Parabolic Trough Solar Concentrator Research Articles

Effect of Angle of Incidence of Sun Rays on the Bending of Absorber Tube of Solar Parabolic Trough Concentrator

In a parabolic trough system, the solar flux distribution on the surface of absorber tube is non-uniform which results in circumferential temperature gradient. Thus, bending moment is induced and leads to the deflection in absorber tube from the focal line of trough. It is concluded that during zero angle of incidence of sun rays (angle made by sun rays with trough's aperture normal), absorber tube will not deflect from the focal line. However, during non-zero angle of incidence, the absorber tube will deflect. It is because of the fact that during non-zero angle of incidence, the absorber tube does not receive any concentrated flux near the end facing the sun. In the current work, an analytical expression is derived for finding the deflection in the central axis of absorber tube from the focal line of trough. Results for deflection are plotted for different values of angle of incidence taking the dimensions of LS3 parabolic trough with Schott 2008 PTR70 receiver.

Exergy and thermo-economic analysis of solar thermal cycles powered multi-stage flash desalination process

Solar thermal power cycles assisted multi-stage flash brine recycle (MSF-BR) distillation process are thermo-economically analyzed and evaluated. In this work, the analyses are compared according to three different configurations via two techniques of solar thermal power cycles. The first technique is considered for only desalination process; however, the second is considered for desalination and electric power generation via organic Rankine cycle. Solar parabolic trough concentrator (PTC) field is considered to dominate sufficient thermal power for MSF plant. Water steam working fluid is used for a direct vapor generation (DVG); however, Therminol-VP1 working substance is used for an indirect vapor generation (IDVG) through the PTC field. Moreover, the optimized configuration from the first technique is compared with the power generation and desalination (the second technique). The comparisons are proceeding for the MSF-BR desalination plant with total productivity in the range of 5,000m3/d which the gain ratio is increased up to 12 with 40 stages. The thermo-economic results reveal that first technique achieves remarkable results related to the PTC area, the SPC, kWh/m3, and the thermo-economic product cost, $/GJ.

Design Point for Predicting Year-Round Performance of Solar Parabolic Trough Concentrator Systems

Thermal efficiencies of the solar field of two different parabolic trough concentrator (PTC) systems are evaluated for a variety of operating conditions and geographical locations, using a detailed 3D heat transfer model. Results calculated at specific design points are compared to yearly average efficiencies determined using measured direct normal solar irradiance (DNI) data as well as an empirical correlation for DNI. It is shown that the most common choices of operating conditions at which solar field performance is evaluated, such as the equinox or the summer solstice, are inadequate for predicting the yearly average efficiency of the solar field. For a specific system and location, the different design point efficiencies vary significantly and differ by as much as 11.5% from the actual yearly average values. An alternative simple method is presented of determining a representative operating condition for solar fields through weighted averages of the incident solar radiation. For all tested PTC systems and locations, the efficiency of the solar field at the representative operating condition lies within 0.3% of the yearly average efficiency. Thus, with this procedure, it is possible to accurately predict year-round performance of PTC systems using a single design point, while saving computational effort. The importance of the design point is illustrated by an optimization study of the absorber tube diameter, where different choices of operating conditions result in different predicted optimum absorber diameters.

Analytical expression for circumferential and axial distribution of absorbed flux on a bent absorber tube of solar parabolic trough concentrator

A parabolic trough has a property to concentrate the incident rays at its focal line, when tracked appropriately. The flux distribution on the absorber tube is non-uniform. Part of the absorber’s periphery facing the sun receives direct incident rays where as part of the other side receives concentrated rays resulting in circumferential non-uniform flux distribution. The intensity of flux also varies along the length of the absorber tube, especially at the sun facing end, depending upon the incidence angle of the sun rays and rim angle of the parabolic cylinder. Such non-uniformity in the flux distribution on the absorber tube leads to non-uniform temperature distribution. Thus the absorber experiences thermal stresses which may lead to bending of the tube thereby creating risk of glass cover damage. In order to estimate the extent of bending, study of the flux distribution is needed. In the present work, expression for the absorbed flux on a bent absorber tube accounting circumferential and axial variations is analytically derived. Optical errors and Gaussian sun shape have also been incorporated. Results have been plotted to study the effect of bending, optical errors and rim angle of the trough on flux distribution.

Three-Dimensional Optical and Thermal Numerical Model of Solar Tubular Receivers in Parabolic Trough Concentrators

Monte Carlo ray tracing, coupled to a finite volume solver, is used to model 3D heat transfer in a parabolic trough solar concentrator system. The nonuniform distribution of the incident solar radiation, the radiative exchange between the various receiver surfaces, and the heat gain/loss around the receiver's circumference and along the system's axis are determined for spectral radiative properties of the receiver and concentrator surfaces. The computed heat losses and thermal efficiencies agree well with experimental data. Besides the beneficial information on peak temperatures and heat flux, the 3D model is able to predict glass temperatures more accurately than previous gray models and temperature correlations.

Design, construction, and testing of a parabolic trough solar concentrator for hot water and low enthalpy steam generation

This paper reports the design, construction, and evaluation of a solar parabolic trough concentrator (PTC) with a rim angle of 45°, a length of 4.88 m, and an aperture area of 5.8 m2. The PTC is made of aluminium in such a way that both the manufacturing and assembly processes do not require complicated technology or skilled labour. Since the PTC is for low enthalpy steam generation and hot water, it is designed with an unshielded receiver and without a glass cover in order to reduce both production and transportation costs. A finite element stress analysis is conducted to determine the mechanical behaviour of the PTC under various simulated wind loads on the structure. A simple solar tracking system is employed when it is oriented in a North-to-South direction. The optical efficiency of the collector is also reported. Said efficiency depends on the optical properties of the materials involved, the geometry of the collector, and the various imperfections arising from the construction of the collector. The thermal performance of the PTC was determined according to the Standard ASHRAE 93-1986 (RA 91). Peak efficiencies close to 60% were obtained.

Performance evaluation of v-trough solar concentrator for water desalination applications

The working principle and thermal performance of a new v-trough solar concentrator are presented in this paper. Compared with the common parabolic trough solar concentrators, the new concentrator has two parabolic troughs which form a V-shape with the focal line at the bottom of the troughs. This is beneficial for the installation and insulation of the receiver, and the shadow on the reflective surface is avoided. The new v-trough collector does not require high precision tracking devices and reflective material. And therefore the cost of the system could be significantly reduced. Various experimental tests were carried out both outdoor and indoor using different types of receiver tubes. The results show that the collector system can have thermal efficiency up to 38% at 100 °C operating temperature. System modelling was used to predict the rate of fresh water produced by four different solar collector systems which include both static and one-axis solar tracking technologies. Comparison of the solar collectors at different temperature ranges for humidification/dehumidification desalination process using specific air flow rate were considered. At each temperature range, suitable solar collectors were compared in the aspect of fresh water production and area of solar collector required. Results showed that the new v-trough solar collector is the most promising technology for small to medium scale solar powered water desalination.

Dynamic model of a solar thermochemical water-splitting reactor with integrated energy collection and storage

Water-splitting solar thermochemical cycles are important in meeting the challenges of global climate change and limited fossil fuels. However, solar radiation varies in availability, leading to unsteady state operation. We propose a solar receiver-reactor with integrated energy collection and storage. The reactor consists of a double-pipe heat exchanger placed at the focal line of a parabolic trough solar concentrator. Molten salt passes through the jacket, absorbing energy from the irradiated outer surface while driving the endothermic oxygen production step of the copper-chlorine water-splitting cycle in the reactor bore. Excess energy is stored in a thermal storage tank to buffer the reactor from changes in insolation. Dynamic simulation indicates that the reactor can sustain steady 100% conversion during 24/7 operation with a reasonable plant layout. The technology employed is extant and mature. This is important in view of the urgency to reduce dependency upon fossil fuels as primary energy sources.

Design, Construction and Testing of a Solar Adsorption Refrigerator Using Synthesised Zeolite A and Water as Adsorbent/Adsorbate Pair

This paper presents the design and construction of a simple Zeolite-water solar adsorption refrigeration system which has been fabricated and tested in the Department of Mechanical Engineering, Ahmadu Bello University, Zaria, Nigeria at a geographical location of latitude 11o11’’NE. The theory on which this design is based is on the use of Zeolite-water adsorbent/ adsorbate pair to produce refrigeration. The energy source is a parabolic trough solar concentrator that collects and radiates solar thermal energy onto an air tight black coated absorber (generator) charged with Zeolite and water placed at the trough’s focal point. The absorber adsorbs and desorbs the adsorbate and produces refrigeration as vapor is released through a condenser and an evaporator. Constructional details of the system show the systems height at 1.2 m, parabolic trough dimensions of 0.6m by 0.45m, the cold chamber, has a capacity of 36 liters. The system was evaluated by leaving it outside under solar radiation and monitoring temperatures at various points inside the collector, the generator, and the evaporator through the use of thermocouple sensors. The highest and lowest temperatures of the absorber were 60.1°C and 25°C respectively. The lowest refrigeration temperature of 9.8°C was attained with 179J of cooling.

Effect of porous disc receiver configurations on performance of solar parabolic trough concentrator

In this article, heat transfer enhancement of line focus solar collector with porous disc receiver is studied with water and therminol oil. A three dimensional (3-D) numerical simulation of porous disc enhanced receiver is carried out using commercial CFD software Fluent 6.3 to evolve the optimum configuration. The 3-D numerical model is solved by renormalization-group based k-e turbulent model associated with standard wall function. The effect of porous disc receiver configurations (solid disc at bottom; porous disc at bottom; porous disc at top; and alternative porous disc) on performance of the trough concentrator is investigated. The effect of porous disc geometric parameters (φ, θ, W, H and t) and fluid parameters (Pr and m) on heat transfer enhancement of the receiver is also studied. The numerical simulation results show that the flow pattern around the solid and porous discs are entirely different and it significantly influences the local heat transfer coefficient. The porous disc receiver experiences low pressure drop as compared to that of solid disc receiver due to less obstruction. The optimum configuration of porous disc receiver enhances the heat transfer rate of 221 W m−1 and 13.5% with pumping penalty of 0.014 W m−1 for water and for therminol oil-55, heat transfer rate enhances of 575 W m−1 and 31.4% with pumping penalty of 0.074 W m−1 as compared to that of tubular receiver at the mass flow rate of 0.5 kg s−1. The Nusselt number and friction factor correlations are proposed for porous disc receiver to calculate heat transfer characteristics. The porous disc receiver can be used to increase the performance of solar parabolic trough concentrator.

A 9-m-Aperture Solar Parabolic Trough Concentrator Based on a Multilayer Polymer Mirror Membrane Mounted on a Concrete Structure

A large-span solar parabolic trough concentrator is designed based on a multilayer polymer mirror membrane mounted on a rotatable concrete structure. The multilayer membrane is contained in a transparent protective air tube and generates a multicircular profile that approaches the trough parabolic shape. An analytical model of the mechanical behavior of the membrane mirror construction coupled to a Monte Carlo ray-tracing simulation is formulated and applied for design and optimization and for elucidating the influence of manufacturing and operational parameter variations on the radiative flux distribution. It is found that the parabolic shape can be well approximated with four stacked membranes that generate an arc-spline of four tangentially adjacent circular arcs. A 45-m-long 9-m-aperture full-scale prototype concentrator was fabricated and experimentation was carried out to validate the simulation model. Highest measured peak solar radiative flux concentration was 18.9, corresponding to 39% of the theoretical maximum value for an ideal parabolic trough concentrator.

Computer Modelling of Hybrid Solar Parabolic Trough Concentrator Systems—Electrical Part

This paper is to develop a mathematical model for hybrid solar parabolic trough concentrator (PTC) systems. The model is for estimation of energy outputs, losses and efficiencies of various parts of the system which operates under different climate condition, diverse configurations and a range of loading conditions. Automated system optimization can be quickly obtained by trying numerous different system configurations. In hybrid PTC system, photovoltaic cells are also installed on the receiver pipes. Solar energy is directly converted to electricity by photovoltaic cells. The working fluid circulating in the receiver pipes is for solar thermal purpose as well as to cool down the temperature of solar cells. The overall yield of the system is increased and therefore capital cost is reduced. A detailed analytical model simulating a hybrid PTC system has been developed by modelling and integrating sub-components into one model and a simulation software has been developed. The software is a valuable design tools for engineers whenever they are designing hybrid PTC systems, which are likely feasible in application to densely populated city with sub-tropical climatic conditions in southern part of China. System performance has been tested with a set of initial parameters and preliminary results have been produced.

A new trough solar concentrator and its performance analysis

The operation principle and design method of a new trough solar concentrator is presented in this paper. Some important design parameters about the concentrator are analyzed and optimized. Their magnitude ranges are given. Some characteristic parameters about the concentrator are compared with that of the conventional parabolic trough solar concentrator. The factors having influence on the performance of the unit are discussed. It is indicated through the analysis that the new trough solar concentrator can actualize reflection focusing for the sun light using multiple curved surface compound method. It also has the advantages of improving the work performance and environment of high-temperature solar absorber and enhancing the configuration intensity of the reflection surface.

Use of flat plate solar collectors and parabolic trough concentrators for greenhouse soil disinfestation

The aim of the present work was to investigate the use of low and medium temperature active solar energy systems for the disinfestation of greenhouse soils. Four flat plate solar collectors (low-temperature solar thermal energy devices) and six parabolic trough concentrators (medium-temperature solar thermal energy devices) were used to heat water, which, via a buried heat exchange system, was used to heat the soil of greenhouse plots. These treatments were compared to no solar (control) and solarized (using a 50 micro m-thick transparent polyethylene sheet) plots. Experiments performed in the summers of 2004 and 2005 showed that: 1) the temperatures reached and the energy accumulated in the soil - and therefore the disinfestation capacity - were greater with either of the active solar treatments (40-60 deg C and 10.222.438-18.102.054 J, respectively) than with solarization (< 40 deg C and 6.628.760 J, respectively) and 2) the temperatures reached using the parabolic trough concentrators (50-60 deg C) were higher than those achieved with the flat plate solar collectors (40-50 deg C). The soil temperatures reached suggest these systems could be used to disinfest greenhouse soils.

Prospectives for China's solar thermal power technology development

China's total installed electrical power capacity reached 700 GW by the end of 2007 and is predicted to surpass 900 GW in 2010. The rapid increase in energy demand and increasing global warming have both pushed China to change its current electrical power structure where coal power accounts for nearly 75% of the total electric power generation. China has already become the world's largest solar water heater producer and user. However, there is still much to be done in the solar thermal power field before its commercialization. Solar thermal power technologies including solar power towers, solar parabolic trough concentrators, solar dish/stirling systems, linear Fresnel reflectors, and solar chimneys have been studied in China since the 1980s. A 10 kW dish/stirling project was funded by the Ministry of Science and Technology (MOST) during 2000–2005 with a 1 MW solar power tower and research of trough concentrator metal–glass evacuated tubes supported during 2006–2010. This paper describes a continued solar thermal power development roadmap in China in 5-year intervals between 2006 and 2025.

Numerical Investigation of Energy-Efficient Receiver for Solar Parabolic Trough Concentrator

In this paper, a thermal analysis of an energy-efficient receiver for solar parabolic trough concentrator is presented. Various porous receiver geometries are considered for the performance evaluation of a solar parabolic trough concentrator. Numerical models are proposed for a porous energy-efficient receiver for internal heat gain characteristics and heat loss due to natural convection. The internal flow and heat transfer analysis is carried out based on a RNG k-ϵ turbulent model, whereas external heat losses are treated as a laminar natural convection model. The numerical models have been solved using the commercial engineering package, FLUENT. The thermal analysis of the receiver is carried out for various geometrical parameters, such as fin aspect ratio, thickness, and porosity, for different heat flux conditions. The inclusion of porous inserts in tubular receiver of solar trough concentrator enhanced the heat transfer about 17.5% with a pressure penalty of 2 kPa. The Nusselt number correlation is proposed based on the extensive numerical data for internal heat transfer inside the receiver. The proposed model is compared with more well-known natural convection models. A comparative study is carried out with different porous geometries to evolve an optimum configuration of energy-efficient receivers.

Optimal Heat Collection Element Shapes for Parabolic Trough Concentrators

For nearly 150years, the cross section of the heat collection tubes used at the focus of parabolic trough solar concentrators has been circular. This type of tube is obviously simple and easily fabricated, but it is not optimal. It is shown in this article that the optimal shape, assuming a perfect parabolic figure for the concentrating mirror, is instead oblong and is approximately given by a pair of facing parabolic segments.

Numerical Study of Porous Finned Receiver for Solar Parabolic Trough Concentrator

In this article a new receiver for parabolic trough concentrator is proposed to enhance heat transfer. A 3-D numerical model is developed to evaluate the performance of the receiver with various configurations of porous inserts of square, triangular, trapezoidal and circular shapes. The model is solved by k-ε RNG with standard wall function approach using the CFD package FLUENT. The performance of the receiver is investigated under various solar radiation and heat loss conditions. The effect of porous fin geometry on heat transfer characteristics and pressure drop is studied. The trapezoidal fin receiver with a tip-to-base ratio (λ) = 0.25 showed better performance than other receiver configurations. The trapezoidal porous inserts in the tubular receiver of the solar trough concentrator enhanced the heat transfer for about 13.8% at a fluid mass flow rate of 6.4 kg/s with only 1.7 kPa of pressure penalty.

Experimental and theoretical study of a solar desalination system located in Cairo, Egypt

The experimental and theoretical study of a solar desalination system located in Cairo, Egypt, is presented in this research. A modification unit is provided to enhance the performance of the solar desalination. The modification unit includes a solar parabolic trough (solar energy concentrator) with focal pipe and simple heat exchanger (serpentine) Oil is selected as working fluid. Oil is flowing as cycle through the focal pipe and serpentine. Oil has high thermal properties. The modification unit is utilized during sun duration and night. The oil in the heat exchanger is heated during the sunlight by two purposes, direct solar radiation and solar energy concentrator (solar parabolic trough). The parabolic trough is tracking the sun using simple mechanism to collect the highest amount of solar radiation by optimum angle. The trough is covered with transparent plastic sheet to avoid the heat transfer by convection to the surrounding (i.e. the green house effect is utilized). Copper serpentine of the heat exchanger is painted by Black color and is installed in the bottom of the still basin. It is attached extremely with thermally insulated pipelines through the trough. The oil is forced flow using small pump which may be powered by PV system. The saline water is heated directly by solar radiation and also, by the oil in the heat exchanger as the oil cycle. The thermal analysis of the proposed solar desalination system is expressed using the energy balance equations for different components of the system. The performance curve of the pump and the characteristics of the motor are illustrated. The overall efficiency of the proposed system is computed. Two experiments are carried out at April and June 2005. Type-K thermocouples (±0.5°C), digital temperature devise and remote control unit are used for measuring the system temperature points. The forecast of the typical climatic conditions of the experimental Cairo site at the selected days are obtained from the “Egyptian Solar Radiation Atlas” of the Geophysical Institute. The comparison between the performance of the conventional and the modified solar desalination systems is presented. The economic study of the present system is determined. The results show that fresh water productivity is increased by an average of 18%, due to the modification.

Structural Design Criteria for Steel Components of Parabolic-Trough Solar Concentrators

Starting from the R&D experience acquired, within the Italian context, in the field of the development of new technologies for solar energy exploitation, structural design criteria have been selected here to define a guideline for steel structures design and assessment of components of parabolic-trough solar concentrators. The main codes of practice used in Italy and in the European community have been considered and design criteria chosen to find a compromise between requirements of rules that should be followed precisely and costs. Loads, actions, and more generally, the whole design procedure has been considered in agreement with the limit state method; a new approach is critically and carefully proposed to use this method in designing and testing “special structures,” such as the one analyzed here (e.g., wind and snow actions are evaluated and newly interpreted according to both the angular position of the collectors and the characteristic effects). A method for evaluating variable loads is proposed to integrate current Italian and European rules, and a dimensional reduction for some elements due to the limit state design approach is underlined.