Two-diode Model Research Articles

Resistive Effects on the Spatially Resolved Absolute Electroluminescence of Thin-Film Cu(In, Ga)Se2 Solar Cells Studied by a Distributed Two-Diode Model

Electroluminescence (EL) images with absolute photon emissions from Cu(In, Ga)Se2 (CIGS) solar cells were obtained under different forward current injections, with the spatially distributed EL emission becoming non-uniform as the current density gradually increases. A distributed two-diode electrical three-dimensional model was established which simulated the dark current density-voltage curves and the absolute EL images of the CIGS solar cells very well. Then, the resistive effects were analyzed using this model and simulation results show that the sheet resistance of the transparent conductive oxide (TCO) layer dominates the non-uniform distribution of the EL emission in the studied CIGS thin-film solar cells. The effect of the sheet resistance of the TCO and the series resistance of the micro-diode on the EL variations is found to become obvious under high-current-injection conditions, whereas the effect of shunt resistance of the micro-diode on the EL variations becomes more obvious under low-resistance value or low-current-injection conditions.

Coyote optimization algorithm for the parameter extraction of photovoltaic cells

In this paper, a new and powerful metaheuristic optimization technique known as the Coyote Optimization Algorithm (COA) is proposed for the parameter extraction of the PV cell/module. It is utilized to identify the parameters of the single diode and two-diode models. Inspired by the social norms adopted by the coyotes to ensure the survivability of their species, the COA possesses several outstanding merits such as low number of control parameters, ease of implementation and diverse mechanisms for balancing exploration and exploitation. For physically meaningful solutions, a set of parametric constraints is introduced to prevent the coyotes from straying outside of the predefined boundaries of the search space. Extensive tests indicate that the proposed optimizer exhibits superior accuracy compared to other state-of-the-art EA-based parameter extraction methods. It achieved root-mean-square error (RSME) as low as 7.7301E-04 A and 7.3265E-04 A, for the single-diode and two-diode models, respectively. Moreover, the algorithm maintains outstanding performance when tested on an assortment of modules of different technologies (i.e. mono-crystalline, poly-crystalline, and thin film) at varying irradiance and temperature. The standard deviations (STDs) of the fitness values over 35 runs are measured to be less than 1 × 10−5 for both models. This suggests that the results produced by the algorithm are highly consistent. With these outstanding merits, the COA is envisaged to be a competitive option for the parameter extraction problem of PV cell/module.

Relationship between the ideality factor and the iron concentration in silicon solar cells

Abstract The ideality factor value of silicon n + − p solar cells with iron contaminants has been studied by means of computer simulation. The iron concentration range of 1 0 10 − 1 0 13 cm−3, base doping level range of 1 0 15 − 1 0 17 cm−3, and temperature range of 290 − 340 K were used in the investigation. The Solar Cells Capacitance Simulator (SCAPS) was the tool used for numerical simulation of these devices. The two-diode model was used to extract the ideality factor. The following cases were considered: (i) Shockley–Read–Hall (SRH) recombination; (ii) both intrinsic recombination and SRH recombination; (iii) unpaired interstitial iron atoms; (iv) both iron–boron pairs and interstitial iron atoms. The algorithms of iron concentration evaluation in silicon solar cell by using current–voltage curve are proposed. The analytic expressions are suggested as well as calibration curves are calculated.

A new approach for parameter estimation of the single-diode model for photovoltaic cells/modules

Solar energy has become a popular renewable energy source, leading to wide use of photovoltaic (PV) cells/modules in energy production. For this reason, realistic modeling of PVs and determining the equivalent circuit parameters is of great importance in terms of planning and operation. Hence, in this study, an analytical model for identifying the single-diode equivalent circuit parameters; series resistance (Rs ), shunt resistance (Rp ), diode ideality factor (a), diode reverse-saturation current (Io ), and photon current (Ipv ) for PV cells/modules is developed without neglecting any term. In order to test the accuracy of the model, a number of PV modules from different manufacturers are taken into account and the results are compared with those obtained by using such analytical models given in the literature. Current-voltage (I-V ) characteristics of the PV modules, which are studied here, are also simulated by comparing with the experimental I-V curves provided by the manufacturers. Results show that the values of the parameters obtained for the PV modules are consistent with those extracted by using other analytical models. In addition, I-V curves created by using the obtained parameters are in full agreement with the experimental data. The curves also show a high degree of compatibility with the ones created by using the optimal parameters of the two-diode models given in the literature. Moreover, the proposed model provides a great advantage in estimating equivalent circuit parameters in terms of ease of use, requirements for input data, dependency on initial conditions as well as considering the parameters which are neglected in such methods given in the literature.

Photovoltaic emulator based on PV simulator RT implementation using XSG tools for an FPGA control: Theory and experimentation

This paper presents an efficient field-programmable gate array (FPGA) implementation method for a photovoltaic (PV) simulator based on two-diode model applied to control a PV emulator. The hardware set up allows to repeat the real PV system behavior in the laboratory regardless of external climatic conditions change. The proposed approach has been designed through Xilinx System Generator (XSG) tools and MATLAB/Simulink environment and verified across cosimulation method. A real-time test bench is built based on the implemented PV simulator with a closed loop control using proportional integral (PI) regulator, a direct current/direct current (DC/DC) buck converter and a resistive load. Experimental results are in agreement compared with simulation ones and prove the high accuracy and efficiency of the proposed implementation method for allowing a good emulation of PV characteristics. From some experiments, the development of PV emulator constitutes an important challenge task in the PV energy field.

An accurate one-diode model suited to represent the current-voltage characteristics of crystalline and thin-film photovoltaic modules

In this paper a new one-diode model, conceived in order to be used to represent the current-voltage curves of both crystalline and thin-film photovoltaic modules, is presented. The model parameters are calculated from the information contained in the datasheets issued by manufactures by means of simple iterative procedures that do not require the assumption of simplifying hypotheses. Some innovative relations describing the dependence of the parameters from the solar irradiance and cell temperature are adopted in order to permit the model to reliably simulate the electrical behaviour of photovoltaic devices operating in real conditions.The ability of the model to calculate the current-voltage characteristics issued by manufacturers for values of the solar irradiance and cell temperature also far from the standard rating conditions was verified for various photovoltaic technologies, such as monocrystalline, polycrystalline, amorphous silicon, CIS, CIGS and tandem junction photovoltaic modules. The percentage ratio of the mean absolute difference of current to the rated current at the maximum power point ranges from 0.071% to 1.807%; the analogous ratio of power varies between 0.056% and 1.720%. A comparison with the results obtained with other recognised two-diode models is also presented.

Potential-induced degradation: Recombination behavior, temperature coefficients and mismatch losses in crystalline silicon photovoltaic power plant

In recent years, potential-induced degradation (PID) has gained considerable attention due to the significant negative impact on output power of photovoltaic power plant. In this paper, the recombination behavior of PID-affected solar modules dismounted from the photovoltaic power plant was investigated by the two-diode model of photovoltaic module. The mechanism of PID shunting, which is caused by sodium decorated stacking faults across n+-p junction, was further verified by analyzing changes in the quasi-neutral region and the space-charge region for PID-affected p-type crystalline silicon solar modules. It was found that the depletion region recombination increases with the extent of PID. The electroluminescence images also revealed that there exist strong ohmic shunts for PID-affected modules. Then the fundamental temperature coefficients of PID-affected solar modules were investigated. It was found that the increased depletion region recombination leads to a larger temperature coefficient of maximum power for PID-affected solar modules. The result was also verified by the thermography images of PID-affected modules. Finally, the relative mismatch losses (RML) of PID-affected module strings were analyzed. The results revealed that the RML of PID-affected module strings increase as the root-mean-square error (RMSE) of current at maximum power point progressed for the first time.

Evaluation of mathematical methods to characterize the electrical parameters of photovoltaic modules

The effectiveness and accuracy of the methods used in modeling photovoltaic (PV) cells are necessary for predicting the performance of PV systems. This article presents and analyses four methods used to estimate the unknown parameters of photovoltaic devices for one- (four and five parameters) and two-diode (seven parameters) models. The study has three main objectives: (i) extract the unknown parameters by the four methods for the 28 modules of different PV technologies (mono-crystalline, multi-crystalline, HIT, and amorphous) and manufacturers under standard test conditions, (ii) verify the effectiveness and the accuracy of the methods, at each current-voltage curve data point (category 1), and the error relative at each short-circuit current (Isc), open circuit voltage (Voc) and peak power (Pp) points (category 2) and (iii) study the accuracy and reliability of the four methods for the energy measurement of a PV plant of 1.75 kW over three days installed in desert environment. The results show that the most accurate method is obtained by the four parameters one-diode model. It was shown that there is a good agreement with all important points of the I–V curves; especially at Isc, Voc and Pp points, and with the energy delivered by the PV system in the three days.

Measurement Uncertainty Propagation through Basic Photovoltaic Cell Models

This paper presents measurement uncertainty propagation through four basic photovoltaic cell models: One-diode model without resistances, with one resistance and with two resistances and two-diode model with two resistances. The expressions for the output current of all photovoltaic cell models is presented as a function of global irradiance G and temperature T. Next, the expressions for all fill factor parameters: short-circuit current, open-circuit voltage, current and voltage at the maximum power point, depending on the global irradiance G and temperature T are derived as well. For each parameter, Monte Carlo simulations to calculate the measurement uncertainty of the parameter are performed and the results were used as input values for the calculation of measurement uncertainty of fill factor. Practical calculations are performed in laboratory for renewable energy sources located on 45°32′ N and 18°44′ E. Final fill factor calculations are compared for three different module technologies.

Unexpected two-step response in AlGaAs/GaAs heterostructure-based SBD

ABSTRACT While analyzing current–voltage characteristics in the forward region of the MBE grown Al/Al0.3Ga0.7As/GaAs Schottky barrier diode (SBD) at a higher voltage it has been found out that for a range of voltage the current does not change exponentially, rather the current seems to be saturated. In this work, the cause of such a saturation is analyzed with the help of a two-diode model. Here another secondary diode is assumed to be formed due to improper ohmic contact. Possibilities of having this kind of unwanted saturation in devices with proper ohmic contacts have also been analyzed.

A procedure to evaluate the seven parameters of the two-diode model for photovoltaic modules

The paper presents an analytical procedure to calculate the seven parameters of the two-diode model of photovoltaic (PV) panels for any value of the solar irradiance and cell temperature. Six parameters (the photocurrent, the diode reverse saturation currents, the quality factor of the first diode and the series and shunt resistances), are evaluated by solving the equations related to the properties of the main points of the current-voltage (I-V) characteristics. The further information, necessary to calculate the entire set of seven truly independent parameters, is based on two conditions that have to be simultaneously satisfied: 1) the exclusion of negative values of the model parameters; 2) the minimization of the difference between the diode quality factors, which permits to obtain more precise I-V curves of the PV modules. A method to extend the application of the two-diode model to conditions that are different from the standard rating conditions (SRC) is presented.The comparison with alternative two-diode models showed that accurate representations of the I-V characteristics can be achieved using the proposed procedure regardless of the typology of the PV devices (monocrystalline, polycrystalline, HIT, amorphous silicon, CIS, CIGS, tandem).

Exploration of the two-diode model of deep level transient spectroscopy signal originating from secondary barriers

Deep level transient spectroscopy (DLTS) measurements on multilayer devices can be influenced by secondary barriers. Our starting point is a simple model used in the literature for simulations of DLTS signals induced by such barriers: the structure is represented by two diodes connected back-to-back and separated by a neutral region. Although the calculations confirm that capacitance transients can occur in multilayer structures without defects, we find that the quantitative modeling of corresponding DLTS peaks resembling the N1 signal in Cu(In,Ga)Se2 solar cells requires unphysical input parameters. Therefore, we carefully analyze the assumptions of the model and investigate the limits of its applicability. We look into details of the formation of a DLTS signal and unveil the connection between observed kinetics, capacitance-voltage profiles, and the shape of DLTS peaks. We show that the signals originating from secondary barriers exhibit a logarithmic dependence on the pulse duration which can mimic a response from extended defects. We also verify the validity of the criterion existing in the literature allowing to distinguish signals coming from a back contact and deep defects and show that it can be used only in very specific situations.

On the Grid Metallization Optimization Design for Monofacial and Bifacial Si-Based PV Modules for Real-World Conditions

This work proposes an approach to optimize the grid metallization design (number, width, and height of fingers, as well as number and width of busbars and interconnector ribbons) of monofacial and bifacial photovoltaic (PV) Si-based solar modules mounted at a fixed tilt. We aim to optimize the module energy generation at the locations where they will be installed. Our approach starts by collecting the historical weather conditions (irradiance and temperature profiles) of the locations of interest. These are then processed to generate their typical meteorological year data, which are used to calculate the energy generation of the modules. The electrical performance of the solar modules are estimated considering the two-diode model and the influence that the metallization design has on the PV current, dark saturation currents, and series resistance. A total of six locations worldwide are analyzed for our case study and the difference between the metallization designs based on the selected objectives are examined.

Assessment of High Concentrated Photovoltaic/Thermal Collector in Hot Climate

This work investigates the performance of combined hybrid high concentrated photovoltaic/thermal collector (HCPV/T) in Kuwait harsh climate. The proposed system consists of triple junction solar cells (InGaP/InGaAs/Ge) attached to heat source to discharge thermal energy to cooling media. Published HCPV/T models do not consider the effect of shunt resistance which greatly affects the system performance. So, a single diode model employing five parameters including the effect of shunt resistance is adapted to analyze the proposed system. To analyze the thermal performance of the proposed system, a two-dimensional thermal model based on the technique of finite difference is introduced to determine the efficiency of the hybrid HCPV/T system. The present developed subroutines are integrated with other involved codes in TRNSYS software to calculate HCPV/T system efficiency. Electrical and thermal as well as the whole system efficiency at different weather circumstances are evaluated and assessed. The effect of different weather conditions, cell temperature, concentration ratio and the temperatures of the coolant fluid on system performance are studied. Current results indicate that the model of single diode is a reliable one rather than using the two-diode complex model. Compared to measurements provided by high concentrated PV manufacturer, the current results revealed a total root mean square error of approximately 1.94%. Present predictions show that PV cell temperature has logarithmic increase with the rise in concentration ratio but with low values till concentration ratio of 400 suns after that the rise is faster at higher concentration values up to 1500 suns. Results also revealed that hybrid HCPV/T system works effectively specially in severe hot climate where thermal efficiency increases with high surrounding temperature for higher values of concentration ratio. In addition, an increase of approximately 15% in thermal efficiency and 10% in total efficiency can be achieved by utilizing active cooling device in HCPV/T system.

Modeling of Snow-Covered Photovoltaic Modules

Accurate modeling of photovoltaic (PV) modules is required to predict performance of PV systems in various climatic conditions, often far different than manufacturer specifications. Snowfall during cold months reduces output of PV modules. As the application of PV systems is increasing in cold areas, it is vitally important to address this issue through an appropriate method capable of estimating PV performance due to snow effect. This paper proposes a novel PV modeling approach that can represent instantaneous electrical characteristics of PV modules in the presence of uniform snow coverage. The proposed model utilizes the Bouguer–Lambert Law to estimate the level of insolation reaching surface of snow-covered PV cells. This is achieved by introducing an extinction coefficient which depends on the snow properties. To study the efficiency of PV cells at low insolation levels, a two-diode equivalent circuit model is employed. The simulation results of the proposed model are validated with experimental measurements from field tests for different commercial PV modules as well as real data collected by the SCADA system of a 12-MW grid-connected PV farm. Good agreement was observed between power generation results estimated from the proposed model and those obtained experimentally on snow-covered PV systems. This model would be helpful for researchers and PV systems developers in cold regions.

Estimation of Photovoltaic Module Parameters based on Total Error Minimization of I-V Characteristic

Mathematical Modelling of photovoltaic (PV) modules is important for simulation and performance analysis of PV system. Therefore, an accurate parameters estimation is necessary. Single-diode and two-diode model are widely used to model the PV system. However, it required to determine several parameters such as series and shunt resistances that not provided in datasheet. The main goal of PV modelling technique is to obtain the accurate parameters to ensure the I-V characteristic is closed to the manufacturer datasheet. Previously, the maximum power error of calculated and datasheet value are considered as objective to be minimized for both models. This paper proposes the PV parameter estimation model based minimizing the total error of open circuit voltage (VOC), short circuit current (ISC) and maximum power (PMAX) where all these parameters are provided by the manufacturer. The performance of single-diode and two-diode models are tested on different type of PV modules using MATLAB. It found that the two-diode model obtained accurate parameters with smaller error compared to single-diode model. However, the simulation time is slightly higher than single-diode model due extra calculation required.

Sensitivity analysis and parameters calculation of PV solar panel based on empirical data and two-diode circuit model

In this paper, a simple algorithm based on a two-diode circuit model of the solar cell is proposed for calculating different parameters of PV panels. The input parameters required for this algorithm are available from datasheets of the standard PV modules. The values of series and parallel resistances, as well as the recombination factor of Diode 2, are estimated through an iterative solution process. This method is based on maximum power point matching (MPPM) in which the maximum power of PV panel is calculated by the model reaching a minimum error from maximum power proposed in the datasheet. Unlike the other methods, this method is very straightforward and does not require any additional information apart from that of the datasheet. The objective of this paper is to calculate the recombination factor of both diodes in a two-diode PV model, which then leads to further accuracy of the PV model. This novelty in the calculations further improves the accuracy of the model. The simulation is performed in MATLAB, and the effect of altering the temperature of PV cell and level of radiation on the current, voltage, and output power of the PV panel is investigated. The accuracy of the simulation is validated by data extracted from the datasheets of two different PV modules (polycrystalline and monocrystalline).

Comparison of potential-induced degradation (PID) of n-type and p-type silicon solar cells

Potential-induced degradation (PID) of photovoltaic (PV) modules is one of the most severe types of degradation, where power losses on system level may even exceed 30%. The PID process depends on the strength of the electric field, the temperature, the relative humidity, conductive soiling, time and the PV module materials. For p-type cells, it has been established that the decrease of the shunt resistance, due to migration of sodium ions across the n/p junction is the root cause of the degradation. On the other hand, it has recently been confirmed for n-type cells that the PID occurs due to an increase in recombination as charges are driven to the anti-reflection (AR) coating/emitter interface. In this paper, we present the comparison between PID of p-type and n-type crystalline silicon (c-Si) solar cells and their progression of PID. The time evolution of PID is studied by light and dark I-V curve measurements, electroluminescence images and progressions of the one- and two-diode equivalent model parameters, viz. photocurrent, 1st and 2nd diode reverse saturation currents, 1st and 2nd diode ideality factors, shunt resistance and series resistance.

Simple and easy approach for mathematical analysis of photovoltaic (PV) module under normal and partial shading conditions

This paper presents a detailed modeling and analysis of photovoltaic (PV) module using MATLAB-Simulink. The simulation study utilizes single and two-diode model to represent the PV cell and the results are analysed under normal and partial shading conditions. The PV module performance is influenced by the environmental variables, especially temperature and irradiance level. Under partial shading conditions, the solar irradiance level on each PV cell in a PV system is uneven. This degrades the PV module performance and causes the output characteristic curves to have multiple peaks. Therefore, the PV module is modeled to analyse the performance under such conditions. This paper is divided into two parts. First, a detailed mathematical modeling of PV module using single and two-diode model is analysed during aforesaid conditions. The obtained results are compared in terms of the number of unknown parameters, accuracy, and computation time to justify the advantages and disadvantages of each model. Next, different types of PV modules (i.e. monocrystalline and multi-crystalline) are simulated to justify the precision of the two-diode model as well as the accurateness of the PV simulator.

Estimating various losses in c-Si solar cells subjected to partial shading: insights into J–V performance reduction

This article reports the effect of partial shading (PS) on the electrical output of a solar cell using the two-diode model. The reduction in electrical performance parameters induced by various recombination losses has been explained for c-Si solar cells under the effect of PS. The PS mainly affects the short-circuit current density $$({J}_{\mathrm{SC}})$$ and efficiency $$(\eta )$$ of the solar cells. $${J}_{\mathrm{SC }}$$ and $$\eta $$ decrease from 37.84 to 5.48 mA $$\hbox {cm}^{-2}$$ and from 18.31 to 2%, respectively. Among all the energy losses encountered for PS, spatial relaxation and recombination losses are the dominating factors responsible for the reduction in $${J}_{\mathrm{SC}}$$ . PC1D and Griddler simulations have been performed to evaluate the effect of front surface and bulk recombination. The PC1D simulated external quantum efficiency is governed by the front and back surface recombination velocity and carrier life time of the charge carriers under PS. The power loss ( $${P}_{\mathrm{e}}$$ ) of $${\sim }$$ 34% from the emitter region has been determined by resistance analysis in correlation with the recombination in the emitter region of the solar cells under PS.