» Photo Voltaics

A NEW METHOD FOR THE EVALUATION OF SOLAR CELL PARAMETERS

arjun — Fri, 07 Nov 2008 14:16:01 +0000

Abstract A new method is presented that is capable of resolving the parameters in a double-exponential model with which the electrical characteristics of a crystalline-silicon solar cell are analysed. This method gives not only opencircuit voltage, short-circuit current, fill factor and efficiency, but also diode saturation currents, light-generated current, series resistance and shunt resistance, all from one measurement under AM 1 illumination. The experimental set-up used for I-V measurement and automated data handling is described. A fast computer fit procedure is introduced which resolves all parameters from one measurement. The errors in the parameter values obtained are studied. A comparison of these values for a number of I-V measurements of solar cells with different internal read more

A NEW EQUATION CORRELATING THE PARAMETERS INFLUENCING THE PERFORMANCE OF SOLAR MODULES

arjun — Fri, 07 Nov 2008 14:11:29 +0000

Abstract The correlation of environmental parameters, module parameters and time of operation into one equation seems to he important to study the performance characteristics of the solar cell. Two programmes have been developed to formulate the suggested equation. The first is based on the general equation of the unsteady state temperature used to evaluate the distribution of heat inside and on the boundaries of the solar cell. The second programme is used to evaluate the constants obtained in the first programme using the least squares method. The final equation can be expressed in terms of the following: environmental conditions (solar radiation, wind velocity, ambient air temperature), module parameters (cell efficiency, cell thickness, glass thickness), and time of operation (real read more

A MODEL FOR AMORPHOUS SOLAR CELL ANALYSIS

arjun — Fri, 07 Nov 2008 14:06:16 +0000

Abstract In the endeavour to improve conversion efficiency by the effective use of incident light, a detailed model which takes into account such optical processes as transmission, absorption and reflection in the cell has been tried out. By the treatment of an amorphous solar cell as a multilayer interference filter and with suitable choices of antireflection coating materials and thicknesses of the various layers, an increase in the performance characteristics of the cells has been attained. When a double-layer antireflection coating is used, higher efficiencies can be achieved. Efficiencies of about 16% for hydrogenated amorphous silicon (a-Si:H)/ polycrystalline silicon and of about 20% for a-Si:H/polycrystalline germanium tandem-type cells can be obtained. Our work shows that a read more

A METHOD FOR THE MEASUREMENT OF THE PHOTOVOLTAIC

arjun — Fri, 07 Nov 2008 13:57:45 +0000

Abstract For the measurement of the current-voltage characteristic of a photovoltaic (PV) cell or module, an experimental “self testing” method is proposed which uses as “load” one or more PV cells (modules), appropriately connected to the test cell and subjected to a variable irradiance. Depending on the irradiance values towards the test cell (module), the “load” cell will behave as a true load, a reverse voltage generator or a reverse current generator. Therefore, it is possible to obtain, by an automatic data acquisition system, the points of the test cell I = I(U) characteristic in quadrants I, II and IV. On this basis, a simple three quadrant I = I(U) curve tracer, based on a digital or analog storage oscilloscope, is produced. Laboratory and read more

A Method For The Direct Measurement Of The Solar Cell Junction Ideality Factor

arjun — Fri, 07 Nov 2008 13:52:20 +0000

Abstract A method, which can measure the junction ideality factor n directly from the illuminated output J-V curve, is described. The following cases are treated separately: infinite shunt resistance and zero series resistance; finite shunt resistance or finite series resistance; finite shunt resistance and finite series resistance. The method is used to measure the junction ideality factor of metal/insulator n-p, metal/insulator/semiconductor and n+-p silicon solar cells which are fabricated in our laboratory. The n values are in the range 1.25 – 1.89. Download Share and Enjoy: read more

A Method For The Determination Of The Standard Deviations Of The Solar Cell I-V Characteristics Parameters

arjun — Fri, 07 Nov 2008 13:45:56 +0000

Abstract A method for the determination of the standard deviations of the solar cell characteristic curve fitting parameters is presented for the first time. In this method, a Taylor series expansion of the parameters, around their best values, is made resulting in linear functions which permit the determination of the standard deviations with the least-squares method. The parameters, with the respective standard deviations, were determined from the experimental I-V characteristic curves obtained under illuminated and dark conditions. For the studied experimental I-V curves, the diode saturation currents, the diode factor and the shunt resistance showed smaller standard deviations in the dark condition, and the series resistance appeared to be more precise in the illuminated I-V read more

A Method For The Determination Of The Material Parameters T, D, L0, S And a From Measured A.C. Short-Circuit Photocurrent

arjun — Fri, 07 Nov 2008 13:36:22 +0000

Abstract A procedure is described to determine accurately the material parameters L0, D, T, S and absorption coefficient a which characterize the base region of a solar cell from measured a.c. short-circuit photocurrent (both amplitude and phase) at certain low (cot < 1) and high (cot > 50) frequencies. The method is general in the sense that it is valid for any arbitrary value of back surface recombination velocity S and thickness of the base region Xj. Earlier methods consisted in obtaining only one or two material parameters using theoretical expressions for the phase shift under different approximations, in particular, taking S ~ ~ and Xj/Lo >> 1. Here, we have only assumed that the back surface of the solar cell is illuminated uniformly with light of short wavelength read more

A low cost, user-friendly photovoltaic cell curve tracer

arjun — Fri, 07 Nov 2008 13:28:53 +0000

Abstract Hardware and software studies strongly indicate that the feasibility of commercially producing A low cost, user-friendly photovoltaic cell curve tracer.The instrument will be used in conjunction with an IBM compatible PC.or a MAC and a printer.The system will print out a J versus V curve and compute various parameters/The author hope to market this instrument in near future. Download Share and Enjoy: read more

A High Power Current-Voltage Curve Tracer Employing A Capacitive Load

arjun — Fri, 07 Nov 2008 13:18:18 +0000

Abstract A portable photovoltaic voltage versus current curve tracer is discussed. The curve tracer employs a capacitive load to provide automatic sweeping of the array voltage. The unit is capable of measuring arrays of up to 10 kW in power but is smaller and lighter than a conventional 2.5 kW dissipative load. The current versus voltage (I-V) plot of a photovoltaic array or module is a powerful diagnostic aid. Many recently built photovoltaic installations are in remote locations, which presents the problem of transporting bulky testing equipment. As photovoltaic power becomes more common, a service industry will be needed to develop and supply portable diagnostic instruments capable of measuring modules or entire arrays. Extensions of the present steady state dissipative methods for read more

A Comparative Study Of Extraction Methods For Solar Cell Model Parameters

arjun — Fri, 07 Nov 2008 13:11:21 +0000

A comparative study of three methods for extracting solar cell parameters of the single-diode lumped-circuit model is presented. The methods compared are the curve-fitting method, an iterative 5-point method and a recently proposed analytical 5-point method. Parameter values were extracted using these three methods from experimental characteristics collected from two silicon cells over a range of illuminations and temperatures. The results show that the curve-fitting method can often give erroneous parameter values and the reasons for the errors are discussed. The 5-point methods are found to be reliable and accurate in situations where the model is a good approximation of cell performance. The analytical 5-point method, however, has the added advantage of simplicity. It is also found read more