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.     

Improved parametric empirical determination of module short circuit current for modelling and optimization of solar photovoltaic systems

Correct modelling of solar photovoltaic (PV) system yields is necessary to optimize system design, improve reliability of projected outputs to ensure favourable project financing and to facilitate proper operations and maintenance. An improved methodology for fine resolution modelling of PV systems is presented using module short-circuit current (I_sc) at 5-min time-scales, and clearly identifies pertinent error mechanisms that arise when working at this high resolution. This work used a modified version of the Sandia array performance model, and introduces new factors to the calculation of I_sc to account for identified error mechanisms, including instrumentation alignment, spectral, and module power tolerance errors. A simple methodology was introduced and verified where specific module parameters can be derived solely from properly filtered performance time series data. In particular, this paper focused on methodologies for determining the predicted I_sc for a variety of solar PV module types. These methods of regressive analysis significantly reduced the error of the predicted model, and demonstrate the need for this form of modelling when evaluating long term PV array performance. This methodology has applications for current systems operators, which will enable the extraction of useful module parameters from existing data in addition to more precise continuous monitoring of existing systems, and can also be used to more accurately model and optimize new systems.     

Polycrystalline silicon solar cells with V-grooved surface

Mechanical grooving techniques are effective to uniform reduction of surface reflectance over all polycrystalline silicon solar cells. Furthermore, to reduce the surface reflectance, a V-shaped grooving technique was newly examined. To improve the short-circuit current (I_sc) and the open-circuit voltage (V_oc), a shallow n⁺/p junction was also examined for the grooved surface. By forming the shallower junction, both I_sc and V_oc remarkably increased. Consequently, a record high conversion efficiency of 17.2% has been confirmed at Japan Quality Assurance Organization (JQA) for a 10 × 10 cm² area polycrystalline silicon solar cell.     

An analytical-numerical approach for parameter determination of a five-parameter single-diode model of photovoltaic cells and modules

Parameter extraction of the five-parameter single-diode model of solar cells and modules from experimental data is a challenging problem. These parameters are evaluated from a set of nonlinear equations that cannot be solved analytically. On the other hand, a numerical solution of such equations needs a suitable initial guess to converge to a solution. This paper presents a new set of approximate analytical solutions for the parameters of a five-parameter single-diode model of photovoltaic (PV) cells and modules. The proposed solutions provide a good initial point which guarantees numerical analysis convergence. The proposed technique needs only a few data from the PV current-voltage characteristics, i.e. open circuit voltage V_oc, short circuit current I_sc and maximum power point current and voltage I_m; V_m making it a fast and low cost parameter determination technique. The accuracy of the presented theoretical I–V curves is verified by experimental data.     

PECVD grown silicon nitride AR coatings on polycrystalline silicon solar cells

Silicon nitride films produced by plasma enhanced chemical vapor deposition (PECVD) have been studied as antireflection (AR) coating on polycrystalline silicon solar cells. A substantial enhancement (28%) in the short circuit current (I_sc) has been obtained. The open circuit voltage (V_oc) of these cells has also been found to improve after silicon nitride deposition. The deposition conditions to optimise the improvement in the cell performance have been discussed.     

Power output of Al/SnO2/n-Si solar cell

An Al/SnO₂/n-Si solar cell from n-type silicon (6.5 Ω-cm, 100) wafers using chemical vapour deposition (CVD) has been fabricated. The fabrication details, I–V characteristics determining conversion-efficiency (η_max), open circuit voltage (V_oc) and short circuit current (I_sc) have been presented. A maximum conversion efficiency of 6.3% for an unencapsulated cell of area 85.20 mm² has been obtained.     

Interface effects on the carrier transport and photovoltaic properties of hydrogenated amorphous silicon/crystalline silicon solar cells

Current-voltage-temperature (I-V-T) characteristics evaluated near 150K and 300K were used to study the photovoltaic property variations in hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) solar cells. The possible carrier transport mechanisms in such devices were examined from the I-V-T data which indicated a significant influence of the amorphous /crystalline interface on the short-circuit current density (J_sc) and open-circuit voltage (V_oc) of the solar cells. Carrier transport near 300K for forward biases was by a multi-tunneling mechanism and became space charge limited with increasing bias. For devices having low J_sc and V_oc an additional region was seen in both forward and reverse biases, at low temperatures, where the current simply varied linearly with the applied bias. This characteristic manifested in both high and low temperatures region for devices with still lower photovoltaic properties, which has been reasoned to be due to a higher interface density. Passivating the c-Si surface with HF just prior to the amorphous layer deposition resulted in a large improvement in the properties. The most significant effect was on the J_sc which improved by an order of magnitude. The treatment also affected the lower temperature I-V-T data in that the current fell to very low levels. The spectral response of the treated solar cells showed enhanced blue/violet response compared with the unpassivated devices. The interface passivation plus reducing a-Si thickness has improved the solar cell efficiency from 0.39% to 9.5%.     

Production of large-area polymer solar cells by industrial silk screen printing, lifetime considerations and lamination with polyethyleneterephthalate

The possibility of making large area (100 cm²) polymer solar cells based on the conjugated polymer poly 1,4-(2-methoxy-5-ethylhexyloxy)phenylenevinylene (MEH-PPV) was demonstrated. Devices were prepared by etching an electrode pattern on ITO covered polyethyleneterephthalate (PET) substrates. A pattern of conducting silver epoxy allowing for electrical contacts to the device was silk screen printed and hardened. Subsequently a pattern of MEH-PPV was silk screen printed in registry with the ITO electrode pattern on top of the substrate. Final evaporation of an aluminum electrode or sublimation of a Buckminsterfullerene (C₆₀) layer followed by an aluminum electrode completed the device. The typical efficiency of the prototype devices consisting of three solar cells in series were 0.0046% (under AM1.5 conditions) with open-circuit voltages (V_oc) of 0.73 V and short-circuit currents (I_sc) of 20 μA cm⁻². The half-life based on I_sc in air for the devices were 63 h. The cells were laminated in a 125 μm PET encasement. Lamination had a negative effect on the lifetime.We demonstrate the feasibility of industrial production of large area solar cells (1 m²) by silk screen printing and envisage the possibility of production volumes 10000 m² h⁻¹ at a cost that is on the order of 100 times lower than that of the established monocrystalline silicon solar cells in terms of materials cost.     

Current collecting channels in RGS silicon solar cells—are they useful?

Ribbon growth on substrate (RGS) silicon could be the crystalline silicon material for PV of the future. The extremely fast production technique avoiding any material losses due to sawing drastically reduces the wafering costs. On the other hand, one has to deal with more crystal defects (grain boundaries, dislocations, impurities), which especially limit the diffusion length and normally result in small short-circuit current densities J_sc. The charge carrier collection probability can be increased by a macroscopic V-texture of the surface, but even more effective would be a 3-dimensional emitter structure within the whole bulk cell volume. This was observed in some RGS solar cells showing minority carrier lifetimes of only around 0.4 μs after cell processing, but J_sc of above 34 mA/cm². In these cells, the whole bulk volume collects current despite the small diffusion lengths. This behaviour was investigated using spatially resolved lifetime and internal quantum efficiency mappings, capacitance measurements and a special EBIC technique, where the electron beam hits the backside of the wedge-shaped solar cell. From our results, we conclude that the collecting structures may be caused by inversion in combination with a high O content. Cells with large areas of collecting channels exhibit lower fill factors, but nearly no loss in open-circuit voltage as compared to the standard RGS cells. For both types of cells, confirmed record efficiencies of 12.5% have been obtained.     

ESTI-LOG PV plant monitoring system

The European Solar Test Installation developed the ESTI-sensor (Ossenbrink and Münzer, Proc. 11th EC Photovoltaic Solar Energy Conf., 1992, pp. 333–336, Ossenbrink and Helmke, German 1000 Roofs Programme Coordination Meeting, January 1994) a low-cost solar irradiance measuring device which in a short period of time has become a well-known device for monitoring and evaluation of PV installations and a new standard for PV power plant monitoring systems. To further lower the cost of a monitoring system, and to increase performance, ESTI proposed a lowest-cost system, where all necessary electronics are laminated within the sensor. For this purpose a single-chip controller was foreseen, which measures both solar cell signals (V_oc, and I_sc) and performs the algorithm to determine irradiance and temperature.     

Dependence of efficiency on slat angles of microgrooved solar cells

The short circuit current of a monocrystalline silicon solar cell can be enhanced further by suitably modifying the slat angle of its microgroove surface due to reduction in reflection coefficient and increase in optical trapping with decreasing slat angle. In this paper the dependence of I_sc, V_oc and η of a solar cell on the slat angle have been computed taking into account the variation of the reflection coefficient with the slat angle.It is observed that I_sc increases while V_oc decreases significantly with decreasing slat angles leading to a maximum efficiency of about 22% corresponding to a slat angle range lying between 30° and 45° without antireflection coating. However, the efficiency can be increased further to about 25% with AR coating.     

Solar cells based on the heterojunction a-C/p-Si

The heterostructure n-CdO/a-C/p-Si is proposed for use as a solar cell device. The heterostructure consists of two semiconductor layers having different optical band gaps. An ultrathin layer of a-C with a narrow optical band gap is located between these layers. The photovoltaic effect in this device has been investigated. It is shown that the short-circuit current I_sc=46 mA/cm² for heterostructure n-CdO/a-C/p-Si corresponds to the values obtained in the best solar cells based on crystalline silicon. It is also shown that the heterostructure n-CdO/p-Si (without a-C) has a short circuit current which is much weaker.     

Low-energy proton irradiation effects on GaAs/Ge solar cells

This paper reports the low-energy proton irradiation effects on GaAs/Ge solar cells for space use. The proton irradiation experiments were performed with a fluence of 1.2×10¹³ cm⁻², energies ranging from 0.1 to 3.0 MeV. The results obtained demonstrate that the irradiation with a proton energy of 0.3 MeV gives rise to the most degradation rates of I_sc, V_oc and P_max of the solar cells with no coverglass, which is related to the proton irradiation-induced vacancies near the pn junction in GaAs/Ge cells. The degradation rates of I_sc, V_oc and P_max of the solar cells with coverglass increase as the proton energy increases due to the cascade ions induced by collision processes. It is found that the coverglass has an obvious protection effect against the irradiation with the proton energy below 0.5 MeV.     

Bacterial Foraging Algorithm based solar PV parameter estimation

The abundance and non-polluting nature of solar energy has aroused the interest of many researchers. This worldwide attention of photovoltaic panels has led to the need of generating accurate model for solar photovoltaic (PV) module before proceeding to the installation part. However, accurate modeling of solar PV characteristics is difficult; since the manufacturer’s datasheet provides only four values such as V_mp, I_mp, V_oc, and I_sc. Further, for accurate modeling precise estimation of model parameters at different environmental conditions are very essential. On the other hand, optimization technique is a very powerful tool to obtain solutions to complex non-linear problems. Hence, in this paper, Bacterial Foraging Algorithm is proposed to model the solar PV characteristics accurately. A new equation has been evolved to determine the values of V_oc, V_mp accurately; since these values decides the closeness of the simulated characteristics. Model parameters are extracted for three different types of solar PV panels. A systematic evaluation and performance comparison of Bacterial Foraging Algorithm with other optimization techniques such as Genetic Algorithm and Artificial Immune System has been done and the best computational technique is derived based on performance criteria such as accuracy, consistency, speed of convergence and absolute error. Extensive computations are carried out for the proposed method, as well as for Genetic Algorithm and Artificial Immune System to substantiate the findings.     

Embodied energy analysis of photovoltaic (PV) system based on macro- and micro-level

In this paper the energy payback time and CO₂ emissions of photovoltaic (PV) system have been analyzed. The embodied energy for production of PV module based on single crystal silicon, as well as for the manufacturing of other system components have been computed at macro- and micro-level assuming irradiation of 800–1200 W/m² in different climatic zones in India for inclined surface. The energy payback time with and without balance-of-system for open field and rooftop has been evaluated. It is found that the embodied energy at micro-level is significantly higher than embodied energy at macro-level. The effect of insolation, overall efficiency, lifetime of PV system on energy pay back time and CO₂ emissions have been studied with and without balance of system. A 1.2 kW_p PV system of SIEMENS for mudhouse at IIT, Delhi based on macro- and micro-level has been evaluated. The CO₂ mitigation potential, the importance and role of PV system for sustainable development are also highlighted.     

Effect of illumination intensity and temperature on the I–V characteristics of n-C/p-Si heterojunction

Krishna et al. (Sol. Energy Mater. Sol. Cells 65 (2001) 163) have recently developed an heterojunction n-C/p-Si in order to achieve low cost and high-efficiency carbon solar cell. It has been shown that for this structure, the maximum quantum efficiency (25%) appears at wavelength λ (600 nm). In this paper, the dependence of I–V characteristics of this heterojunction solar cell on illumination intensity and temperature has been systematically investigated. An estimation of the stability of the solar cell with temperature has been made in terms of the temperature coefficient of I_sc and V_oc. The intensity variation study has been used to estimate the series resistance R_s of the solar cell.The effect of illumination intensity on I–V of n-C/p-Si heterojunction is more complex because the carrier lifetime and the carrier mobility of amorphous carbon are small and also because drift of carriers by built-in electric field plays an important role in these cells. Therefore, the conventional analytical expression for I–V characteristic is not applicable to such solar cells. These structures will not obey the principle of superposition of illuminated and dark current. The experimental results have been analysed by developing empirical relation for I–V.The temperature sensitivity parameters α, the change in I_sc and β, the change in V_oc per degree centigrade have been computed and are found to be 0.087 mA/°C and 1 mV/°C, respectively. This suggests that the heterojunction n-C/p-Si has good temperature tolerance. The value of series resistance has been estimated from the family of I–V curves at various intensities. The R_s is found to be ≈12 Ω, which is on the higher side from the point of view of photovoltaic application.     

Electrocoagulation of a synthetic textile effluent powered by photovoltaic energy without batteries: Direct connection behaviour

The feasibility of the use of an electrocoagulation system (EC) directly powered by a photovoltaic (PV) array has been demonstrated. The model pollutant used was a reactive textile dye Remazol Red RB 133. It has been proved that PV array configuration is a factor of great influence on the use of the generated power. The optimum PV array configuration must be reshaped depending on the instantaneous solar irradiation. A useful and effective methodology to adjust the EC–PV system operation conditions depending on solar irradiation has been proposed. The current flow ratio, J_v, is established as the control parameter.     

Influence of growth conditions on photovoltaic effect of ZnO/Si heterojunction

A series of heterojunctions consisting of intrinsic zinc oxide (ZnO) films and p-type Si substrates have been prepared by DC reactive sputtering. The ZnO films were grown at different conditions, and the influence of growth conditions on photovoltaic (PV) property was discussed. It was found that both growth temperature and oxygen partial pressure play important roles for enhancing the PV effect of the samples. By optimizing growth conditions, the PV efficiency has been improved and also by more magnitudes. The open circuit voltage (V_oc) and short circuit current (I_sc) per square centimeter arrived at 350 mV and 2.5 mA, respectively. The variation mechanism of PV effect with growth conditions has been investigated in order to understand the photoelectric conversion behavior of the ZnO/Si heterojunction.     

Analysis of 10 years’ flight data of solar cell monitor on ETS-V

This paper describes the analysis of NASDA's various space solar cells by analyzing the data measured in space. NASDA launched the Engineering Test Satellite-V (ETS-V) on August 27, 1987 and put into the geostationary orbit at a longitude 150°E. This satellite was in operation until electronics stopped on September 12, 1997. On this satellite, the solar cell monitor (SCM) was equipped as a part of the Technical Data Acquisition Equipment (TEDA) for observation of the space environment. SCM consisted of 24 kinds of solar cells including silicon (Si) cells and gallium arsenide (GaAs) cells as shown in Table 1. The short-circuit current (I_sc) characteristic of each cell were measured in the radiation environment of geostationary orbit for 10 years. The degradation data due to a solar flare, occurred in October 19, 1989, were also recorded. All flight data agree qualitatively with ground test data.     

Performance of amorphous silicon solar cell module and solar lantern

The solar lantern (manufactured by BHEL) could regularly be lit for 5–6 h up to a maximum of 7 h, if the battery was fully charged. It is desirable, for regular use, that the solar lantern should be lit for not more than 5 h a day if the clear sky condition exists. If the weather is partially cloudy, use of the lantern should be reduced accordingly. A performance study of the amorphous silicon (a-Si) module shows that the maximum power transfer voltage (V_mp) and corresponding current is ca. 65 and 75% of the open circuit voltage (V_oc) and short circuit current (I_sc), respectively. Efficiency of the module is 3–4% under field conditions and is slightly greater for a higher ambient temperature.