局部阴影条件下光伏模组特性的建模与分析

以考虑了反向雪崩击穿的光伏电池元的双二极管电路模型为基础,建立了适用于阴影效应分析的光伏模组的数学仿真模型,分析了光伏模组在局部阴影条件下I-V和P-V特性及输出能力的变化,提出了增强光伏模组抗阴影能力的方法.     

Determination of energy output losses due to shading of building-integrated photovoltaic arrays using a raytracing technique

In this contribution a simulation procedure is described which was developed as a working tool to calculate the energy output of building-integrated photovoltaic (PV) arrays experiencing shading or reflection effects. A three-quadrant solar cell model incorporating the reverse bias characteristics and breakdown voltage is verified by current-voltage (I–V) measurements performed on commercially manufactured mc-Si solar cells under controlled laboratory conditions. For the simulations, a point matrix giving the irradiation distribution over the PV array is calculated for each hour using a raytracing technique. With a raytracing technique, shading of both beam and diffuse irradiation as well as primary and secondary reflections can be modelled. The results of two cases studies simulated using this technique are presented and analysed. In conclusion, general guidelines based on the simulation results are drawn up. These guidelines aim to assist architects and engineers in planning an optimized layout strategy of building-integrated PV arrays to reduce energy losses caused by shading.     

Solar energy—A look into power generation,challenges, and a solar‐powered future

Sun is an inexhaustible source of energy capable of fulfilling all the energy needs of humankind. The energy from the sun can be converted into electricity or used directly. Electricity can be generated from solar energy either directly using photovoltaic (PV) cells or indirectly using concentrated solar power (CSP) technology. Progress has been made to raise the efficiency of the PV solar cells that can now reach up to approximately 34.1% in multi‐junction PV cells. Electricity generation from concentrated solar technologies has a promising future as well, especially the CSP, because of its high capacity, efficiency, and energy storage capability. Solar energy also has direct application in agriculture primarily for water treatment and irrigation. Solar energy is being used to power the vehicles and for domestic purposes such as space heating and cooking. The most exciting possibility for solar energy is satellite power station that will be transmitting electrical energy from the solar panels in space to Earth via microwave beams. Solar energy has a bright future because of the technological advancement in this field and its environment‐friendly nature. The biggest challenge however facing the solar energy future is its unavailability all‐round the year, coupled with its high capital cost and scarcity of the materials for PV cells. These challenges can be met by developing an efficient energy storage system and developing cheap, efficient, and abundant PV solar cells. This article discusses the solar energy system as a whole and provides a comprehensive review on the direct and the indirect ways to produce electricity from solar energy and the direct uses of solar energy. The state‐of‐the‐art procedures being employed for PV characterization and performance rating have been summarized . Moreover, the technical, economic, environmental, and storage‐related challenges are discussed with possible solutions. Furthermore, a comprehensive list of future potential research directions in the field of direct and indirect electricity generation from solar energy is proposed.     

Performance of a multifunctional PV/T hybrid solar window

A building-integrated multifunctional PV/T solar window has been developed and evaluated. It is constructed of PV cells laminated on solar absorbers placed in a window behind the glazing. To reduce the cost of the solar electricity, tiltable reflectors have been introduced in the construction to focus radiation onto the solar cells. The reflectors render the possibility of controlling the amount of radiation transmitted into the building. The insulated reflectors also reduce the thermal losses through the window. A model for simulation of the electric and hot water production was developed. The model can perform yearly energy simulations where different features such as shading of the cells or effects of the glazing can be included or excluded. The simulation can be run with the reflectors in an active, up right, position or in a passive, horizontal, position. The simulation program was calibrated against measurements on a prototype solar window placed in Lund in the south of Sweden and against a solar window built into a single family house, Solgården, in Älvkarleö in the central part of Sweden. The results from the simulation shows that the solar window annually produces about 35% more electric energy per unit cell area compared to a vertical flat PV module.     

Distributed dynamic modeling and experimental study of PV evaporator in a PV/T solar-assisted heat pump

A novel photovoltaic/thermal solar-assisted heat pump (PV/T-SAHP) system is described in this paper. A specially designed direct-expansion evaporator (PV evaporator), which is laminated with PV cells on the front surface of the thermal absorber, has been adopted in our system to acquire simultaneously thermal energy and electricity from solar radiation. A dynamic model of the PV evaporator based on the distributed parameter approach is also presented. Given the instantaneous solar irradiance and ambient temperature, the numerical model is able to output the spatial distributions of refrigerant conditions, including pressure, temperature, vapor quality and enthalpy. A two-dimensional temperature distribution of the evaporator body is also computed. Comparisons between the simulation results and the experimental measurements show that the model is able to give satisfactory predictions. The results show that high electrical and thermal performance can be achieved. The PV efficiency and thermal efficiency are above 12% and 50% during the testing period.     

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.     

Ten years of collaborative photovoltaic research and education: University of Florence—Slovak University of Technology

This paper deals with research and development (R&D) activities in the area of photovoltaic (PV) renewable energy within collaboration between the Slovak University of Technology, Bratislava and University of Florence. Activities covered include the development of all-implanted monocrystalline silicon cells with screen-printed contacts, PV modules technology for the manufacture of large-area components for power roofs, building and acoustic barriers applications, power conditioning for PV supply units for railway applications, and technological solutions for the realization of PV arrays operating at direct-current voltages in excess of 500 V. Other activities have been related to CdTe thin films for solar cells. Educational activities in the field of photovoltaic engineering for an undergraduate course are briefly outlined as well.     

Simulation model for sizing of stand-alone solar PV system with interconnected array

Solar PV arrays made of interconnected modules are comparatively less susceptible to shadow problem and power degradation resulting from the aging of solar cells. This paper presents a simulation model for the sizing of stand-alone solar PV systems with interconnected arrays. It considers the electricity generation in the array and its storage in the battery bank serving the fluctuating load demand. The loss of power supply probability (LPSP) is used to connote the risk of not satisfying the load demand. The non-tracking (e.g., fixed and tilted) and single-axis tracking aperture arrays having cross-connected modules of single crystalline silicon solar cells in a (6×6) modular configuration are considered. The simulation results are illustrated with the help of a numerical example wherein the load demand is assumed to follow uniform probabilistic distribution. For a given load, the numbers of solar PV modules and batteries corresponding to zero values of LPSP on diurnal basis during the year round cycle of operation are presented. The results corresponding to the surplus and deficit of energy as a function of LPSP are also presented and discussed to assess the engineering design trade offs in the system components.Furthermore, a simple cost analysis has also been carried out, which indicates that for Delhi the stand-alone solar PV systems with fixed and tilted aperture arrays are better option than those with single-axis tracking aperture (with north–south oriented tracking axis) arrays.     

Numerically study on a new hybrid photovoltaic thermal (PVT) collectors with natural circulation

Traditional design of Hybrid photovoltaic thermal (PV/T) system has the solar cells fixed on the top of the absorber. A new PV/T system in which the solar cells are pasted on the bottom of the glass cover is suggested with the aim of realizing higher electricity output considering the lower temperature of glass cover compared with that of absorber. A numerical analysis model is set up to compare the performances of the traditional PV/T and the new PV/T in this study. It is found that compared to the traditional PV/T, the new PV/T shows higher daily electric efficiency. But this superiority is not as apparent as expected. The key point to increase the daily electric efficiency of a PV/T lies in increasing the solar energy transfer efficiency of the solar cell. The total energy gain of the new PV/T is about 7% lower than that of the traditional PV/T because of smaller mass rate and more energy loss from glass cover with higher temperature.     

Parametric study of various configurations of hybrid PV/thermal air collector: Experimental validation of theoretical model

In this paper, an attempt has been made to evaluate the overall performance of hybrid PV/thermal (PV/T) air collector. The different configurations of hybrid air collectors which are considered as unglazed and glazed PV/T air heaters, with and without tedlar. Analytical expressions for the temperatures of solar cells, back surface of the module, outlet air and the rate of extraction of useful thermal energy from hybrid PV/T air collectors have been derived. Further an analytical expression similar to Hottel–Whiller–Bliss (HWB) equation for flat plate collector has also been derived in terms of design and climatic parameters. Numerical computations have been carried out for composite climate of New Delhi and the results for different configurations have been compared. The thermal model for unglazed PV/T air heating system has also been validated experimentally for summer climatic conditions. It is observed that glazed hybrid PV/T without tedlar gives the best performance.     

A power-rating model for crystalline silicon PV modules

A model for the performance of generic crystalline silicon photovoltaic (PV) modules is proposed. The model represents the output power of the module as a function of module temperature and in-plane irradiance, with a number of coefficients to be determined by fitting to measured performance data from indoor or outdoor measurements. The model has been validated using data from 3 different modules characterized through extensive measurements in outdoor conditions over several seasons. The model was then applied to indoor measurement data for 18 different PV modules to investigate the variability in modeled output from different module types. It was found that for a Central European climate the modeled output of the 18 modules varies with a standard deviation (SD) of 1.22%, but that the between-module variation is higher at low irradiance (SD of 3.8%). The variability between modules of different types is thus smaller than the uncertainty normally found in the total solar irradiation per year for a given site. We conclude that the model can therefore be used for generalized estimates of PV performance with only a relatively small impact on the overall uncertainty of such estimates resulting from different module types.     

Simulation and experimental validation of heat transfer in a novel hybrid solar panel

A hybrid solar panel has been invented to integrate photovoltaic (PV) cells onto a substrate through a functionally graded material (FGM) with water tubes cast inside, through which water serves as both heat sink and solar heat collector. Therefore, the PV cells can work at a relatively low temperature while the heat conduction to the substrate can be minimized. Solar panel prototypes have been fabricated and tested at different water flow rates and solar irradiation intensities. The temperature distribution in the solar panel is measured and simulated to evaluate the performance of the solar panel. The finite element simulation results are very consistent with the experimental data. The understanding of heat transfer in the hybrid solar panel prototypes will provide a foundation for future solar panel design and optimization. The finite element model is general and can be extended for different material design and other size of panels.     

Device performance characterization and junction mechanisms in CdTe/CdS solar cells

The performance of CdTe/CdS solar cells has been successfully characterized in terms of a device model based on Shockley–Read–Hall (SRH) recombination theory. The model has been applied to a large number of devices from our laboratory in the 10–15% efficiency range and is able to provide key insights into the diode properties of our devices and the fundamental mechanisms that determine performance. Methods for the reliable measurement of key device parameters are presented, and the results are verified by simulating the characterization data in a self-consistent manner. Crossover between the dark and light J–V curves has been identified as a front contact phenomenon arising from the presence of CdS. Junction mechanisms and an observed relationship between reverse saturation current and diode quality factor are discussed. Our techniques indicate that all values of diode quality factor are between 1 and 2 which is consistent with SRH recombination theory and explainable in terms of the location and lifetimes of the recombination centers. It is found that devices with large diode factors are dominated by midgap states. Reduction of midgap states results in a reduction of the diode factor and improved performance.     

Multitude of progress and unmediated problems of solar PV in Bangladesh

The aims of this paper are to demonstrate a critical review of the multitude of progress in solar PV research and applications in Bangladesh since its inception in 1996 till 2010. Our studies show that Bangladesh has been experiencing an accelerated shift towards solar PV to meet the gap between demand and supply of electricity along with conventional electricity generation. Despite the present generation of electricity from solar PV is 15-20 MW, both public and private sectors have started several solar PV projects to generate several hundred of MW by the upcoming years. This paper has also tried to identify the critical barriers for widespread dissemination of solar PV in Bangladesh and has discussed possible ways to overcome those barriers as well.     

Understanding China's renewable energy technology exports

China became a major player in renewable energy (RE) technology during the 2000s. Chinese solar PV cell and module makers quickly dominated global sales in that industry, while the country's wind turbine producers became poised for significant exports after capturing their rapidly growing home market. In countries like the US, Chinese RE technology strength has been met with claims of excessive governmental support of exports. This study examines to what extent Chinese firms' solar PV and wind technology successes have been enabled by policy supports, and whether those policies appear to have been driven by broader goals versus RE export promotion per se. The evidence suggests that governmental policy toward both wind and solar originated in a push for export-competitive Chinese companies. But the specifics differed substantially due to the particular requirements of building technological capabilities in each: export readiness necessitated substantial support for domestic installation of wind but not solar PV power. The findings also suggest that as the decade of the 2000s progressed, environmental goals played an increasing role alongside export promotion in motivating and shaping Chinese RE technology policies.     

Experimental evidence of very high open-circuit voltages of inversion–layer silicon solar cells

In this paper the first experimental evidence of the high V_oc-potential of inversion-layer silicon solar cells is given. Minority-carrier lifetime measurements on inversion-layer emitters have been performed and the diffused p–n contact of PN-IL silicon solar cells has been optimized for high open-circuit voltages. PN-IL silicon solar cells with open-circuit voltages of 693 mV have been fabricated on 0.2 and 0.5-Ω cm FZ p-Silicon wafers. These values are the highest ever reported V_oc's for inversion-layer silicon solar cells on p-Silicon. This demonstrates that inversion-layer silicon solar cells exhibit a similar potential for achieving high open-circuit voltages as silicon solar cells with a diffused p–n junction.     

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.     

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%.     

串并联太阳能电池弧形光伏组件的发电性能研究

将弧形光伏组件安装在建筑和汽车上获取电能,已受到人们越来越多的关注。为获得更高的输出功率,有必要研究由互连太阳能电池组成的、电流不匹配的弧形光伏组件的特性。研究重点关注由串并联太阳能电池组成的弧形光伏组件的发电性能,设计了不同曲率的非平面微型光伏模块,并通过测量获取光伏模块的参数。与平面光伏模块相比,弧形光伏模块的发电量较小。此外,利用二极管模型分析了光伏模块的特性,说明并联比串联功率高的原因。最后研究了实际应用中太阳能电池的互连问题。结果表明,在理想模型下并联能获取更多电能,但大尺寸的光伏模块会产生更大电流,可能会在实际运行中产生额外损耗。因此,在实际应用中设计弧形光伏组件时也应考虑太阳能电池的互连。     

Indoor simulation and testing of photovoltaic thermal (PV/T) air collectors

An indoor standard test procedure has been developed for thermal and electrical testing of PV/T collectors connected in series. For this, a PV/T solar air heater has been designed, fabricated and its performance over different operating parameters were studied. Based on the energy balance equations, in a steady state condition, a thermal model has been developed. Comparison between experimental and theoretical results were also been carried out. The thermal and electrical efficiency of the solar heater is 42% and 8.4%, respectively. This test procedure can be used by manufacturers for testing of different types of PV modules in order to optimize its products.