the electrical sub-circuit) and illumination history. Since the model has been built in SPICE, it can be used to evaluate PV module characteristics during transient and non-uniform conditions. The complete model can be used to calculate the energy yield, to investigate thermal and electrical characteristics of the module and to evaluate energy yield losses due to non-steady-state and non-uniform illumination and ambient conditions.

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