Shaded Solar Cells Research Articles

Accuracy of Simscape Solar Cell Block for Modeling a Partially Shaded Photovoltaic Module

With half-cut photovoltaic (PV) modules being the dominant technology on the market, there is an increasing necessity for accurate modeling of this module type. Circuit simulators such as Simulink are widely used to study different topics regarding photovoltaics, often employing a solar cell block available from the Simcape library. The purpose of this work is to validate this model against measurements for a partially shaded half-cut PV module. Diverse shading scenarios are created by varying the number of shaded substrings, the number of shaded solar cells in the substring, and the shading level. For every shading scenario, the PV module’s I-V curve is measured, along with in-plane irradiance, air temperature, and module temperature. A comprehensive evaluation of simulation accuracy is presented. The results confirm a high accuracy of the model with mean nRMSE values of 2.2% for I-V curves and 2.8% when P-V curves are considered. It is found that the simulation errors tend to increase when increasing the number of shaded substrings. At the same time, no obvious dependency of simulation accuracy on the shading level or the number of shaded solar cells in the substring is found.

Matlab-Simulink of photovoltaic system based on a two-diode model simulator with shaded solar cells

This paper proposes a photovoltaic system modeling and characterization software based on Matlab-Simulink in order to estimate the parameters and the characteristic and electrical behavior of a cell/module with respect to changes in environmental parameter regarding irradiance, temperature, and surface conditions (partial shading). The first objective is to find the parameters of the nonlinear I–V equation by adjusting the curve regarding three particular points: open circuit, maximum power, and short circuit. Given these three points, which are provided by all commercial module datasheets, the method finds the best I–V equation for the two-diode photovoltaic (PV) model, with the best series and parallel resistances estimates. The accurateness of the simulator is verified by applying the model to different manufacturer’s modules. Thanks to an interactive graphic interface, this software offers a great flexibility to PV professional and to researchers.

How the absorber thickness influences the formation of reverse bias induced defects in CIGS solar cells

When a PV module is partially shaded, the shaded solar cells operate in a reverse bias condition. For Cu(In,Ga)Se2 cells this condition can cause defects that irreversibly reduce the output of these cells and the full module. In order to design robust shade-tolerant CIGS modules details need to be known of the conditions at which these defects will be formed. In this study a large number of cells were exposed to different reverse bias conditions. By using simple statistics the probability of the occurrence of defects as a result of reverse bias at any given voltage has been determined. Based on our experiments we have found that the absorber thickness is one of the main parameters that affects the shade-tolerance: the thicker the absorber, the more shade tolerant the CIGS module will be.

A novel electrical approach to protect PV modules under various partial shading situations

Partial shading is one of the challenges of PV modules. Even very small partial shading can lead to a considerable power loss in PV modules. Reoccurring partial shading in combination of the presence of local defects increases the risk of hot-spots in PV modules. Hot-spots could lead to failure (e.g. browning, bubble formation and breakdown of insulation system) and therefore to a decrease of service life of the PV modules. In typical crystalline silicon PV modules, every module string is protected by a bypass diode. The bypass diodes protect the shaded solar cell from high reverse current before its breakdown voltage is reached. However, it bypasses also the other unshaded solar cells of the string and therefor typically a third of the module output power is lost. In this work, we analyze and compare a standard 60-cell c-Si PV module with 3 bypass diodes with a hot-spot-free module in which every solar cell is protected with an individual bypass diode. Different partial shading conditions are applied to both modules and the results show that under different shading scenarios, hot-spot-free module show 32% and 80% higher power production compared to the standard module. To investigate the reliability of the bypass diode under shading conditions, we have developed a novel testing setup which switches the bias every 60 s and monitors the temperature by IR camera. The results show that the module is reliable enough to meet 25 years lifetime.

Simulation of perovskite solar cell temperature under reverse and forward bias conditions

We have developed a model to calculate the temperature of an illuminated perovskite solar cell (PSC) under the forward bias and that of a shaded one under the reverse bias at different ambient conditions. The results show that the dissipated power due to the reverse bias (PRB) should be more than around 6 W to have a higher temperature in the shaded solar cell than that in the illuminated solar cell at the solar irradiance of 1000W/m2, and this result is almost ambient temperature and wind velocity independent. It is also found that the generated thermal power due to the nonradiative recombination (PRec) becomes significant at the open circuit voltage (Voc) condition, leading to illuminated solar cell temperature (Tcr) higher than that at the short circuit current (Jsc) condition by about 12.7 K, 13.3 K, and 13.9 K at the ambient temperatures of 270 K, 300 K, and 330 K, respectively. In addition, the influence of the thickness of the illuminated solar cell on its temperature at the Voc condition is investigated, which reveals that, by increasing the thickness from 100 nm to 300 nm, the solar cell temperature can increase by 20 K.

An improved model to predict thermal runaway in concentrator III–V multi-junction solar cells

Thermal runaway is a serious problem leading to the sudden death of solar cells connected in parallel in concentrator photovoltaic (CPV) modules when those cells are not protected by string diodes. In this paper, an improved thermal runaway model is proposed with consideration of temperature dependence of external quantum efficiency (EQE), short-circuit current and diode behavior. Based on this model, the influence of key parameters, such as concentration ratio (CR), the number of solar cells connected in parallel, the shaded area of the solar cell, air mass and aerosol optical depth on the thermal runaway effect in CPV modules, has been analyzed. For a given CR, the maximum number of parallel-connected solar cells is determined in order to avoid the sudden death of the shaded solar cell.

A modified bypass circuit for improved hot spot reliability of solar panels subject to partial shading

A new bypass strategy for monocrystalline and polycrystalline solar panels allowing significant hot spot temperature reduction in both partial and full shading conditions is presented. The approach relies on a series-connected power MOSFET that subtracts part of the reverse voltage from the shaded solar cell, thereby acting as a voltage divider. Differently from other active bypass circuits, the proposed solution does not require either a control logic or power supply and can be easily substituted to the standard bypass diode. The operation of the new circuit is described with reference to the shading condition prescribed by the EN 61215 qualification procedure. Experiments performed on two commercial solar panels have shown that the shaded cell can be cooled up to 24°C with respect to the case in which the standard bypass diode is adopted.

An I–V model based on time warp invariant echo state network for photovoltaic array with shaded solar cells

This paper proposes a new current–voltage (I–V) modeling approach for photovoltaic arrays based on time warp invariant echo state network (TWIESN). I–V characteristic model of a PV array is not only nonlinear and implicit, but also strictly dependent on material types, manufacturing process, ageing and environmental influence. Therefore, in this paper, TWIESN method is proposed to predict I–V characteristic curves of a PV array at any operating conditions, including partially shading conditions. I–V characteristic curves can be quickly obtained by only reading load voltage sequence, irradiation and temperature of each solar cell of the PV array without solving any nonlinear implicit equations that are necessary in conventional methods. The modeling approach based on TWIESN, obtained by using real operating data information of PV arrays, can really describe the dependency of solar cell on the dynamic variations of environment and cell parameters. Therefore, the method in this paper can accurately predict I–V characteristic for the PV array in operation, from different manufacturers, and of different material types. In addition, compared with conventional numerical methods, the time-consuming of the TWIESN model is very low. To verify the proposed TWIESN model, a KC200GT module and a KC200GT array are tested under different shading conditions. The comparison between the proposed model and the model based on back propagation (BP) network is made. Experiment results show the proposed TWIESN model is a simple, accurate, robust and effective model for PV modules and PV arrays at any operating conditions.

SPICE Network Simulation to Calculate Thermal Runaway in III–V Solar Cells in CPV Modules

Current injection into solar cells may occur if cells in modules are connected in parallel without the protection of string diodes. This current injection can cause heating of the cell, which increases the recombination currents and, thus, the current injection. In this manner, a self-feeding process called thermal runaway is started. In concentrator photovoltaics modules, thermal runaway can cause substantial damage. In this paper, a model is introduced that calculates the conditions causing thermal runaway. This model is based on the two-diode model. As inputs for the model, three dependences were experimentally determined from dark IV measurements on the triple-junction cell: 1) series resistance on cell temperature, 2) saturation currents for each of the three junctions on cell temperature, and 3) cell temperature on the injected current. The model was tested by comparing the simulated and measured temperature increase in a triple-junction cell and their dependencies on the applied voltage. A reasonable agreement between the experiment and model was found whereby the voltage at which a thermal runaway occurred differs slightly by 0.04 V. The model was then applied to estimate the dependence of an expected temperature increase in a shaded solar cell on the number of cells connected in parallel and on the concentration factor of the sunlight.

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%.

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.

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

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

In photovoltaics the actual curve of the current-voltage characteristics of a solar generator is often needed, for example if the maximum power point is to be determined. It is convenient to use a model for the description of the relationship between current and voltage, which is able to describe the solar cell in the generation region as well as the breakdowns at positive and negative voltages. As the mathematical expression cannot be given in an explicit form, a set of suitable numerical algorithms to compute the currents for a given voltage and vice versa is given. For more complex solar generators, it can neither be assumed that the solar cells have identical electrical characteristics, nor that they are evenly illuminated. A general model for the description of solar generators is proposed that gives all voltages and currents as well as the voltage and current at the outputs of the solar generator itself. This new model is also implemented in a numerical algorithm. The characteristics of partially shaded solar generators were calculated and discussed using the proposed models.