Shaded Cells Research Articles

Output characteristics of PV module considering partially reverse biased conditions

In this paper, a mathematical model for the output characteristics of a photovoltaic (PV) module including shaded solar cells in series is proposed. The proposed model was developed using a general one diode solar cell model and is useful for predicting the output of a partially reverse biased module. To obtain an appropriate model for output of a PV module under partially shaded conditions, we applied three key factors to the one diode solar cell model. First, the equation for the avalanche effect is altered in order to include a parameter to relate the number of shaded solar cells to the number of non-shaded solar cells. Second, a resistance component is added in order to express the variable current originating from the avalanche effect depending on the different resistances in the PV module. Third, a compensational voltage source is included to reduce the difference in current near open circuit voltage. A special PV module that can easily change the number of solar cells in series was fabricated to validate the proposed model. By comparing the theoretical results with the measured data, we confirmed that the newly proposed equation is valid showing a root mean square error (RMSE) of less than 2.37%.

Model-Based Method for Partially Shaded PV Module Hot-Spot Suppression

Hot Spot Suppression is a new method to operate a PV module that prevents the formation of hot spots without the need for bypass diodes. By comparing the operating voltage, current and temperature to an intrinsic I(V) model based on calibrated flash test data, Hot Spot Suppression determines the solar modules' shading condition and, if required, seeks a new operating power point that reduces the formation of hot spots on shaded cells. Hot Spot Suppression works in concert with a model-based Maximum Power Point Tracking algorithm to seek the best operating point for maximum output power while limiting stress on shaded cells on the solar module. Theoretical and experimental results show that the power density dissipated in the shaded cell(s) is reduced by a factor of four when the operating conditions are determined by Hot Spot Suppression.

Guidelines for pre‐transfusion compatibility procedures in blood transfusion laboratories

Guidelines for pre‐transfusion compatibility procedures in blood transfusion laboratories

Light-enhanced reverse breakdown in Cu(In,Ga)Se2 solar cells

Partial shading of solar modules can subject shaded cells to significant reverse bias, often large enough to force them into electrical breakdown, possibly resulting in irreversible damage. Therefore, better understanding of reverse current–voltage characteristics might lead to improvements in the design of solar modules. The focus of this study is the breakdown behavior of Cu(In,Ga)Se2 (CIGS) cells in darkness and under illumination. Two series of CIGS cells were investigated, with CdS and Zn–Sn–O buffer layers of varying thickness. Electrical breakdown was found to be highly dependent on the buffer layer. Under blue illumination a remarkable decrease in breakdown voltage was observed for both buffer types. Metastable defects in the buffer/CIGS interface region are tentatively proposed as the source of this effect and tunnelling is suggested as the main mechanism responsible for breakdowns.

Higher PV Module Efficiency by a Novel CBS Bypass

There is an increasing focus on reducing costs and improving efficiency for photovoltaic (PV) cells and modules as well as finding a more efficient approach to the product manufacturing. This letter introduces an innovative solution to bypass shaded PV cells instead of a traditional Schottky diode, in order to avoid overheating of cells in the case of partial shading. The goal is to reduce the power dissipation and improve the general efficiency of a PV generator. A novel device called cool bypass switch is then presented. It is made up of a Power MOS driven by a controller with the task to charge a storage capacitor. Tests and comparisons with standard Schottky diodes are then performed and experimental results are reported in terms of current intensity and operating temperature. The resulting circuit shows better diode performances and considerably lower dissipated power in shading condition. The little packing cases allow an easy integration inside the PV module. In comparison with traditional diodes, the integrated power switch provides a negligible leakage current during PV panel energy production.

Photovoltaic Cell/Panel/Array Characterizations and Modeling Considering Both Reverse and Direct Modes

In this paper, we present a generalized physical model used for simulation of photovoltaic (PV) cells, panels and arrays taking into account the direct and the reverse modes. This model is useful for power electronic systems. This model named Direct-Reverse Model is simple, fast, accurate and can help designers to study industrial systems. It is based on the basic two diodes model representing a PV cell/panel/array. It allows the investigation of the I-V and P-V characteristics at different situations such as mismatches due to the partial or global shaded PV cell at various environmental conditions by changes in PV cell surface temperature and/or solar radiation. Also the effect of the by-pass diode protection and its contributions to reduce the magnitude of the hot spots heating in a shaded PV cell are analysed. A set of experimentations on the behaviour of solar cells and solar panels have been made to validate our physical model.

Numerical model analysis of the shaded dye-sensitized solar cell module

On the basis of a numerical model analysis, the photovoltaic performance of a partially shadowed dye-sensitized solar cell (DSC) module is investigated. In this model, the electron continuity equation and the Butler–Vollmer equation are applied considering electron transfer via the interface of transparent conducting oxide/electrolyte in the shaded DSC. The simulation results based on this model are consistent with experimental results. The influence of shading ratio, connection types and the intensity of irradiance has been analysed according to experiments and numerical simulation. It is found that the performance of the DSC obviously declines with an increase in the shaded area due to electron recombination at the TCO/electrolyte interface and that the output power loss of the shadowed DSC modules in series is much larger than that in parallel due to the ‘breakdown’ occurring at the TCO/electrolyte interface. The impact of shadow on the DSC performance is stronger with increase in irradiation intensity.

Development of a suitable model for characterizing photovoltaic arrays with shaded solar cells

The aim of this study is to investigate the effects of non-uniform solar irradiation distribution on energy output of different interconnected configurations in photovoltaic (PV) arrays. In order to find which configuration is less susceptible to mismatch effects, a PV module model is developed. This model can take into consideration the effects of bypass diodes and the variation of the equivalent circuit parameters with respect to operating conditions. The proposed model can provide sufficient degree of precision as well as solar cell-based analysis in analyzing large scale PV arrays without increasing the computational effort. In order to produce more reliable and robust simulations, improved and extended algorithms are presented. Some results are discussed in detail and some recommendations are extracted by testing several shading scenarios.

A Tokyo Elevator Puzzle

Figure 1 represents an eight-storey building with three elevators. The shaded cells represent those floors at which a particular elevator calls. Notice that all elevators call at both top and bottom floors and four floors in between. It is possible, given this configuration, to travel between any two floors by riding a single elevator. The question is, if each lift called at three floors in between top and bottom, how many lifts would be required such that any two floors are connected by a single elevator?

Visualizing Coevolution with CIAO Plots

In a previous article, we introduced a number of visualization techniques that we had developed for monitoring the dynamics of artificial competitive coevolutionary systems. One of these techniques involves evaluating the performance of an individual from the current population in a series of trials against opponents from all previous generations, and visualizing the results as a 2D grid of shaded cells or pixels: qualitative patterns in the shading can indicate different classes of coevolutionary dynamics. As this technique involves pitting a current individual against ancestral opponents, we referred to the visualizations as CIAO plots. Since then, a number of other authors studying the dynamics of competitive coevolutionary systems have used CIAO plots or close derivatives to help illuminate the dynamics of their systems, and it has become something of a de facto standard visualization technique. In this very brief article we summarize the rationale for CIAO plots, explain the method of constructing a CIAO plot, and review important recent results that identify significant limitations of this technique.

Visualizing Coevolution with CIAO Plots

In a previous article, we introduced a number of visualization techniques that we had developed for monitoring the dynamics of artificial competitive coevolutionary systems. One of these techniques involves evaluating the performance of an individual from the current population in a series of trials against opponents from all previous generations, and visualizing the results as a 2D grid of shaded cells or pixels: qualitative patterns in the shading can indicate different classes of coevolutionary dynamics. As this technique involves pitting a current individual against ancestral opponents, we referred to the visualizations as CIAO plots. Since then, a number of other authors studying the dynamics of competitive coevolutionary systems have used CIAO plots or close derivatives to help illuminate the dynamics of their systems, and it has become something of a de facto standard visualization technique. In this very brief article we summarize the rationale for CIAO plots, explain the method of constructing a CIAO plot, and review important recent results that identify significant limitations of this technique.

Computer simulation of shading effects in photovoltaic arrays

A simulation of shading effects in arrays with different string configurations has been done. Simulation has been performed using as the basic unit the solar cell, modelled in direct bias by the conventional one exponential model, and in reverse bias by an equation previously validated in different types of photovoltaic cells reverse characteristics. The influence of the amount of shading, the type of reverse characteristic of the cell, the string length and the number of shaded cells has been analysed, and some recommendations are extracted.

Numeric Instability of Predictive Values

In this month’s Annals, Hogg et al examine the performance of the Simplify D-dimer among patients presenting to the emergency department (ED) with pleuritic chest pain. The authors conclude that this test cannot be relied on to exclude pulmonary embolism in these patients, despite reporting a negative predictive value of 99% for the Simplify D-dimer . How can such a conclusion be compatible with a near-perfect negative predictive value? To answer this question, we must begin with the standard 2 2 matrix shown in the Figure. This 4-fold table clearly displays the dichotomous relationship between the presence or absence of a target disorder (disease) and a positive or negative test result. The 4 shaded central cells of the Figure, generated by superimposing 2 rows on 2 columns, contain the 4 mutually exclusive elements (true positive [TP], false positive [FP], true negative [TN], and false negative [FN]) from which the traditional triad of test performance characteristics is derived: (1) positive/negative predictive values, (2) sensitivity/specificity, and (3) positive/negative likelihood ratios. The definitions and attributes of these 3 pairs of test characteristics are summarized in Table 1. At first glance, positive and negative predictive values appear to be highly attractive test properties. Indeed, they seem to tell us exactly what we wish to know from a diagnostic test: if the test result is positive, then the positive predictive value (defined in Table 1 as [TP/(TPCFP)]) provides us with a numeric probabilitydexpressed as a simple percentage ranging from 0% to 100%dof ‘‘ruling in’’ the target disorder at which the test is aimed. Conversely, if the test is negative, the negative predictive value (defined in Table 1 as [TN/(TNCFN)]) provides a similarly straightforward probabilitydalso expressed as a simple percentagedof ‘‘ruling out’’ the target disorder we wish to exclude. Unfortunately, there is a hitch: predictive values are highly vulnerable to fluctuations in disease prevalence, causing numeric instability, which markedly constrains their clinical usefulness. When disease prevalence (defined as the proportion of patients in a population with the target disorder) increases, the positive predictive value of any given diagnostic test must increase, and, reciprocally, the negative predictive value of that same test must decrease. Similarly, as prevalence

Interconnecting dye solar cells in modules— I– V characteristics under reverse bias

The upscaling of the dye solar cell (DSC) technology involves a series connection of single cells to form modules. Thus an utilisable voltage is reached. In an outdoor situation, one or more cells connected in series might be shaded. The shaded cells then have to transport the current of the module in reverse bias. Here, a study of the processes and interfaces involved in the electron transport of a DSC under reverse bias is presented. Furthermore, the effect of these processes on the long-term stability of a DSC is evaluated. The I– V characteristic of a DSC under reverse bias differs significantly from a typical diode I– V characteristic. Compared to other solar cell technologies, in particular crystalline silicon solar cells, the largest sustainable reversed biased voltage (breakdown voltage) of a DSC is extremely low (approximately 500 mV). Therefore, in terms of power output, no bypass diodes are required, when connecting DSC in series. In order to identify the processes and the interfaces involved in the charge carrier transport in reverse bias, a batch of different electrode set-ups was built that consisted of single components of a standard DSC. It was shown that charge transport under reverse bias directly occurs via the electrolyte/TCO (transparent conducting oxide) interface, catalysed by the dye molecules. The charge transfer is highly asymmetrical, with a symmetry parameter of approximately 0.35, using a simple Butler-Vollmer model. Electrical impedance spectroscopy revealed that the TiO 2-layer is not significantly involved in the electron transport under reverse bias. To study the effect of reverse biasing on the long-term stability of DSC, solar cells were subjected to a constant reverse current in the dark for more than 100 h. The voltage drop over the cell was monitored. It increased only slightly, without reaching critical values, which would damage the cell irreversibly. No degradation in overall efficiency was observed for more than 100 h.

Experimental study of mismatch and shading effects in the – characteristic of a photovoltaic module

Abstract A conventional photovoltaic module has been prepared with the purpose of accessing its cells either individually or associated. Measurements of every cell and of the whole module have been performed in direct and reverse bias, with the objective of documenting the scattering in cell parameters, working point of the cells and shading effects. Several shading profiles have been tested, and the influence of the reverse characteristic of the shaded cell in module output is stressed.

Linear reversible second-order cellular automata and their first-order matrix equivalents

Linear or one-dimensional reversible second-order cellular automata, exemplified by three cases named as RCA1–3, are introduced. Displays of their evolution in discrete time steps, , from their simplest initial states and on the basis of updating rules in modulo 2 arithmetic, are presented. In these, shaded and unshaded squares denote cells whose cell variables are equal to one and zero respectively. This paper is devoted to finding general formulas for, and explicit numerical evaluations of, the weights N(t) of the states or configurations of RCA1–3, i.e. the total number of shaded cells in tth line of their displays. This is achieved by means of the replacement of RCA1–3 by the equivalent linear first-order matrix automata MCA1–3, for which the cell variables are matrices, instead of just numbers () as for RCA1–3. MCA1–3 are tractable because it has been possible to generalize to them the heavy duty methods already well-developed for ordinary first-order cellular automata like those of Wolfram's Rules 90 and 150. While the automata MCA1–3 are thought to be of genuine interest in their own right, with untapped further mathematical potential, their treatment has been applied here to expediting derivation of a large body of general and explicit results for N(t) for RCA1–3. Amongst explicit results obtained are formulas also for each of RCA1–3 for the total weight of the configurations of the first times, .

Simulation of I-V characteristics of a PV module with shaded PV cells : Kawamura, H. et al. Solar Energy Materials and Solar Cells, 2003, 75, (3–4), 613–621

Simulation of I-V characteristics of a PV module with shaded PV cells : Kawamura, H. et al. Solar Energy Materials and Solar Cells, 2003, 75, (3–4), 613–621

Simulation of I–V characteristics of a PV module with shaded PV cells

The authors are studying a diagnostic method of a PV power generating system. We consider that the change of I–V characteristics can be utilized for the diagnosis. However, the report on the change of I–V characteristics is very little. In this paper, we investigate the relation between the output lowering due to shaded PV cells and the change of I–V characteristics, utilizing the computer simulation. It was proven from the simulation that I–V characteristics are changed by the condition of the shadow, which covered the module. The change of I–V characteristics of a PV module with shaded PV cells is discussed by the shift of the avalanche breakdown voltage of shaded PV cells.

Survey of Current Research in Art Education

Research in art education is often conducted by independent researchers working without coordination or knowledge of other ongoing research studies. Zimmerman, in Briefing Papers: Creating A Visual Arts Research Agenda Toward the 21st Century (1996), notes, Both Davis (1977) and Hamblen (1989) observed that art educators have worked inductively and idiosyncratically without the base-line data and descriptive information about the field that is necessary for informing art education theory and practice. In art education, there is a preponderence of individual, independent studies that have not been replicated (p. 8). In the last several years NAEA has worked vigorously to create rational, comprehensive strategies for research in art education, including publications, and the creation of the NAEA Commission on Research in Art Education, and its eight task forces representing research in demographics, conceptual issues, curriculum, instruction, learning, teacher education, and evaluation. Each of these strategies seeks a clearer conception of research, promotes discussion of research issues and priorities, and encourages research through coordination, communication, and collaboration. For research to proceed in a purposeful manner, art educators need a comprehensive view of ongoing research in the field. The broad array of practical and theoretical issues in art education begs the question, What is the current state of research in art education? In order to answer that question, I surveyed 332 art educators, including 137 members of the Seminar for Research in Art Education (SRAE) and 195 other higher education faculty at U.S. institutions with doctoral and/or masters' programs in art education. The survey asked respondents to identify one or two categories corresponding to the eight NAEA Research Task Forces that most typified each research study. Of the 332 art educators surveyed, 75 (or 22.6%) responded, reporting on a total of 254 studies completed in 1995 and/or ongoing in 1996. Of these, 102 (or 40.1 %) were done by 68 higher education faculty and 10 independent scholars (without an institutional affiliation), 60 (or 23.6%) were doctoral dissertations, and 92 (or 36.2%) were masters' theses. The results are shown in Tables 1-3. Each study is classified by one or two categories corresponding to the eight research task forces. The categories are hierarchically ranked from left to right, and from top to bottom, resulting in a different categorical order for each matrix. In Table 2 and 3, another category, Technology, has been added to reflect write-ins. Higher Education Faculty's Research Research in contexts, concepts, and curriculum dominate the higher education faculty's studies. The first three columns comprise 78% of the studies, while the six cells comprising the first three columns represent over 57%! The shaded cells in the three matrices represent studies in which only one category was listed. Doctoral Dissertations Among the 60 doctoral dissertations, 47 (or 78%) fall in the concepts, contexts, and student learning categories. …

96/06224 Numerical simulation of current-voltage characteristics of photovoltaic systems with shaded solar cells

96/06224 Numerical simulation of current-voltage characteristics of photovoltaic systems with shaded solar cells