无盖板渗透型集热器热性能的对比试验

利用太阳能空气加热系统实验台,对黑、深绿和深蓝3种颜色无盖板渗透型集热器的热性能进行了户外瞬态对比试验。试验结果表明:太阳辐射照度和风量是影响系统热性能的重要因素。在高档和低档两种风量下,黑色集热器的瞬时平均热效率分别为76.04%和67.50%,高于普通平板太阳能空气集热器;集热器表面颜色对其热性能有一定影响,在高档和低档两种风量下,深绿色和深蓝色集热器的瞬时平均热效率比黑色集热器低15%～22%,空气温升低3～4℃,但仍然优于普通平板空气集热器。从保持建筑立面美观考虑,无盖板渗透型集热器的集热板可以采用颜色较深的彩色,不会对系统热性能造成较大影响。     

An improved thermal and electrical model for a solar photovoltaic thermal (PV/T) air collector

In this paper, an attempt is made to investigate the thermal and electrical performance of a solar photovoltaic thermal (PV/T) air collector. A detailed thermal and electrical model is developed to calculate the thermal and electrical parameters of a typical PV/T air collector. The thermal and electrical parameters of a PV/T air collector include solar cell temperature, back surface temperature, outlet air temperature, open-circuit voltage, short-circuit current, maximum power point voltage, maximum power point current, etc. Some corrections are done on heat loss coefficients in order to improve the thermal model of a PV/T air collector. A better electrical model is used to increase the calculations precision of PV/T air collector electrical parameters. Unlike the conventional electrical models used in the previous literature, the electrical model presented in this paper can estimate the electrical parameters of a PV/T air collector such as open-circuit voltage, short-circuit current, maximum power point voltage, and maximum power point current. Further, an analytical expression for the overall energy efficiency of a PV/T air collector is derived in terms of thermal, electrical, design and climatic parameters. A computer simulation program is developed in order 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. Since some corrections have been down on thermal and electrical models, it is observed that the thermal and electrical simulation results obtained in this paper is more precise than the one given by the previous literature. It is also found that the thermal efficiency, electrical efficiency and overall energy efficiency of PV/T air collector is about 17.18%, 10.01% and 45%, respectively, for a sample climatic, operating and design parameters.     

基于太阳能光伏热利用的光伏/热电(PV/TV)建筑一体化试验研究

将太阳能电池板、集热器、热电发电片结合起来,设计并制成了一套光伏/热电(PV/TV)系统,在利用太阳能电池发电的同时,收集热量并利用其发电。在北京地区进行了该系统的室外模拟试验,测试并讨论了该系统在不同结构和不同环境下的性能,探讨该系统在光伏建筑中的应用。试验结果表明,与单纯的光伏发电系统或太阳能热水系统相比,PV/TV系统具有占地面积小、综合效率高等优点。     

Advancement in solar photovoltaic/thermal (PV/T) hybrid collector technology

This article presents an overview on the research and development and application aspects for the hybrid photovoltaic/thermal (PV/T) collector systems. A major research and development work on the photovoltaic/thermal (PVT) hybrid technology has been done since last 30 years. Different types of solar thermal collector and new materials for PV cells have been developed for efficient solar energy utilization. The solar energy conversion into electricity and heat with a single device (called hybrid photovoltaic thermal (PV/T) collector) is a good advancement for future energy demand. This review presents the trend of research and development of technological advancement in photovoltaic thermal (PV/T) solar collectors and its useful applications like as solar heating, water desalination, solar greenhouse, solar still, photovoltaic-thermal solar heat pump/air-conditioning system, building integrated photovoltaic/thermal (BIPVT) and solar power co-generation.     

Performance of a building integrated photovoltaic/thermal (BIPVT) solar collector

The idea of combining photovoltaic and solar thermal collectors (PVT collectors) to provide electrical and heat energy is an area that has, until recently, received only limited attention. Although PVTs are not as prevalent as solar thermal systems, the integration of photovoltaic and solar thermal collectors into the walls or roofing structure of a building could provide greater opportunity for the use of renewable solar energy technologies. In this study, the design of a novel building integrated photovoltaic/thermal (BIPVT) solar collector was theoretically analysed through the use of a modified Hottel-Whillier model and was validated with experimental data from testing on a prototype BIPVT collector.The results showed that key design parameters such as the fin efficiency, the thermal conductivity between the PV cells and their supporting structure, and the lamination method had a significant influence on both the electrical and thermal efficiency of the BIPVT. Furthermore, it was shown that the BIPVT could be made of lower cost materials, such as pre-coated colour steel, without significant decreases in efficiency.Finally, it was shown that by integrating the BIPVT into the building rather than onto the building could result in a lower cost system. This was illustrated by the finding that insulating the rear of the BIPVT may be unnecessary when it is integrated into a roof above an enclosed air filled attic, as this air space acts as a passive insulating barrier.     

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%.     

System performance studies on a photovoltaic/thermal (PV/T) air heating collector

A computer simulation model is presented for the analysis of a solar photovoltaic/thermal (PV/T) hybrid collector with air as heat transfer fluid and algorithm for making quantitative prediction regarding the performance of the system is described. Thermal efficiency curves for the solar PV/T hybrid collectors corresponding to various type of absorbers have been derived. In order to appreciate the model, numerical calculations have been made for evaluating the system performance corresponding to typical climate of Delhi, India     

A review on photovoltaic/thermal hybrid solar technology

A significant amount of research and development work on the photovoltaic/thermal (PVT) technology has been done since the 1970s. Many innovative systems and products have been put forward and their quality evaluated by academics and professionals. A range of theoretical models has been introduced and their appropriateness validated by experimental data. Important design parameters are identified. Collaborations have been underway amongst institutions or countries, helping to sort out the suitable products and systems with the best marketing potential. This article gives a review of the trend of development of the technology, in particular the advancements in recent years and the future work required.     

Annual performance of building-integrated photovoltaic/water-heating system for warm climate application

A building-integrated photovoltaic/water-heating (BiPVW) system is able to generate higher energy output per unit collector area than the conventional solar systems. Through computer simulation with energy models developed for this integrative solar system in Hong Kong, the results showed that the photovoltaic/water-heating (PVW) system is having much economical advantages over the conventional photovoltaic (PV) installation. The system thermal performance under natural water circulation was found better than the pump-circulation mode. For a specific BiPVW system at a vertical wall of a fully air-conditioned building and with collectors equipped with flat-box-type thermal absorber and polycrystalline silicon cells, the year-round thermal and cell conversion efficiencies were found respectively 37.5% and 9.39% under typical Hong Kong weather conditions. The overall heat transmission through the PVW wall is reduced to 38% of the normal building facade. When serving as a water pre-heating system, the economical payback period was estimated around 14 years. This greatly enhances the PV market opportunities.     

非晶硅太阳能光伏/光热空气集热器性能对比实验研究

文章设计了新型非晶硅太阳能PV/T空气集热器,该空气集热器能够解决传统太阳能PV/T热水器在高温波动情况下,晶硅电池热应力大的问题,同时避免了冬季管道发生霜冻的现象。文章通过实验对比,分析了非晶硅太阳能PV/T空气集热器、单独非晶硅光伏电池和传统太阳能空气集热器的能量效率和[火用]效率的差异。分析结果表明:非晶硅太阳能PV/T空气集热器的平均热效率为45.70%,比传统太阳能空气集热器的平均热效率降低了约25.88%;当空气质量流量增大至0.048 kg/s时,非晶硅太阳能PV/T空气集热器中的非晶硅光伏电池的平均电效率高于单独非晶硅光伏电池,它们的平均电效率分别为4.70%,4.54%;非晶硅太阳能PV/T空气集热器的总[火用]效率高于传统太阳能空气集热器的热[火用]效率和单独非晶硅光伏电池的电[火用]效率,非晶硅太阳能PV/T空气集热器总[火用]效率最大值为7.14%。文章的分析结果为非晶硅太阳能PV/T空气集热器的推广提供了参考。     

小型菲涅尔式CPV/T集热器光热特性研究

为充分利用建筑屋顶,解决光伏光热一体化(PV/T)集热器光电转换效率的高温减益问题,并提高太阳能综合利用率和集热品位,文章构建了一种基于太阳光谱分频利用技术的光伏/光热模块分离式的小型聚光式PV/T集热器。通过建立其光/电/热理论分析模型及TracePro/Fluent数值仿真模型,以南京地区气象数据为例,综合分析其光/电/热性能,结果表明:该集热器以与安装地纬度等值的倾角南北轴向放置时,其年均光学效率为64.97%,工质出口温度为90℃时的系统光电/光热效率分别为12.47%,40.09%,系统综合热效率达72.91%,且其结构简单、外形轻薄,有望实现与普通建筑的有效结合。     

Simulation of a photovoltaic/thermal heat pump system having a modified collector/evaporator

A new photovoltaic/thermal heat pump (PV/T-HP) system having a modified collector/evaporator (C/E) has been developed and numerically studied. Multi-port flat extruded aluminum tubes were used in the modified C/E, as compared to round copper tubes used in a conventional C/E. Simulation results suggested that a better operating performance can be achieved for a PV/T-HP system having such a modified C/E. In addition, using the meteorological data in both Nanjing and Hong Kong, China, the simulation results showed that this new PV/T-HP system could efficiently generate electricity and thermal energy simultaneously in both cities all-year-round. Furthermore, improved operation by using variable speed compressor has been designed and discussed.     

Performance analysis of a double-pass photovoltaic/thermal (PV/T) solar collector with CPC and fins

The use of PV/T in combination with concentrating reflectors has a potential to significantly increase power production from a given solar cell area. A prototype double-pass photovoltaic-thermal solar air collector with CPC and fins has been designed and fabricated and its performance over a range of operating conditions was studied. The absorber of the hybrid photovoltaic/thermal (PV/T) collector under investigation consists of an array of solar cells for generating electricity, compound parabolic concentrator (CPC) to increase the radiation intensity falling on the solar cells and fins attached to the back side of the absorber plate to improve heat transfer to the flowing air. Energy balance equations have been developed for the various nodes of the system. Both thermal and electrical performance of the collector are presented and discussed.     

太阳能光电/光热一体化技术及其应用进展研究

太阳能光电/光热一体化系统主要由光伏电池组件和太阳能集热器组成,可同时实现光伏发电和光热利用,从而有效地提高了太阳能的综合利用效率。文章首先从光伏组件和光热部件着手,分析了PV/T系统的结构和各项性能;然后,概述了目前常用的PV/T热水系统性能评估方法;最后,提出了在推广PV/T系统时还须解决的问题。     

A steady state thermal duct model derived by fin-theory approach and applied on an unglazed solar collector

This paper presents the thermal modelling of an unglazed solar collector (USC) flat panel, with the aim of producing a detailed yet swift thermal steady-state model. The model is analytical, one-dimensional (1D) and derived by a fin-theory approach. It represents the thermal performance of an arbitrary duct with applied boundary conditions equal to those of a flat panel collector. The derived model is meant to be used for efficient optimisation and design of USC flat panels (or similar applications), as well as detailed thermal analysis of temperature fields and heat transfer distributions/variations at steady-state conditions; without requiring a large amount of computational power and time. Detailed surface temperatures are necessary features for durability studies of the surface coating, hence the effect of coating degradation on USC and system performance. The model accuracy and proficiency has been benchmarked against a detailed three-dimensional Finite Difference Model (3D FDM) and two simpler 1D analytical models. Results from the benchmarking test show that the fin-theory model has excellent capabilities of calculating energy performances and fluid temperature profiles, as well as detailed material temperature fields and heat transfer distributions/variations (at steady-state conditions), while still being suitable for component analysis in junction to system simulations as the model is analytical. The accuracy of the model is high in comparison to the 3D FDM (the prime benchmark), as long as the fin-theory assumption prevails (no ‘or negligible’ temperature gradient in the fin perpendicularly to the fin length). Comparison with the other models also shows that when the USC duct material has a high thermal conductivity, the cross-sectional material temperature adopts an isothermal state (for the assessed USC duct geometry), which makes the 1D isothermal model valid. When the USC duct material has a low thermal conductivity, the heat transfer course of events adopts a 1D heat flow that reassembles the conditions of the 1D simple model (for the assessed USC duct geometry); 1D heat flow through the top and bottom fins/sheets as the duct wall reassembles a state of adiabatic condition.     

Advances in liquid based photovoltaic/thermal (PV/T) collectors

In order to get more power and heat from PV/T system, it is necessary to cool the PV cell and decrease its temperature. This is not an easy task especially in hot and humid climate areas. There is a lack of an effective cooling strategy of PV/T panels. The liquid based photovoltaic thermal collector systems are practically more desirable and effective than air based systems. Temperature fluctuation in liquid based PV/T is much less than the air based PV/T collectors which subjected to variation in solar radiation levels. In this study a review of the available literature on PV/T collector systems which utilize water and refrigerant (working fluid) as heat removal medium for different applications has been conducted. Future direction of water-cooled and refrigerant hybrid photovoltaic thermal systems was presented. This study revealed that the direct expansion solar-assisted heat pump system achieved better cooling effect of the PV/T collector.     

Optimizing the energy and exergy of building integrated photovoltaic thermal (BIPVT) systems under cold climatic conditions

Building integrated photovoltaic thermal (BIPVT) system has the potential to become a major source of renewable energy in the urban environment. In this paper, the system has been used as the roof top of a building to generate higher electrical energy per unit area and to produce necessary thermal energy required for space heating. One-dimensional transient model has been developed using basic heat transfer equations. On the basis of this model, an analysis has been carried in order to select an appropriate BIPVT system suitable for the cold climatic conditions of India. The PV performances, net energy gain and exergy of the building are determined. The results show that for a constant mass flow rate of air the system connected in series gives a better performance whereas for a constant velocity of air flow the system connected in parallel gives a better performance. The BIPVT system, fitted on the rooftop in an effective area of 65 m², is capable of annually producing the net electrical and thermal exergies of 16,209 kW h and 1531 kW h, respectively, at an overall thermal efficiency of 53.7%.     

A numerical investigation of a photovoltaic thermal (PV/T) collector

The photovoltaic thermal collector can provide thermal and heat power at the same time.In this paper, a photovoltaic/thermal sheet and tube collector has been numerically investigated. The paper focuses on the development of a hybrid solar collector PV/T. This model will be applied to optimize the operation of the PVT collector in the semi-arid climate. A mathematical model has been developed to determine the dynamic behavior of the collector, based on the energy balance of six main components namely a transparent cover, a PV module, a plate absorber, a tube, water in the tube and insulation. It has been validated by comparing the obtained simulation results with experimental results available in literature, where good agreement has been noted. Using our developed model, the heat and electrical power of sheet and tube collector has been analyzed for four typical days of year with the meteorological parameters of Monastir, Tunisia. Furthermore, the effect of solar radiation, the inlet water temperature, the number of glazing covers and the conductive heat transfer coefficient between plate absorber and PV module have been involved to identify their influence on the thermal and electrical efficiencies. The monthly thermal and electrical energies is also evaluated.     

U型管式全玻璃真空管集热器热效率及性能研究

在能量平衡分析的基础上，建立了U型管式全玻璃真空管太阳能集热器热效率方程，推导了集热器热损系数、效率因子等性能参数的计算公式，理论计算热效率与实验数据吻合良好。计算分析表明，真空管热损系数与吸热管和环境温差并非线性关系，将其关联式按环境温度分段整理将使计算结果更接近实际；涂层发射比对集热器的热效率影响较大，降低涂层发射比是提高集热器效率的有效途径；采取适当的措施降低吸热管与肋片间的接触热阻后，采用U型管连接方式不会时热利用系统集热器效率造成太大影响。     

The study of the performance and efficiency of flat linear Fresnel lens collector with sun tracking system in Iraq

Two flat linear Fresnel lenses and two absorbers connected in series. Tracking system is constructed so that it tracks the sun in two directions. Thermal and optical losses are introduced. The thermal efficiency of the first lens is higher than the second lens and reaches 0.65. The FLFL all-day collector efficiency reaches 0.58 and it varies depending on weather condition.