A novel multiple curved surfaces compound concentrator

A novel multiple curved surfaces compound concentrator is developed in this paper. It is composed of a parabolic and a flat contour. This new concentrator has a focus at the backside which is extremely useful and convenient for some applications. The reflected rays here are transmitted forward instead of backward as in the conventional parabolic concentrators. The design method of the concentrator is introduced. Some of important parameters are discussed and the value rang of them is determined. Simple comparisons between proposed concentrators and traditional paraboloid and CPC are made. Light rays tracing are carried out in the concentrator.     

新型槽式太阳能聚光集热器的研究与试验

设计了一种新型槽式太阳能聚光集热器,分析了工作原理和设计参数,建立了由该集热器组成的太阳能集热系统,并进行了试验测试。文章给出了采用不同接收器的升温曲线和效率计算值,对不同布置方式的集热性能进行了比较。试验结果表明,该装置具有较高的集热效率,运行温度在80℃时,效率达到35%以上。     

Thermal performance analysis of small-sized solar parabolic trough collector using secondary reflectors

ABSTRACT

In this paper, theoretical analysis of receiver tube misalignment, the design of secondary reflector and experimental analysis of a small-sized solar parabolic trough collector (PTC) with and without secondary reflectors are represented. Experimental analysis of PTC has been done using a parabolic secondary reflector (PSR) and triangular secondary reflector (TSR) and compared with PTC without secondary reflector (WSR). The maximum outlet temperature of heat transfer fluid is observed as 49.2°C, 47.3°C and 44.2°C in the case of PSR, TSR and WSR conditions, respectively. The maximum thermal efficiency of 24.3%, 22.5% and 17.8% is observed in the case of PSR, TSR and WSR conditions, respectively. The circumferential temperature difference on the outer surface of the receiver tube is obtained more uniform in the case of PSR and TSR than WSR condition. This indicates that the use of a secondary reflector can improve the performance of a solar PTC system.     

Experimental study on a new solar boiling water system with holistic track solar funnel concentrator

A new solar boiling water system with conventional vacuum-tube solar collector as primary heater and the holistic solar funnel concentrator as secondary heater had been designed. In this paper, the system was measured out door and its performance was analyzed. The configuration and operation principle of the system are described. Variations of the boiled water yield, the temperature of the stove and the solar irradiance with local time have been measured. Main factors affecting the system performance have been analyzed. The experimental results indicate that the system produced large amount of boiled water. And the performance of the system has been found closely related to the solar radiance. When the solar radiance is above 600 W/m², the boiled water yield rate of the system has reached 20 kg/h and its total energy efficiency has exceeded 40%.     

太阳时角对槽式聚光器焦线位置的影响

在讨论太阳时角对槽式聚光器焦线位置影响的基础上,建立了因焦线运动导致太阳辐射损失的理论模型.通过对昆明晴天不同节气下的焦线运动和太阳辐射损失的分析和计算,得到了焦线随时角变化的一般规律以及瞬时太阳辐射强度损失和不同时段的太阳辐射相对损失率,并与实验进行了对比.针对焦线运动的特点,提出了对槽式集热系统接收器的改进措施和建议,认为对于大规模的槽式聚光集热器利用,因焦线运动造成的太阳辐射损失可不必考虑.     

Development and testing of a solar air-heater with conical concentrator

The free convection performance of a solar air heater with a cylindrical absorber centred to a conical concentrator for focusing incident solar radiation was studied. The primary objective was to heat air to higher temperatures than those obtainable in flat-plate collectors.The experiments were carried out and the data recorded in summer daytime, considering collector tilting angle and type of absorbing surface as the investigation parameters.It was found that a tilting angle under local latitude would be appropriate for collector installation. Although the efficiency of the heater at free convection conditions was very much smaller than flat-plate solar air-heaters, exit air temperatures reached up to 150 °C, which could allow utilisation in high temperature applications. A selective absorber surface improved appreciably the performance of the solar air-heater.     

A new low-cost tracking ridge concentrator

A new very simple, reliable solar tracker is described. The solar tracker is based on a new arrangement of auxiliary bifacial solar cell connected directly to D.C. motor. Auxiliary solar cells (panels) can both sense and provide energy for tracking.     

Radiation performance of dish solar concentrator/cavity receiver systems

The Monte-Carlo ray-tracing method is applied and coupled with optical properties to predict radiation performance of dish solar concentrator/cavity receiver systems. The effects of sunshape and surface slope error have been studied and the corresponding probability models are introduced in this paper. Taking into account the above-mentioned factors, we show that the directional features of the focal flux affect the radiation flux distribution of cavity receiver, present criteria for the characterization of directional attributes, and describe a method for their calculation. Based on the concept of equivalent radiation flux, an upside-down pear cavity receiver is proposed in view of directional attributes of focal flux. Receiver design and modelling guidelines are presented. The uniformity performance of the wall flux is compared with five traditional geometries.     

Design and investigation of a novel concentrator used in solar fiber lamp

A novel concentrator used in solar fiber lamp has been designed and made. The method of the design has been introduced. The lamp has been tested under the real solar condition and the experiment curves have been given. The light transmission will be influenced by the structure of the lamp and the diameter of the fiber, which has been studied in this paper. The experimental results show that the brightness of this solar fiber lamp is about the brightness of a 6-W ordinary electrical energy-saving lamp. The computer simulation for the lamp has been presented and the improvement schemes are proposed.     

Numerical investigations of solar cell temperature for photovoltaic concentrator system with and without passive cooling arrangements

The numerical study of solar cell temperature for concentrating PV with concentration ratio of 10× is presented in this paper. A two dimensional thermal model has been developed to predict the temperature for PV concentrator system (solar cell and lens) with and without passive cooling arrangements. Based on a thermal model, the result shows that maximum of four numbers of uniform fins of 5 mm height and 1 mm thickness can be effectively used to reduce the solar cell temperature. In addition to that, the effects of ambient temperature and solar radiation intensity on the solar cell temperature have also been investigated for the system with and without cooling fins. Based on the influencing parameters of ambient temperature and solar radiation, two separate solar cell temperature correlations has been proposed for systems with and without cooling fins to predict the cell temperature for the range of given parameters. In our previous studies, the present 2-D model was extensively validated with a comprehensive unified model [8], [9] and [10].     

Performance analysis of non-isothermal solar reactors for methanol decomposition

A procedure for analyzing the performance of non-isothermal solar reactors for methanol decomposition was developed, based on a model of thermal loss from direct steam generation collector and a comprehensive kinetic model of methanol decomposition employing BASF K3-110 catalyst. It was found that catalytic bed temperature tends towards a certain value, which depends on the chemical reaction type, radiation intensity and collector structure mainly. For a beam incidence angle of 0°, system efficiency increases from 56% at a radiation intensity of 400 W m⁻² to almost 58% at a radiation intensity of 1000 W m⁻². For a radiation intensity of 400 W m⁻², beam incidence angle of 20°, absorber length of 10 m, feed temperature of 373 K and ratio of reaction section of 0.9, the mole flow rate of feed in the range of 0.21–0.23 mol s⁻¹ results in a maximum quantity of reacted methanol of 0.146 mol s⁻¹, while a mole flow rate of feed of 0.15 mol s⁻¹ leads to a maximum system efficiency of 54.2%. The research indicates that the pre-heating section should be as short as possible for effective use of solar energy.     

A bilinear model for the thermal behaviour of a point focusing solar collector

An important task when designing point focusing (paraboloidal) solar-collectors is to model the thermal behaviour of their receivers by an approximate dynamic model in view of thermal loop automatization. In general, this is very difficult or impossible by studying the exact physical phenomena which occur in the receiver. However, approximations can be made and approximate models can always be derived. Using filtering and estimation theory these models can be identified to represent reality very well.     

A new design of nontracking seasonally adjusted plane mirror linear trough solar concentrator with a flat horizontal absorber

This paper presents an optical design based on a single-reflection criterion, and performance characteristics of an east-west aligned nontracking seasonally adjusted linear trough solar concentrator with a flat horizontal absorber, using plane mirror elements. The design procedure allows the use of any desired number of mirror elements to reflect solar energy onto the base absorber in one reflection. The angle of inclination of each mirror element with respect to the absorber surface, and the width of the mirror element, are determined so that a ray incident on the extreme upper edge of the mirror element at a specified angle to the normal to the concentrator aperture (acceptance half-angle), after reflection, strikes the extreme edge of the absorber on the opposite side of the mirror element. Other rays making angles less than the design acceptance half-angle are also reflected onto the base absorber in one reflection. Concentrator designs resulting from this approach appear to have the important characteristic of relatively smaller heights, and hence appear highly cost-effective in terms of the amount of material required for fabrication. Some numerical calculations have been carried out to illustrate the performance of concentrators for different acceptance half-angles. Results obtained are presented in graphic and tabular forms, and are discussed.     

Development of a low-cost dish solar concentrator and its application in zeolite desorption

This paper deals with the development and performance characteristics of a low-cost dish solar concentrator and its application in zeolite desorption. The dish solar concentrator consists of an old damaged satellite dish, purchased from a scrap yard, and a polymer mirror film used as reflecting surface. The proposed concentrator is connected to a sun-tracking system which is based on an electronic circuit that processes the input signals from a set of sensors and drives the dish actuator. The solar thermal energy application to adsorption technology (with the sorption pair water/zeolite) is simulated using the ‘Ice-Quick’ device manufactured by Zeo-Tech GmbH. Samples from two types of zeolites were initially brought to saturation condition and then mounted on the focal point of the dish solar concentrator in order to be regenerated. Experimental results are presented and useful conclusions are drawn.     

槽式聚光热电联供系统抛物反射面的性能参数分析

分析了跟踪方式和太阳张角对理想槽式抛物面反射镜的影响,给出了几何聚光比、相对口径、能流分布、边界角之间的函数关系式。在理想情况下,边界角δ为44.87°时,槽式聚光器的最大聚光比为212.59,此时相对口径为1.652 m。讨论了北京、上海、昆明等地单轴跟踪在全年不同时刻入射角余弦值的变化规律。采取东-西水平轴跟踪时,入射角余弦值与各地纬度无关;采取南-北水平轴跟踪时,春冬两季每天不同时刻入射角的变化范围较大,夏秋两季的变化范围较小。文章针对不同宽度太阳电池和聚光比对抛物镜面参数进行了设计分析。     

Thermal analysis of solar parabolic trough with porous disc receiver

In this paper, 3-D numerical analysis of the porous disc line receiver for solar parabolic trough collector is presented. The influence of thermic fluid properties, receiver design and solar radiation concentration on overall heat collection is investigated. The analysis is carried out based on renormalization-group (RNG) k–ε turbulent model by using Therminol-VP1 as working fluid. The thermal analysis of the receiver is carried out for various geometrical parameters such as angle (θ), orientation, height of the disc (H) and distance between the discs (w) and for different heat flux conditions. The receiver showed better heat transfer characteristics; the top porous disc configuration having w = d_i, H = 0.5d_i and θ = 30°. The heat transfer characteristic enhances about 64.3% in terms of Nusselt number with a pressure drop of 457 Pa against the tubular receiver. The use of porous medium in tubular solar receiver enhances the system performance significantly.     

A simplified approach for evaluating performance of a solar water heater with side losses

We present a simplified method which could be used to calculate, to a first approximation, the energy losses from the sides of a solar collector/water heater. The inclusion of energy losses through the side walls of a reasonable thickness reduce the efficiency of the system by about 5%. The integrated side energy losses for the whole day are not equal for the various segments of the wall. Hence, it will be economical to construct wedge shape walls, thickness decreasing downward, instead of usual rectangular walls.     

Experimental performance investigation of modified cavity receiver with fuzzy focal solar dish concentrator

In this paper, thermal performance analysis of 20 m² prototype fuzzy focal solar dish collector is presented. The focal image characteristics of the solar dish are determined to propose the suitable design of absorber/receiver. First, theoretical thermal performance analysis of the fuzzy focal solar parabolic dish concentrator with modified cavity receiver is carried out for different operating conditions. Based on the theoretical performance analysis, the total heat loss (conduction, convection and radiation heat losses) from the modified cavity receiver is estimated. It is observed that the maximum theoretical efficiencies of solar dish collector are found to be as 79.2% for no wind conditions and 78.2% and 77.8% for side-on and head-on winds speed of 5 m/s respectively. Latter, real time analysis of parabolic dish collector with modified cavity receiver is carried out in terms of stagnation test, time constant test and daily performance test. From stagnation test, the overall heat loss coefficient is found to be 356 W/m² K. The time constant test is carried out to determine the influence of sudden change in solar radiation at steady state conditions. The daily performance tests are conducted for different flow rates. It is found that the efficiency of the collector increases with the increase of volume flow rates. The average thermal efficiencies of the parabolic dish collector for the volume flow rate of 100 L/h and 250 L/h are found to be 69% and 74% for the average beam radiation (I_bn) of 532 W/m² and 641 W/m² respectively.     

A new solar powered adsorption refrigerator with high performance

An adsorptive solar refrigerator was built in September 2000 in Yverdon-les-Bains, Switzerland. The adsorption pair is silicagel + water. The machine does not contain any moving parts, does not consume any mechanical energy except for experimental purposes and is relatively easy to manufacture. Cylindrical tubes function as both the adsorber system and the solar collector (flat-plate, 2 m² double glazed); the condenser is air-cooled (natural convection) and the evaporator contains 40 l of water that can freeze. This ice functions as a cold storage for the cabinet (320 l).The first tests (September 2000) showed a very promising performance, with a gross solar cooling COP_SR of 0.19. After minor modifications, a second test series was carried out during summer 2001. This test series shows how the external parameters influence the machine with respect to the COP_SR (irradiation and external temperature). The latter varies between 0.10 and 0.25 with a mean value of 0.16. These values are higher than those obtained by earlier solar powered refrigerators (0.10–0.12).This paper describes the principle of the cycle, the different components of the machine, and the test procedure. The test procedure includes a constant daily cooling requirement. The experimental results presented were taken over a period of two months.     

A new solar concentrating system: Description, characterization and applications

Solar concentrating systems are usually very expensive and require a large space for their installation. This article presents a new solar concentrating device which is low-cost, small-scale, and has very good features for materials treatment. It consists of two sets of mirrors that reflect solar radiation in two steps with a beam array similar to a Fresnel lens. The power density was measured with Gardon-type radiometers. The results are in good agreement with previous work. The system has a nominal power of 2.5 kW, a measured concentration factor of 1040, and a measured focal diameter of 20 mm (90% of power level).