Concentrated Solar Collector Research Articles

Fabrication, spectral properties and thermal stability of AlCrON solar selective absorbing coating

Highly efficient AlCrON solar selective coating has been deposited experimentally by reactive dc magnetron sputtering and heat treatment at 300°C for 2 h in air. The coating consists of an IR-reflective metallic layer, an absorption bilayer and an anti-reflection layer from substrate to top. The IR-reflective metallic layer is Al. The absorption bilayer consists of a high metal volume fraction AlCr–AlCrON cermet sublayer and a low metal volume fraction AlCr–AlCrON cermet sublayer. The anti-reflection layer is AlON. The spectral properties and thermal stability of the as synthesised AlCrON coatings were characterised, respectively. The new coating exhibits a high solar absorptance (α) of 0·926 and a low thermal emittance (ϵ) of 0·065. In addition, after heat treatment at 300°C for 500 h in air, the spectral properties of the AlCrON coating are virtually unchanged. The results indicate that the AlCrON coating has good spectral properties and thermal stability, which will be a good solar selective absorbing coating for mid-temperature concentrated solar thermal collector.

Optical and thermal characterization procedure for a variable geometry concentrator: A standard approach

Concentrating solar collectors are mentioned in the International Standards, but the general testing methods for solar collectors mentioned cannot easily be applied to such unusual collector designs. In this study, the best optical and thermal model for a variable geometry solar concentrator has been investigated. In the particular case of a collector with a fixed mirror concentrator, the relative position of the receiver with respect to the reflector is not constant during the day, and this variable geometry is not taken into account in the current testing Standards. An optical characterization of the prototype using a ray-tracing program has been performed, and the results have been used as an initial hypothesis to define two thermal models adapted from the European Standard. Those two different models have been compared. The optical results obtained from experiments have been compared to ray-tracing simulation results, and they have been found to be quite similar, considering the measurement uncertainties. This validation procedure of the optical simulation could be an important point to be taken into account in a future Standard revision for variable geometry collector types for which the normal incidence is not easy to obtain.

Quantifying Optical Loss Factors of Small Linear Concentrating Collectors for Process Heat Application

Concentrating solar collectors such as small Parabolic Troughs and Linear Fresnel Collectors are well suited to generate industrial process heat in the medium temperature range between 150°C and 300°C. For detailed optical yield simulations and performance evaluation of process heat applications state of the art assumptions and model simplifications (e.g. models for incidence angle modifier and end losses) are analyzed and compared to exact ray tracing results. An approach towards an optical model and exemplary values for geometrical optical losses and materials are presented. Optical loss factors are quantified and a corrective function is proposed for end loss modeling. The main focus of the paper lies on the analysis of Linear Fresnel Collectors.

Thermal Performance Testing of Heat Pipe Evacuated Tube with Compound Parabolic Concentrating Solar Collector by ISO 9806 - 1

Solar collector is an important component of solar hot water system. The purpose of this research is design, fabricate and test thermal efficiency of the heat pipe evacuated tube with compound parabolic concentrating (CPC) solar collector. The advantage of this system is it produces hot water over a period of time without adjusting the direction of the CPC to track the sun. The thermal performance of solar collector is critically important for the end users in order to ensure the efficiency of the system. The testing of CPC according to ISO 9806 - 1 found that the thermal efficiency was equal to 78%. The heat loss coefficient of the solar collector a1 and a2 are equal to 3.55 and 0.06 W/m2-oC respectively. The mathematical model was developed to determine the energy production base on solar radiation and ambient temperature data of Phitsanulok province. It was found that the monthly average energy of the CPC produced throughout the year is equal to 286.16 kWh or equal to 3,433.87 kWh/year.

Solar cooling with water–ammonia absorption chillers and concentrating solar collector – Operational experience

Concentrating solar collectors provide high efficiency at high driving temperatures favourable for thermally driven chillers. Therefore, they offer applications for hot climates and industrial process integration, especially in combination with NH3–H2O chillers that provide refrigeration temperatures below 0 °C. The presented solar cooling installation comprises a linear concentrating Fresnel collector that provides the driving heat for two NH3–H2O absorption chillers at temperatures up to 200 °C. Chilled water temperatures are produced in the range between −12 °C and 0 °C. Collector capacities reached up to 70 kW at peak times and the total cooling capacity of both chillers showed peak values up to 25 kW. For good operating conditions, the thermal system EER was 0.8 and an electrical system EER of 12 was easily achieved. The system showed a sound operating behaviour. The performance of different operation and control strategies was analysed, evaluated and enhanced within the two year operation phase.

Development and evaluation of a prototype concentrating solar collector with thermocline based thermal energy storage for residential thermal usage

A prototype of a concentrating solar collector (CSC) receiver was designed, built, and evaluated on-sun at the University of Texas at El Paso in El Paso, TX. This prototype receiver consists of two parabolic trough-reflectors but, in principle, the design can be efficiently extended to multiple units for achieving a higher temperature throughput. Each reflector has a vacuum tube collector at the focal point of the trough. The solar collector system was combined with a single-tank thermocline thermal energy storage (TES) for off-solar thermal usage. The main goal of this study is to develop an advanced solar hot water system for most residential applications. The focus of this study is to investigate the feasibility and performance of the solar thermal system by employing the recent advancement in the TES—a thermocline based TES—system for the concentrating solar power technologies developed by the Sandia National Laboratories and National Renewable Energy Laboratories for electricity production. A CSC when combined with TES has potential to provide uninterrupted thermal energy for most residential usages. This paper presents a detailed description of prototype design and materials required. The thermal energy storage tank utilizes an insulated 170 l (45 gal) galvanized steel tank. In order to maintain thermocline in the TES tank, with hot water on top and cold water at the bottom, two plate distributors are installed in the tank. The data showed a significant enhancement in thermal energy generation. This thermocline based single tank presented a thermal energy storage potential for at least three days (with diminishing storage capacity) that test were performed. The whole prototype was made for approximately USD 355 (excludes any labor costs) and hence also has strong potential for supplying clean thermal energy in most developing countries. Tests of the prototype were conducted in November 2011.

Hybrid of solar dish concentrator, new boiler and simple solar collector for brackish water desalination

This work presents a design and installation of solar dish concentrator (SDC), simple solar collector and modified boiler for brackish water desalination. The design of two axes tracking system is performed using an open-loop control based on programmable logic controllers (PLC). Glass mirrors are used as reflective surface for dish concentrator. A coiled black rubber hose is used to preheat brackish water before feeding to the boiler. A mini single slope-air tight solar still is designed and installed at the focus of dish concentrator which is used as a boiler. The automatic tracking system, new boiler design; and with and without preheating of brackish water are investigated. The developed desalination system is evaluated and compared with the conventional solar still (CSS). The results indicated that, the daily average of distillate water was 6.7l/m2/day for SDC with preheating of brackish water, while the distillate productivity was 1.5l/0.5m2/day for CSS. In the present study, the daily average efficiency of SDC and CSS was 68 and 34%, respectively. The increase in distillate production for SDC is about 244% and 347% higher than that of CSS without and with preheating, respectively.

Error analysis for concentrated solar collectors

Error sources introduced into mirror tracking systems, arising from component limitations, construction and placement of the reflectors, and the discrete motion of the tracking system itself, are examined. The main mechanisms contributing to these sources are identified and modeled. The effect of these optical and geometrical errors is numerically simulated using a ray-tracing code and their relative significance is assessed.

A new modelling method and unified code with MCRT for concentrating solar collectors and its applications

The main objective of the present work is to develop a general-purpose numerical method for improving design/simulation tools for the concentrating solar collectors (CSCs) of concentrated solar power (CSP) systems. A new modelling method and homemade unified code with the Monte Carlo Ray-Trace (MCRT) method for the CSCs are presented firstly. The details of the new designing method and homemade unified code with MCRT for numerical investigations on solar concentrating and collecting characteristics of the CSCs are introduced. Three coordinate systems are used in the MCRT program and can be totally independent from each other. Solar radiation in participating medium and/or non-participating medium can be taken into account simultaneously or dividedly in the simulation. The criteria of data processing and method/code checking are also proposed in detail. Finally the proposed method and code are applied to simulate and analyze the involuted photo-thermal conversion processes in three typical CSCs. The results show that the proposed method and model are reliable to simulate various types of CSCs.

Rancang Bangun Sistem Kontrol Mekanisme Pelacakan Matahari Beserta Fasilitas Telekontrol Hemat Energi

Solar energy produced by concentrated solar heat collector panels requires tracking mechanisms for a more optimal direction. This paper presents the design and construction of a low energy solar tracking control system with telecontrol facilities. To accelerate the movement of the panel in always adjusting itself to the direction of the sun, a combination of the timer and light sensor was used. In this control system, the reference signal is taken from two pieces of light sensors while the feedback is taken from the position and temperature sensors. The program has been developed using C language and was implemented on the microcontroller ATMega8535 as the brain of the system. Telecontrol facilities for monitoring the data to a computer uses transceiver modules via RS-232 connection. A DC motor having power capacity of 0.74 watts was used and was clutched with 1:7,300 gearbox ratio. Experiments on light sensor characteristics and simulated movement of the panel were carried out. From the light sensor experiment it can be concluded that the sensor produces 0-4 volt output signal when bright 3.3-3.9 volts, when cloudy and 1.5-3.3 volts when sunny. From the simulation of panel movement, it is known that the solar tracking control system moves the panel and tracks the direction of the sun movement.

Performance evaluation of parabolic dish type solar collector for industrial heating application

From Indian perspective there is a large potential available for low cost solar water heating systems. The described system can instantly fulfil needs of hot water in industrial sector. This type of system can be used for heating boiler feed water, laundry applications and other steam generation applications. In general, concentrated solar collectors have high efficiency as compared to flat plate and evacuated tube solar collectors. Therefore, for water heating application, high efficiency can be achieved. Authors used parabolic dish collector for instant water heating application. This paper reveals prototype design of solar parabolic dish collector with truncated cone shaped helical coiled receiver made up of copper and coated with nickel chrome at focal point. Instantaneous efficiency of 63.9% has been achieved with the system explained in this paper. This prototype has been evaluated for its performance during month of April and May 2010 at Shivaji University, Kolhapur, Maharashtra, India [Latitude: 16.42° North, Longitude: 74.13° West].

양축 추적제어에 의한 고효율 태양열 발전시스템의 개발

Recently, interest in renewable energy is increased due to exhaustion of fossil fuel and environmental pollution all over the world, therefore the solar power generation using solar energy is many researched. The solar power generation is required solar tracking control and high concentration solar thermal collector because generation performance is depended on concentrator efficiency. This paper proposes high efficiency solar power generation with two-axis tracking control using dish-type solar thermal collector that has excellent thermal collector performance and tracking algorithm that can be accurately tracked solar position. This paper proves validity through analysis with accuracy of tracking algorithm and generating efficiency.

Roof Integrated Mini-Parabolic Solar Collectors. Comparison Between Simulation and Experimental Results

Concentrating solar collectors systems and especially the mini Parabolic solar reflecting systems have been one of the main research topics due to their ability for integration into the building structure. In the present work the mini parabolic collector was considered in the East - West orientation with such a slope so that the suns vector impinging nor- mal to the parabola during the day. The behavior of the thermal efficiency for various values of small concentrating ratios and mass flow rate was studied. Data input such as solar radiation (direct and diffuse) and temperature ambient were ob- tained by the meteorological station of R.E.S. Laboratory in the Technological Educational Institute of Patras. The fluid inlet and outlet temperatures in the absorber, the total solar radiation incident on the aperture surface, the ambient tem- perature and the fluid flow measurements were managed using a data logging system. The paper presents a comparison between theoretical and experimental results.

Solar Rankine Cycle System Using Scroll Expander

A unique solar thermal electric system is proposed and tested in the present study. In this system, an organic working fluid, which is suitable for a temperature range appropriate for solar energy, is adopted. We call this system as “solar organic Rankine cycle system” (SORCS). In order to improve the thermal efficiency by using solar energy, a displacement-type scroll expander and compound parabolic concentrator (CPC) solar collector are used. This system consists of very simple components that are similar to the ones used in an air conditioner and is very cost effective. The present paper reports on the experimental results of the scroll expander unit and the practical operation of the proposed SORCS under actual solar radiation input. The total thermal efficiency of the present SORCS attains 7% (42% when cooling water is used for the cogeneration system).

Advanced 3‐D CPC solar collector for thermal electric system

AbstractIn 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

Micro 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). The proposed 3-D CPC collector has a moderate concentration ratio and does not need tracking. First, the tentative 3-D CPC collector was fabricated and its thermal performance and principal characteristics were clarified. Next, numerical simulations of the optical characteristics of the 3-D CPC collector were carried out with the ray-tracing method. Finally, the specification of the optimal 3-D CPC collector will be shown.

Solar desalination using humidification–dehumidification processes. Part II. An experimental investigation

An experimental investigation of a humidification–dehumidification desalination (HDD) process using solar energy at the weather conditions of Suez City, Egypt, is presented. A test rig is designed and constructed to conduct this investigation under different environmental and operating conditions. The test rig consists of a solar water heater (concentrator solar collector type), solar air heater (flat plate solar collector type), humidifier tower and dehumidifier exchanger. Different variables are examined including the feed water flow rate, the air flow rate, the cooling water flow rate in the dehumidifier and the weather conditions. Comparisons between the experimental results and other published results are presented. It is found that the results of the developed mathematical model by the same authors are in good agreement with the experimental results. The tested results show that the productivity of the system is strongly affected by the saline water temperature at the inlet to the humidifier, dehumidifier cooling water flow rate, air flow rate and solar intensity. The wind speed and ambient temperature variation were found to have a very small effect on the system productivity. A general correlation is developed to predict the unit productivity under different operating conditions. The results of this correlation have a reasonable confidence level (maximum error ±6%).

Solar sorption refrigerator using a CPC collector

A prototype Compound Parabolic Concentrating (CPC) solar energy collector for a sorption refrigerator is presented. It consists of two CPC reflectors, two absorbers and a single glazing cover. The absorber is made with seamless steel tube covered in a selective surface (absorptance: 0.95) and contains aluminium fins, activated carbon and ammonia. The parabolas are manufactured from aluminium foil and a reflective microfilm is bonded on its surfaces to provide high solar reflectance (0.95). The concentration ratio of the collector is about 2.4 and corresponds to an incidence half angle of 25°. A numerical model of the absorber is described. Simulations with a daily solar radiation corresponding to tropical areas are presented.

Optimization of the tubular absorber using a compound parabolic concentrator

The paper deals with the optimization of the tubular absorber of a compound parabolic concentrator (CPC) solar collector. In order to minimize the radiation thermal losses from the absorber, a modified absorber with multi-cavities is proposed. The cavities are introduced at the circumferential area with relatively high solar intensities. These areas were determined by the use of a ray-tracing technique. This has been adopted using the AutoCAD ® package. The analysis was carried out and applied to a CPC with an acceptance angle of 10 and a concentration ratio of × 4.0.

Solar distillation systems: The state-of-the-art in design development and performance analysis

A review of recent research that has been undertaken on the design and development of various solar distillation systems is reported. A techno-economic analysis is carried out to measure the cost of effectiveness of various distillation systems. Novel designs of solar distillation systems utilizing the basic geometry of an inverted absorber assymetric line axis Compound Parabolic Concentrating (CPC) solar energy collector are reported. It is envisaged that these distillation systems will be more efficient due to the higher temperatures available at the absorbing surface and lower temperatures at the condensing surface.