Uneven Shading Research Articles

A comprehensive analysis of environmental factors affecting solar cells: Dust accumulation, ambient temperature, and humidity

This paper aims to investigate the impact of environmental factors on solar cells, focusing on dust accumulation, ambient temperature, and humidity. The utilization of solar cells as a renewable source of energy has garnered significant attention in recent years, with three main types of solar cells: silicon-based, thin-film, and calcium titanium ore solar cells. While each type possesses unique strengths and weaknesses, understanding the impact of environmental factors is essential for monitoring quality and assessing their performance. Dust accumulation on photovoltaic (PV) panels reduces output power by blocking solar radiation transmission, causing uneven shading and reducing heat dissipation. High temperatures also negatively impact PV system operation by reducing the operating voltage of the cells, while humidity can block or diffract sunlight, reducing the output power of the system. This paper provides an analysis of existing literature and empirical studies, aiming to provide valuable insights into improving the efficiency and durability of solar cells and contributing to the widespread adoption of this renewable energy source.

Performance Analysis of Novel Solar PV Array Configurations with Reduced Tie Interconnection to Extract Maximum Power under Partial Shading

The non-uniform irradiation pattern causes the partial shading effects and decreases the performance of the solar Photovoltaic (PV) array. The effect of uneven shading condition depends on its pattern and area. The PV array’s performance is determined by the cross ties that are connected within the array. This research proposes eight different PV array tie interconnection configurations to obtain the maximum power output under uneven insolation conditions. Experimental analysis is done in the PV array consists of 16 numbers of 10 W PV panels which has a total capacity of 160 W. The practical results reveal that the losses due to partial shading are influenced by the shade pattern, shade area, and the placement of the cross ties. Overall, among the conventional configurations, the hybrid bridge link total cross tied interconnection pattern produced the best results, followed by the hybrid series parallel total cross tied and bridge link patterns. In the proposed configurations, the plus tie configuration outperformed the others in maximum of the partial shading scenarios. In general, the PLT configuration demonstrated an average power efficiency increase of 19.17%, 8.37%, and 8.28% compared to the series parallel, hybrid series parallel total cross-tied, bridge link, and bridge link total cross-tied configurations, respectively. The effectiveness of the proposed configurations is validated by the practical verifications.

Combining PPO and incremental conductance for MPPT under dynamic shading and temperature

As solar generation gains an increased importance in a smart grid, an efficient control of a photovoltaic (PV) array has to be considered. However, energy efficiency of a PV array greatly depends on environmental conditions, such as uneven shading, solar irradiance and temperature. Maximum power point tracking (MPPT) algorithms aim to dynamically find an optimal operation voltage in order to compensate for changes in the environment, as well as degradation of solar panels. Besides generating a maximum amount of power, an MPPT controller aims for stability in order to avoid additional losses. Reinforcement Learning (RL) is a flexible training method that can produce a controller for a complex problem without a detailed prior knowledge of the environment. In this work we propose an approach that combines an optimized neural network, trained through deep reinforcement learning (DRL), with a classical closed-loop control. Experimental results suggest that the proposed approach outperforms a recently proposed DRL network both in terms of efficiency and stability. A compact and discrete version of the proposed controller is also evaluated and shown to further increase performance. The implemented algorithms and the RL simulation environment are made available in an open-source repository.

Impact of Uneven Shading by Neighboring Buildings and Clouds on the Conventional and Hybrid Configurations of Roof-Top PV Arrays

Partial shading is the commonly encountered scenario of building roof-top based PV arrays that mainly occur due to the shadow of the neighbouring buildings and clouds resulting in unexpected losses and deteriorated system performance. The arrays are connected in various configurations to enhance the system performance during shading. In this paper, various conventional and hybrid interconnection configurations based on series-parallel (SP), bridge-linked (BL), and total cross tied (TCT) topologies of the roof-top PV arrays are examined under various partial shading scenarios caused by the neighbouring building and clouds. The investigation is done for a $9\times 9$ roof-top array in MATLAB/Simulink environment considering various comparison parameters. It has been found that during 1.23%, 7.40%, 11.11%, 17.75%, 18.51%%, 22.22%, and 24.69% of total array shading, SP generated the maximum power whereas, during 30.86%, 61.72% shading, TCT has the generated only a slightly higher power as compared to SP. Hence, the study concludes that the configurations have a puny effect on the power generation of the arrays during uneven shading patterns caused by buildings and clouds.

Effective Binarization of Document Images with Uneven Shading

With rapid popularization of mobile camera, capturing a document and storing it become easy. However, when the document is illuminated under poor conditions, the document image may appear uneven shading. In that case, it is difficult to restore texts for character recognition and document analysis etc. In this paper, we propose an effective and simple approach to remove uneven shading from a document image. First, a local uneven shading is estimated using a constant time weighted median filter. Then, reflectance is computed by removing the uneven shading based on retinex theory, followed by a bandpass thresholding to partially binarize the clean document image. Finally, the unbinarized pixels are classified into text and background by using contrast map weighted graphcut approach. A host of experimental results demonstrate that the proposed method runs effectively and has pleasurable performance.

Paper] Using Gaussian Kernels to Remove Uneven Shading from a Document Image

Paper] Using Gaussian Kernels to Remove Uneven Shading from a Document Image

Shading Surface Estimation using Piecewise Polynomials for Binarizing Unevenly Illuminated Document Images

As a pre-processing step for document analysis, binarizing document image is often performed. The bina- rization is regarded as a necessary step to separate text and background. When document images are acquired under poor lighting circumstances, the images are soiled with uneven shading. This paper presents an improved approach for binarizing document images which are illuminated unevenly. We employ 2D polynomials with order 3 to fit very complicated uneven shading surface of document images. The document image is divided into several blocks over- lapped partially with each other to reduce the discontinuity between polynomials. To improve the estimation accuracy, we normalize pixel coordinates to establish a stable equation system for computing the polynomial coefficients. After removing the uneven shading, most part of the background is filled with the maximum of surface and then a global thresholding is applied. In the experiment section, we demonstrate that the binarization results are satisfied, compared with other methods.

Shading and bypass diode impacts to energy extraction of PV arrays under different converter configurations

A solar photovoltaic (PV) energy conversion system requires power converters for maximum power extraction and grid integration. At present, typical converter configurations used in a solar PV system include central, string and micro-converter based PV systems. In order to develop efficient and reliable photovoltaic energy conversion technologies, this paper compares the energy extraction characteristics of a PV system for different converter schemes. The paper particularly focuses on how energy extraction characteristics of a PV array are affected by uneven shading and how different bypass diode arrangements improve and affect PV system energy extraction characteristics under different converter configurations. A detailed comparison study is conducted for central, string and micro-converter based PV systems. It is found that compared to micro-converter based PV systems, the central converter PV systems with large-scale distributed bypass diode connections could be an economic solution to enhance PV system efficiency, reliability and performance, in particular for utility-scale PV generators.

Impact of uneven shading and bypass diodes on energy extraction characteristics of solar photovoltaic modules and arrays

Solar photovoltaic (PV) energy is becoming an increasingly important part of the world's renewable energy. In order for effective energy extraction from a solar PV system, this paper investigates I–V and P–V characteristics of solar PV modules and arrays. The paper particularly focuses on I–V and P–V characteristics of PV modules and arrays under uneven shading conditions, and considers both the physics and electrical characteristics of a solar PV system in the model development. The article examines how different bypass diode arrangements could affect maximum power extraction characteristics of a solar PV module or array. It is found in this article that under uneven shading conditions, solar PV cells may perform in very different ways and a solar PV system may exhibit multiple peaks in its P–V characteristics. The study of this article also shows that the arrangement of largely distributed bypass diodes within a PV module could effectively improve efficiency and maximum power point tracking strategies for energy conversion of solar PV systems.

Automatic snow surface roughness estimation using digital photos

AbstractA surface roughness measurement system for snow is presented. It is based on a background board with scales on the edges and a digital camera. Analysis software is developed for automatic processing of images to produce calibrated profiles. The image analysis and calibration was fully automatic in >99% of the studied cases. In the others, the intensity adjustment or board detection needed manual intervention. Profile detection, control point picking and calibration always worked autonomously. The accuracy of the system depends on the photographing configuration, and is typically of the order of 0.1 mm vertically and 0.04 mm horizontally. The method tolerates relatively well cases of snowfall, traces of wiping the black background dry, uneven shading, reflected sunlight, reflected flash light, litter on the snow surface and a tilted plate. The repeatability of the system is at least 1%.

A software package to improve image quality and isolation of objects of interest for quantitative stereology studies of rat hepatocarcinogenesis

In the studies of quantitative stereology of rat hepatocarcinogenesis, we have used image analysis technology (automatic particle analysis) to obtain data such as liver tissue area, size and location of altered hepatic focal lesions (AHF), and nuclei counts. These data are then used for three-dimensional estimation of AHF occurrence and nuclear labeling index analysis. These are important parameters for quantitative studies of carcinogenesis, for screening and classifying carcinogens, and for risk estimation. To take such measurements, structures or cells of interest should be separated from the other components based on the difference of color and density. Common background problems seen on the captured sample image such as uneven light illumination or color shading can cause severe problems in the measurement. Two application programs (BK_Correction and Pixel_Separator) have been developed to solve these problems. With BK_Correction, common background problems such as incorrect color temperature setting, color shading, and uneven light illumination background, can be corrected. With Pixel_Separator different types of objects can be separated from each other in relation to their color, such as seen with different colors in immunohistochemically stained slides. The resultant images of such objects separated from other components are then ready for particle analysis. Objects that have the same darkness but different colors can be accurately differentiated in a grayscale image analysis system after application of these programs.

Abiotic factors limiting photosynthesis in Abies lasiocarpa and Picea engelmannii seedlings below and above the alpine timberline.

Most research on the occurrence and stability of alpine timberlines has focused on correlations between adult tree growth and mean temperatures rather than on specific mechanisms. Timberline migration to higher altitude is dependent on new seedling establishment in the tree-line ecotone; however, reductions in photosynthetic carbon gain in establishing seedlings have previously been interpreted solely in terms of decreased seedling survival. Our objective was to evaluate the impact of abiotic factors (temperature, light and water) on photosynthetic carbon gain in young seedlings of the two dominant conifer tree species occurring naturally above (tree-line ecotone site, TS) and below (forest site, FS) a Rocky Mountain timberline in southeastern Wyoming, USA. Coincidentally, measurements were made during an unusually dry summer. Mean daily photosynthesis in seedlings of both Abies lasiocarpa (Hook.) Nutt. (subalpine fir) and Picea engelmannii Parry ex Engelm. (Engelmann spruce) was less at TS than at FS (19 and 29%, respectively). Minimum nighttime temperatures below 2 degrees C were more frequent at TS than at FS and were associated with reduced maximum photosynthesis the following day. Low midday water potentials were associated with a reduction in carbon gain at both sites early in the season, prior to snowmelt, as well as late in the season when soils began to dry. However, the lower photosynthetic rates at TS than at FS appeared to be unrelated to seedling water status because seedlings at both sites had similar xylem pressure potentials. Solar irradiance was highly variable at both sites as a result of uneven shading by neighboring trees, although this variation was substantially reduced on cloudy days (44% of all days observed). Compared with sunny days, cloudy days resulted in greater integrated daily carbon gain at both sites (41% increase at TS and 69% increase at FS), based on a simulated photosynthesis model. Photosynthetic responses to temperature, sunlight and water suggest that variable solar irradiance and nighttime temperatures were major abiotic factors limiting photosynthetic carbon acquisition in these young seedlings, especially for seedlings growing in the tree-line ecotone.

Rapid reconnaissance of heat-flow patterns in snow-covered thermal areas

Visual surface manifestation of continuing thermal activity in an area of recent volcanism is generally limited to point features such as hot springs, geysers, and steam jets. Delineation of complete patterns of heat flow requires that direct or indirect determinations of surface or shallow subsurface temperatures be made at numerous points. Rapid reconnaissance of a snow-covered thermal area for the purpose of identifying gross patterns and locations of abrupt changes in heat-flow intensity can be made by plotting variations in the depth of overlying snow. Sources of error include drifts, filled hollows, uneven shading, and effects of above-ground hot water or steam.