Hot Spot Phenomenon Research Articles

An enhanced global MPPT method to mitigate overheating in PV systems under partial shading conditions

The hot-spot phenomenon in photovoltaic modules is a reliability issue typically caused by many reasons, including partial shading conditions. In such situations, the P-V curve exhibits a unique global maximum power peak (GMPP) and several local maximum power peaks (LMPPs). However, all the existing tracking methods (GMPPT) track the GMPP, even for a slight difference between peaks. For this purpose, an experimental investigation of the relationship between the operating point of a PV module and the temperature of their shaded parts has been carried out. In the studied case, it was found that the shaded cells’ temperature exceeds 99 °C, and it is directly related to the GMPP position on the P-V curve, where it decreased as the operating point is moved from the short circuit current towards the open-circuit voltage. As the shaded cells' temperature may reach high levels, which can result in early degradation of PV modules, an enhanced GMPPT method is proposed in this paper to handle the overheating issue. The proposed method aims to track the secure peak when two peaks or more have closer power values. Consequently, it alleviates the overheating and hot-spotting risks. Furthermore, the scanning voltage interval of this technique is bounded by lower and upper voltage limits. The proposed technique is experimentally validated and compared to two existing methods: the 0.8 Voc and the full sweeping method. The results show that when the power peaks have approximately the same value, the proposed method tracks the peak with the upper voltage (automatically the lower current) to minimize the thermal stress within the shaded cells. Moreover, the proposed method exhibits a 40 % saving in tracking time compared to the full sweeping method thanks to the efficient tracking mechanism that allows skipping certain intervals in the search space.

Design aspects in consideration of hotspot phenomena in high-performance photovoltaic modules featuring different silicon solar cell architectures

Mitigating degradation or failure of high-performance photovoltaic modules due to hotspot phenomena requires the knowledge of the reverse bias behavior of different architectures like the passivated emitter and rear cell (PERC), tunnel oxide passivated contacts (TOPCon), silicon heterojunction (HJT) and perovskite silicon tandem (PVST) solar cells to understand the hotspot response for various module designs with different interconnection layouts of the solar cells. In this study, the current-voltage characteristics of mini-modules featuring one single PERC, TOPCon, HJT or PVST solar cell are measured in forward and reverse bias direction for different shading ratios and a model for evaluating different module designs is established, allowing the prediction of the hotspot temperature of a shaded solar cell in the worst-case scenario of a hotspot endurance test. It is shown that a strong correlation between the solar cell architecture and the module design in terms of maximum hotspot temperature exists. PERC, TOPCon, HJT and PVST solar cells show very different reverse bias behaviors, leading to different hotspot temperatures under various shading ratios whereas HJT and TOPCon solar cells exhibit higher hotspot temperatures than PERC solar cells. Furthermore, it is shown that alternative module designs with a reduced number of solar cells per string and more bypass diodes, but also with parallel substrings, are beneficial in terms of minimizing the hotspot temperature, especially for PVST solar cells which are more susceptible and prone to degradation at high temperatures.

PERFORMANCE OF SCREW HORIZONTAL AND BRIDGE LINKAGE PHOTOVOLTAIC ARRAY CONFIGURATIONS

Due to partial shading effects on the productivity of solar panels which in turn negatively impacts the performance characteristics of photovoltaic systems, researchers work on different studies to overcome this phenomenon and improve solar system productivity. Therefore, this study aims to investigate different techniques to enhance the output power, fill factor, and efficiency of the PV system by reducing the number of local maximum power peaks, power losses, and mismatch losses. The configurations include a novel static reconfiguration technique, called a Screw Horizontal photovoltaic array, and a recently developed technique known as a Bridge Linkage array. Both of these are modeled using MATLAB/Simulink software and examined during six shading patterns. The novelty of this study is that we combined the above static reconfiguration technique with another modern technique called blocking and bypass diode technology to prevent the effect of reverse current and hotspot phenomena respectively. According to the results, the Bridge Linkage configuration performs the most efficiently under partial shading conditions compared to the Screw horizontal PV array configuration.

The Hot Spot phenomena in Shadowed ENR System

Model to represent the behaviour of photovoltaic (PV) solar cells in reverse bias is reviewed, concluding with a proposal of new model. This model comes from the study of avalanche mechanisms in PV solar cells, it can be adapted to PV cells witch reverse characteristic is dominated by avalanche mechanisms, and also dominated by shunt resistance. A simulation of shading effects in arrays with parallel series configuration has been done; an analysis has been made of the power dissipation with the influence of the number of shaded cells and the effect of shadowing degree.

Analyzing GOES-R ABI BRDF-adjusted EVI2 time series by comparing with VIIRS observations over the CONUS

The Advanced Baseline Imager (ABI) instruments onboard the Geostationary Operational Environmental Satellite-R series (GOES-R) provide new opportunities to expand their applications in global terrestrial ecology and environmental sciences. It offers a 5–15 min temporal resolution and 0.5–1 km spatial resolution that greatly benefit those environmental applications where spatial resolution can be compromised in favor of more frequent imagery. However, ABI captures reflected radiation at varying sun positions throughout the day, causing significant diurnal variations. The varying off-nadir view across ABI full disk presents further challenges for generating comparable and consistent vegetation observations, such as the two-band Enhanced Vegetation Index (EVI2). To address these challenges, three Bidirectional Reflectance Distribution Function (BRDF) models (RossThick-LiSparse-Reciprocal (RTLSR), Walthall, and Tian models) are examined to generate high-quality BRDF-adjusted EVI2 based on GeoNEX GOES-16 ABI surface reflectance. The ABI BRDF retrievals are then systematically compared to the corresponding VIIRS (Visible Infrared Imaging Radiometer Suite) Nadir BRDF-Adjusted Reflectance (NBAR) products (VNP43 V001) retrieved from RTLSR model. The viewing geometry effects are further analyzed over various land cover types using time series analysis, Pearson Correlation Coefficients (PCC), and Relative Difference (RD) between ABI and VIIRS high-quality time series inversions. The results indicate that the RTLSR model fits well the diurnal ABI observed reflectance and EVI2 values (even for the hot-spot phenomena), and outperforms the Walthall and Tian models for generating ABI high-quality BRDF retrievals with consistently low Root Mean Square Error (RMSE<0.02) and Weight of Determination (WoD < 0.5) across the CONUS. The annual proportion of ABI high-quality BRDF retrievals with a 3-day moving window using the RTLSR model is spatially and statistically comparable to that of VIIRS NBAR with a 16-day retrieval period. Compared to the time series of high-quality VIIRS NBAR EVI2, the BRDF adjusted ABI EVI2 time series still show considerable impacts of view zenith angles over evergreen forest, shrubland, and savanna pixels. However, such impacts are not significant over spatially homogeneous pixels such as cropland and deciduous forests. These results emphasize the need for BRDF correction when considering the impact of off-nadir observations from geostationary satellites on vegetation monitoring. They also demonstrate the advantages of geostationary satellites in capturing rapid changes in greenness trajectories.

Impact of Climate Change on Coral Reefs Degradation at West Lombok, Indonesia

Coral reefs are one of the ecosystems that provide economic and environmental benefits to coastal communities in Indonesia. However, coral reef ecosystems are also one of the ecosystems threatened by climate change at the local scale. The waters of North Sekotong, West Lombok, Indonesia, are a tropical coastal system with beautiful coral reefs and marine ecosystems. Coral reef damage has been widespread in this area due to increased water temperatures. Increased water temperature results in coral reef degradation. Field surveys were conducted on May 23-28, 2016, in collaboration with the Marine and Coastal Resources Research and Development Center, Ministry of Marine Affairs and Fisheries, and coral reef mapping using Landsat 7 and Landsat 8 during 2002 - 2016 as well as processing monthly sea surface temperature (SST) data from the AquaModis and Oi SST V2 satellites and daily SST data from the NOAA Coral Reef Watch satellite. Changes in coral cover area were compared with temperature changes due to climate change. The increase in temperature creates a hotspot phenomenon in the coral reef ecosystem, resulting in coral reef degradation. The results showed that coral reefs in this area have degraded by 17.55% or 78.21 Ha from 455.68 Ha (2002) to 367.46 Ha (2016), with a degradation rate of 2.8 Ha/year in 2002 - 2014; 8.1 Ha/year (2014 - 2014) and 36 Ha/year (2015 - 2016) caused by an increase in SST which caused a hotspot phenomenon with a high enough intensity that there was an increase in temperature in 2016 which reached 9.77oC.

Attenuation of hotspot phenomenon in PV systems

ABSTRACT PV waste management is a looming problem and a growing concern for environmental engineers and energy policymakers, as the early PV installations are approaching their end-of-life. Hence, improvement of PV reliability and prevention of early failures has now become more important than ever. Notably, the formation of hotspots in PV cells under partial shading and other mismatch conditions remains a dominant cause of early failures in PV modules. In this study, we undertake an experimental investigation to assess the effectiveness of the extant bypass mechanism in preventing hotspot formation in PV modules. The findings reveal several limitations associated with the conventional bypass approach. Although the bypass diode partially fulfills its intended purpose within a string array configuration, its effectiveness is entirely compromised when connected in the configuration of real-world installations, such as in a series-parallel (SP) array. The hotspot temperature in the SP array increased up to 70.7°C under partial shading conditions at the operating point (i.e., at MPP), whereas no hotspot was created (below 46.1°C) in a string array, except in the single-cell shading scenario. To make the bypass circuits effective, in the present work, a novel bypass strategy is proposed.

Assessment of Methods to Limit The Impact of Hot Spot Phenomenon on Photovoltaic Power

Assessment of Methods to Limit The Impact of Hot Spot Phenomenon on Photovoltaic Power

A comprehensive study on the pyrolysis behavior of pine sawdust catalyzed by different metal ions under conventional and microwave heating conditions

The Russia-Ukraine conflict and the COVID-19 pandemic have made fossil energy more urgent, and the catalytic pyrolysis of biomass is conducive to energy transformation to achieve global sustainable development. In this paper, the influence mechanisms of different metal ions on biomass pyrolysis under conventional heating and microwave heating conditions were studied. Through thermogravimetric analysis, it was found that the existence of metal ions could change the pyrolysis behaviors of biomass, leading to different degrees of changes in the main pyrolysis temperature and range. Compared with conventional heating conditions, metal ion-loaded biomass samples exhibited higher heating rates under microwave heating conditions due to the possible hotspot phenomenon, resulting in increased gas yields and decreased bio-oil yields. Among them, the trivalent iron ion exhibited excellent catalytic properties for gas generation, with a high gas yield of 57.9% and a bio-oil yield of 12.1%. The components in bio-oil were greatly simplified by microwave irradiation, the number of the bio-oil compounds from the pyrolysis of Fe-loading pine sawdust was reduced to 77, and the GC-MS area of light compounds with carbon number less than 10 was increased to 84.4%. Phenol and furan in bio-oil are also catalytically converted into aromatic hydrocarbons, which are ideal chemical raw materials.

Numerical simulation of flow and heat transfer induced by periodic motion of dual piezoelectric fans in confined volume

Piezoelectric (PE) fan is a novel type of active cooling device which enhance heat transfer with less power consumption. In order to achieve the theoretical limit of heat transfer performance of multiple PE fans system in confined volume, the blade location effects on that were investigated in detail by conducting three-dimensional simulations. Here, the blade pitch ranges from 1.6 to 4.2 times the fan width, and the optimal values of blade pitch with respect to four typical vibration phase angles (0°, 60°, 120°, 180°) were obtained, respectively. For all vibration modes, the air volume variation curve follows a parabola trend with blade pitch. The largest air volume is obtained when fans operating in-phase mode (φ = 0°), a conclusion that differs from that in infinite space. We attribute this to the vortex action, and its formation is determined by two effects. The positive one is the attenuation of counteracting effect from normal forces with the increasing blade pitch, where the force was exerted by two blades onto their inner fluid. The negative one is weakening of the coupling effect of two jets formed by the blade tips when spacing of dual fans is gradually increased. In addition, the local hot spot phenomenon was observed in both in-phase and counter-phase mode. It was observed that the distance between local hot spots broadens with the increasing blade pitch for in-phase mode while remains substantially constant for counter-phase mode. Our work provides a design principle for heat transfer optimization of dual PE fans in confined volume and will benefit both theoretical understanding and application in thermal management of PE fan system.

Experimental investigation of hotspot phenomenon in PV arrays under mismatch conditions

The global installed capacity of photovoltaic (PV) plants is increasing exponentially since the beginning of the 21st century. And as the early installations have started nearing their end-of-life, presently, PV waste management has started raising concerns amongst environmental researchers. The cumulative PV waste generation is estimated to reach 8 million tonnes by 2030, however, interestingly, this humungous volume may be reduced by 79% if early failures could be averted. And one of the major contributors to the early failure of the PV modules is the hotspot generation under partial shading and other mismatch conditions. Various innovative array configurations have been proposed in the past to minimize power loss under partial shading conditions, however, the performance of those from the perspective of hotspot formation and PV reliability is neglected. In the present work, the efficacy of the hotspot prevention mechanism is investigated, both in an experimental setup and in real installations. The results revealed that the extant mechanism is ineffective in preventing the occurrence of hotspots in total cross-tied (TCT) array configuration, which is hailed as the best performing one in the literature, when studied from the perspective of mismatch power loss only.

Learning About the Incidence and Lethality of COVID-19 in Vulnerable Neighborhoods: The Case of Malaga (Spain)

This research delves into the need to use granular analyses at the neighborhood level to study the preexisting conditions of vulnerability that best explain the waves of COVID-19 incidence and mortality. It seems most appropriate to use the comprehensive approach of the sustainable development with variables that analyze the economic, social, environmental, and governance dimensions, given the extensive literature that identifies each as a determining factor for the impact of disease. The work utilizes a composite vulnerability index that allows the city of Malaga to be divided into 434 census sections; waves of incidence and mortality for each section are constructed for the period of March 2020 to March 2021. Cluster analysis reveals that there are five different cluster incidence patterns, whereas the lethality waves are found to behave as a hot-spot phenomenon. The results reveal that neighborhoods that are the most vulnerable in terms of their demographic conditions (large proportion over 65 years of age and dependent) and socioeconomic conditions (severe material deprivation), have been the most affected by COVID-19 infection and mortality.

Partial shading detection and hotspot prediction in photovoltaic systems based on numerical differentiation and integration of the P − V curves

Hotspot phenomenon is an expected consequence of long-term partial shading condition (PSC), which results in early degradation and permanent damage of the shaded cells in the photovoltaic (PV) systems. Hence, partial shading detection and estimation of its intensity is a significant factor to predict the possibility of hotspotting process and its occurrence time for PV system protection. In this paper, two partial shading detection indices are introduced based on the extracted power-voltage ( P − V $P - V$ ) curves. The first P − V $P - V$ characteristic is related to the real shaded PV system and the second P − V $P - V$ curve is numerically obtained from the equivalent single-diode circuit model. The proposed PSC detection indices are established according to the difference between the numerical differentiation and integration of the P − V $P - V$ curves from the real PV system and the virtual reference model. These techniques have the advantages to distinguish between temporary and permanent PSC. Moreover, it is possible to estimate the intensity of the shading level and predict the hotspot occurrence time, accordingly. The performance of these methods are confirmed using some simulations and an experimental setup. The results verify the capabilities of the methods for partial shading detection without the requirement of an extra physical cell/module as a reference model.

Experimenting with a Battery-Based Mitigation Technique for Coping with Predictable Partial Shading

In this paper, the authors propose to use batteries to improve the performance of grid-connected photovoltaic plants when their photovoltaic fields are subject to partial shading phenomena. Particular attention is devoted to predictable and repetitive partial shadings, such as those that often appear in urban residential environments. Firstly, battery packs with proper nominal voltage and capacity are connected in parallel to partially shaded photovoltaic submodules. Then, the shaded photovoltaic submodules are properly disconnected and connected to the respective photovoltaic string by using a “battery control unit”, which is operated by taking into account characteristics of the specific partial shading phenomenon to cope with. To demonstrate the effectiveness of the proposed technique, an experimental study is performed to compare the performances of two identical prototypal grid-connected photovoltaic generators subject to identical artificial and repetitive partial shadings. Only one of the photovoltaic generators is equipped with batteries together with their respective battery control unit, while the second one is simply equipped with conventional bypass diodes. The main advantages of the proposed technique are a greatly improved whole power generation together with the elimination of hotspot phenomena.

Multi-scale modeling of shock initiation of a pressed energetic material. II. Effect of void–void interactions on energy localization

Heterogeneous energetic materials (EMs) contain microstructural defects such as voids, cracks, interfaces, and delaminated zones. Under shock loading, these defects offer potential sites for energy localization, i.e., hotspot formation. In a porous EM, the collapse of one void can generate propagating blast waves and hotspots that can influence the hotspot phenomena at neighboring voids. Such void–void interactions must be accounted for in predictive multi-scale models for the reactive response of a porous EM. To infuse such meso-scale phenomena into a multi-scale framework, a meso-informed ignition and growth model (MES-IG) has been developed, where the influence of void–void interactions is incorporated into the overall reaction rate through a function, fv−v. Previously, MES-IG was applied to predict the sensitivity and reactive response of EM, where fv−v was assumed to be a function of the overall sample porosity alone. This paper performs a deeper analysis to model the strong dependency of fv−v on other factors, such as void size and shock strength. The improved model for void–void interactions produces good agreement with direct numerical simulations of the HE microstructures and, thus, advances the predictive capability of multi-scale models of the shock response and sensitivity of EM.

Development of fire safety best practices for rooftops grid-connected photovoltaic (PV) systems installation using systematic review methodology

• Installation of PV system as green energy initiative is showing a rising trend. • Poor installation practices of PV system by installers have resulted in PV fires. • Collation of best fire safety practices for rooftop PV system installation. • A systematic review to scrutinize aspects of fire safety in PV system installation. • Fire safety checklist is suggested to be part of PV system installation guidelines. Numerous photovoltaic (PV) fire incidents are caused by overheating of PV system components, direct current (DC) arc-fault or hot spot phenomenon. These causes happen mainly due to poor installation practices by the installers. Many PV system installation guides do not emphasise much on the fire hazard during installation. As the PV system is becoming increasingly popular nowadays, it is crucial to establish a specific and comprehensive guideline pertaining to fire safe installation of the system. Therefore, this paper aims to assess and incorporate such fire safety practices from all PV installation guidelines that are publicly accessible. A total of 40 PV installation publications have been systematically reviewed and classified into two categories – design consideration and installation stage. The analysis pointed out a compilation of fire safety practices during PV system installation focusing on residential rooftop applications from the reviewed publications. Although DC isolators have been reported as the top component of PV fire causes, many guidelines do not emphasise the fire hazards involved as well as the things that should and should not be done during installation. The inclusion of a fire safety checklist is suggested as part of the installation guideline.

Microstructural interactions contribute to the hotspot in the living cochlea

The mechanism of the active cochlea relies on a complex interaction between microstructures in the organ of Corti. A significant longitudinal vibration "hotspot" was recently observed in the high-frequency region of the living gerbil cochlea between the Deiters cells and the outer hair cells. A similar phenomenon was also found in guinea pigs with a relatively smaller magnitude. The cause is unknown, but one hypothesis is that this phenomenon is due to the structural constraints between different microstructures. It is not easy to explain the mechanism of hotspots directly from experimental observations. It may also be difficult to image or test if the hotspot will occur in the low-frequency region in the cochlea. We built two three-dimensional finite element models corresponding to the high- and low-frequency regions in the guinea pig cochlea. Responses of the organ of Corti to passive acoustic and outer hair cell electrical excitation were calculated. The two excitations were then superimposed to predict the active response of the organ of Corti. The hotspot phenomenon in the experiment was reproduced and analyzed in-depth about influencing factors. Our results indicate that hotspots appear in the low-frequency region of the cochlea as well. We hypothesize that the hotspot is a locally originated phenomenon in the cochlea, and the traveling wave further enhances the response to low-frequency excitation. The movement of outer hair cells inclined in the longitudinal direction is the leading cause of the hotspot.

SpotFuzz: Fuzzing Based on Program Hot-Spots

AFL is the most widely used coverage-guided fuzzer, which relies on rough execution information to assign seeds energy, which can lead to waste. We track the program executed by AFL and discover that the hit counts of each edge might vary greatly when using different seeds as inputs. Some seeds, which are continuously given too much energy, experience very high hit counts of several edges without new crashes or edges being explored, which results in invalid execution and waste of performance. We also define time-consuming edges and discover that they only occupy a small part of the program. In this paper, we define invalid execution edges and time-consuming edges as hot-spots and propose a fuzzing solution SpotFuzz to solve energy waste caused by the above hot-spot phenomenon. It allocates seeds with more hot-spots during execution and uses less energy to reduce energy waste. Moreover, it preferentially selects seeds with less time-consuming edges as test cases, allowing for more edges to be explored in a limited time. We implement an SpotFuzz prototype based on AFL and test it on several real programs for 600 CPU days. The experimental results show that minimizing the invalid and time-consuming execution of edges can improve the fuzzing efficiency. On average, SpotFuzz could find 42.96% more unique crashes and 14.25% more edges than AFL on GNU Binutils and tcpdump.

Hot Spot Analysis of Photovoltaic Module under Partial Shading Conditions by Using IR-Imaging Technology

The probable appearance of localized overheating (hot spot) represents one of the main matters for the reliability and safety of c-Si cells. It entails both a risk for the photovoltaic module's lifetime and a decrease in its operational efficiency. Partial shading is the most common cause of a hot spot in a PV system. The main aim of this work is to analyze the hotspot phenomena by I-V curve as well as IR thermography and investigate the impact of partial shading on the hottest cell experimentally to find its effect on the output power. The results show that at normal operating conditions (G=865W/m2 and Ta=39.7°C) the output power is 89.05W; the temperature difference between the hottest and cooled cell was about 6°C. Moreover, the short circuit current and consequently, the maximum output power reduced if only one cell fully or partially shaded. However, when the hottest cell is shaded by 25%, 50%, 75%, and 100% of the shaded area, the power losses were 37.17 %, 50.05%, 48.61%, and 52.86% respectively. Wheals, the hottest cell temperature was 80.6, 99.1, 101.4, and 62.4°C for 25, 50, 75, and 100% of the shading area, the major temperature difference observed at 75% of the shading area.

A new approach of PV system structure to enhance performance of PV generator under partial shading effect

The PV generator performance depends closely on the weather conditions, especially on solar irradiance. Besides, the partial shading effects still one of the most complicated problems that have a direct impact on the PV performance in terms of power output, multiple peaks exhibition on the power–voltage (P–V) characteristic curve, and hot-phenomena occurrence. In this paper, an efficient PV system structure has been proposed in order to enhance the performance of the PV generator under the partial shading effect. In such a way, the proposed PV structure will overcome mainly the following major partial shading effect problems: eliminating the local multiple peaks exhibition on the characteristic curve and increase the power output yield of the PV generator. On the other hand, the impact of hot-spot phenomena is reduced as well which leads to an increased in PV generator lifespan. On referring to the literature, many maximal power point tracking (MPPT) techniques have been developed in view to track the global maximal power point GMPP, alongside with proposing several PV configurations and arrangements to increase the power output yield and eliminate the local maximal power peaks (LMPPs). This paper intends to compare and discuss these techniques and configurations individually and by combining them in terms of effectiveness, complexity and cost ... etc. In which, this comparison ends up by selecting and proposing a suitable PV system structure that can mitigate the partial shading effect with high cost-effectiveness.