A review of collector and energy storage technology for intermediate temperature applications

The technology and thermal performance of intermediate temperature solar collectors is summarized and the status of thermal and thermo-chemical storage methods is reviewed. It is concluded that collector technology is commercially available to achieve delivery temperatures up to 350°F at averaged yearly efficiencies better than 30 per cent in good solar climates and that linear parabolic, single-axis tracking troughs are the best types of collectors currently available for intermediate temperature applications. On the other hand, energy storage options commercially available today are generally limited to sensible heat systems, which are bulky and expensive for long-term storage. More research is necessary to develop new storage concepts, such as intermediate temperature chemical heat pumps based on reversible reactions, suitable for intermediate temperature solar systems with significant storage capability.     

Performance of a self-regulating solar multistage flash desalination system

A 10,000-1 solar multistage flash desalination system was designed and tested at Kuwait Institute for Scientific Research. The system consisted of a 220 m² solar line-concentrating collector field, 7000-1 thermal storage tank and a self-regulating 12-stage multistage flash desalination subsystem. The collector field, equipped with closed-loop tracking system, was installed with individual troughs oriented in the north-south direction. The thermal storage subsystem was useful in leveling off the thermal energy supply and allowing the production of desalinated water to continue during periods of low radiation and nighttime. The self-regulating capability of the desalination subsystem allowed for the adjustment of the flow rate and pressure, in the various stages of the desalination subsystem, according to the relative difference between the hot brine and input sea water temperatures. This allowed for maintaining a relatively high overall efficiency.     

Heat losses from parabolic trough solar collectors

Parabolic trough solar collector usually consists of a parabolic solar energy concentrator, which reflects solar energy into an absorber. The absorber is a tube, painted with solar radiation absorbing material, located at the focal length of the concentrator, usually covered with a totally or partially vacuumed glass tube to minimize the heat losses. Typically, the concentration ratio ranges from 30 to 80, depending on the radius of the parabolic solar energy concentrator. The working fluid can reach a temperature up to 400°C, depending on the concentration ratio, solar intensity, working fluid flow rate and other parameters. Hence, such collectors are an ideal device for power generation and/or water desalination applications. However, as the length of the collector increases and/or the fluid flow rate decreases, the rate of heat losses increases. The length of the collector may reach a point that heat gain becomes equal to the heat losses; therefore, additional length will be passive. The current work introduces an analysis for the mentioned collector for single and double glass tubes. The main objectives of this work are to understand the thermal performance of the collector and identify the heat losses from the collector. The working fluid, tube and glass temperature's variation along the collector is calculated, and variations of the heat losses along the heated tube are estimated. It should be mentioned that the working fluid may experience a phase change as it flows through the tube. Hence, the heat transfer correlation for each phase is different and depends on the void fraction and flow characteristics. However, as a first approximation, the effect of phase change is neglected. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance of Cylindrical Parabolic Collector with Automated Tracking System

Parabolic solar collector collects the radiant energy emitted from the sun and focuses it at a point. Parabolic trough collectors are the low cost implementation of concentrated solar power technology that focuses incident sun light on to a tube filled with a heat transfer fluid. However, the basic problem with the cylindrical parabolic collector without tracking was the solar collector does not move with the orientation of sun. Development of automatic tracking system for cylindrical parabolic collectors will increase solar collection as well as efficiency of devices. The main aim of this paper is to design, fabricate and analyze the performance of parabolic collector with automated tracking system. The automated tracking mechanism is used to receive the maximum possible energy of solar radiation as it tracks the path of sun. The performance of the parabolic trough collector is experimentally investigated with the water circulated as heat transfer fluid. The collector efficiency will be noted.     

具有二次聚光器的新型大开口槽式太阳集热器设计与光学性能分析

针对大开口和更高运行温度的槽式太阳能热发电系统,提出一种可实现高聚光比、低辐射热损及能流密度均匀的新型槽式太阳集热器,即在集热管内放置外壁具有太阳选择吸收膜层和内壁具有反射膜层二次聚光器的大开口槽式太阳集热器。建立圆弧为微元段的自适应设计新方法,提出3种典型的二次聚光器面型,利用蒙特卡洛光线追迹方法仿真新型集热器的能流密度分布特性,验证该光学仿真方法,分析影响集热器光学性能的各种因素。结果表明,该集热器可显著提升集热效率。     

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     

Study of thermal characteristics of a heating module with parabolic trough concentrator and linear wedge-like photoelectric receiver

New solar modules intended for typical solar collectors containing semiparabolic trough concentrators and receivers that convert solar energy into thermal energy are considered. Mathematical modeling is carried out to develop an algorithm for estimating the structure of a heating module with the assigned energy parameters according to the laws of geometrical optics, as well as heat and mass transfer. When using such modules, which are based on a parabolic concentrator and a receiver with a system of coolant flow, cogeneration plants can be designed to produce electricity and heat. The mockups developed using this procedure are studied on the corresponding facilities and are tested under in-situ conditions. A solar module with an asymmetric parabolic trough concentrator and a linear wedge-like photoelectric receiver of concentrated radiation with a system of coolant flow provides the maximum power of 386 W at a temperature of 40°C and an efficiency of 60%, and 319 W at 60°C and 49%, respectively. Such modules are proposed for use to design solar collectors with the required performance.     

Optics of a two-trough solar concentrator

A linear focusing solar concentrator is described that uses two reflecting troughs, one is a large, stationary hemi-cylinder and the other is small and tracks the sun. The small reflector weighs less than a parabolic trough with the same concentrator aperture therefore diurnal steering is more feasible. Energy is carried to the job by solar heated fluid in a pipe at focus in the secondary reflector assembly. Theory is presented and comparisons are given for east-west and north-south oriented parabolic and two-trough collectors. In the ideal world, the parabolic outperforms the two-trough collector however in the real world, the simplifications due to the immobile, hemi-cylinder, large reflector may outweigh its disadvantages.     

Design specifications and application of a100 kWc(700 kWth) cogeneration solar power plant

A 100 kW_e/700 kW^th distributed receiver, solar-thermal power plant was installed in remote desertlocation 35 km southwest of Kuwait City in the country of Kuwait. The co-generation solar power plant is designed to supply the electric power and fresh water, needs of a small agricultural desert settlement. The power plane utilizes 56 point-focusing, parabolic collectors, each five meters in diameter and equipped with a two-axis tracking system. A synthetic fluid is circulated in the collector field via a pipeline network, where it is heated to 400°C. In the energy conversion system, the heat-transfer fluid enters a series of heat exchangers where it heats and vaporizes another organic fluid (Toluene). The vapor, under high pressure, operates a radial flow turbine, producing mechanical and, subsequently, electric energy. The rejected heat is ultimately to be used for powering of a multistage flash desalination system to provide the fresh water needs for the integrated food-water-power complex which also includes desert greehouses and outdoor irrigation system.     

Experimental investigation of effect of variation of mass flow rate on performance of parabolic dish water heater with non-coated receiver

Concentrated solar collectors have high efficiency. Therefore, when concentrating collectors are used for water heating application, the system yields higher efficiency. From a hot climate perspective, there is a huge potential available for low-cost solar water heating systems. With the system described in this paper, the needs of hot water in the domestic sector can be fulfilled instantly. Authors used the parabolic dish collector for instant water heating. This paper describes the effect of variation of mass flow rate on performance of the parabolic dish water heater prototype. Design of the solar parabolic dish collector consists of a novel truncated cone-shaped helical coiled receiver made up of copper at focal point. This prototype was evaluated for its performance during the month of April and May 2010.     

Simple procedure for predicting long term average performance of nonconcentrating and of concentrating solar collectors

The Liu and Jordan method of calculating long term average energy collection of flat plate collectors is simplified (by about a factor of 4), improved, and generalized to all collectors, concentrating and nonconcentrating. The only meteorological input needed are the long term average daily total hemispherical isolation on a horizontal surface and, for thermal collectors the average ambient temperature. The collector is characterized by optical efficiency, heat loss (or U-value), heat extraction efficiency, concentration ratio and tracking mode. An average operating temperature is assumed. If the operating temperature is not known explicitly, the model will give adequate results when combined with the , f-chart of Klein and Beckman.A conversion factor is presented which multiplies the daily total horizontal insolation to yield the long term average useful energy delivered by the collector. This factor depends on a large number of variables such as collector temperature, optical efficiency, tracking mode, concentration, latitude, clearness index, diffuse insolation etc., but it can be broken up into several component factors each of which depends only on two or three variables and can be presented in convenient graphical on analytical form. In general, the seasonal variability of the weather will necessitate a separate calculation for each month of the year; however, one calculation for the central day of each month will be adequate. The method is simple enough for hand calculation.Formulas and examples are presented for five collector types: flat plate, compound parabolic concentrator, concentrator with east-west tracking axis, concentrator with polar tracking axis, and concentrator with 2-axis tracking. The examples show that even for relatively low temperature applications and cloudy climates (50°C in New York in February), concentrating collectors can outperform the flat plate.The method has been validated against hourly weather data (with measurements of hemispherical and beam insolation), and has been found to have an average accuracy better than 3 per cent for the long term average radiation available to solar collectors. For the heat delivery of thermal collectors the average error has been 5 per cent. The excellent suitability of this method for comparison studies is illustrated by comparing in a location independent manner the radiation availability for several collector types or operating conditions: 2-axis tracking versus one axis tracking; polar tracking axis versus east-west tracking axis; fixed versus tracking flat plate; effect of ground reflectance; and acceptance for diffuse radiation as function of concentration ratio.     

A novel PVT/PTC/ORC solar power system with PV totally immersed in transparent organic fluid

A novel hybrid PVT/parabolic trough concentrator (PTC)/organic Rankine cycle (ORC) solar power system integrated with underground heat exchanger has been proposed. The evaporator unit consists of a transparent flat PVT solar collector and a PTC connected in series. The first transparent solar collector has transparent covers and consists of solar cells totally immersed within a pressurized transparent organic fluid that allows the solar radiation to reach the solar cells, cools them effectively, and captures all thermal losses from the solar cells. The second concentrator is a conventional one with opaque black receiver used to reheat the transparent organic fluid to higher temperatures. Both solar collectors (the PVT and PTC) perform as the boiler and superheater for the ORC. The performance of the proposed system is investigated by a steady‐state mathematical model. The results show that, at design conditions, the efficiency of the PV modules stabilizes around 12%, absorber efficiency varies within 64% to 75%, and the ORC efficiency varies within 7% to 17%.     

Efficiency investigation of a new-design air solar plate collector used in a humidification–dehumidification desalination process

The aim of this research is to experimentally study the efficiency of a new-design plate collector used to heat air in a new desalination humidification–dehumidification process. In fact, in such processes, the air solar collectors work at unusual experimental parameters (forced convection, elevated air humidity, high solar irradiation…). At these stressed experimental conditions, few published works are available in literature. Furthermore, the comparison of the efficiency of collectors running with normal air humidity content (about 10–20 g kg⁻¹) and air of elevated humidity (20–50 g kg⁻¹) were not yet published as our knowledge. In the present investigation, a new air solar plate collector was designed and developed for its use in a desalination process. Moreover, a characterization of such collector was performed under different experimental conditions. The effect of different parameters, namely: the solar radiation, the wind velocity, the ambient temperature, the air mass flow rate, the inlet air humidity and temperature, on the collector efficiency was also investigated. The collector was optimized for its use in a new solar desalination process. In fact, the air solar collector was designed in order to lower its economic cost making them applicable for water desalination.     

Performance analysis of Azimuth Tracking Fixed Mirror Solar Concentrator

The fixed mirror solar collector (FMSC) fixes reflector and mobiles receiver to collect solar energy. However, this type of concentrator has a low efficiency and short operating duration in practical applications. In this paper, we propose to install the FMSC on an azimuth tracking device (ATFMSC) and the reflectors are arranged by intermission to avoid the shading of neighbor reflector for incidence angle of less than 10° to improve its optical performance. Through the integration of the reflected solar radiation distribution function over any reflection point, and then the whole collector aperture, we develop the analytical expressions of various system efficiencies to numerically simulate the performance of ATFMSC with evacuated tube receiver in different design parameters. It is validated by the ray tracing results. The result shows that the mean annual net heat efficiency of the whole system would be up to 61% with the operating temperature of 400 °C, which is higher than parabolic trough collector and traditional FMSC. This is because the longitudinal incidence angle of ATFMSC always remains zero by tracking the sun azimuth, so the end loss of the concentrator can be avoided and enables it to operate with high efficiency continually.     

基于三角腔体吸收器的透射式菲涅尔定焦线系统聚光特性分析

为解决线性菲涅尔太阳能集热系统单轴跟踪过程中出现的聚光焦线偏移以及降低系统跟踪能耗等问题,提出一种透射式菲涅尔定焦线太阳能聚光器.该聚光器采用极轴跟踪方式与线性菲涅尔透镜定期滑移调节方式相结合,可实现固定焦线聚光.将该聚光器与三角腔体吸收器所组成的太阳能集热系统,利用基于蒙特卡罗光线追迹法的TracePro光学软件分析...     

A stationary evacuated collector with integrated concentrator

A comprehensive set of experimental tests and detailed optical and thermal models are presented for a newly developed solar thermal collector. The new collector has an optical efficiency of 65 per cent and achieves thermal efficiencies of better than 50 per cent at fluid temperatures of 200°C without tracking the sun. The simultaneous features of high temperature operation and a fully stationary mount are made possible by combining vacuum insulation, spectrally selective coatings, and nonimaging concentration in a novel way. These 3 design elements are “integrated” together in a self contained unit by shaping the outer glass envelope of a conventional evacuated tube into the profile of a nonimaging CRC-type concentrator. This permits the use of a first surface mirror and eliminates the need for a second cover glazing. The new collector has been given the name “Integrated Stationary Evacuated Concentrator”, or ISEC collector. Not only is the peak thermal efficiency of the ISEC comparable to that of commercial tracking parabolic troughs, but projections of the average yearly energy delivery also show competitive performance with a net gain for temperatures below 200°C. In addition, the ISEC is less subject to exposure induced degradation and could be mass produced with assembly methods similar to those used with fluorescent lamps. Since no tracking or tilt adjustments are ever required and because its sensitive optical surfaces are protected from the environment, the ISEC collector provides a simple, easily maintained solar thermal collector for the range 100–300°C which is suitable for most climates and atmospheric conditions. Potential applications include space heating, air conditioning, and industrial process heat.     

Performance analysis of a hybrid photovoltaic/thermal (PV/T) collector with integrated CPC troughs

In the present investigation a theoretical analysis has been presented for the modelling of thermal and electrical processes of a hybrid PV/T air heating collector coupled with a compound parabolic concentrator (CPC). In this design, several CPC troughs are combined in a single PV/T collector panel. The absorber of the hybrid PV/T collector under investigation consists of an array of solar cells for generation of electricity, while collector fluid circulating past the absorber provides useful thermal energy as in a conventional flat plate collector. In the analysis, it is assumed that solar cell efficiency can be represented by a linear decreasing function of its temperature. Energy balance equations have been developed for the various components of the system. Based on the developed analysis, both thermal and electrical performance of the system as a function of system design parameters are presented and discussed. Results have been presented to compare the performance of hybrid PV/T collector coupled with and without CPC. Copyright © 1999 John Wiley & Sons, Ltd.     

Design and simulation of a low concentrating photovoltaic/thermal system

The advantages of photovoltaic/thermal (PV/T) collectors and low solar concentration technologies are combined into a photovoltaic/thermal system to increase the solar energy conversion efficiency. This paper presents a prototype 11X concentration rate and two axis tracking system. The main novelty is the coupling of a linear Fresnel concentrator with a channel photovoltaic/thermal collector. An analytical model to simulate the thermal behaviour of the prototype is proposed and validated. Measured thermal performance of the solar system gives values above 60%. Theoretical analysis confirms that thermal conduction between the PV cells and the absorber plate is a critical parameter.     

Comparative analysis of direct-absorption parabolic-trough solar collectors considering concentric nanofluid segmentation

Nanofluids have been actively used in direct-absorption solar collectors. In a direct-absorption parabolic-trough solar collector (DAPTSC) for medium-high temperature regime, the nanofluids used to be contained in a transparent glass receiver located at the focal line of a parabolic mirror so that the solar radiation is concentrated to the glass receiver and absorbed volumetrically inside the collector. In order to further increase the thermal efficiency of a DAPTSC, we propose to insert an extra glass tube inside the nanofluid so that the nanofluid is separated into two concentric segmentations (ie, an inner section and an outer section), and apply a nanofluid of lower concentration in the outer section while a nanofluid of a higher concentration in the inner section. The proposed idea is numerically tested on four pairs of DAPTSCs (the variants obtained depending on whether there is a vacuum envelope and whether there is a reflective semicylindrical coating on the receiver). The results show that at the same particle concentration parameter, the DAPTSCs with two concentric segmentations of nanofluids outperform those with one uniform nanofluid for all configurations considered in this work. For a transparent case without an envelope, this efficiency increase is as high as 12.5% point when the inlet temperature is 350 K. In addition, parametric studies are performed for this best configuration to evaluate the effect of absorption coefficient, mass flow rate, collector length, solar irradiance, and convection heat transfer coefficient on the collector performance.     

太阳能中温闪蒸海水淡化系统产水性能研究

为提高系统产水性能并降低内部结垢,提出一种由非跟踪复合抛物面聚光器加热导热油至100 ℃以上作为供能热源,采用喷雾辅助闪蒸的海水淡化系统。实验研究实际天气中,不同太阳辐照度下进水口温度、进水流量对系统产淡水性能的影响。采用密封压力桶可将进水口温度升至沸点以上,最高可达123 ℃。太阳辐照度波动较大时,进水口温度保持稳定,系统可稳定运行。进水口温度对产水速率影响显著,平均进水口温度从100 ℃升至120 ℃时,产水速率提高47.61%。当进水流量为50 kg/h,压力维持在0.045 MPa时,系统产水速率最大,日累计淡水产量可达11.14 kg/（d·m²）,小时效率为81.45%,单级生产率为9.15%。