Advanced 3‐D CPC solar collector for thermal electric system

In this paper, the authors propose an innovative non‐tracking three‐dimensional compound parabolic concentrator (3‐D CPC) solar collector, which has excellent thermal efficiency for a high‐temperature range (100–200°C). In the past studies, in order to improve the thermal efficiency of the solar collector in a high‐temperature range, very high concentration ratios and tracking systems have been adopted. However, conventional high concentration solar collectors are not cost‐effective and are inappropriate for small‐rating thermal electric generation systems for residential use. The proposed 3‐D CPC collector has a moderate concentration ratio and does not need tracking. Initially, the tentative 3‐D CPC collector was fabricated and its thermal performance was tested. Next, numerical simulations of the optical characteristics of the 3‐D CPC collector were carried out via the ray‐tracing method. Finally, the specification of the optimal 3‐D CPC collector was clarified. Applications of the thermal electric system will also be mentioned. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(5): 323–335, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20121     

Parametric study of a thermal trap solar energy collector

A parametric study of a thermal trap solar energy collector with the help of a modified Hottel-Whillier-Bliss equation, is presented. The developed analysis is used to optimize the typical parameters, namely the trap's thickness and the number of flowing channels. The variation of the rating parameters of a collector with typical quantities, such as the fin distance, mass flow rate and thickness of the absorber plate, is discussed in detail.     

Heat retaining integrated collector storage solar water heater with asymmetric CPC reflector

A novel integrated collector storage solar water heater (ICSSWH) was designed, optically analysed and experimentally studied. The unit was based around a heat retaining ICS vessel design consisting of two concentric cylinders mounted horizontally inside a stationary truncated asymmetric compound parabolic concentrating (CPC) reflector trough. The annulus between the cylinders was partially evacuated and contained a small amount of water, which changed phase at low temperature, producing a vapour and creating a thermal diode transfer mechanism from the outer absorbing surface to the inner storage vessel surface. The absorbing outer vessel surface covered with selective absorber film and was partially exposed to solar radiation. The remaining vessel surface area (including the vessel ends) was thermally insulated to improve heat retention during the night. Curved reflectors with a high reflectance along with high transmittance glazing were also used to improve effective operation of the ICS system. The thermal behaviour of the ICS system was compared to that of a Flat Plate Thermosiphonic Unit (FPTU). The experimental results showed that the ICS system is as effective during daily operation as it is during the night. Furthermore, the thermal loss coefficient during night gives similar values between the ICS system and FPTU.     

Performance of a thermal trap solar collector/storage system

This paper presents an analysis of a novel solar collector/storage system consisting of a network of pipes buried in a mass of sand; the sand is covered with a glazed thermal trap. The heat can be extracted by flow of fluid in the pipes at a constant flow rate. An expression has been derived for the periodic rate at which useful heat can be collected, keeping the flow rate constant. Numerical calculations for a typical cold day in Delhi predict that the collection efficiency of the system is about 50% for flow rate of 10 kg/h. The efficiency increases with thermal trap thickness and with flow rate.     

Studies on semi-cylindrical solar tunnel dryers: year round collector performance

In this paper, the results of year round thermal performance of collector of semi-cylindrical solar tunnel dryers (STD) has been presented. The calculations have been made under natural circulation and forced circulation mode. The day-long average of solar irradiance, ambient temperature, rise in the inlet air temperature, natural circulation volume flow rates, and collector efficiency have been calculated for each month of the year. The effect of collector length, cover radius, collector inclination with horizontal have been made for rise in inlet air temperature, volume flow rate and for the efficiency. All calculations have been made for Delhi climate. © 1998 John Wiley & Sons, Ltd.     

配合集热器的盐梯度太阳池热性能实验与分析

构建表面积为1.50 m×1.50 m的小型实验用盐梯度太阳池,并与平板太阳能集热器配合使用,分别对普通太阳池和集热增强型太阳池进行了储热、放热实验。实验研究与理论分析表明:单独盐梯度太阳池的放热量为3.5×103k J,热效率为13.6%;集热增强型太阳池放热量可以达到4.8×103k J,且热效率增至28.1%。另外后者下对流层温度最高可提升10℃以上,从而证明太阳能集热器可以有效提高太阳池热效率,增加下对流层储热量。此外,考虑了放热过程换热器对太阳池下对流层的扰动,对比实验前后的溶液浓度,可以看出实验后太阳池盐度曲线合理,非对流层呈良好梯度分布,太阳池稳定性并未遭到破坏。     

Thermal performance study of a vacuum integrated solar storage collector (ISSC) with compound parabolic concentrator (CPC)

This paper deals with the energy performance of a new integrated solar storage collector (ISSC) with compound parabolic concentrator (CPC) conceived in the Thermal Process Laboratory in CRTEn Borj Cedria (North of Tunisia). The novelty in this system is the use of transparent vacuum insulation in the annulus between double half-Cylindrical Plexiglass, and the use of automated nocturnal insulation system, which suppresses heat loss during night. Also, the system is equipped with a mobile support permitting to have many collector orientations toward south, east-south, and west-south in order to maximize the incident solar flux. The experimental study of the ISSC system showed that the thermal loss coefficient of ISSC system is equal to 6.16 W/K for ISSC without nocturnal insulation and without vacuum, 4.69W/K for ISSC without nocturnal insulation and with vacuum, and 4.00 W/K for ISSC with nocturnal insulation and with vacuum. The thermal efficiency of the solar collector is equal to 42.92% for ISSC system fixed without vacuum, 45.95% for ISSC system fixed with vacuum, and 50.56% for ISSC system mobile with vacuum. In order to determine the long-term performance of the vacuum ISSC with CPC, the TRNSYS simulations were carried out by using the component modules modeling the ISSC with CPC concentrator (type 74 and type 60f). Comparison between experimental and predicted results for the temperature difference inside the storage tank during 3 days of January showed reasonable agreement. The numerical results for the ISSC system showed that the annual total energy collected (solar) and auxiliary energy were about 4670 and 1561 MJ, respectively. The annual total auxiliary energy represents about 33.4% of the annual total energy collected (solar). During the summer months (June, July, and August), no auxiliary is needed and the solar fraction (SF) is equal to 100%, where as the annual average SF is about 75%.     

A systematic review on parametric dependencies of transpired solar collector performance

Zero or low‐carbon buildings can be achieved through novel technology solutions and integrating renewable energy into the buildings. One method of reducing the fossil fuel dependency of buildings and limiting greenhouse gas emissions is integrating the solar thermal system into the built environment. Recently, transpired solar collector has been identified as 1 of the most efficient solar thermal conversion technologies where a very high efficiency can be achieved. The proposed review paper investigates the performance of transpired solar collectors (TSCs) and discusses the relevant case studies in this context. This paper introduces the background and concept of TSCs. It mainly focuses on the study of parametric dependency of the performance of TSCs. The paper also investigates various mathematical models, experimental study, and numerical simulations particularly CFD used for TSC performance analysis. This proposed paper concluded that wind speed and airflow rate are the most dominant factor in TSC performance but solar irradiation, hole diameter, hole geometry, and pitch size have limited effect on TSC performance; also, profile with longer pitch tends to lower the collector efficiency and heat transfer coefficient. However, profile with shorter pitch tends to reduce the wind effect.     

Thermal performance of the double-pass solar collector with and without porous media

This paper presents the thermal performance of a double-pass solar collector with and without porous media in the second or lower channel of the collector. The experimental setup has been designed to study the thermal performance over a range of design and operating conditions. Several important relationships between the design and operating conditions have been obtained. These relationships effect the thermal performance of the double-pass solar collector. The relationships include the effect of changes in upper and lower channel depth on the thermal efficiency with and without porous media. Moreover, the effects of mass flow rate, solar radiation, and temperature rises on the thermal efficiency of the double-pass solar collector have been studied. The study concluded that the presence of porous media in the second channel increases the outlet temperature, therefore increases the thermal efficiency of the systems.     

Thermal performance of a solar cooker based on an evacuated tube solar collector with a PCM storage unit

The thermal performance of a prototype solar cooker based on an evacuated tube solar collector with phase change material (PCM) storage unit is investigated. The design has separate parts for energy collection and cooking coupled by a PCM storage unit. Solar energy is stored in the PCM storage unit during sunshine hours and is utilized for cooking in late evening/night time. Commercial grade erythritol was used as a latent heat storage material. Noon and evening cooking experiments were conducted with different loads and loading times. Cooking experiments and PCM storage processes were carried out simultaneously. It was observed that noon cooking did not affect the evening cooking, and evening cooking using PCM heat storage was found to be faster than noon cooking. The cooker performance under a variety of operating and climatic conditions was studied at Mie, Japan.     

Performance model of a novel evacuated-tube solar collector based on minichannels

Thermal performance of a novel minichannel-based solar collector is investigated numerically. The particular collector consists of a U-shaped flat-tube absorber with a selective coating on its external surface. The working fluid flows inside an array of minichannels located in the cross-section of the absorber along its length. The absorber is enclosed in an evacuated-glass envelope to minimize convective losses. Performance and pressure drop are evaluated for different inlet temperatures and flow rates of the working fluid. Thermal performance of minichannel-based solar collector is compared to that of an evacuated tube collector without minichannels from the literature. Configurations with and without a concentrator are analyzed.     

Review on solar water heater collector and thermal energy performance of circulating pipe

The effect of thermal conductivity of the absorber plate of a solar collector on the performance of a thermo-siphon solar water heater is found by using the alternative simulation system. The system is assumed to be supplied of hot water at 50 °C and 80 °C whereas both are used in domestic and industrial purposes, respectively. According to the Rand distribution profile 50, 125 and 250 l of hot water are consumed daily. The condition shows that the annual solar fraction of the planning functions and the collector's configuration factors are strongly dependent on the thermal conductivity for its lower values. The less dependence is observed beyond a thermal conductivity of 50 W/m °C for the solar improper fraction and above 100 W/m °C for the configuration factors. In addition, the number of air ducts and total mass flow rate are taken to show that higher collector efficiency is obtained under the suitable designing and operating parameters. Different heat transfer mechanisms, adding natural convection, vapor boiling, cell nucleus boiling and film wise condensation is observed in the thermo-siphon solar water heater with various solar radiations. From this study, it is found that the solar water heater with a siphon system achieves system characteristic efficiency of 18% higher than that of the conventional system by reducing heat loss for the thermo-siphon solar water heater.     

空气-水复合平板型太阳能集热器

提出了一种适用于太阳能供热采暖工程的新型太阳能空气-水复合平板集热器。该集热器可以单独使用空气、水或同时以空气和水作为集热工质。测试显示,该集热器空气循环集热效率为55%～65%,水循环集热效率为32%～34%,能够满足太阳能供热采暖工程的要求。该集热器成本不高,适用于在我国北方广大农村地区推广使用。     

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。     

Energy consumption minimization in an innovative hybrid power production station by employing PV and evacuated tube collector solar thermal systems

Combination of a grid connected photovoltaic (PV) plant with a compressed air energy storage system (CAES) and a city gate station (CGS) has been proposed and investigated recently, leading to satisfactory performance results. The only deficiency of this system is the huge amount of fuel required to provide its heating demand. In this work, feasibility of employing evacuated tube solar thermal systems to supply the heating demand of the hybrid power plant is studied. After presenting detailed mathematical modeling, the solar heating units and other components of the power plant are properly sized. The results of simulations demonstrate that a total of 7000 evacuated tube collectors are required in the system, leading to elimination of the air heater from the CAES system completely and 17.2% fuel saving at the CGS. The total annual solar heat of 17.5 GWh is supplied for the system, 214 GWh power could directly be sold to the grid, 9.7 GWh power slumps is recovered and 53.5 GWh power is produced at nights. In the end, internal rate of return (IRR) method is used to compare economically the proposed system with similar systems proposed previously, outperforming all of the other candidates with an IRR of 11.1%.     

Comparative thermal performance evaluation of an active solar distillation system

In this paper, thermal models of all types of solar collector‐integrated active solar stills are developed based on basic energy balance equations in terms of inner and outer glass temperatures. In this paper, hourly yield, hourly exergy efficiency, and hourly overall thermal efficiency of active solar stills are evaluated for 0.05 m water depth. All numerical computations had been performed for a typical day in the month of 07 December 2005 for the climatic conditions of New Delhi (28°35′N, 77°12′E, 216 m above MSL). The thermal model of flat‐plate collector integrated with active solar still was validated using the experimental test set‐up results. Total daily yield from active solar still integrated with evacuated tube collector with heat pipe is 4.24 kg m^?2 day^?1, maximum among all other types of active solar stills. Copyright © 2007 John Wiley & Sons, Ltd.     

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.     

Cost effective asymmetric CPC solar collectors

Low cost CPC solar collectors were designed, constructed and tested. The collectors consist of two separate absorbers, which are horizontally incorporated in a stationary asymmetric CPC mirror. The efficient operation of the proposed collectors is due to the direct absorption of a large part of the incoming solar radiation and to the thermal losses suppression by the inverted surface of both absorbers. Two collector types with the same basic design are presented. The first type has tubular absorbers which are used for direct water heating and the second has flat fin type absorbers with pipe. Test results showed that the proposed collectors operate efficiently and are suitable for hot water applications.     

Thermal characteristics of a building-integrated dual-function solar collector in water heating mode with natural circulation

As a modified building-integrated solar thermal system, building-integrated dual-function solar collector here proposed is able to provide passive space heating in cold winter, and water heating in warm seasons. In this study, evaluations were made on this modified collector system for the warm period operation under the water heating mode with natural circulation of flow. A dynamic numerical model has been developed and validated by experimental data. Based on practical air-conditioned room design conditions, numerical analysis was performed to study the water heating performance, as well as to compare the solar transmission through building facade in different seasons with or without its presence. The results show that when working in the water heating mode, the system performs well in providing services hot water in the warm seasons without bringing in summer overheating problem.     

Improvement of basin type solar still performance : Use of various absorber materials and solar collector integration

Experimental measurements to determine conditions necessary for efficient solar desalination are given. The effects on performance of using various different absorber materials together with the integration of flat-plate collectors with storage systems in basin type solar stills are investigated. Correlations between daily yield (Y, in litres) and solar insolation (I, in MJ/m²day) are found to be, Y = 0.152I − 0.706 (for black-paint absorbers), Y = 0.180I − 0.987 (for charcoal absorbers), Y = 0.225I − 0.467 (for integrated solar collector and storage system, with black-paint absorbers). The calculated daily-average monthly yields for each case are also given.