Output variation of photovoltaic modules with environmental factors—I. The effect of spectral solar radiation on photovoltaic module output

In this study, it was investigated how changes in spectral solar radiation effects the output of photovoltaic modules. First, there was a precise examination of the seasonal changes in spectral solar radiation. Consequently, it was found that the ratio of spectral solar radiation available for solar cell utilization, to global solar radiation, changes from season to season. It varied, from 5% for polycrystalline silicon cells, to 14% for amorphous silicon cells, throughout one year. Obviously a cell made from amorphous silicon is more severely effected by seasonal variations.

Next, the seasonal changes of photovoltaic module output were examined. The output was calculated by the conventional output evaluation method using irradiance and cell temperature. This calculated value and the subsequently measured value were accumulated and the two values compared. As a result, the accumulated output of photovoltaic modules was confirmed as changing seasonally in the same way as spectral solar radiation. The output ratio of polycrystalline silicon was found to change by 4%, while that of amorphous silicon varied by 20%. Hence the seasonal variations in spectral solar radiation should be taken into account for optimum photovoltaic power system design.     

CdTe solar cell degradation studies with the use of CdS as the window material

We present in this work the degradation effects with time in thin film CdTe/CdS solar cells, where the CdS and CdTe layers are deposited by chemical bath deposition (CBD) and close space vapor transport (CSVT), respectively. The CdS thin films were grown from different baths by varying the S/Cd ratio. The variation of the S/Cd ratio allowed us to control the morphology and the density of defects, thus giving rise to better quality CBD CdS films. Depending on the S/Cd ratio an improvement of the morphology and capacitance signal was observed, these factors have also an influence on the open-circuit voltage, short-circuit current density, fill factor and conversion efficiency of the solar cell. The variation with time of these parameters in our devices was tracked during a period of 3 years measured directly on the exposed back contact regions (CdTe/Cu/Au). A discussion on the deterioration of the photovoltaic (PV) performance of the solar cells is presented in correlation with the local environmental conditions. This particular environment has contamination, and represents another type of stress for standard PV operations. These conditions reduce the mean life time of solar cells beyond short periods; this can be of interest for PV community.     

The effect of temperature on the power drop in crystalline silicon solar cells

The influence of temperature and wavelength on electrical parameters of crystalline silicon solar cell and a solar module are presented. At the experimental stand a thick copper plate protected the solar cell from overheating, the plate working as a radiation heat sink, or also as the cell temperature stabilizer during heating it up to 80°C. A decrease of the output power (−0.65%/K), of the fill-factor (−0.2%/K) and of the conversion efficiency (−0.08%/K) of the PV module with the temperature increase has been observed. The spectral characteristic of the open-circuit voltage of the single-crystalline silicon solar cell is also presented. It is shown that the radiation-rate coefficient of the short-circuit current-limit of the solar cell at 28°C is 1.2%/(mW/cm²).     

Outdoor testing of single crystal silicon solar cells

The evaluation and assessment of the performance of photovoltaic (PV) cells requires the measurement of the current as a function of voltage, temperature, intensity, wind speed and radiation spectrum. Most noticeable of these parameters is the PV conversion efficiency η (defined as the maximum electrical power P_max produced by the PV cell divided by the incident photon power P_in) which is measured with respect to standard test conditions (STC). These conditions refer to the solar spectrum , solar radiation intensity , cell temperature and wind speed (2 mph). Tests under STC are carried out in laboratory-controlled environment.With an increase of ambient temperature, there is a deficiency in the electrical energy that the solar cell can supply. This situation is especially important in hot climates. Outdoor exposure tests of solar cells have been conducted in the Department of Physics, University of Brunei Darussalam. Preliminary results demonstrate that the efficiency of the single crystal silicon solar cell strongly depends on its operating temperature. It has been noted that at the operating temperature of 64 °C, there was a decrease of 69% in the efficiency of the solar cell compared with that measured at STC. Investigation of the effect of variation in intensities of sunlight on the solar cell performance showed that the efficiency of the cell is reduced as intensities of sunlight are reduced but at a rate different from the reduction in intensities.     

Seasonal variation analysis of the outdoor performance of amorphous Si photovoltaic modules using the contour map

The effects of module temperature (T_mod) and spectral irradiance distribution on the outdoor performance of amorphous Si (a-Si) photovoltaic (PV) modules were investigated using contour maps. Compared to PV modules based on crystalline Si, such as single-crystalline Si (sc-Si) and multicrystalline Si, a-Si PV modules exhibit complex behavior with seasonal variation. In this study, we statistically analyzed the outdoor performance of a-Si and sc-Si PV modules. The influence of environmental factors on outdoor performance of a-Si PV modules was analyzed for two seasons, spring and autumn, in which the data periods had nearly the same average T_mod and integrated irradiation. The outdoor performance of the a-Si PV module depends on both temperature history and light-induced degradation.     

Non-concentrating and asymmetric compound parabolic concentrating building façade integrated photovoltaics: An experimental comparison

Concentration of solar energy increases the illuminated flux on the photovoltaic (PV) surface thus less PV material is required. A novel asymmetric compound parabolic photovoltaic concentrator has been characterised experimentally with a similar non-concentrating system. Different numbers of PV strings connected within the system have been analysed and a power ratio of 1.62 measured compared to a similar non-concentrating PV panel with the same cell area. The solar to electrical conversion efficiency of 8.6% and 6.8% was achieved for the non-concentrating panel the concentrating system, respectively. The measured average solar cell temperature of the PV in the concentrator system was only 12 °C higher than that of the similar non-concentrating system with same cell area.     

A review on PV cells and nanocomposite‐coated PV systems

Solar radiation can be converted into electrical energy and generate electric power that can be utilized in multiple ways. The technological improvements have provided enormous solutions to the mankind for utilizing the solar energy although photovoltaic's (PV) by consuming sunlight. Photovoltaic is popularly known by the process of converting light to electricity. The current estimated growth by producing global power around 368 GW in 2017 and projecting 3000 to 10 000 GW by 2030. Looking at all the available solar cells, it has been observed that the dye‐sensitized solar cell (DSSC) when compared to mono‐Si or poly‐Si has been effective in its performance and also reduces production cost to a great extent. The power conversion efficiency (PCE) of DSSC has reached to a better extent and been discussed in the paper. There are other mechanisms through which the efficiency can be improved like applying the antireflection coating. Reflection is a usual phenomenon that happens when light incident from one medium to another varies in refractive index. This reflection is one of the important reasons for the loss of power in the PV Cell. So to improve the PCE, the Mono‐Si or DSSC PV Cells can be applied with a thin film antireflection coating by the nanocomposite film consisting of single‐ or multi‐wall carbon nanotubes with TiO₂ and other efficient nanoparticles. This paper discusses on different kinds of nanocomposite materials, and their functionalities has been clearly given. Remarkable improvements have been recorded in the last 1 year by applying the antireflection coating; the PCE has further been increased enormously when compared to the uncoated solar cell for both DSSC and Mono‐Si PV cells.     

PL and PLE studies of KMgF3:Sm crystal and the effect of its wavelength conversion on CdS/CdTe solar cell

We studied the effect on conversion efficiency of a CdS/CdTe solar cell by applying a wavelength conversion of a rare earth ion. Both photoluminescence (PL) and photoluminescence excitation (PLE) spectra of the Sm-doped KMgF₃ crystal were investigated. As a result, we found that both the divalent and the trivalent Sm ions coexist in the grown KMgF₃ crystals. Also, all the PLE spectra below 500 nm were effectively converted to PL spectra above 540 nm and the solar cell possessed a high spectral response. The quantum efficiency of Sm ions was estimated to be 0.84 from the comparison of the experimental curve with the calculated one for the increased spectral response below 500 nm. When a thin disc crystal of KMgF₃:Sm was placed on the top of CdS/CdTe solar cell as a precursor for wavelength conversion, both the maximum output power and the conversion efficiency increased by 5% as compared with the case of a pure KMgF₃ crystal.     

Photovoltaic cells energy performance enhancement with down‐converting photoluminescence phosphors

Phosphors, synthesized by the urea homo‐precipitation method, were examined as ultraviolet‐spectral down conversion materials for improving the light absorption and electrical characteristics of commercial single‐junction silicon solar cells. The photovoltaic (PV) cells were coated with erbium and terbium doped gadolinium oxysulfide phosphors encapsulated in ethyl vinyl‐acetate binder using blade screen printing technique, and the optimum concentration of phosphor in the composite resulted in the largest light conversion, and superior electrical output and energy transfer efficiency. Moreover, the results demonstrated that the composition of dispersed phosphors has a strong influence on the amount of ultraviolet‐light converted and electron transition capacity of PV cells. The experimental results showed in an optimized PV cell, an enhancement of 0.54% (from 12.11% to 12.65%) in the energy conversion of a Si‐based PV cell was achieved. Copyright © 2015 John Wiley & Sons, Ltd.     

Performance evaluation of photovoltaic/thermal–HDH desalination system

The efficiency of photovoltaic (PV) panel drops with increase in cell temperature. The temperature of the PV panel can be controlled with various cooling techniques. In the proposed work the PV panel is cooled by circulating water and the recovered heat energy is used to run a humidification and dehumidification desalination to produce distilled water from sea water (or) brackish water. This work deals with a detailed analysis of performance of combined power and desalination (Photovoltaic/Thermal–Humidification and Dehumidification) system. A mathematical model of PV/thermal–humidification dehumidification plant was developed and simulations were carried out in MATLAB environment. The performance of photovoltaic/ thermal desalination (Photovoltaic/Thermal–Humidification and Dehumidification) system was investigated under various solar radiation levels (800–1000 W/m²). For each solar radiation level the effect of mass flow rate of coolant water (30–110 kg/h) on water outlet temperature, PV efficiency, PVT thermal efficiency, distilled water production, and plant efficiency was studied. Results show that under each solar radiation level increasing coolant flow rate increases efficiency of PV panel and reduces the plant efficiency. The highest PV efficiency (16.598%) was reached under 800 W/m² at mass flow rate of 110 kg/h and the highest plant efficiency (43.15%) was reached under 800 W/m² at a mass flow rate of 30 kg/h. The maximum amount of distilled water production rate (0.82 L/h) was reached under 1000 W/m² at water mass flow rate of 30 kg/h.     

Gamma irradiated CdS(In)/p-Si heterojunction solar cell

An n-CdS(In)/p-Si heterojunction solar cell was fabricated by vacuum evaporation of a single source of a stoichiometric mixture of CdS and In on a p-Si single crystal wafer at a low temperature of 120°C. The open circuit voltage, short circuit current density, fill factor and conversion efficiency under AM1 were 0.47 V, 20 mA/cm², 0.74 and 7%, respectively. The physical and photoelectric characteristics were measured and discussed. In addition, the cell was irradiated by gamma radiation of 1.25 MeV and its effect on the cell performance was studied. Various preparation parameters such as composition and CdS layer thickness affecting the cell characteristics were investigated before and after exposure to the radiation.     

Photovoltaic/thermal solar hybrid system with bifacial PV module and transparent plane collector

Electric energy production with photovoltaic (PV)/thermal solar hybrid systems can be enhanced with the employment of a bifacial PV module. Experimental model of a PV/thermal hybrid system with such a module was constructed and studied. To make use of both active surfaces of the bifacial PV module, we designed and made an original water-heating planar collector and a set of reflecting planes. The heat collector was transparent in the visible and near-infrared spectral regions, which makes it compatible with the PV module made of crystalline Si. The estimated overall solar energy utilization efficiency for the system related to the direct radiation flux is of the order of 60%, with an electric efficiency of 16.4%.     

Evaluation of electric energy performance by democratic module PV system field test

A systematic investigation has been made on annual accumulated generated PV power from different solar arrays consisting of three kinds of silicon-based solar cells. To clarify seasonal output power variations with temperature in c-Si and a-Si cells might be an important issue for the operations of PV system. It has been shown from the results that electric output power from a-Si array in summer is 20% larger than that from c-Si. On the other hand, in winter, this scene should be reverted. However, output power from c-Si array is only 5% larger than that from a-Si. The analyzed data also shows that annual accumulated electric power generated from a-Si array corresponds to 90% of its nominal efficiency in the year. While in case of c-Si array, this ratio is about 84%.     

Direct beam and hemispherical terrestrial solar spectral distributions derived from broadband hourly solar radiation data

Multiple junction and thin film photovoltaic (PV) technologies respond differently to varying terrestrial spectral distributions of solar energy. PV device and system designers are concerned with the impact of spectral variation on PV specific technologies. Spectral distribution data are generally very rare, expensive, and difficult to obtain. We modified an existing empirical spectral conversion model to convert hourly broadband global (total hemispherical) horizontal and direct normal solar radiation to representative spectral distributions. Hourly average total hemispherical and direct normal beam solar radiation, such as provided in Typical Meteorological Year (TMY) data, are spectral model input data. Default or prescribed atmospheric aerosols and water vapor are possible inputs. Individual hourly and monthly and annual average spectral distributions are computed for a specified tilted surface. The spectral range is from 300 nm to 1800 nm. The model is a modified version of the Nann and Riordan SEDES2 model. Measured hemispherical spectral distributions for a wide variety of conditions at the Solar Radiation Research Laboratory at the National Renewable Energy Laboratory, Golden, Co. and Florida Solar Energy Center (Cocoa, FL) show that reasonable spectral accuracy of about ±10% is obtainable with exceptions for weather events such as snow. Differing cloud climatology and variable albedo and aerosol optical depth atmospheric conditions can lead to spectral model differences of 30–40%.     

Photovoltaic cell characteristics for high-intensity laser light

The series resistance value of a photovoltaic (PV) cell required for high-intensity light and the effects of both the α parameter (the ratio of the open-circuit voltage to the bandgap) and temperature on conversion efficiency are investigated by a calculation method derived from the fundamental characteristics of PV cell. The PV cell characteristics for high-intensity laser light, including Si, GaAs, InGaAs PV cells and InGaAs uni-traveling-carrier photodiode (UTC-PD), are experimentally investigated. The small series resistance as large as 20–30 μΩ cm² and the suppression of recombination are important for obtaining higher conversion efficiency, especially for high-intensity laser light.     

Optimal design of orientation of PV/T collector with reflectors

Hybrid conversion of solar radiation implies simultaneous solar radiation conversion into thermal and electrical energy in the PV/Thermal collector. In order to get more thermal and electrical energy, flat solar radiation reflectors have been mounted on PV/T collector. To obtain higher solar radiation intensity on PV/T collector, position of reflectors has been changed and optimal position of reflectors has been determined by both experimental measurements and numerical calculation so as to obtain maximal concentration of solar radiation intensity. The calculated values have been found to be in good agreement with the measured ones, both yielding the optimal position of the flat reflector to be the lowest (5°) in December and the highest (38°) in June. In this paper, the thermal and electrical efficiency of PV/T collector without reflectors and with reflectors in optimal position have been calculated. Using these results, the total efficiency and energy-saving efficiency of PV/T collector have been determined. Energy-saving efficiency for PV/T collector without reflectors is 60.1%, which is above the conventional solar thermal collector, whereas the energy-saving efficiency for PV/T collector with reflectors in optimal position is 46.7%, which is almost equal to the values for conventional solar thermal collector. Though the energy-saving efficiency of PV/T collector decreases slightly with the solar radiation intensity concentration factor, i.e. the thermal and electrical efficiency of PV/T collector with reflectors are lower than those of PV/T collector without reflectors, the total thermal and electrical energy generated by PV/T collector with reflectors in optimal position are significantly higher than total thermal and electrical energy generated by PV/T collector without reflectors.     

蓄冷降温式太阳电池组件的实验研究

根据太阳电池温度特性,研究通过工程热物理途径来提高太阳电池光电转换效率的方法,开发出新型蓄冷降温式太阳电池组件,利用夜间大气自然冷量吸收太阳电池热量,降低其工作温度。室外试验于07年10月～08年11月在广州地区进行,测试分析了该组件及对照组平板式太阳电池组件的温度—电能输出及转换效率特性。结果表明:与平板式组件相比,蓄冷降温式太阳电池组件工作温度大大降低,效率相应提高。蓄冷降温式组件最大温降达26.5℃,瞬时电能输出相对提高18%,全天电能输出增长14%以上。     

A thermoelectric generator and water-cooling assisted high conversion efficiency polycrystalline silicon photovoltaic system

Solar energy has been increasing its share in the global energy structure. However, the thermal radiation brought by sunlight will attenuate the efficiency of solar cells. To reduce the temperature of the photovoltaic (PV) cell and improve the utilization efficiency of solar energy, a hybrid system composed of the PV cell, a thermoelectric generator (TEG), and a water-cooled plate (WCP) was manufactured. The WCP cannot only cool the PV cell, but also effectively generate additional electric energy with the TEG using the waste heat of the PV cell. The changes in the efficiency and power density of the hybrid system were obtained by real time monitoring. The thermal and electrical tests were performed at different irradiations and the same experiment temperature of 22°C. At a light intensity of 1000 W/m², the steady-state temperature of the PV cell decreases from 86.8°C to 54.1°C, and the overall efficiency increases from 15.6% to 21.1%. At a light intensity of 800 W/m², the steady-state temperature of the PV cell decreases from 70°C to 45.8°C, and the overall efficiency increases from 9.28% to 12.59%. At a light intensity of 400 W/m², the steady-state temperature of the PV cell decreases from 38.5°C to 31.5°C, and the overall efficiency is approximately 3.8%, basically remain unchanged.     

抛物面聚光太阳能PV/T系统的热电性能分析

建立了带有散热翅片的聚光太阳能PV/T热电联产系统内部传热过程的一维稳态数学模型,对传热过程进行了数值模拟,分析了空气质量流速、入射光强度、聚光比、环境温度、上部通道高度及翅片参数对系统的空气温度、电池板温度及系统热、电效率的影响.结果表明:随着入射光强、聚光比的增加,空气出口温度和电池板温度都会增加,系统热电总效率增加;通过增空气流量可以有效降低电池温度,提高电池的光电转换效率和系统的总能量利用效率;吸热板背面的翅片可以强化通道内空气的传热过程,降低电池板的温度,系统效率可增加约2%;在相同的光照条件下,人口空气温度越低,上部通道越窄,系统热效率越高.研究结果为聚光太阳能PV/T热电联产系统的设计和运行提供了理论依据.     

Evaporation Cooling Using a Bionic Micro Porous Evaporation System

The temperature increase due to incident solar radiation has an adverse impact on the electrical output of photovoltaic (PV) modules. A theoretical model of the fabricated and tested bionic evaporation backside cooling was established and verified by experimental investigation. A microfluidic structure featuring micropores consists of two polymer layers attached on the backside of a PV cell model. The thermal performance of roof-mounted PV modules with rear panel air ventilation was mathematically described and extended by the cooling capabilities of the developed bionic evaporation foil. The results of experimental investigations performed in a roof equivalent test environment consisting of a wind tunnel within a climate chamber are in good accordance to the established model. Experimentally, temperature reductions at low incident solar power of less than 575 W causing an efficiency gain for up to 4.8% have been demonstrated while the model implicates an efficiency increase of 10% for real roof systems at an incident solar radiation of 1000 W.