Parabolic Trough Mirror Research Articles

Parameter optimization of the parabolic solar trough mirror with a cavity receiver unit

In this article, we discuss design approaches to a receiver enclosed in an opaque cavity and heated by a solar parabolic trough collector. Most cavity receivers are only capable of receiving radiation through an aperture, or “cavity window”, at a very limited angle. This paper discusses how to optimize a realistic interaction of a cavity receiver with the solar radiation from a collector mirror, which presents challenges not found in conventional receivers and is vital in order to benefit from the advantages of using a cavity sleeve. We needed our mirror to minimize the focal line to allow passage of the concentrated solar radiation through the aperture window and used COMSOL Multiphysics simulation software to obtain the heat map of radiation incident on the absorber pipe. We proposed three different focal plane positions relative to the receiver and found their efficiency regimes via our own simulations. We also determined the relative sizes of the receiver elements. A focal plane close to the surface of the absorber pipe was the most efficient in our temperature range, with maximum efficiency at 62%. We built an experimental cavity receiver and parabolic trough system guided by our generic simulations. We validated the simulation of our experimental setup against the measured data and found a maximum discrepancy of 8%. We also applied a novel method using the cooling behavior of the receiver to confirm our physical parameters via simulations. The results of this paper illustrate a novel, systematic method for integrating a parabolic collector mirror with a cavity-type receiver in a generic way.

Parameter Optimization of the Parabolic Solar Trough Mirror with a Cavity Receiver Unit

Parameter Optimization of the Parabolic Solar Trough Mirror with a Cavity Receiver Unit

A tool to minimize the need of Monte Carlo ray tracing code for 3D finite volume modelling of a standard parabolic trough collector receiver under a realistic solar flux profile

AbstractThe energy collection element of a parabolic trough collector includes a selective coated metallic receiver tube inside an evacuated glass tube. Perpendicularly incident sun light on the parabolic trough mirror aperture is concentrated on the receiver tube highly nonuniformly along its circular direction. This solar energy is collected as thermal energy circulating a suitable heat transfer fluid (HTF) through the tube. This conjugate heat transfer phenomenon under nonuniform heat flux boundary condition is computationally studied applying 3D finite volume (FV) modelling technique of computational fluid dynamics coupled with Monte Carlo ray tracing (MCRT) optical data. The MCRT model simulates the actual flux profile around the receiver tube. Apart from a FV model, this coupled study requires expertise in, and access to, a suitable MCRT code. A combination of polynomial correlations and user‐defined function (UDF) is introduced in this article in order to minimize the need of MCRT codes from subsequent FV modelling of the receiver tube of the Luz Solar 2 (LS2) collector. The correlations are developed from a verified 3D MCRT model, which is equivalent to the local irradiation data as a function of receiver circular location. The UDF includes two algorithms: one to develop solar flux profile from the correlations around the receiver, and the other to calculate heat loss from the receiver. Interpreting the UDF into ANSYS Fluent, a 3D FV model of the LS2 receiver is developed and validated with experimental results. The effectiveness of the UDF as an alternative to MCRT code is verified. The FV model is capable to investigate the heat transfer characteristics of the LS2 collector receiver at different solar irradiation level, optical properties of the collector components, glass tube conditions, HTFs, inserts or swirl generators, collector length, and internal diameter of the tube.

Experimental and Theoretical Performance Evaluation of Parabolic trough Mirror as Solar Thermal Concentrator to Thermoelectric Generators

This paper presents the prospects of harnessing radiative heat from the sun with a parabolic trough mirror, as a solar thermal concentrator, in comparison to the mathematical model and experimental quartz-halogen concentrator model for the electrical energy conversion utilizing thermoelectric generators (TEG). The construction and design of TEG-setup along with Parabolic trough mirrors and quartz-halogen lamps are presented. The Parabolic trough mirror used as a focal point at a distance of 19.05 cm. With eight quartz-halogen concentrated heat, the maximum performance achieved at ?T of 11.8 K, Voc of 292 mV and Isc of 95.8 mA, recorded at the concentrated hot-side surface temperature of 317.8 K. When compared to the natural solar concentrated heat, higher temperature of 473.15 K at the hot-side surface temperature of TG was achieved. It is concluded that the heat concentration of the parabolic mirror increases with an increase in the intensity of heat using natural solar radiations. The Voc of 1.76 V and Isc of 1.1 A at a temperature difference of 110 K were measured, which are in good agreement with validated mathematical results. The parabolic through mirror utilized is smaller in size and thus collected lesser sun rays than the larger dish style mirror, and hence the heat in the focal point was very low, for better results, parabolic trough mirror with higher surface area would be important for future experiments.

Theoretical and Numerical Study of Solar Co-Generation Under Climatic Conditions in the Region (Rabat-Salé-Kénitra) of Morocco

In this paper, a numerical study of a new design for the solar co-generation system is presented. The process consists of integrating several solar cells with the Parabolic Trough Solar Concentrator (PTSC). The goal of the additional cells is to receive the lost sunlight reflected by the parabolic trough mirror. The hybrid model performance is then analyzed and monitored by the Software Matlab. The program based on the development of mathematical equations algorithm which characterized the efficiency of the two devices. These algorithms consist of the two basic designs. The first design is to simulate the thermal system and the second the distribution of solar cells on PTSC. The effectiveness of this proposed model was verified by using the DNI data within a year in the (Rabat-Salé-Kénitra) region in Morocco. The results obtained are related to voltage and energy produced by the new system. These results are examined and their quality compared to several published experimental measurements related to the performance of the two systems used. At all, they indicate a positive compatibility between numerical studies and experimental studies. Thus, these results clearly indicate a significant improvement in the efficiency for the solar co-generation system.

Thermoeconomic comparison of integrating seawater desalination processes in a concentrating solar power plant of 5 MWe

In this work a thermoeconomic analysis of the joint production of electricity and water for a simulated 5 MWe Solar Thermal Power Plant (STPP) based on parabolic trough mirrors and Direct Steam Generation (DSG) is carried out. The location considered for this plant is Almería, in southeast of Spain. Two different seawater technologies have been selected to be coupled with the STPP: Multi-Effect Distillation (MED) and Reverse Osmosis (RO). The Power Block (PB) has been designed to maximize the thermal efficiency, including regeneration and reheating. Four coupling arrangements have been investigated: the MED replacing the condenser of the PB, the MED being fed by one steam extraction of the PB, the RO directly using the electricity generated in the PB and the RO connected to the local grid. Results show that the best coupling option is with the RO unit being connected to the local grid, which produces the lower Levelized Water Cost (LWC).

Enclosed Solar Chimney Power Plants with Thermal Storage

The main problem associated with intermittent operation of the wind and PV power plants is the lack of low cost electrical storage methods. In the present paper a new type of solar chimney technology that we shall heretofore call “Enclosed Solar Chimney Power Plant technology (ESCP technology) stands for an effective alternative of combining both low cost electricity generation as well as smooth, uninterrupted operation for 24 hours/day and for all 365 days/year. The ESCP technology also has the following benefits in relation to PV technologies: 1) Local manufacturing and use of common material for their construction (steel, glass, concrete and conventional axial fans as air turbines); 2) Easy and low cost maintenance; 3) Longer operating life up to 50 years (its solar chimney up to 100 years); 4) No water consumption; 5) Zero effect on living nature and ambient; 6) Their empty protected surface area beneath the glassed roofs of their greenhouses can be used for desalination with parabolic trough mirrors.

The Simulation Model of Flux Density Distribution on an Absorber Tube

Abstract A parabolic trough collector (PTC) is an important component of parabolic trough solar thermal power generation system. The main purposes of calculating the flux density distribution are as follows: (1) the heat flux distribution on the absorber tube surface is a key boundary condition in the heat transfer performance analysis; (2) it can present a reference for design and optimization of PTCs, and make PTCs more cost effective. In this paper, coordinate transformations and Monte Carlo Ray Trace (MCRT) method are combined to simulate the circumferential flux distribution of absorber tubes. In the simulation process, non-parallelism of solar rays with cone optics, geometric concentrating ratio (GC), rim angle, transmittance of the glass tube, absorption of the absorber tube, reflectivity of the glass tube and reflectivity of the parabolic trough mirror are considered. The results show good agreement with references.

E242 太陽熱スターリングエンジン発電システムの基礎研究 : 集光方法の相違による集熱特性の比較検討(OS7 再生可能エネルギー(4))

Aiming at reduction of the energy consumed in domestic use, research of an energy system corresponding to ZEH (Zero Energy House) is advanced. The authors are developing a hybrid heat source Stirling engine CHP (combined heat and power) system, which uses solar and woody biomass for a heat source and supplies power generation and warm water. This paper describes a comparative examination of characteristics on heat collection by difference of solar concentration. Specifically, solar collectors made by a Fresnel lens and a parabolic trough mirror are compared, so that the Fresnel type is better than the trough type hi an absorbed heat efficiency.

Conversion of parabolic trough mirror shape results measured in different laboratory setups

Shape accuracy of mirror panels for parabolic trough solar collectors has a significant impact on the optical performance of the collectors in a solar power plant and is therefore carefully assessed by test laboratories and manufacturers. Relevant deformation is induced by gravity or mounting forces, so that shape accuracy data measured in different setups cannot be compared.This paper presents a method for conversion of shape measured in a vertical laboratory setup into data for a horizontal laboratory setup. Characteristic deformation matrices for parabolic trough mirror panels of RP3 geometry are determined by deflectometric shape measurements on various mirror panels and by validated finite element analyses (FEA).The resulting root mean square (rms) of measured slope deviation difference (i.e. the gravity induced deformation) between vertical and horizontal setup is on average 2.4mrad for inner mirrors and 1.25mrad for outer mirrors loosely positioned on a frame.Measured data from vertical setup, transformed by such characteristic deformation matrices into horizontal shape results, differ by less than 0.2mrad in rms slope deviation value from data measured in horizontal setup. Whereas the presented approach to convert shape accuracy measurement results is suitable for the calculation of rms values, some of the analyzed mirror samples show differences in local slope deviation values larger than the deflectometric measurement uncertainty. The amount of deviation depends on details of the accuracy of the positioning of the mirrors on the measurement frame and is affected by the fixation and associated mounting forces at the pads.

Blue Sky Cooling for Parabolic Trough Plants

At most locations with sufficient solar resources for a viable exploitation of solar power plants water is too precious to be wasted in cooling towers. However, application of air cooling increases the levelized cost of electricity up to 16%. An alternative for air cooling is radiation cooling. A new function is given to the parabolic trough mirror, which is the realization of optical contact between a radiating plane and the sky. The sky is cold, therefore the radiating plane cools down. This cooling is available day and night and can supply most of the cooling power that is needed for the condenser of the Rankine cycle. When there is wind, the radiating plane also dissipates heat. Radiation cooling and wind are sufficient for cooling the solar thermal power plant.Storage of cold in a water basin is an essential component, because wind cooling and radiation cooling are more effective at night, when the air temperature is low. Pumping the cold night-air through heat exchangers in the basin is an alternative when wind speeds are generally low.An additional function is given to the water basin, namely the support of a floating parabolic mirror field. A field of floating parabolic trough mirrors that are stationary with respect to each other rotates collectively around a vertical axis in order to follow the sun. We expect that this simple concept will lead to a substantial cost reduction, in spite of the less favorable average angular orientation of the mirrors. Floating parabolic trough fields are most suited for applying radiation cooling in solar power plants.

Analysis of Parabolic Trough Concentrator Mirror Shape Accuracy in different Measurement Setups

Mirror shape accuracy as a key optical performance parameter for parabolic trough collectors can be assessed accurately by common measurement systems proving the high quality of state-of-the-art mirror panels. However, measurement results cannot always be compared directly because critical boundary conditions are not yet standardized. This paper quantifies the differences in shape accuracy results between the most common measurement setups for parabolic trough mirror panels and identifies measurement position, mounting mode and support frame employed for the measurement as relevant boundary conditions.Deflectometric measurements of mirror panels of RP3 geometry were performed at DLR's QUARZ Center Cologne in vertical (mounting points vertically and curved direction horizontally aligned) and horizontal measurement position (mirrors facing upward with mounting points horizontally aligned), both with and without tightening the mirrors to a support frame with screws. Finite element models were applied to calculate gravity-induced deformation and resulting slope and focus deviation on three different types of support frame: an ideally rigid support frame, a laboratory support frame, and an ideal support frame with elastic brackets.The measurement results demonstrate that the difference in position and mounting mode can lead to relevant deviations of the shape accuracy results higher than the uncertainty of the employed deflectometric measurement system. For RP3 inner mirror panels a difference of up to 0.7 mrad in root mean square slope deviation (SDx) and 3.3mm in root mean square focus deviation (FDx) from vertical to horizontal position was measured. Mirror shape specifications may thus not be applicable in all positions. Concerning the mounting onto different types of modeled support frame (in horizontal position) a variation of 0.5 mrad (SDx) and 1.8mm (FDx) was calculated for perfectly shaped RP3 inner mirrors mounted onto an ideally rigid support frame compared to the case when mounted to a support frame with elastic brackets.

Towards a Commercial Parabolic Trough CSP System Using Air as Heat Transfer Fluid

We report on major design innovations related to the trough concentrator, solar receiver, and thermal storage of a parabolic trough CSP system. A 9.7 m aperture parabolic trough mirror is formed by inflated, metallized, polymeric films mounted on a rigid and durable concrete support structure. The novel receiver design, which uses air as the heat transfer fluid at ambient pressure, is based on an array of absorber cavities coupled to secondary concentrating optics for operating temperatures exceeding 600°C. The solar-heated air is directly fed to a thermal energy storage unit based on a packed bed of rocks to guarantee round-the-clock dispatchability of high-temperature heat to the power block. A commercial CSP plant with a projected peak thermal power output of 3.9 MWth is currently under construction in Ait Baha, Morocco.

Improving Optical Qualification of Solar Concentrator by FOCuS Tool

An improved tool for the shape qualification of parabolic trough mirror modules used in concentrated solar power plants was developed. The tool is based on the fringe reflection theory, in which sinusoidal fringe patterns are projected on a screen and their reflection over a specular surface is recorded by a camera. The observed distortions in the image are related directly to surface deviations from ideal geometry. Relevant aspects of the technique are its high spatial resolution (more than 1 million points per facet), short measurement time and easy setup. The so called FOCuS tool is capable of calculating the mirror slope deviations from its ideal design and the RMS value as a quality factor. Furthermore, the tool generates a file which can be loaded on CENER'S TONATIUH ray tracing software, through a specially developed plug-in, for mirror modeling and intercept factor calculation with several tube absorber geometries.

Improving parabolic trough mirror module qualification by FOCuS tool

An improved tool for the shape qualification of parabolic trough mirror modules used in concentrated solar power plants was developed. The tool is based on the fringe reflection theory, in which sinusoidal fringe patterns are projected on a screen and their reflection over a specular surface is recorded by a camera. The observed distortions in the image are related directly to surface deviations from ideal geometry. Relevant aspects of the technique are its high spatial resolution (more than 1 × 106 points per mirror facet), short measurement time and easy setup. The developed tool (called FOCuS) is capable of calculating the local mirror slope deviations from its ideal design and the RMS value as a quality factor. Furthermore, the tool generates a file which can be loaded into CENER's TONATIUH ray tracing software, through a specially developed plug-in, for mirror modeling and intercept factor calculation with several tube absorber geometries.

Evaluation of the Moroccan Power Grid Adequacy with Introduction of Concentrating Solar Power (CSP) Using Solar Tower and Parabolic Trough Mirrors Technology

The objective of this research work is to provide a effective assistance to all those who have to make decisions concerning the planning and implementation of projects in the renewable energy. Indeed, The integration in the Moroccan power grid of electrical power via Concentrating Solar Power (CSP) units using parabolic mirrors or solar tower is expected to have a significant impact on the reliability of the electrical system. In this context. Therefore, in this work, firstly, we assess the reliability of the Moroccan grid at hierarchical level HL1 (HL1: load covering under the assumption of infinite node) by use of a non-sequential Monte Carlo simulation in which CSP units (with parabolic through mirrors and with Solar tower) are introduced. Secondly objective of this paper is to assess the reliability of the Moroccan grid with an expected common integration of 14% wind and 14% solar energy.

Prospect of using alternative energy for power and desalted water productions in Kuwait

Extensive research is conducted in Kuwait to apply renewable energy (RE) for electric power (EP) generation. The Kuwaiti Ministry of Electricity and Water (MEW) formed a committee to study the introduction of solar energy to generate EP. Meanwhile, the government formed a committee to take the necessary steps to build the first nuclear power plant (NPP) for EP production and desalting seawater. This study addresses the technical and economical aspects of using NPP and RE in generating EP in Kuwait in comparison with presently used combined cycle stations which are operated with natural gas or oil fuel. The results of this study indicate that installing wind energy (WE) or solar cells photovoltaic solar cells (PV) power plant (PP) cannot be considered a capacity addition. Capacity addition is required to handle the ever increasing peak load. The WE and PV PPs are primarily fuel savers for the existing fossil fuel plants. The intermittent and the non-dispatchable nature of the WE and PV plants make them unable to generate consistent output like fuel-fired PPs. Their output should be taken by the grid and this decreases the load on the operating dispatchable PPs and thus reduces their fuel consumption. Among the thermal solar concentrating PP options (solar tower, solar dish with Stirling engine, and parabolic trough mirrors), the ones using parabolic trough are the only solar type PP that have reached commercial maturity with well-proven records of reliability and availability. This type of PP should be augmented with supplementary fossil fuel or thermal storage system to become a dispatch-able plant.

Modeling and optimization of hybrid solar thermoelectric systems with thermosyphons

► Proposed hybrid solar thermoelectric (HSTE) system using a thermosyphon for heat transfer to a bottoming cycle. ► Developed and optimized the HSTE model showing efficiencies as high as 52.6%. ► Comparable efficiency for low cost thermosyphons with k as low as 1.2 W/mK and C < 4 suns. ► Proposed five bottoming cycle applications for potential HSTE integration. We present the modeling and optimization of a new hybrid solar thermoelectric (HSTE) system which uses a thermosyphon to passively transfer heat to a bottoming cycle for various applications. A parabolic trough mirror concentrates solar energy onto a selective surface coated thermoelectric to produce electrical power. Meanwhile, a thermosyphon adjacent to the back side of the thermoelectric maintains the temperature of the cold junction and carries the remaining thermal energy to a bottoming cycle. Bismuth telluride, lead telluride, and silicon germanium thermoelectrics were studied with copper–water, stainless steel–mercury, and nickel–liquid potassium thermosyphon-working fluid combinations. An energy-based model of the HSTE system with a thermal resistance network was developed to determine overall performance. In addition, the HSTE system efficiency was investigated for temperatures of 300–1200 K, solar concentrations of 1–100 suns, and different thermosyphon and thermoelectric materials with a geometry resembling an evacuated tube solar collector. Optimizations of the HSTE show ideal system efficiencies as high as 52.6% can be achieved at solar concentrations of 100 suns and bottoming cycle temperatures of 776 K. For solar concentrations less than 4 suns, systems with thermosyphon wall thermal conductivities as low as 1.2 W/mK have comparable efficiencies to that of high conductivity material thermosyphons, i.e. copper, which suggests that lower cost materials including glass can be used. This work provides guidelines for the design, as well as the optimization and selection of thermoelectric and thermosyphon components for future high performance HSTE systems.

Practical Field Alignment of Parabolic Trough Solar Concentrators

In this paper a new technique for parabolic trough mirror alignment based on the use of an innovative theoretical overlay photographic (TOP) approach is described. The technique is a variation on methods used to align mirrors on parabolic dish systems. It involves overlaying theoretical images of the heat collection element (HCE) in the mirrors onto carefully surveyed photographic images and adjustment of mirror alignment until they match. From basic geometric principles, for any given viewer location the theoretical shape and location of the reflected HCE image in the aligned mirrors can be predicted. The TOP approach promises to be practical and straightforward, and inherently aligns the mirrors to the HCE. Alignment of an LS-2 mirror module on the rotating platform at the National Solar Thermal Test Facility (NSTTF) with the TOP technique along with how it might be implemented in a large solar field is described. Comparison of the TOP alignment to the distant observer approach on the NSTTF LS-2 is presented and the governing equations used to draw the theoretical overlays are developed. Alignment uncertainty associated with this technique is predicted to be less than the mirror slope error.

Characterisation of a 300× photovoltaic concentrator system with one-axis tracking

A solar concentrator with one-axis tracking is being developed at our institute. This concentrator system achieves a high geometrical concentration ratio of 300 using a parabolic trough mirror and a three-dimensional second stage consisting of compound parabolic concentrators. The design of the system as well as the characterisation of the second stage is described in this paper.