Half-cell Modules Research Articles

Sequential thermomechanical stress and cracking analysis of photovoltaic modules with full and half-cut cells

The transition from conventional full-cell patterns to half-cell modules in the photovoltaic (PV) industry promises enhanced stability and efficiency. This study investigates the thermomechanical behaviour and stress distribution within half-cell and full-cell PV modules during the manufacturing and operational phases. Using finite element modeling, the research simulates sequentially the manufacturing and operating processes such as laser cutting, soldering, lamination, mechanical loading and thermal cycling. The Extended Finite Element Method (XFEM) predicts crack initiation and propagation in the crack-sensitive regions in PV modules during their entire life. Key findings highlight stress concentrations during manufacturing, influenced by parameters like laser power, scribing length and Silicon wafer size. Mechanical loading (ML) and thermal cycling (TC) induce additional stresses, impacting module reliability. The results are useful for the optimization of material properties and the development of advanced design strategies contributing to the durability and efficiency of PV systems.

Evaluation of Light-Induced Electroluminescence in Photovoltaic Field Applications

We present a performance analysis of the new measurement method Light-Induced Electroluminescence (LIEL) in a PV system. The LIEL method is applied to photovoltaic (PV) modules consisting of two PV module halves which are internally connected in parallel. Today’s main stream half-cell modules are constructed this way. To measure the electroluminescence of one half of the module, the other half is illuminated by an LED array. Our LIEL prototype system is a hood-based setup. It is equipped on one half with a LED array that is separated by a wall from the other half. This other half is observed by an InGaAs camera. We measure the impact of a LIEL hood misalignment to the electroluminescence intensity, the influence of the PV generator working point to the electroluminescence intensity and determine the measurement speed under realistic conditions. We show that the experimentally realized LIEL hood alignment to the PV modules is in 97.7% of the cases sufficient for acquiring high quality EL images. The LIEL system work with a switched off and on inverter. Under inverter on working condition the luminescence intensity is a function of the intensity of the sun. The effect of hood alignment and sun intensity on the luminescence intensity is successfully reproduced by an analogue electronic circuit simulation using LT Spice. The maximum measuring speed of a full module is in this study 12 s including the time for movement and alignment of the measurement hood from PV module to PV module

A comparative experimental study on front and back laser cutting technology for mass separation of N-TOPCon crystal silicon solar cells

Generally, the Thermal Laser Separation (TLS) technology is used to pre-groove from the back of the cell, which is the first process of half-cell module preparation. However, this benchmark practice may result in forming new leakage points in the grooves at both ends of the cell. Hence, we investigate the mechanism behind the formation of leakage points after grooving and the impact on N-TOPCon's cell efficiency and module power. It is discovered that the diffusion of P element is the main reason for the increase in the proportion of leakage points. The front cutting is accordingly proposed to alleviate problem. A comprehensive experimental study on its feasibility has been conducted. It has been confirmed that the leakage current under the reverse bias voltage is smaller, the data convergence is better, and the breakdown performance is more stable for N-TOPCon. Furthermore, the module power is higher.

Challenges and advantages of cut solar cells for shingling and half-cell modules

Cutting silicon solar cells from their host wafer into smaller cells reduces the output current per cut cell and therefore allows for reduced ohmic losses in series interconnection at module level. This comes with a trade-off of unpassivated cutting edges, which result in power losses. This performance drop can be seen in fill factor FF and open-circuit voltage VOC losses on cut cell level. Based on experimental realization of different solar cell layouts on the same industrial blue wafers (solar cell precursors), a combined simulation method to predict the performance on module level is demonstrated. This method uses Gridmaster+ for cell simulation and SmartCalc. Module for module simulation. The accuracy of the simulations is demonstrated by comparing with experimental results both from host and cut cell level. In addition, significant influence of the current–voltage (I–V) measurement configuration is demonstrated, mainly affecting FF. Using flexible methods like GridTOUCH® for I–V testing gives fast results but can also lead to overestimation of the host cell performance, resulting in overestimated cell-to-module losses or unreasonable comparisons between hosts and cut cells. It is also demonstrated that application of the passivated edge technology (PET) yields I–V characteristics close to those of cells with ideal edges, i.e., without edge recombination. The implications on the module efficiency are also compared between modules built using cells with and without edge passivation, giving the highest efficiency for a shingled module with PET.

Comparative Analysis of Edge Soiling Resilience: Full-Cell vs. Half-Cell Photovoltaic Modules in Different Mounting Orientations

The performance of distributed PV systems is often hindered by edge soiling, mainly due to the challenges associated with centralized cleaning. In recent years, half-cell modules have gained popularity over conventional full-cell modules due to their potential for improved performance. However, limited research has been conducted to compare the effects of edge soiling on full-cell and half-cell modules, particularly in various mounting orientations. Furthermore, there is a scarcity of methods that integrate simulation and experimentation to analyze the characteristics of shaded PV modules. This study aims to optimize module selection and mounting orientation to mitigate the impact of edge soiling. Simulated models and experimental setups were developed for both full-cell and half-cell modules in both landscape and portrait orientations. The results reveal that the degree of shading correlates with the ratio of shaded substrings within a module. In addition, module performance can be significantly enhanced by altering the mounting orientation. Specifically, the findings demonstrate that half-cell modules outperform full-cell modules when mounted in the portrait orientation. However, in the landscape orientation, the advantage of half-cell modules diminishes. Remarkably, the choice of mounting orientation is found to be contingent on the severity of edge soiling for half-cell modules. This work significantly contributes to the understanding of shading effects in PV systems and offers practical guidance for optimizing distributed PV systems against edge soiling.

Electronic Half-Cell Module to Demonstrate an Electrochemical Series and a Citrus Fruit Battery for Remote Students

Electronic Half-Cell Module to Demonstrate an Electrochemical Series and a Citrus Fruit Battery for Remote Students

Techno-Economic Assessment of Half-Cell Modules for Desert Climates: An Overview on Power, Performance, Durability and Costs

Photovoltaic modules in desert areas benefit from high irradiation levels but suffer from harsh environmental stress factors, which influence the Levelized Cost of Electricity by decreasing the lifetime and performance and increasing the maintenance costs. Using optimized half-cell module designs mounted in the most efficient orientation according to the plant requirements can lead to reduced production costs, increased energy yield and longer service lives for PV modules in desert areas. In this work, we review the technical advantages of half-cell modules in desert regions and discuss the potential gains in levelized costs of electricity due to reduced material consumption, a higher cell-to-module power ratio, lower module temperatures, better yields, reduced cleaning cycles and finally, reduced fatigue in interconnection due to thermal cycling. We show that half-cell modules are the most cost-effective option for desert areas and are expected to have a relevant lower Levelized Cost of Electricity.

Relationship between module performance and the shading area for modules with different circuit connection mode

Partial shading is very common in photovoltaic (PV) systems. The mismatch losses and hot-spot effects caused by partial shading can not only affect the output power of a solar system, but also can bring security and reliability problems. This paper centers on the silicon crystalline PV module technology subjected to operating conditions with some cells partially or fully shaded. A comparison of the electrical and hot-spot performance results for four different connection mode PV modules without shading and with partial or full shading is presented. Bypass diode of different modules would start up in the different conditions with increasing shading area. We found that the regular half-cell module degraded about 60% than its non-shaded power, which is about 30% less than the other three modules, when the short edges of these modules were shaded. The highest hot-spot temperature of the regular half-cell module was 75.5 °C, which is the lowest among the four modules before the diode started up.

Output performance analysis and power optimization of different configurations half-cell modules under partial shading

The performance of photovoltaic (PV) modules is influenced by environmental variables, especially shading. Partial shading makes the solar irradiance level of solar cells in PV modules uneven, thus reducing the performance of PV modules and even damaging the PV modules. In this work, the single diode model and the Bishop model are used to simulate the I–V characteristics of various half-cell modules in detail, and the results under normal and shading conditions are analyzed. Investigations of module configurations include a series-parallel-series connections half-cell module with 3 bypass diodes, one configuration with a series of 120 half-cells with 3 bypass diodes, and another configuration with a series of 120 half-cells with 5 bypass diodes. In the simulation, the working modes of the shaded half-cells can be clearly understood. Electrical performances of three modules in different shading scenarios are obtained. Through the practical shading experiment, the optimal output power of different configurations half-cell modules under two power optimization schemes is analyzed.

Hotspot development and shading response of shingled PV modules

The shingled architecture has gained attention in recent years for its improved packing density and reduced ohmic losses that have led to greater module efficiencies. In the photovoltaics industry where land and auxiliary costs scale with area utilization, shingling is a promising emergent technology. However, because current designs use smaller cell areas and upwards of 34 cell strips in series per string, shingled modules are vulnerable to hotspots, particularly due to smaller shading elements. In this work, we experimentally characterize the hotspot and power response of shingled modules. Two operating scenarios are considered, simulating both utility scale systems and standardized testing conditions. We report maximum hotspot temperatures of 145 °C at partial shading and show how non-uniformities in the cell properties lead to variations in module shading response and hotspot temperature. Furthermore, we observe that shingled modules develop higher hotspot temperatures than conventional half-cell modules. Finally, we demonstrate how unshaded parallel strings in a shingled module can concurrently develop minor hotspots at the onset of bypass diode activation.

Modeling and Simulation of the Influence of Interconnection Losses on Module Temperature in Moderate and Desert Regions

Photovoltaic (PV) modules in desert environments benefit from higher irradiation levels and, therefore, better energy yield. However, higher irradiation leads to higher temperature and higher electrical losses in module interconnections, which could influence the lifetime and energy yield of PV modules. The electrical losses in module interconnection act as heat sources. The interconnections’ electrical properties are also affected by solar cell temperature. In this paper, we simulate and evaluate the performance of the interaction between thermal and electrical losses in module interconnections and the influence of tab on module power and temperature. We compare the impact of tab losses on module power and temperature under different irradiation and ambient temperature levels, as well as compare the module in Qatar and Germany as desert and moderate climates. We show that the thermal influence of tab on module power is maximum 0.8%rel compared to a module without any thermal influence from tab, which, in this case, are the thermal coefficients of the tab and temperate elevation due to joule heating. This change is 0.2%rel and 0.6%rel for Qatar and Germany during one year, respectively. As a solution for desert applications, apart from full-cell layout, we have evaluated modules with half-cell design due to increased optical gains and reduced electrical losses. We determined the optimum tab width for the modules with half-cell and full-cell design and for two to five busbars under normal operating cell temperature (NOCT) conditions. We show that in NOCT conditions, the optimized tab width on half-cell modules is almost half of the tab width for full-cell modules. Furthermore, the temperature of half-cell modules is always less than that of full-cell modules for the similar tab widths. By considering the optimum tab width for half-cell and full-cell modules, an average increase of 0.2 °C is simulated, which is due to the higher active area and narrower tabs and, thus, higher irradiance and thermal loads.

Analysis of Hotspots in Half Cell Modules Undetected by Current Test Standards

Today, hotspots are a major source of failure for photovoltaic modules in the field. Modules based on half-cut solar cells are an attractive pathway to reduce cell-to-module losses and are projected to have a 40% market share by 2028. However, the current standard for module testing IEC 61215-2 can leave critical hotspots undetected in such a module configuration. In this paper, the hotspot effect of half-cell modules using parallel connected cell substrings is studied in comparison with conventional full-cell modules. Significant hotspots are induced in both half- and full-cell modules, when suffering current mismatch, in this case induced by partial shading. When shaded by the same area, the hotspot temperature of the cell in a half-cell module is 19 °C lower than the full-cell module in this experimental work. Critically, multiple unshaded weak cells are found to dissipate heat when the parallel-connected substring is shaded. In an experimental situation with a total shading ratio of only 4%, we measure hotspots of over 90 °C—a situation that can occur in the field due to uncontrolled plant growth and bird droppings.

Evaluation and Comparison of PV Modules With Different Designs of Partial Cells in Desert and Moderate Climates

Modules with partial cells show better performance compared to full-cell modules due to lower electrical losses and increased optical gains. In this paper, we compare photovoltaic (PV) modules made of full, half, and third cells with tab widths of 0.8 and 1.5 mm under moderate and desert conditions, respectively. Initially, a statistical assessment of indoor characterization results of the modules is presented. The efficiency and fill factor of the modules are evaluated to analyze the electrical and optical losses of the modules. It is shown that the modules with partial cells and narrower tab widths show higher efficiencies and implying cell-to-module power ratios over 100%. The modules are characterized under different intensity levels to assess their performance under various illumination conditions. Based on the measured data, the energy yields in Morocco and Germany representing desert and moderate climates, respectively, are calculated. It is demonstrated that increased energy yield can be achieved by selecting appropriate module design and optimized tab width for each climate. The optimized half-cell modules show a yield gain of 3.77% and 4.51% compared to full-cell modules in moderate and desert climates, respectively. These values rise to 4.72% and 5.68% by moving to third-cell modules, respectively.

Comparison of Half-Cell and Full-Cell Module Hotspot-Induced Temperature by Simulation

The impact of partial shading on cell operating current, voltage, and temperature is simulated, for a half-cell module with series–parallel–series connections and for the conventional full-cell module. When shaded, we find the half-cell modules comprising two parallel 60-half-cell strings benefit from a reduced heat dissipation compared to a 60-full-cell series connected design. The maximum hotspot cell temperature of the shaded half-cell module is 28 °C lower than that of the full-cell module. Our result suggests that half-cell module design could mitigate hotspot degradation or failure in crystalline-silicon photovoltaic modules.

Study on the Benefit of Half-Cut Cells towards Higher Cell-to-Module Power Ratio

Half-cut cell technology has been proposed as an effective way to largely decrease the cell to module loss by decreasing the current level in the cell string. The type of laser is strongly correlated with the quality of the cut cells and further performance of the half-cell based modules. We investigated the effect of laser on the quality and performance of half-cut cells. And different types of half-cut cells were made into modules, the cell-to-module power ratio of which was evaluated and compared with full-size cells. Electroluminescence was employed to characterize the quality of the cut cells as well as the half-cell modules. Our results demonstrate that an approximately 2.2% average extra power gain can be obtained using half-cut cells for module encapsulation.

Optimized Tab Width in Half-cell Modules

Modules with half-cell layout show an increased efficiency due to reduced electrical losses and increased optical gains. In this work, we demonstrate that by reducing the tab width, additional benefits can be obtained and the demands for reducing costs of material consumption and higher Cell-To-Module power (CTM) ratios can be met. First, we present simulation results on the optimal tab width under different insolation levels and calculation of the energy yield over a year. Second, an experimental setup based on mini-modules which verifies our findings is described. It can be shown that the reduction of the tab width to about 50% does not lead to any significant loss for standard cells and an increase of efficiency by 0.85% for half-cell modules compared to full-cell modules is measured. Furthermore, the loss mechanisms in locations with different insolation levels for both half-cell and full-cell modules with different size of tab widths are discussed. Finally, energy yield based on optimized tab widths for both modules at desert (Morocco) and moderate (Germany) climates is calculated. We show that half-cell modules with optimized tab width have better performance than standard modules with full-cells in both moderate and desert regions with 1.52% and 2.20% more energy yield respectively.

High Quality Half-cell Processing Using Thermal Laser Separation

Half-cell modules are promising candidates for a new generation of PV-modules as the electrical losses can be reduced while the optical gains are increased. This technological approach requires a cell separation process which does not induce any significant electrical or mechanical damages on cell level. Thermal laser separation (TLS) is a damage free and kerfless dicing technology for brittle materials such as silicon. We investigate the applicability of TLS for the solar cell splitting and compare it to a reference cell-splitting process based on laser scribing and subsequent cleavage. It is found that the electrical properties of the TLS-half-cells are slightly better compared to the reference process and that compared to a laser separation there is no mechanical damage due to the TLS process.

Investigation of the short-circuit current increase for PV modules using halved silicon wafer solar cells

It is well established that using halved silicon wafer solar cells in a photovoltaic (PV) module is an efficient way to reduce cell-to-module resistive losses. In this work we have shown that PV modules using halved cells additionally show an improvement in their optical performance, resulting in a higher current generation. We attribute this increase in current to gains in light reflected from the backsheet area. An optical model is presented that quantitatively determines the influence of the backsheet on the short-circuit current of a PV module. We find that, for an accurate prediction, several factors have to be taken into account, including the geometry of the module, the backscattering properties of the backsheet and the illumination spectrum. Particularly the angularly and spectrally resolved scattering properties of the backsheet are shown to have a large impact on the current generation. Furthermore, light beam induced current (LBIC) measurements are used to test the backscattering properties of the backsheet and also the influence of the illumination spectrum. LBIC measurements are also used to verify the simulation results, giving good agreement. Thus the design of a PV module can be optimized by simulation. A standard full-size cell module and a halved-cell module with optimized cell spacing are fabricated. Compared to the standard module, the half-cell module is shown to have 4.60% more power (315.3 vs. 329.8W), 1.46% higher fill factor (75.5 vs. 76.6%), and 3.08% more current (9.08 vs. 9.36A).

Loss Analysis for Laser Separated Solar Cells

Half-cell modules are promising candidates for new innovative module designs as they offer major advantages. Modified connection schemes reduce the serial resistance losses yielding a higher overall module performance. The reduced size of the cells allows a more flexible module design that is needed for special applications such as implementations on curved surface. Furthermore, a better performance under partial shading can be achieved. However, these advantages lead to a benefit only if the losses induced by the cell separation process are negligible. In this work, we study the different sources of power reduction, i.e. increased shunting and recombination, for mono-crystalline and multi-crystalline silicon solar cells separated using different laser process parameters. It is shown that recombination plays the major role for an optimized laser separation process. Additionally we identify the laser scribing process as the major source of losses in comparison to the mechanical breaking.

Design and study of a high-current 5-cell superconducting rf cavity

The Advanced Photon Source (APS) at Argonne National Laboratory is considering the development of a superconducting linac-based fourth-generation hard X-ray source to meet future scientific needs of the hard X-ray user community. This work specifically focuses on the design of an optimized 5-cell superconducting radio-frequency structure well suited for a high-energy, high-beam-current energy recovery linac. The cavity design parameters are based on the APS storage ring nominal 7 GeV and 100 mA beam operation. A high-current 5—cell cw superconducting cavity operating at 1.4 GHz has been designed. In order to achieve a high current, the accelerating cavity shape has been optimized and large end-cell beam pipes have been adopted. The beam break-up threshold of the cavity has been estimated using the code TDBBU, which predicts a high threshold beam current for a 7 GeV energy recovery linac model. A copper prototype cavity has been fabricated that uses half-cell modules, initially assembled by clamping the cells together.