Shadow Conditions Research Articles

Reconfiguration technique for Optimization of the Photovoltaic array output power under partial shading conditions

A partial shading condition is a case under which the PV array is exposed to many problems such as losses of the output power of the PV array, and the PV array has more than one maximum power point (MPP), which makes it so difficult to track the MPP. This paper presents the effect of different partial shading patterns on PV array characteristics and the effect on the output power of the PV array, and provides a comparative literature review on methods to mitigate these effects and the drawbacks of these methods. It also proposed a new reconfiguration strategy that increases the output power of the PV array by 13.8 % from the total power under shadow condition, and a new technique for enhancing the output power of the PV array by 20 % of the total power under fully illumining conditions by controlling the switch matrix between the photovoltaic array and adaptive batteries bank. This paper gives a solution for the problem of the difficulty of tracking the MPP, because the proposed strategy makes only one MPP. The simulation was carried out by using MATLAB Simulink under different shading patterns. Citation: Mohamed, A. M., Saafan, S. M., Attalla, A. M., and Elgohary, H. (2018). Reconfiguration technique for Optimization of the Photovoltaic array output power under partial shading conditions. Trends in Renewable Energy, 4, 111-124. DOI: 10.17737/tre.2018.4.2.0068

Analysis of ANFIS MPPT Controllers for Partially Shaded Stand Alone Photovoltaic System with Multilevel Inverter

<p>This work presents a unique combination of an boost converter run by a set of two photovoltaic panels (PV) with a MPPT, suitable to guarantee MPP even under partial shadowed conditions, managed by an adaptive neuro fuzzy inference system (ANFIS) trained by the training data derived from a Perturb and observation (P&O) conventional algorithm. The single phase cascaded H bridge five-level inverter (CHI) driven by the individual outputs of the boost converter, with selective harmonic elimination scheme to eliminate typically the seventh order harmonics. Simulation was carried out in the MATLAB/SIMULINK environment validated the proposed scheme. It has been thus established; by both simulations the ANFIS model of MPPT scheme outperforms other schemes of conventional control algorithm.</p>

A Low Ratio of Red/Far-Red in the Light Spectrum Accelerates Senescence in Nest Leaves of Platycerium Bifurcatum

AbstractThe fern Platycerium bifurcatum is a valuable component of the flora of tropical forests, where degradation of local ecosystems and changes in lighting conditions occur due to the increasing anthropogenic pressure. In ferns, phytochrome mechanism responsible for the response to changes in the value of R/FR differs from the mechanism observed in spermatophytes. This study analyzed the course of ontogenesis of nest leaves in P. bifurcatum at two values of the R/FR ratio, corresponding to shadow conditions (low R/FR) and intense insolation (high R/FR). The work used only non-destructive research analysis, such as measurements of reflectance of radiation from the leaves, their blue-green and red fluorescence, and the chlorophyll a fluorescence kinetics. This allowed tracing the development and aging processes in the same leaves. Nest leaves are characterized by short, intense growth and rapid senescence. The study identified four stages of development of the studied leaves related to morphological and anatomical structure and changing photochemical efficiency of PSII. Under the high R/FR ratio, the rate of ontogenesis of the leaf lamina was much slower than under the low R/FR value. As shown, the rapid aging of the leaves was correlated with faster decline of the chlorophyll content. It was shown that leaf senescence was accompanied by accumulation of polyphenols, anthocyanins and carotenoids on the basis of reflectance and fluorescence measurements in the blue-green range.

Plant growth evaluation of Cajanus cajan (L.) Millsp., Canavalia ensiformis (L.) DC. and Cratylia argentea (Desvaux) O. Kuntze., in soils degraded by sand and gravel extraction

In this research, the adaptability of pigeon pea (Cajanus cajan (L.) Millsp., canavalia (Canavalia ensiformis (L.) DC.) and veranera (Cratylia argentea (Desvaux) O. Kuntze) species, was evaluated in soils degraded by sand and gravel extraction. The three species were planted in bags as follows: 20 x 10cm, each with 3 seeds, with a substrate 2:1 soil and sand, respectively. The plants were grown under shadow conditions with 50% for 60 days, and received irrigation according to climate conditions. Therefore, were transplanted at field conditions, plant height (PH), fully developed leaves (FDL) and stem diameter (SD) variables, were measured every week for 10 weeks. A randomized block design was used with a fixed balanced effect. The number of replicates per treatment was four, the multivariate technique MANOVA variance with orthogonal type was included and the method of maximum likelihood was used to establish the dimensionality of the contrast. In fact, one-dimensional comparisons were carried out using Tukey method, which had achieved type I error of 5% statistical significance. Significant difference among plants for PH (p<0.05) variable was obtained. In addition, SD variable showed differences from the third week for all evaluated plants (p<0.05). A highly significant and directly proportional relationship among HP, FDL and SD variables (p<0.0001), was found. MANOVA Multivariate Analysis showed a highly significant difference among evaluated species (p<0.0001), which confirms the hypothesis. It was expected that species were developing and growing despite having contrasting conditions in the study area.

Shade response of a full size TESSERA module

A full size TESSERA shade tolerant module has been made and was tested under various shadow conditions. The results show that the dedicated electrical interconnection of cells result in an almost linear response under shading. Furthermore, the voltage at maximum power point is almost independent of the shadow. This decreases the demand on the voltage range of the inverter. The increased shadow linearity results in a calculated increase in annual yield of about 4% for a typical Dutch house.

The Dynamic Behavior of Once-Through Direct Steam Generation Parabolic Trough Solar Collector Row Under Moving Shadow Conditions

Compared with recirculation and injection modes, once-through direct steam generation (DSG) parabolic troughs are simpler to construct and require the lowest investment. However, the heat transfer fluid (HTF) in once-through DSG parabolic trough systems has the most complicated dynamic behavior, particularly during periods of moving shadows caused by small clouds and jet contrails. In this paper, a nonlinear distributed parameter dynamic model (NDPDM) is proposed to model the dynamic behavior of once-through DSG parabolic trough solar collector row under moving shadow conditions. Compared with state-of-the-art models, the proposed NDPDM possesses three characteristics: (a) adopting real-time local values of the heat transfer and friction resistance coefficients, (b) simulating the whole collector row, including the boiler and the superheated sections, and (c) modeling the disturbance of direct normal irradiance (DNI) level on DSG parabolic trough solar collector row under moving shadow conditions. Validated using experimental data, the NDPDM accurately predicts the dynamic characteristics of HTF during periods of partial and moving DNI disturbance. The fundamental and specific dynamic process of fluid parameters for a DSG parabolic trough solar collector row is provided in this paper. The results show the following: (a) Moving shadows have a significant impact on the outlet temperature and mass flow rate, and the impact lasts up to 1000 s even after the shadows completely leave the collector row. (b) The time for outlet steam temperature to reach a steady-state value for the first time is independent of the shadow width, speed, and moving direction. (c) High-frequency chattering of the outlet mass flow rate can be observed under moving DNI disturbance and will have a longer duration if the shadow width is larger or the shadow speed is slower. Compared with cases in which the whole system is shaded, partially shading cases have shown a longer duration of high-frequency chattering. (d) Both wider widths and slower speeds of shadow will cause a larger amplitude of responses in the outlet temperature and mass flow rate. When the shadow speed is low, there is a longer delay time of response in the mass flow rate of the outlet fluid. (e) The amplitude of response in the outlet temperature does not depend on the direction of clouds movement. However, if the DNI disturbance starts at the inlet of the collector row, there will be significant delay times in both outlet temperature and mass flow rate, and a larger amplitude of response in outlet mass flow rate.

A Hybrid Neur-Fuzzy Optimization Method for PV Steady State Improvement in Maximum Power Point Tracking Controller

This paper presents ahybrid Neural-Fuzzy optimization method for the purpose of assuringthe steady state case of the Maximum Power Point (MPP) for a Photovoatic (PV) system. Also, it works to decrease the oscillation occurring around MPP. The proposed method implemented via using an improved intelligent control method, neural fuzzy networks (Nueural-Fuzzy). The results showed that the PV system with Maximum Power Point Tracking (MPPT) always tracks the peak powerpoint of the PV module under various operating conditions. Afterwards, these results are validated by the comparison with the conventional and most used methods (P&O) and showed that the proposed MPPT method has better steady state and therefore less oscillation around the MPP than the P&O. It is also shown that, the increase in the output power due to usingthe MPPT is about 48.2% for a clearweather conditions and 34.8% for a shadow conditions

Automatic Traffic Data Collection under Varying Lighting and Temperature Conditions in Multimodal Environments: Thermal versus Visible Spectrum Video-Based Systems

Vision-based monitoring systems using visible spectrum (regular) video cameras can complement or substitute conventional sensors and provide rich positional and classification data. Although new camera technologies, including thermal video sensors, may improve the performance of digital video-based sensors, their performance under various conditions has rarely been evaluated at multimodal facilities. The purpose of this research is to integrate existing computer vision methods for automated data collection and evaluate the detection, classification, and speed measurement performance of thermal video sensors under varying lighting and temperature conditions. Thermal and regular video data was collected simultaneously under different conditions across multiple sites. Although the regular video sensor narrowly outperformed the thermal sensor during daytime, the performance of the thermal sensor is significantly better for low visibility and shadow conditions, particularly for pedestrians and cyclists. Retraining the algorithm on thermal data yielded an improvement in the global accuracy of 48%. Thermal speed measurements were consistently more accurate than for the regular video at daytime and nighttime. Thermal video is insensitive to lighting interference and pavement temperature, solves issues associated with visible light cameras for traffic data collection, and offers other benefits such as privacy, insensitivity to glare, storage space, and lower processing requirements.

Improved multiple feedback successive interference cancellation algorithms for near‐optimal MIMO detection

In this study, the authors propose an improved multiple feedback successive interference cancellation (IMF-SIC) algorithm and an ordered IMF-SIC (OIMF- SIC) algorithm for near-optimal multiple-input multiple-output (MIMO) detection. In particular, the multiple feedback (MF) strategy in successive interference cancellation (SIC) detector is based on the concept of shadow region, where, if a decision falls in the shadow region, then multiple neighbouring constellation points are used in the decision feedback loop followed by the SIC technique, and the best candidate symbol is selected by using maximum likelihood cost. However, while deciding the best symbol, the shadow condition is not checked in the subsequent layers which may result in an unreliable decision. Thus, to improve the accuracy of a decision, the authors propose an improved MF strategy where the shadow region condition is checked recursively. Further, the authors also propose an OIMF-SIC algorithm where the log likelihood ratio based dynamic ordering is utilised for ordering the detection sequence. Simulation results validate superiority of the proposed algorithms over the other SIC based detection techniques. In addition, to validate robustness of the proposed algorithms, BER performance is computed and compared under channel state information mismatch.

Application of Particle Swarm Optimization for Extracting Global Maximum Power Point in PV System under Partial Shadow Conditions

Application of Particle Swarm Optimization for Extracting Global Maximum Power Point in PV System under Partial Shadow Conditions

Modeling and characteristic study of solar photovoltaic system under partial shading condition

The ever-increasing energy demand along with the rapid reduction of fossil fuels and to mitigate environmental issues, nowadays renewable energy becomes the main source of electrical energy across the globe. The recent upsurge in the demand of Photovoltaic(PV) systems is due to the fact that they produce electrical energy which requires less maintenance and is clean in nature .PV energy can be obtained directly by converting the solar energy into electrical energy. The main challenge in the PV system is that its characteristics depends upon environmental conditions and it is highly non-linear in nature. With change in temperature and irradiance conditions, the PV characteristic changes. For large power applications, photovoltaic arrays are required in the place of modules. To extract the maximum power from the PV array, maximum power point tracking algorithms (MPPT) with converters are essentially required. For large array, there is a possibility of shadow condition because of the nearby buildings, trees and the array itself causing partial shading of PV system. PV array experience partial shading under the condition where different modules of the array get different solar irradiance. This paper focuses on modelling and study of current-voltage and power-voltage characteristics of a PV array under the condition where different modules get different irradiance level. For ease the series-parallel and total-cross-tied configuration analysis is being done in the paper. The MATLAB simulation results show the occurrence of multiple peaks in current voltage and power voltage characteristic under partial shading condition.

Simulation of global MPPT based on teaching–learning-based optimization technique for partially shaded PV system

The power against voltage curve for PV power system during shadow condition contains number of local maximum power points (MPPs) and only one global. The classical maximum power point tracking (MPPT) algorithms are designed to follow the global MPP, but they stuck around local MPPs such as fuzzy logic controller (FLC). Therefore, A global MPPT based on teaching–learning-based optimization (TLBO) algorithm has been presented in this paper. The performance of PV system under abnormal conditions such as partial shading has been improved. TLBO algorithm is simple computational steps and faster convergence to optimal solution. A comprehensive assessment of TLBO-based tracker is carried out against FLC and particle swarm optimization (PSO) techniques for same conditions. Six different partial shading patterns have been employed to investigate TLBO performance using MATLAB/Simulink. The parameters of comparison include the tracking speed and overall tracking efficiency. The results confirm that TLBO-based tracker exactly convergence to global MPP under different studied cases. TLBO has best performance compared to the other studied techniques. The tracking speed is increased using TLBO-based tracker; the average tracking time of global MPP is reduced by more than 23.8 % compared with PSO in all studied different partial shading patterns.

Robust road detection in shadow conditions

Image-based road detection is a vital task for many real-world applications, such as autonomous driving and obstacle detection. We propose a method for segmenting road regions from a single image based on horizon line estimation and clustering technology. The key idea is to leverage normalized cross correlation to search for the line separating the road image. Additionally, we divide the lower part of the road image into several identical parts horizontally and utilize a density-peak clustering algorithm in terms of gray and HSV value of each pixel. Clustering results are further labeled as road and nonroad based on the assumption that two adjacent horizontal parts share similar clustering size and average gray value. For road images with shadows, we also propose a new shadow-free space derived from HSV space. By calculating maximum entropy and reconstructing images, we show that shadows are eliminated to achieve better road detection. Experimental results on four datasets and shadow images demonstrate the effectiveness and robustness of our method.

AMELIORATIVE EFFECTS OF VITAMIN C ON THE HEAT-STRESSED MALE ZARAIBI GOATS

The present work was designed to assess the effect of vitamin C doses on heat stress in male Zaraibi goats, during summer season. Climatic parameters; including ambient temperature (AT), relative humidity (RH) and temperature humidity index (THI); were estimated under the sunny and shadow conditions. Under sunny circumstances, the climatic parameters were meaningfully elevated as compared to the shadow conditions. The experimental periods (1, 2, 3, 4, 5 & 6 weeks), vitamin C doses (0, 8, 15 and 30 mg/kg body weight) and their interactions exhibited significant effects on all the studied parameters including: rectal temperature (RT), respiratory rate (RR), red blood cells count (RBCC), white blood cells count (WBCC), concentrations of total antioxidant capacity (TAC), triiodothyronine (T3), thyroxine (T4), total proteins (TP), albumin (Alb), total cholesterol (TC), triglycerides (TG), creatinine (Creat) and Urea (U) as well as the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). In heat-stressed goats, the RT, RR, RBCC and levels of TP, Alb, TC, TG, Creat, U and activities of AST and ALT were significantly increased as compared to those under shadow, and were correlated positively to the THI, whereas inversely to the vitamin C doses. However, the WBCC, TAC and T3 and T4 levels were reduced with increasing THI, but were significantly enhanced by increasing the dose of vitamin C. In conclusion, the daily vitamin C intake was effective against the signs of heat stress.

Decadal evolution of a very small heavily debris-covered glacier in an Alpine permafrost environment

AbstractGlacier response to climate forcing can be heterogeneous and complex, depending on glacier system characteristics. This article presents the decadal evolution of the Tsarmine Glacier (Swiss Alps), a very small and heavily debris-covered cirque glacier located in the Alpine periglacial belt. Archival aerial photogrammetry and autocorrelation of orthophotos were used to compute surface elevation, volume and geodetic mass changes, as well as horizontal displacement rates for several periods between 1967 and 2012. A GPR survey allowed us to investigate glacier thickness (15 m mean) and volume (4 × 106m3) in 2015 and to anticipate its future evolution. Different dynamics occurred in recent decades because of the heterogeneous surface characteristics. The climate-sensitive upper debris-free zone contrasts with the progressively stagnant heavily debris-covered glacier tongue. Between 1967 and 2012, the glacier lost 1/3 of its initial volume (2 × 106m3). The average mass balance stabilised at ~−0.3 m w.e. a−1since 1999. Compared with other local glaciers, the Tsarmine Glacier shows a particular decadal behaviour both in time (divergence of mass balance since the 2000s) and space (inverted ablation pattern). This might be explained by the combined influence of debris cover, shadow, snow redistribution and permafrost conditions on this very small glacier.

Structural and functional diversity and quantitative parameters of two-year shoot systems of pregenerative individuals of <em>Quercus robur</em> L. (Fagaceae) in different light conditions in the central part of European Russia

Based on topological characteristics and functional role in crown, diversity of the two-year shoot systems in pregenerative individuals of Q. robur L. growing in communities with different light level in southern part of Moscow region and reserve “Kaluzhskiye Zaseki” in Kaluga region have been typified. In full light conditions uniform branching, mesotonic and acrotonic two-year shoot systems with a great number of lateral twigs mainly contribute to the crown structure. In shadow conditions crown is formed basically from non-branching systems and two-year shoot systems with a small number of casually located lateral twigs. The number of nodes of the elementary shoots of different two-year system types is more constant than their internodes’ length. Branching types of two-year shoot systems have longer internodes than nonbranching ones do. In branching types of two-year shoot systems internodes become longer with the improvement of light conditions. Refs 26. Figs 3. Tables 3.

Evaluation of Shadow Reconstruction Algorithm for Very High Resolution Satellite Imagery

The Very High Resolution images have opened a new era for remote sensing applications such as object detection, classification, object mapping and change detection. However, the effects of shadow in these images are remarkable. The objective of this paper is to propose algorithm for shadow reconstruction. The primer stage, shadow detection and classification are carried out which separates shadow from rest of environment. For doing reconstruction the preprocessing is done by morphological operations which extract image components such as region and shape. It is followed by border creation and finally the reconstructed of an original image is accomplished border interpolation. The reconstruction accuracy is calculated by using Kappa Coefficient. Here Experimental results are obtained on three VHR images representing different shadow conditions. The performance analysis is carried out which shows better sensitivity and specificity.

Optical bidirectional beacon based visible light communications.

In an indoor bidirectional visible light communications (VLC), a line-of-sight (LOS) transmission plays a major role in obtaining adequate performance of a VLC system. Signals are often obstructed in the LOS transmission path, causing an effect called optical shadowing. In the absence of LOS, the performance of the VLC system degrades significantly and, in particular, at uplink transmission this degradation becomes severe due to design constraints and limited power at uplink devices. In this paper, a novel concept and design of an optical bidirectional beacon (OBB) is presented as an efficient model to counter the performance degradation in a non-line-of-sight (NLOS) VLC system. OBB is an independent operating bidirectional transceiver unit installed on walls, composed of red, green, and blue (RGB) light emitting diodes (LEDs), photodetectors (PDs) and color filters. OBB improves the coverage area in the form of providing additional or alternate paths for transmission and enhances the performance of the VLC system in terms of bit error rate (BER). To verify the effectiveness of the proposed system, simulations were carried out under optical shadowing conditions at various locations in an indoor environment. The simulation results and analysis show that the implementation of OBB improves the performance of the VLC system significantly, especially when the LOS bidirectional transmission paths are completely or partially obstructed.

The effect of the Earth’s oblateness on predicting the shadow conditions of a distant spacecraft: Application to a fictitious lunar explorer

The effect of the Earth’s oblateness on predicting the shadow events of a lunar spacecraft caused by the Earth’s shadow is analyzed in this study. To ensure a reliable analysis, the proven ‘line-of-intersection’ method is modified and directly applied to predict the shadow conditions using a spheroidal model of the Earth and a conical shadow model. Two major lunar mission phases, namely, transfer and orbiting, are considered with corresponding fictitious initial conditions, and eclipse events are predicted and the results are compared using both spherical and spheroidal Earth models. For the lunar transfer phase, for which an Earth-bound highly elliptical orbit is assumed, not only the predicted entry and exit times of an event but also its duration are found to be more strongly shifted as the apogee altitude increases; for perigee and apogee altitudes of 1000 and 380,000km, respectively, the maximum difference in predicted duration is found to be approximately 0.76min for a penumbra event. For the lunar orbiting phase, for which a circular orbit around the Moon at an altitude of 100km is assumed, a prediction difference of approximately half a minute on average and approximately one minute at maximum (e.g., 0.73min for qumbra events, 1.03min for penumbra events and 1.32min for ‘instantaneous’ full sunlight events) can occur. The results of the present analysis highlight the importance of modeling the oblate shape of the Earth when predicting the shadow events of a distant spacecraft, and they are expected to provide numerous insights for any missions involving highly elliptical orbits around the Earth or travel to the Moon.

Robust Localization of Texts in Real-World Images

Localization of texts in natural images could be an important stage in many applications such as content-based image retrieval, visual impairment assistance systems, automatic robot navigation in urban environments and tourist assistance systems. However due to the variations of font, script, scale, orientations, color, shadow and lighting conditions, robust scene text localization is still a challenging task. In this paper, we propose a novel method to localize not only Farsi/Arabic and Latin texts with different sizes, fonts and orientations but also low luminance contrast and poor quality ones in the natural images taken with uneven illumination conditions. Firstly, fast weighted median filtering as a nonlinear edge-preserving smoothing filter and then color contrast preserving decolorization are exploited to make the text localization system more robust for low luminance contrast and poor quality texts. In order to extract the Farsi/Arabic and Latin scene texts and also filter the nontext ones, a unified framework is proposed incorporating the maximally stable extremal regions and a novel proposed region detector called Stable Width Stroke Regions which is based on closed boundary regions. Phase congruency and Laplacian operators are exploited to extract the closed boundary regions. Finally, to extract the single text lines, the Meanshift clustering and radon transform were used. Experimental results show that the proposed method localize low luminance contrast and low quality scene texts for both Farsi/Arabic and Latin scripts encouragingly.