Energy and exergy analysis of PV/T air collectors connected in series

In this paper an attempt has been made to derive the analytical expressions for N hybrid photovoltaic/thermal (PV/T) air collectors connected in series. The performance of collectors is evaluated by considering the two different cases, namely, Case I (air collector is fully covered by PV module (glass to glass) and air flows above the absorber plate) and Case II (air collector is fully covered by PV module (glass to glass) and air flows below the absorber plate). This paper shows the detailed analysis of energy, exergy and electrical energy by varying the number of collectors and air velocity considering four weather conditions (a, b, c and d type) and five different cities (New Delhi, Bangalore, Mumbai, Srinagar, and Jodhpur) of India. It is found that the collectors fully covered by PV module and air flows below the absorber plate gives better results in terms of thermal energy, electrical energy and exergy gain. Physical implementation of BIPV system has also been evaluated. If this type of system is installed on roof of building or integrated with building envelope will simultaneously fulfill the electricity generation for lighting purpose and hot air can be used for space heating or drying.     

Exergetic performance assessment of a solar photovoltaic thermal (PV/T) air collector

In this paper, an attempt is made to evaluate the exergetic performance of a solar photovoltaic thermal (PV/T) air collector. A detailed energy and exergy analysis is carried out to calculate the thermal and electrical parameters, exergy components and exergy efficiency of a typical PV/T air collector. Some corrections are done on related heat loss coefficients. An improved electrical model is used to estimate the electrical parameters of a PV/T air collector. Further, a modified equation for the exergy efficiency of a PV/T air collector is derived in terms of design and climatic parameters. A computer simulation program is also developed to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Finally, parametric studies have been carried out. It is observed that the modified exergy efficiency obtained in this paper is in good agreement with the one given by the previous literature. It is also found that the thermal efficiency, electrical efficiency, overall energy efficiency and exergy efficiency of PV/T air collector is about 17.18%, 10.01%, 45% and 10.75% respectively for a sample climatic, operating and design parameters.     

高铁建筑表皮与光伏一体化设计分析

目前高铁建筑表皮与光伏一体化设计在形态上过于单一,限制了高铁建筑形式表达和更大生态节能效益的实现。基于对高铁建筑形态特征的分析,和对当前光伏组件性能的总结,探讨了在高铁建筑屋面、立面和构件系统中,创新光伏组件类型选择和集成模式的可行性。发现：①通过优化光伏组件类型的选择,可以将光伏组件转变成高铁建筑形式表达的积极要素;②随着光伏组件性能的提升,相关集成设计可以突破当前集中于屋面系统的现状,拓展到高铁立面、构件系统中。研究为进一步丰富高铁建筑表皮形式,扩大建筑光伏一体化应用规模提供了依据。     

Evaluation of an Active Building Envelope window-system

Active Building Envelope (ABE) systems are a new enclosure technology which integrate photovoltaic (PV) and thermoelectric (TE) technologies. In ABE systems, a PV-system transfers solar energy directly into electrical energy, which can be used to power a TE heat-pump system. ABE-technologies allow for the development of thermal enclosure systems that have the ability to regulate their temperature (cooling or heating) by interacting with the sun. Applications include various enclosures that require thermal control, including building enclosures. This study considers the performance of the overall prototype ABE window-systems, and also includes the PV systems. This paper reports experimental results to establish the efficiency of the ABE system prototype. Computational analysis based upon PV modeling theories are carried out to simulate the performance of the PV system directly connected to a series of TE modules. The number and type of electrical connections for the TE modules is discussed in order to pursue the maximum power point for PV operation.     

Effect of building integrated photovoltaics on microclimate of urban canopy layer

Building integrated photovoltaics (BIPV) has potential of becoming the mainstream of renewable energy in the urban environment. BIPV has significant influence on the thermal performance of building envelope and changes radiation energy balance by adding or replacing conventional building elements in urban areas. PTEBU model was developed to evaluate the effect of photovoltaic (PV) system on the microclimate of urban canopy layer. PTEBU model consists of four sub-models: PV thermal model, PV electrical performance model, building energy consumption model, and urban canyon energy budget model. PTEBU model is forced with temperature, wind speed, and solar radiation above the roof level and incorporates detailed data of PV system and urban canyon in Tianjin, China. The simulation results show that PV roof and PV façade with ventilated air gap significantly change the building surface temperature and sensible heat flux density, but the air temperature of urban canyon with PV module varies little compared with the urban canyon of no PV. The PV module also changes the magnitude and pattern of diurnal variation of the storage heat flux and the net radiation for the urban canyon with PV increase slightly. The increase in the PV conversion efficiency not only improves the PV power output, but also reduces the urban canyon air temperature.     

A heat pipe photovoltaic/thermal (PV/T) hybrid system and its performance evaluation

Building-integrated photovoltaic/thermal (BIPV/T) system has been considered as an attractive technology for building integration. The main part of a BIPV/T system is PV/T collector. In order to solve the non-uniform cooling of solar PV cells and control the operating temperature of solar PV cells conveniently, a heat pipe photovoltaic/thermal (PV/T) hybrid system (collector) has been proposed and described by selecting a wick heat pipe to absorb isothermally the excessive heat from solar PV cells. A theoretical model in terms of heat transfer process analysis in PV module panel and introducing the effectiveness-number of transfer unit (?-NTU) method in heat exchanger design was developed to predict the overall thermal-electrical conversion performances of the heat pipe PV/T system. A detailed parametric investigation by varying relevant parameters, i.e., inlet water temperature, water mass flow rate, packing factor of solar cell and heat loss coefficient has been carried out on the basis of the first and second laws of thermodynamics. Results show that the overall thermal, electrical and exergy efficiencies of the heat pipe PV/T hybrid system corresponding to 63.65%, 8.45% and 10.26%, respectively can be achieved under the operating conditions presented in this paper. The varying range of operating temperature for solar cell on the absorber plate is less than 2.5 °C. The heat pipe PV/T hybrid system is viable and exhibits the potential and competitiveness over the other conventional BIPV/T systems.     

A proposed framework for dynamic modelling of photovoltaic systems for DG applications

Dynamic modelling and simulation is essential to predict the overall electrical performance of photovoltaic (PV) systems. PV simulation models in the literature are not suitable for dynamic analysis with decentralised generation (DG) applications. This article proposes a framework for PV system dynamic modelling and simulation process. This framework presents the steps required to model the process of solar power generation, reflecting the environmental variables affecting the generation process. Based on the framework steps, a computer simulation model is developed in MATLAB-Simulink of the PV generator, and validated by comparing the developed PV electrical performance characteristic curves with those of the manufacturer's data sheet and the ones developed by commercial software. The last step of the proposed framework is dedicated for testing the developed PV model for grid-connected operation. The proposed framework resulted in a simulation photovoltaic decentralised generation model which constitutes a computer-aided design tool that is helpful for real-world solar energy engineering.     

Effect of fluid flow and packing factor on energy performance of a wall-mounted hybrid photovoltaic/water-heating collector system

Façade-integrated photovoltaic/thermal (BiPV/T) technology is a relatively new concept in improving the overall energy performance of PV installations in buildings. With the use of wall-mounted water-type PV/T collectors, the system not only generates electricity and hot water simultaneously, but also improves the thermal insulation of the building envelope. A numerical model of this hybrid system was developed by modifying the Hottel–Whillier model, which was originally for the thermal analysis of flat-plate solar thermal collectors. Computer simulation was performed to analyze the system performance. The combined effects of the solar cell packing factor and the water mass flow rate on the thermal and electrical efficiencies were investigated. The simulation results indicated that an optimum water mass flow rate existed in the system through which the desirable integrated energy performance can be achieved.     

Temperature of a photovoltaic module under the influence of different environmental conditions – experimental investigation

The climate changes affect photovoltaic (PV) module temperature significantly. The module temperature is one of the most important factors that influence the PV module efficiency and a deep analysis of PV module temperature will aid in better understanding of the environmental influences on the PV module performance. The module temperature depends on many parameters such as solar radiation, ambient temperature, air humidity, speed and direction of the wind, PV module orientation, dust and sand deposition on PV module, and PV module materials. An experimental research was conducted to investigate the effect of these factors on the PV module temperature in the Renewable Energy Laboratory of the Graduate University of Advanced Technology in Iran. The results of this study highlighted that the deposited dust over the PV module surface increases the module temperature and this consequently decreases the PV module power. It was also revealed that a combination of the temperature increase and the incident solar radiation decrease due to the dust deposition over the PV module enhances significantly the module power reduction.     

Performance evaluation of PV module under various parametric conditions

The performance of a photovoltaic (PV) module varies with the change in its internal parameters, namely, series resistance, shunt resistance and ideality factor. They vary due to the manufacturing process involved as well as the material used to fabricate the PV system. For the performance to be as close to the ideal case, a model of the PV system has been used to simulate the performance of the various parameters. This paper presents the effects of variations in the performance of a PV module which occur due to the change in its parameters. One-diode model of a PV cell has been used to plot current–voltage and power–voltage characteristics of a 37-Wp solar module.     

Parameters identification of photovoltaic solar cells and module using the genetic algorithm with convex combination crossover

To design a high-performance photovoltaic (PV) system, the parameters extraction of solar cell models is exceedingly crucial. A new variant of the genetic algorithm (GA) called Genetic Algorithm with Convex Combination Crossover (GACCC) is proposed to identify the unknown electrical parameters of different solar cell models, i.e. single diode, double diode, and PV module. GACCC is achieved by integrating a new crossover operation to maintain a good balance between the intensification of the best solutions and the diversification of the search space. To test the proposed GACCC, we have compared it to the basic GA and with other literature techniques. The results indicate a high performance of developed approach GACCC and a high accuracy of estimated parameters. In addition, the efficiency of the results is confirmed by the good agreement between the experimental I-V data and the simulated results in all cases.     

Enabling the hybrid use of air conditioning: A prototype on sustainable housing in tropical regions

This paper demonstrates how the use of active or passive means only does not give the appropriate answers to a tropical design when considering housing. The author discusses about the idea of both modes of operation being used simultaneously or in parallel, and how this concept has been developed for one experimental building prototype in tropical areas of Brazil (Northeast region). Quantification is given through extensive parametric simulations which have been conducted using different environmental simulation programmes—TAS (EDSL, UK), ESP-r (ESRU, UK) and photovoltaic (PV)-Design PRO-G (Sandia Labs, USA). Thermal comfort levels along with energy use were assessed and compared, in terms of degree hours of overheating/under heating and cooling energy use. The prototype design has also taken into account the appropriate use of resources through sustainable design features: efficient use of energy, water and materials. The results have demonstrated that for regions such as the warm-humid tropics, the use of a mixed running strategy have optimized energy performance and provided better levels of thermal comfort in a much more effective way. For some cases, cooling energy savings up to 80% were feasible on a hybrid mode, where thermal comfort was improved up to 65%. It has also demonstrated the integration of energy efficiency and a PV grid-connected system, while enabling those daytime electrical needs to be accomplished by the photovoltaic component.     

Fire Behaviour and Performance of Photovoltaic Module Backsheets

Given that photovoltaic (PV) power plant can cause and/or contribute to fires in buildings, the fire risk resulting from a PV power plant installation on a building roof or façade should be assessed in order to meet building fire-safety requirements. In fact, PV plant installed on a roof or a façade could fail and cause a fire and/or promote or facilitate its spread. Accident analyses have shown that PV systems are often installed without due consideration of fire propagation and fire spread caused by the presence of modules, cables and electrical boards on the roof. This paper shows a proposal for a method to evaluate the reaction-to-fire characteristics of a PV module and provides experimental results that compare the behaviours and performances of four kinds of PV module backsheet. Some of the commonest type of backsheet materials available on the market have been selected in order to evaluate and compare the reaction-to-fire performances of these products: Backsheet no.1 has three layers (PET/PET/Primer), Backsheet no.2 is composed of four layers (PET/Aluminium/PET/Primer), Backsheet no.3 is a Fluoro-Coating/PET/EVA three-layer sheet and Backsheet no. 4 comprises an outside coating, a PET layer and an inside Coating. Test results show that the choice of a single layer for Backsheet no.4 represents the best solution among the ones tested. Even though Backsheet no.2 shows the same reaction-to-fire rating as that of Backsheet no.4, the PV module production process could be critical as regards the electrical behaviour of the module itself, since aluminium foil is a material that conducts electricity. Moreover, since the fire-performance assessment of PV panels in Europe is left at a national level, the approach reported in this paper could represent a useful reference to be used as a baseline for developing a European standard or, better still, an International standard.     

Power output analysis of transparent thin-film module in building integrated photovoltaic system (BIPV)

The power output of PV module was characterized depending on incidence angle and the azimuth using a transparent thin-film solar cell in a mock-up model at various slopes to the south, as a building integrated photovoltaic system. Simulated data was also evaluated to determine the influence of the inclined angles and the azimuth on the power performance of the PV module. The experimental and computed data fitted comparatively well through the relative error estimation after calibration. It was found that the PV module with a slope of 30°, facing south, provided the best power performance according to an annual power output, producing about 2.5 times higher power output than that with the vertical module. Furthermore, the PV module facing south showed higher power output than that to the east. The varying power output of the PV module with inclined angles can be explained by the impact of the incidence angle modifier of the glass on the PV module. Specifically, the increased inclined slope of the PV module resulted in the reduced solar energy transmission, which producing a significant reduction of power output for the PV module with a slope over 70°.     

Real-time performance models for photovoltaic water pumping systems

This purpose of this paper is to develop and validate a model to accurately predict the cell temperature of a photovoltaic (PV) module that adapts to various mounting configurations, mounting locations, and climates while only requiring readily available data from the module manufacturer. Results from this model are also compared with results from published cell temperature models. The models were used to predict real-time performance from a PV water pumping systems in the desert of Medenine, south of Tunisia using 60-min intervals of measured performance data during one complete year. Statistical analysis of the predicted results and measured data highlights possible sources of errors and the limitations and/or adequacy of existing models, to describe the temperature and efficiency of PV-cells and consequently, the accuracy of performance of PV water pumping systems’ prediction models.     

建筑一体化电热冷联产光伏组件能量特性研究

传统太阳能光伏或光热建筑一体化只能为建筑提供单一电能或热能。通过研究一种集成发电、集热、制冷3种功能的建筑一体化电热冷联产光伏组件,对其夏季工况下能量特性进行了实际检测。结果表明:白天,组件集热同时能有效降低光伏电池温度,组件工作温度高于环境温度约8~16℃,发电和集热效率分别为14.1%~13.7%和40.1%~15.7%;晴朗夜间,组件通过对流和辐射两种传热方式进行散热制冷,总制冷功率为26.0~268.5 W/m~2。电热冷联产光伏组件适合与热泵结合,为建筑提供所需能源。     

建筑用屋顶光伏电池板热斑电热学模拟

目前,世界光伏市场每年保持约30%的增长率。由于光伏系统组件构成的复杂性,光伏组件如光伏板等的整体效率往往低于单个光伏电池的效率。光伏板部分阴影遮挡是造成光伏系统能源效率偏低的主要原因之一。部分阴影遮挡造成的光伏系统组件不匹配将导致太阳能板的局部过热从而降低其使用寿命,严重时导致热斑问题从而可能引起电站火灾。商业光伏板一般采用单晶硅、多晶硅和非晶硅三种材料,其中非晶硅由于特殊的反向电压特性和不同的制作工艺,在发生局部遮挡时会产生与其他两种材料的太阳能电池不一样的电学特性。利用M atlab Simulink平台结合实验数据建立准确的非晶硅电池板局部阴影电学模型,得到当完全遮挡一个或多个非晶硅电池时的阴影区电池工作点,然后输入到Matlab PDE Tool建立的热学模型,分析电池局部温升现象,得到热斑产生条件,从而提出防治热斑的一些措施。     

1st Environmental conference of Thessaly region, 8–10 September 2012, Hotel Skiathos Palace,Koukounaries, Skiathos Island,Greece

This study was conducted with the aim to assess the potential performance of a photovoltaic thermal mechanical ventilation heat recovery (PV/T MVHR) system. The device is currently considered for the application to the Z-en house project undertaken by Scottish homebuilder. The house’s whole energy demand was calibrated based on the UK Government’s standard assessment procedure for energy rating of dwellings, while the PV/T performance was estimated using an ‘EESLISM’ energy and environmental design simulation tool developed by Kogakuin University. This study concluded that PV generates heat, which makes the fresh air running under the PV roof 10–15?°C warmer than the outside temperature even during the Scottish winter and this warm air extracted from roof-integrated PV modules can be used to help reduce the domestic space-heating demand. Thus, the building-integrated PV/T MVHR system was considered as one of the effective means to assist the net zero energy operation of housing in cool and cold climates, whose dominant domestic energy comsumption derives from space heating.     

光伏组件发电量户外实证研究

对于地面用晶体硅和薄膜光伏组件,传统的性能表征主要分为环境、力学、电性能、安全等几个方面。其中电性能表征局限于特定温度和辐照度条件,对于光伏组件户外实际应用过程,本文介绍了光伏组件发电量户外实证测试的三种方法:MPP跟踪的光伏组件发电量测试,基于光伏电流-电压特性测量的光伏组件发电量测试,以及多因子影响光伏组件发电量的评估方法。