I–V curve simulation by multi-module simulator using I–V magnifier circuit

This paper presents an I–V curve simulation of PV array/modules using multi I–V magnifier circuits. The circuit magnifies an I–V output of a pn photo-sensor, which is regarded as a small solar cell, by analog technology. About 30 W I–V curve simulator circuits were made and their characteristics were evaluated. LED light irradiated into the photo-sensor works like irradiation of sun light on real PV modules. It has been confirmed that each voltage gain and current gain of the circuit is independently adjustable and the circuit magnifies an I–V output of the photo-sensor successfully. FF of the circuit can be modified by shunt register connected to the photo-sensor in parallel. The circuit showed enough response ability to apply the maximum power point tracker evaluation of PV inverters. Temperature dependence of module output can be simulated by temperature control of the photo-sensor. The result of output characteristics of series connection of the I–V magnifier circuits suggests that the simulator system composed of multi I–V magnifier circuit could simulate partial shading effect of PV array output.     

Transient analysis of a PV power generator charging a capacitor for measurement of the I–V characteristics

Measuring the I–V characteristics is of high importance since it can be considered as a quality and performance certificate for each PV generator. The most precise and inexpensive measuring method is represented in capacitor charging by the PV generator. Using the equivalent circuit of the PV generator with a capacitor as load and applying transient analysis on the circuit, we obtain the capacitor charging voltage and current as a function of time, as well as their differentials as a function of short circuit current and capacitor size. The derived equations facilitate the calculation of proper capacitance size for measuring the I–V characteristics, and considers the acquisition speed of the measuring system as demonstrated through two measurement samples in this paper. The capacitor size is directly and indirectly proportional to the short circuit current and open circuit voltage of the PV generator, respectively. Accordingly, the paper presents a capacitance calculation chart, which enables selecting the correct capacitance for measuring the I–V characteristics by a computerized data acquisition system.     

Characterization of PV array output using a small number of measured parameters

The purpose of the present study was to develop a sufficiently good fit for the measured I–V curve of a PV module and array using only three easily measurable parameters: —the open-circuit voltage (V_oc); —the short-circuit current (I_sc); —the maximum power (P_m). With an additional three parameters ( ; ; ) it is possible to describe any I–V curve, taking into account cell temperature T and solar radiation Q. This method has been tested on various solar array panels as well as on a single 10 cm dia. solar cell. The difference between the real curve and the proposed fit was found to be less than 3 percent for a fixed temperature and radiation and about 6 percent for various combinations of temperature and radiation.     

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.     

A study of a two stage maximum power point tracking control of a photovoltaic system under partially shaded insolation conditions

A photovoltaic (PV) array shows relatively low output power density, and has a greatly drooping current–voltage (I–V) characteristic. Therefore, maximum power point tracking (MPPT) control is used to maximize the output power of the PV array. Many papers have been reported in relation to MPPT. However, the current–power (I–P) curve sometimes shows multi-local maximum point mode under non-uniform insolation conditions. The operating point of the PV system tends to converge to a local maximum output point which is not the real maximal output point on the I–P curve. Some papers have been also reported, trying to avoid this difficulty. However, most of those control systems become rather complicated. Then, the two stage MPPT control method is proposed in this paper to realize a relatively simple control system which can track the real maximum power point even under non-uniform insolation conditions. The feasibility of this control concept is confirmed for steady insolation as well as for rapidly changing insolation by simulation study using software PSIM and LabVIEW.     

Capacitive load based on IGBTs for on-site characterization of PV arrays

This paper describes the practical design of a portable capacitive load based on insulated gate bipolar transistors (IGBTs), which is used to measure the I–V characteristics of PV arrays with short-circuit currents up to 80 A and open circuit voltages up to 800 V. Such measurement allows on-site characterization of PV arrays under real operating conditions and also provides information for the detection of potential array anomalies, such as broken cells or defective connections. The presented I–V load is easy to reproduce and low-cost, characteristics that are within the reach of small-scale organizations involved in PV electrification projects.     

Monitoring current–voltage characteristics and energy output of silicon photovoltaic modules

Photovoltaic (PV) system designers use performance data of PV modules to improve system design and make systems more cost effective. The collection of this valuable data is often not done due to the high costs associated with data acquisition systems. In this paper, we report on the design of a low-cost current–voltage (I–V) measuring system used to monitor the I–V characteristics of PV modules. Results obtained from monitoring seven crystalline silicon modules between October 2001 and November 2002 are presented and discussed. Results obtained also show the value of being able to continuously monitor the current–voltage characteristics of PV modules.     

Evaluation of performance of photovoltaic system with maximum power point (MPP)

Performance of the photovoltaic system is highly influenced by the weather, especially the irradiation and the temperature. To simplify the design of solar generator power, a mathematical model and its validity of the solar cell are required. In this work, the value of the parameters in the mathematical model is obtained by the measurement of the I–V curve of the module. To get an I–V curve, one of the modules in the system was radiated and loaded by a load simulator. A photovoltaic pumping system with maximum power point tracker was built and tested. The results were analyzed and evaluated by using the parameters and the photovoltaic system was shown to be well optimized.     

New method to extract the model parameters of solar cells from the explicit analytic solutions of their illuminated I–V characteristics

We present a new method to extract the intrinsic and extrinsic model parameters of illuminated solar cells containing parasitic series resistance and shunt conductance. The method is based on calculating the Co-content function (CC) from the exact explicit analytical solutions of the illuminated current–voltage (I–V) characteristics. The resulting CC is expressed as a purely algebraic function of current and voltage from whose coefficients the intrinsic and extrinsic model parameters are then readily determined by bidimensional fitting. The procedure is illustrated by applying it to experimental and synthetic I–V characteristics and an analysis of the errors is presented.     

Properties of an n-C:P/p-Si carbon-based photovoltaic cell grown by radio frequency plasma-enhanced chemical vapor deposition at room temperature

The phosphorus-doped amorphous carbon (n-C:P) films were grown by radiofrequency (RF) power-assisted plasma-enhanced chemical vapor deposition (PECVD) at room temperature using a solid phosphorus target. The influence of phosphorus doping on the material properties of n-C:P based on the results of simultaneous characterization are reported. Moreover, solar cell properties such as series resistance, short-circuit current density, open-circuit current voltage, fill factor and conversion efficiency along with the spectral response are reported for the fabricated carbon-based n-C:P/p-Si heterojunction solar cells by standard measurement technique. The cells’ performances have been given in the dark I–V rectifying curve and I–V working curve under illumination when exposed to AM 1.5 illumination condition (100 mW/cm², 25 °C). The maximum open-circuit voltage (V_oc) and short-circuit current density (J_sc) for the cells are observed to be approximately 236 V and 7.34 mA/cm², respectively, for the n-C:P/p-Si cell grown at a lower RF power of 100 W. The highest energy conversion efficiency (η) and fill factor (FF) were found to be approximately 0.84% and 49%, respectively. We have observed that the rectifying nature of the heterojunction structures is due to the nature of n-C:P films.     

Photovoltaic characteristics of phosphorus-doped amorphous carbon films grown by r.f. plasma-enhanced CVD

The phosphorus-doped amorphous carbon (n-C:P) films were grown by r.f. power-assisted plasma-enhanced chemical vapor deposition at room temperature using solid phosphorus target. The influence of phosphorus doping on material properties of n-C:P based on the results of simultaneous characterization are reported. Moreover, the solar cell properties such as series resistance, short circuit current density (J_sc), open circuit current voltage (V_oc), fill factor (FF) and conversion efficiency (η) along with the spectral response are reported for the fabricated carbon based n-C:P/p-Si heterojunction solar cell were measured by standard measurement technique. The cells performances have been given in the dark I–V rectifying curve and I–V working curve under illumination when exposed to AM 1.5 illumination condition (100 mW/cm², 25 °C). The maximum of V_oc and J_sc for the cells are observed to be approximately 236 V and 7.34 mA/cm², respectively for the n-C:P/p-Si cell grown at lower r.f. power of 100 W. The highest η and FF were found to be approximately 0.84% and 49%, respectively. We have observed the rectifying nature of the heterojunction structures is due to the nature of n-C:P films.     

The design and experimental characterisation of an asymmetric compound parabolic photovoltaic concentrator for building façade integration in the UK

A novel non-imaging asymmetric compound parabolic photovoltaic concentrator (ACPPVC) has been designed, constructed and experimentally characterised at the University of Ulster, Northern Ireland (54°36^′N, 5°37^′W). Different numbers of PV strings connected in series were experimentally characterised under outdoor conditions both with and without concentrators. Transient I–V curves for each set of parameter data points were determined and the maximum power generation, fill factor and efficiency of the system calculated for each individual I–V curve. Experiments showed that the use of an ACPPVC increased the maximum power point by 62% (i.e. the power by a factor of 1.62) when compared to a similar non-concentrating PV panel.     

Calculation of CIS and CdTe module efficiencies

An accurate and fast method to calculate the efficiency of Cu(In,Ga)Se₂ (CIGS) and CdTe thin-film solar modules is presented here. This comprises a new method to calculate the fill factor as a function of discrete and distributed series resistance, and of shunt conductance: a three-dimensional, third-order polynomial approximation is presented, and the expansion of the coefficients as a power series of 1/V_oc is given. Analytical expressions are presented which fit experimental data of the optical absorption in ZnO as a function of its thickness or sheet resistance. Together with a calculation outline of the series and shunt effects of the module integration, this constitutes a practical module design tool. This is illustrated with results of dependence of module efficiency on cell length, window and absorber sheet resistance, interconnect contact resistance, “softness” of the cell I–V curve, and absorber material (CIGS or CdTe). Optimal or critical values for these parameters are given.     

Silver-doped CdS films for PV application

CdS : Ag thin films were deposited by the chemical deposition method (solution growth), on SnO₂ thin transparent electrodes, to obtain n-type window layer for PV-cell. CdS thin films were doped with silver by an ion-exchange process in a neutral 0.025 M thiosulphate Ag-complex solution. Best results were achieved at immersion times of 20–30 s at room temperature. For the sake of comparison, the doping was performed on of the substrate surface, while the remaining part was left undoped. SnS_x thin layer was deposited on the top of such a n-type layer prepared in the same way the p-type layer was selected due to its simplicity of preparation and the possibility for variation of the band gap (E_g), by varying x in the compound. Ohmic contact was produced by graphite paste backelectrodes. Two different types of PV cells were produced on the same test sample, SnO₂/CdS : Ag–SnS_x/C and SnO₂/CdS–SnS_x/C, in order to study the influence of the Ag doping of CdS, on the PV cell parameters. Dark and light I–V characteristics were recorded for the two types of cells at several different light intensities. Considerable enhancement of all cell parameters, efficiency (η), fill factor (FF), diode factor (a), short-circuit current (I_sc), etc., was observed on the CdS : Ag-based sample. Spectral sensitivity in VIS-NIR part of the spectrum, recorded on the two types of cells, showed an improvement on the CdS : Ag-based PV cell.     

Near-maximum-power-point-operation (nMPPO) design of photovoltaic power generation system

The present study proposes a PV system design, called “near-maximum power-point-operation” (nMPPO) that can maintain the performance very close to PV system with MPPT (maximum-power-point tracking) but eliminate hardware of the MPPT. The concept of nMPPO is to match the design of battery bank voltage V_set with the MPP (maximum-power point) of the PV module based on an analysis using meteorological data. Three design methods are used in the present study to determine the optimal V_set. The analytical results show that nMPPO is feasible and the optimal V_set falls in the range 13.2–15.0 V for MSX60 PV module. The long-term performance simulation shows that the overall nMPPO efficiency η_nMPPO is higher than 94%. Two outdoor field tests were carried out in the present study to verify the design of nMPPO. The test results for a single PV module (60Wp) indicate that the nMPPO efficiency η_nMPPO is mostly higher than 93% at various PV temperature T_pv. Another long-term field test of 1 kWp PV array using nMPPO shows that the power generation using nMPPO is almost identical with MPPT at various weather conditions and T_pv variation from 24 °C to 70 °C.     

Extraction and analysis of solar cell parameters from the illuminated current–voltage curve

In this work we describe, apply and analyze a procedure to extract the physical parameters of a solar cell from its I–V curve under illumination. We compare it with other procedures and assess the statistical significance of the parameters. Our method, called APTIV, uses separate fitting in two different zones in the I–V curve. In the first one, near short circuit, current fitting is used because the error in current dominates. In the second one, near open circuit, voltage fitting is used because this is the dominant error. The method overcomes some drawbacks of common procedures: voltage errors are properly managed and no accurate initial guesses for the parameters are needed. In addition, the numerical implementation is very simple.     

Studies on the temperature dependence of I–V and C–V characteristics of electron irradiated silicon photo-detectors

The current transport mechanisms of n⁺–p silicon (Si) photo-detectors in different temperature and bias regions before and after irradiation with a dose of 350 kGy has been investigated and presented in this article. Temperature-dependent dark current–voltage (I–V) studies under forward and reverse bias were carried out for this purpose. In the temperature range studied, the dark current contribution in the low bias range is believed to be due to the generation-recombination of minority carriers in the space-charge region. Electron irradiation does not seem to have altered the dark current conduction mechanism. Capacitance–voltage (C–V) at various temperatures was measured to identify the presence of deep levels in the device.     

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.     

The effect of material inhomogeneities on the characteristics of semicrystalline silicon solar cells: the second diode

The effect of lateral variations in material properties on the I−V characteristic of semicrystalline silicon solar cells is studied by means of numerical simulation. Individual crystallites are described with the aid of a one-diode model; the effective I−V characteristic of the cell under illumination is analyzed in terms of a two-diode model using curve fitting. A wide distribution of diffusion lengths of the minority charge carriers is found to worsen the I−V characteristic. This is reflected in increased values of the effective series resistance and second-diode saturation current. The study shows that the effects of intrinsic inhomogeneities cannot be separated in a straightforward manner from those of recombination in space-charge regions.     

Modeling and maximum power point tracking (MPPT) method for PV array under partial shade conditions

Influenced by partial shade, PV module aging or fault, there are multiple peaks on PV array's output power–voltage (P–V) characteristic curve. Conventional maximum power point tracking (MPPT) methods are effective for single peak P–V characteristic under uniform solar irradiation, but they may fail in global MPP tracking under multi-peak P–V characteristics. Existing methods in literature for this problem are still unsatisfactory in terms of effectiveness, complexity and speed. In this paper, we first analyze the mathematical model of PV array that is suitable for simulation of complex partial shade situation. Then an adaptive MPPT (AMPPT) method is proposed, which can find real global maximum power point (MPP) for different partial shade conditions. When output characteristic of PV array varies, AMPPT will adjust tracking strategies to search for global peak area (GPA). Then it is easy for conventional MPPT to track the global MPP in GPA. Simulation and experimental results verify that the proposed AMPPT method is able to find real global MPP accurately, quickly and smoothly for complex multi-peak P–V characteristics. Comparison analysis results demonstrate that AMPPT is more effective for most shade types.