Parabolic Trough Concentrator Research Articles

A 1.2 MWth solar parabolic trough system based on air as heat transfer fluid at 500 °C — Engineering design, modelling, construction, and testing

We report on the realization of a 212m-long parabolic trough concentrator and associated solar receiver that uses air as the heat transfer fluid at 500°C. The fully pneumatic solar concentrator is based on a stack of reflective polymeric films mounted on a rigid concrete support structure and protected by a transparent polymeric envelope. The solar receiver consists of an array of helically coiled absorber tubes contained side-by-side within an insulated groove having a windowed opening. The multiple absorber tubes are connected via two axial pipes serving as feeding and collecting manifolds. The 1.2MWth solar collector unit, comprising the solar concentrator and solar receiver, is modelled by formulating the energy conservation equation coupling radiation, convection, and conduction and solving it numerically using the finite volume technique. Model validation is accomplished by comparison to on-sun experimental data obtained from tests of the first solar collector unit after its commissioning in Ait Baha, Morocco. The mean absolute and RMS deviations between measured and computed air outlet temperatures of the solar receiver are 7.3°C and 9.5°C, respectively. The validated model is further applied to identify heat losses and predict year-round operation. For a DNI of 2400kWh/m2/yr, the solar plant can deliver 1810MWh of thermal energy at 500°C.

Experimental study of a parabolic trough solar collector with flat bar-and-plate absorber during direct steam generation

The present work aims at investigating an innovative flat aluminum absorber for process heat and direct steam generation in small linear solar concentrating collectors. After defining its optimal width through a Monte Carlo ray-tracing analysis, this absorber has been manufactured with the bar-and-plate technology, including an internal offset strip turbulator in the channel. This technology is cost-effective and extremely flexible, allowing to easily adapt the geometry of the absorber to different reflecting optics configurations. It has been mounted on an asymmetrical parabolic trough concentrator to form a solar collector with a concentration ratio of 42, which has been experimentally investigated. In particular, a new test procedure is presented, applied and validated to characterize the thermal performance of the collector during steam generation. The results show that a promising overall thermal efficiency of 64% at 0.160 K m2 W−1 can be achieved with negligible pressure drop.

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.

Optical sensitivity analysis of geometrical deformation on the parabolic trough solar collector with Monte Carlo Ray-Trace method

This paper evaluated the influences of three kinds of geometrical deformations including global deformation, local rotation deformation and local linear deformation, on the optical performance of parabolic trough solar collector (PTC). An optical analysis of PTC system with different geometrical deformations was performed with the Monte Carlo Ray-Trace method to predict the optical efficiency and the radiation flux distribution on the receiver. The results show that the elliptic profile of the concentrator mirror results in a local hot spot on the receiver, which may shorten the receiver service life, among those cases with different global deformations. The optical performance of parabolic trough concentrator is almost not affected by rotation angle in the range of −0.3 to 0.3°. And the optical efficiency could be maintained above 90% of that under non-deformation condition when the linear deformation length is less than 6.0% of half aperture width. The local deformation at the bottom of the concentrator induces a more apparent deficit of the performance compared with the case of top local deformation. Additionally, the optical efficiency is inversely proportional to the length of part which is removed from the concentrator.

Novel process for performance enhancement of a solar continuous adsorption cooling system

Adsorption cooling is regarded as one of promising clean technologies since it constitutes a rational way for the use of low-grade thermal energy (industrial waste, excess production, etc.) and renewable energy sources. The current paper provides fresh ideas on the relevant issues associated with the intermittence and low performance, which are considered among the main drawbacks of solar-driven adsorption cooling systems. Its primary aim is to design and analyze a solar continuous adsorption cooling system whose design consists mainly of combining a two-tank thermal energy storage system with two adsorbent beds. The operating process is based on storage of excess thermal energy, supplied by means of a solar parabolic trough concentrator, and on its subsequent recovery for producing an additional amount of cold.The simulation results indicate that, under the system conditions (design, working and weather), the solar coefficient of performance and daily cooling production are considerably improved when a latent heat storage unit is integrated with the system. The study reveals also that, thanks to this novel process, the number of refrigeration cycles achieved per day could be significantly increased, which means that the intermittence disadvantage could widely be overcome.

Explicit expression for temperature distribution of receiver of parabolic trough concentrator considering bimetallic absorber tube

The portion of the absorber tube facing the trough surface receives the concentrated sun-rays and the other side of the absorber tube receives the sun-rays directly. Consequently, the temperature of the absorber tube is non-uniform across the circumference which leads to differential expansion of the material of the tube. Thus, the tube experiences compression and tension in its different parts. This may lead to bending of the tube. In literature, the temperature of the absorber tube is computed using CFD software which take large computational time. Thus, in the previous work, an explicit analytical expression was derived for finding the distribution of absorber’s temperature and it was found that the temperature gradient across the circumference of the absorber tube can lead to significant bending. Thus, in the current work, a bimetallic tube has been studied that can reduce the temperature gradient and an explicit analytical expression is derived for finding the temperature distribution of a bimetallic absorber tube. The study of the effects of thicknesses and material selection of the inner and outer layer of bimetallic tube on temperature distribution is a must for choosing right materials and dimensions. The appropriate thicknesses and materials of inner and outer layers can be found out from the current work. The issue of whether to use high conducting material on outside or inside has also been addressed in the current work and concluded that the material with higher thermal-conductivity should be used as outer layer of the bimetallic tube to minimize the non-uniformity across the circumference. It is also concluded that for Schott-2008-PTR70-receiver, 126°, 135° and 139° respectively are the appropriate rim-angles for trough’s aperture-width=3m, 6m and 9m corresponding to minimum non-uniformity across the circumference. 72°, 100° and 112° respectively correspond to maximum solar-flux at the absorber tube.

Performance testing of a spectral beam splitting hybrid PVT solar receiver for linear concentrators

A novel spectral beam splitting photovoltaic/thermal (PVT) solar receiver for linear concentrators has been developed capable of generating high-grade thermal energy concurrently with electricity. This paper evaluates the initial field testing of this receiver which combines a selective absorption heat transfer fluid (Propylene Glycol) with a band pass optical filter to achieve efficient spectral splitting. Wavelengths of light between 700nm and 1100nm are directed to the silicon PV cells, with the remaining wavelengths absorbed directly as heat. A prototype has been constructed and mounted to a parabolic trough concentrator with 42× geometrical concentration ratio. Results demonstrated considerable promise for this technique. High grade heat thermal efficiencies of 31% relative to the thermal beam splitting fraction were achieved at a receiver temperature of 120°C, with a total system efficiency of 50%. Electrical yields of approximately 3.8% relative to the total incident power were measured. While lower than expected we expect with minor modifications system efficiencies beyond 75% will be achievable.

Optimized solar thermal concentrator system based on free-form trough reflector

A solar thermal concentrator system is proposed comprising a free-form-trough (FFT) reflector and a cylindrical heat-pipe receiver. The profile of the reflector is designed using a free-form surface creation (FFSC) method such that each incident ray is directed to a certain user-specified point on the heat-pipe surface. The light ray paths within the concentrator system are analyzed using a skew-ray tracing approach. A method is then proposed for optimizing the geometry of the concentrator system in such a way as to achieve a uniform irradiance distribution on the heat-pipe surface. The validity of the proposed optimization approach is demonstrated by means of ZEMAX/SolidWorks-Flow simulations. The results show that the proposed FFT concentrator yields a significant improvement in both the irradiance uniformity and the heating efficiency compared to conventional cylindrical-trough and parabolic-trough concentrators.

Heating residential water using parabolic trough concentrators: theoretical calculations and analysis

The present work concerns theoretical and case studies related to a new design of residential water heating using parabolic trough. To proceed, the thermal modelling of parabolic trough concentration and flat plate heat collection is drawn. Then, the case of Beirut city is considered to compare the performance of three different configurations of heating water: flat plate, parabolic trough and parabolic trough with tracking. It was shown that the enhancement of water heating using parabolic trough with respect to flat plate collector depends on the criterion of comparison. Particularly for the same volume occupied on the roof, the use of parabolic trough has shown to decrease the time of heating water to 70°C by 22.4% (a decrease from 52.2 h to 40.5 h) without tracking and 33% (a decrease from 52.2 h to 35 h) with tracking.

太阳能槽式系统接收器光学效率的特性研究

太阳能槽式系统接收器光学效率的特性研究

An algorithm for the flux distribution over the flat absorber of a parabolic trough concentrator

Based on the symmetries of the parabolic trough concentrating system and the solar radiation, a descending dimension algorithm has been developed with a computational complexity of O(N2), whereas that of the Monte Carlo ray tracing (MCRT) method and the finite element method are of O(N4) The formula of the energy function ψ(θ) for solar disk slice was constructed to solve the integration of the flux distribution. The numerical results indicated that the results obtained by the presented algorithm have a good agreement with results produced by MCRT, meanwhile CPU time requirement of the algorithm is about a few seconds, much shorter than that of MCRT. The formulas for calculating the number of reflections of ray tracing within a homogenizer and the exact coordinates of the landing location on the absorber of each ray are established from geometrical aspect. The effect of the homogenizer for flux density uniform is clearly characterized.

Experimental investigation of the bending of absorber tube of solar parabolic trough concentrator and comparison with analytical results

The distribution of the solar flux on the circumference of the absorber tube of the parabolic trough concentrator is non-uniform. It leads to circumferential non-uniformity in the tube temperature which causes bending and stresses in the absorber tube. Thus, the absorber tube gets deflected from the focal line of the trough which can damage the glass cover. In the current work, an experimental set-up has been described which is created to achieve a non-uniform distribution of the temperature on the circumference of the tube (using electrical heating) and to measure the corresponding deflection of the tube due to bending (in the vertical plane passing through the central axis of the tube). The deflection of the tube has also been calculated using analytical equations (derived in the previous work) and compared with the measurements. The results show that the analytical calculations differ from the measurements within the range of −0.26mm to +0.50mm (i.e. −15.4% to 16.9%). For the chosen tube dimensions and the maximum circumferential temperature difference of 30°C, the maximum deflection due to bending is 3.2mm. It decreases to 2.6mm for the maximum circumferential temperature difference of 22°C. The bending (due to circumferential temperature gradient) between 1st and 2nd support is downwards. Between 2nd and 3rd support, it is upwards. It is again downwards for the portion of the tube lying between 3rd and 4th support. The same trend of bending has been found out by analytical calculations.

Performance Evaluation of a Nanofluid-Based Direct Absorption Solar Collector with Parabolic Trough Concentrator.

Application of solar collectors for hot water supply, space heating, and cooling plays a significant role in reducing building energy consumption. For conventional solar collectors, solar radiation is absorbed by spectral selective coating on the collectors’ tube/plate wall. The poor durability of the coating can lead to an increased manufacturing cost and unreliability for a solar collector operated at a higher temperature. Therefore, a novel nanofluid-based direct absorption solar collector (NDASC) employing uncoated collector tubes has been proposed, and its operating characteristics for medium-temperature solar collection were theoretically and experimentally studied in this paper. CuO/oil nanofluid was prepared and used as working fluid of the NDASC. The heat-transfer mechanism of the NDASC with parabolic trough concentrator was theoretically evaluated and compared with a conventional indirect absorption solar collector (IASC). The theoretical analysis results suggested that the fluid’s temperature distribution in the NDASC was much more uniform than that in the IASC, and an enhanced collection efficiency could be achieved for the NDASC operated within a preferred working temperature range. To demonstrate the feasibility of the proposed NDASC, experimental performances of an NDASC and an IASC with the same parabolic trough concentrator were furthermore evaluated and comparatively discussed.

Conjugate heat transfer modeling and asymmetric characteristic analysis of the heat collecting element for a parabolic trough collector

We analyzed in this study the conjugate heat transfer process in the heat collecting element (HCE) for a parabolic trough concentrator. The effect of asymmetric characteristics, such as non-uniform heat flux, eccentric configuration, and incident angle, are especially considered in this paper. We constructed a two-dimensional model of surface radiative transfer coupled with convection using the finite volume method combined with the net radiation method. We presented a detailed numerical method in which we applied an additional source term method to the boundary conditions to capture the absorption and emission processes in the coating of the HCE. The results were validated against the experimental data. Thus, we were able to identify the limiting interactions between thermal radiation and convection in the annulus. We systematically analyzed the effect of the incident irradiation angle and the eccentricity of the configuration on heat loss through the annulus of the HCE under two limiting conditions: “air in annulus” and “vacuum in annulus”. The results show that asymmetric characteristics, especially the non-uniform heat flux and eccentricity configuration, have a significant influence on local heat transfer processes. These insights may be used to further optimize the configuration of the HCE for improved thermal performance.

Effect of number of supports on the bending of absorber tube of parabolic trough concentrator

The circumferential non-uniformity in the temperature of absorber tube of parabolic trough leads to bending of the tube. The absorber tube is considered to be equidistantly supported at various points along the length. An analytical expression is presented in the current work for finding the bending and the results are compared with the experimental measurements. Further, the effect of number of supports and spacing between them on the shape of bent tube is analyzed using analytical equations. It is found that, keeping spacing between adjacent supports fixed, as number of supports and length of tube increase, the maximum bending does not vary beyond a certain length of tube. For the chosen system (keeping spacing between adjacent supports as 4 m), the results show that if lengths of tubes are larger than 16 m, the maximum bending remains same. The shape of bent tube is symmetric around the mid length. For one half of the tube, the bending is towards the vertex line of trough for the portion lying between 1st and 2nd support. It is away from the vertex line for the portion lying between 2nd and 3rd support and so on up to the mid length of the tube.

USE OF SOLAR THERMAL PLANT WITH PARABOLIC TROUGH CONCENTRATORS FOR THE PURPOSE OF THE ENHANCED OIL RECOVERY PROCESS IN VENEZUELA

This article expounds an innovative technology for enhanced oil recovery (EOR) based on solar thermal plant. First of all the authors dwell on the problem of the replacement of conventional steam generators operating with fossil fuels by the solar field of parabolic trough concentrators. Then they discuss the impact of intermittent steam injection on overall efficiency of oil production, related to the cyclical nature of the incoming solar energy. Next they analyze the optical and thermal losses in parabolic trough concentrator. The purpose of this article is to show the possibility of using the vast potential of solar energy in Venezuela in order to produce steam with parabolic trough concentrator solar plant.

DETERMINATION OF PARAMETERS OF STEAM PRODUCTION SYSTEMS FOR OIL PRODUCTION USING SOLAR ENERGY FOR BACHAKERO'S REGION IN VENEZUELA

The article discusses the possibility of the use of solar energy technologies meeting the requirements of Steam Based Enhanced Oil Recovery and describes the methods of obtaining parameters of solar steam plant with parabolic trough concentrator considering day steam injection. In order to study standard oil deposit where is used continuous steam injection method in accordance with the solar radiation characteristic for the Bachaquero region of the Republic of Venezuela, the type and orientation of parabolic trough collector, the type and temperature of the working fluid were chosen, the total number of parabolic trough concentrators was calculated.

A study of the effect of design parameters on the performance of linear solar concentrator based thermal power plants in India

The sizing of a solar thermal power plant directly affects its cost and also the annual electricity output and hence its financial attractiveness. It involves deciding appropriate values of design DNI, solar multiple and hours of thermal storage to achieve high annual capacity utilization factor (CUF) with the least cost of electricity delivered. An analysis of the impact of these design parameters on the performance of parabolic trough concentrator (PTC) and linear Fresnel reflector (LFR) based solar thermal power plants is presented using System Advisor Model for eight locations in India. Annual electricity output is estimated using radiation data source of SEC-NREL. Levelized unit cost of electricity (LUCE) is estimated using benchmark capital cost and other financial conditions specified by the Central Electricity Regulatory Commission of Government of India. For a design DNI of 950 W/m2, LUCE is minimum in solar multiple range of 1.4–1.6 for PTC based plants and of 1.8–2.0 for LFR based plants. With a solar multiple of 1.0, LUCE is minimum in design DNI range of 550–700 W/m2 for PTC based plants and 450–550 W/m2 for LFR based plants.

Comparison of line focusing solar concentrator fields considering shading and blocking

The performance of line focusing solar collectors [Parabolic Trough Concentrator (PTC), Linear Fresnel Reflector (LFR) and Compact Linear Fresnel Reflector (CLFR)] is affected by many factors. Due to end effect, inter-row shading and blocking (for LFR and CLFR), the complete aperture of the collector cannot be utilized. Besides, the cosine effect, reflectivity of reflectors, intercept factor, transmissivity of receiver cover, absorptivity of absorber tube and thermal losses are the other major contributors to the energy losses. In the current work, PTC, LFR and CLFR fields are compared in terms of energy losses, net energy collection by fluid, electricity generation and cost of electricity. The ratio of collector aperture area to land area is named as land coverage ratio. The appropriate values of land coverage ratio are found out corresponding to minimum cost of electricity for different technologies. The corresponding annual energy collection by fluid and the annual electricity generation have also been calculated. It is seen that there is no significant difference in the performance of LFR and CLFR fields. For low values of receiver height to collector width ratio, the LFR field results in the largest levelised cost of electricity and the PTC field results in the lowest.

Performance Prediction of Solar Thermal Parabolic Trough Concentrator System (STPTCS) by Enhancement of Heat Transfer

Performance Prediction of Solar Thermal Parabolic Trough Concentrator System (STPTCS) by Enhancement of Heat Transfer