Modelling of parabolic trough direct steam generation solar collectors

Solar electric generation systems (SEGS) currently in operation are based on parabolic trough solar collectors using synthetic oil heat transfer fluid in the collector loop to transfer thermal energy to a Rankine cycle turbine via a heat exchanger. To improve performance and reduce costs direct steam generation in the collector has been proposed. In this paper the efficiency of parabolic trough collectors is determined for operation with synthetic oil (current SEGS plants) and water (future proposal) as the working fluids. The thermal performance of a trough collector using Syltherm 800 oil as the working fluid has been measured at Sandia National Laboratory and is used in this study to develop a model of the thermal losses from the collector. The model is based on absorber wall temperature rather than fluid bulk temperature so it can be used to predict the performance of the collector with any working fluid. The effects of absorber emissivity and internal working fluid convection effects are evaluated. An efficiency equation for trough collectors is developed and used in a simulation model to evaluate the performance of direct steam generation collectors for different radiation conditions and different absorber tube sizes. Phase change in the direct steam generation collector is accounted for by separate analysis of the liquid, boiling and dry steam zones.     

Comparative thermal performance evaluation of an active solar distillation system

In this paper, thermal models of all types of solar collector‐integrated active solar stills are developed based on basic energy balance equations in terms of inner and outer glass temperatures. In this paper, hourly yield, hourly exergy efficiency, and hourly overall thermal efficiency of active solar stills are evaluated for 0.05 m water depth. All numerical computations had been performed for a typical day in the month of 07 December 2005 for the climatic conditions of New Delhi (28°35′N, 77°12′E, 216 m above MSL). The thermal model of flat‐plate collector integrated with active solar still was validated using the experimental test set‐up results. Total daily yield from active solar still integrated with evacuated tube collector with heat pipe is 4.24 kg m^?2 day^?1, maximum among all other types of active solar stills. Copyright © 2007 John Wiley & Sons, Ltd.     

Thermo-economic analysis of solar thermal power cycles assisted MED-VC (multi effect distillation-vapor compression) desalination processes

Solar power assisted different techniques of MED-VC (multi effect distillation-vapor compression) processes is thermo-economically analyzed and evaluated. In this work, two techniques of solar power cycles are considered to power on MED-PF-TVC, MVC (multi effect distillation thermal and mechanical vapor compressions). In the first technique, the developed solar thermal power is directly transmitted from the solar collector field via boiler heat exchanger unit toward the steam ejector of the MED-PF-TVC process. In the second technique, the electrical power generated from the SORC (Solar Organic Rankine Cycle) is used to power on the vapor compressor of the MED-PF-MVC process. The comparison is implemented according to the operation of PTC (parabolic trough collector) with Toluene organic oil and Water working fluids (2nd technique). Therminol-VP1 HTO (Heat Transfer Oil) is considered across the solar field and water is considered for boiler heat exchanger (1st technique). A case study is performed according to 4545 m³/day of distillate product. As a result, reducing the value of compression ratio with increasing the evaporator’s numbers would reduce the specific power consumption, solar field area, and thermo-economic costs. Also it is clear that the operation of steam ejector would increase the gain ratio instead of increasing the evaporator’s numbers.     

An optimal design analysis of a novel parabolic trough lighting and thermal system

In order to reduce the cost and improve the efficiency of daylighting, an innovative parabolic trough solar lighting and thermal (PTL/T) system is designed and analyzed in this paper. Parabolic trough solar lighting and thermal system uses parabolic trough collector (PTC) controlled by two‐axis solar tracking system as solar collector. The collected sunlight is split by a cold mirror into visible light and infrared. The visible light is reflected by cold mirror, re‐concentrated by a second‐stage Fresnel lens, and then delivered by plastic optical fiber to the buildings for daylighting. The infrared goes through cold mirror, reaches thermal system, and is used for heating generation. The basic structure of PTL/T was outlined and described. The dimension of fiber bundle and parabolic trough was chosen after an optimal analysis. The cost of illuminating unit area was expressed as a function of illumination space dimensions and critical components efficiency. A case study was conducted to get a specific optimized illumination area and PTC area for the first time. The optimized result is to use 8‐m² PTC as collector to illuminate 500‐m² office space. The total solar energy utilization efficiency is 39.4%, with the lighting efficiency of 16.3% and thermal efficiency of 23.1%. The maximum energy savings and simple payback period were calculated for 10 typical cities when applied in residential, commercial, and industrial sectors. The amounts of greenhouse gas‐emission reductions were also calculated. The payback period in Sunbelt region is as low as less than 10 years like in Los Angeles. The results show the proposed PTL/T system is competitive compared with traditional solar energy systems. Copyright © 2016 John Wiley & Sons, Ltd.     

Comparative performance analysis of solar powered supercritical-transcritical CO2 based systems for hydrogen production and multigeneration

CO₂ based power and refrigeration cycles have been developed and analyzed in different existing studies. However, the development of a CO₂ based comprehensive energy system and its performance analysis have not been considered. In this study, the integration of a CO₂ based solar parabolic trough collector system, a supercritical CO₂ power cycle, a transcritical CO₂ power cycle, and a CO₂ based cascade refrigeration system for hydrogen production and multigeneration purpose is analyzed thermodynamically. This study aims to analyze and compare the difference in the thermodynamic performance of comprehensive energy systems when CO₂ is used as the working fluid in all the cycles with a system that uses other working fluids. Therefore, two comprehensive energy systems with the same number of subsystems are designed to justify the comparison. The second comprehensive energy system uses liquid potassium instead of CO₂ as a working fluid in the solar parabolic trough collector and a steam cycle is used to replace the transcritical CO₂ power cycle. Results of the energy and exergy performance analysis of two comprehensive energy systems showed that the two systems can be used for the multigeneration purpose. However, the use of a steam cycle and potassium-based solar parabolic trough collector increases the comprehensive energy systems’ overall energy and exergy efficiency by 41.9% and 26.7% respectively. Also, the use of liquid potassium as working fluid in the parabolic trough collectors increases the absorbed solar energy input by 419 kW and 2100 kW thereby resulting in a 23% and 90.7% increase in energetic and exergetic efficiency respectively. The carbon emission reduction potential of the two comprehensive energy systems modelled in this study is also analyzed.     

Geothermal and solar energy–based multigeneration system for a district

In this study, parabolic trough collector with an integrated source of geothermal water is used with regenerative Rankine cycle with an open feedwater heater, an electrolyzer, and an absorption cooling system. The absorption fluids used in the solar collectors were Al₂O₃‐ and Fe₂O₃‐based nanofluids. Detailed energetic and exergetic analyses are done for the whole system including all the components. A comparative analysis of both the used working fluids is done and plotted against their different results. The parameters that are varied to change the output of the system are ambient temperature, solar irradiance, the percentage of nanofluids, the mass flow rate of the geothermal well, the temperature gradient of the geothermal well that had an effect on the net power produced, and the outlet temperature of the solar collector overall energetic and exergetic efficiencies. Other useful outputs by this domestic integrated multigeneration system are the heating of domestic water, space heating (maintaining the temperature at 40°C‐50°C), and desalination of seawater (flash distillation). The hydrogen production rate for both the fluids diverges with each other, both producing average from 0.00490 to 0.0567 g/s.     

Performance of Cylindrical Parabolic Collector with Automated Tracking System

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

Thermodynamic assessment of modified Organic Rankine Cycle integrated with parabolic trough collector for hydrogen production

Hydrogen is one of the most clean energy carrier and the best alternative for fossil fuels. In this study, thermodynamic analysis of modified Organic Rankine Cycle (ORC) integrated with Parabolic Trough Collector (PTC) for hydrogen production is investigated. The integrated system investigated in this study consists of a parabolic trough collector, a modified ORC, a single effect absorption cooling system and a PEM electrolyzer. By using parabolic trough collector, solar energy is converted heat energy and then produced heat energy is used in modified ORC to produce electricity. Electricity is then used for hydrogen production. The outputs of this integrated system are electricity, cooling and hydrogen. By performing a parametric study, the effects of design parameters of PTC, modified ORC and PEM electrolyzer on hydrogen production is evaluated. According to the analysis results, solar radiation is one of the most important factor affecting system exergy efficiency and hydrogen production rate. As solar radiation increases from 400?W/m² to 1000?W/m², exergy efficiency of the system increases 58%–64% and hydrogen production rate increases from 0.1016?kg/h to 0.1028?kg/h.     

Potential of a parabolic trough solar concentrator for electric energy production

At present, parabolic trough technology is considered as the most low‐cost and powerful large‐scale technology to utilize solar energy for electricity generation and produce steam for different industrial usages. This article recommends the generation of electricity by using a parabolic trough solar concentrator in the central area of the Kingdom of Saudi Arabia (KSA) at Dawadmi city. Pressurized water is used as the heat‐transfer working fluid. A computer algorithm was built using the Matlab program to simulate the performance parameters of the Euro Trough collector (ETC). The input data included the properties of the working fluid (pressurized water) and the designing parameters of ETC. The output data were the outlet water temperature, the coefficient of heat transfer, the heat loss, and the thermal, solar, and global efficiencies. The obtained results indicated the ability of this type of parabolic trough in KSA to generate electric power due to the high‐performance parameters achieved. Also, the validity of using the simulation technique was measured and it showed good conformity.     

Potentialities of the solar-operated rankine engine

Small-capacity solar Rankine engines can operate at low and medium temperature ranges. The performance of this engine depends basically on the collector subsystem, the working fluid and the type of expander. The problems and potentialities of different alternatives of these items are discussed. Three working fluids, toluene, Fluorinol-85 and steam, were selected to examine the performance of the Rankine engine and its potentiality in the medium temperature range (150–350°C). Four types of parabolic trough solar collectors, available in the international market, were considered in this analysis. It was concluded that steam provides the best option while FL-85 still has good advantages. Extensive efforts are needed to find the most suitable expander for this system.     

Modeling and optimizing parabolic trough solar collector systems using the least squares support vector machine method

Investigating the complicated thermal physics mechanisms of the parabolic trough solar collector systems plays a vital role in efficiently utilizing the solar energy. In this paper, the least squares support vector machine (LSSVM) method is developed to model and optimize the parabolic trough solar collector system. Numerical simulations are implemented to evaluate the feasibility and efficiency of the LSSVM method, where the sample data derived from the experiment and the simulation results of two solar collector systems with 30 m² and 600 m² solar fields, and the complicated relationship between the solar collector efficiency and the solar flux, the flow rate and the inlet temperature of the heat transfer fluid (HTF) is extracted. Some basic rules, such as the solar collector efficiency increases with the increase of the solar flux and the flow rate of the heat transfer fluid, and decreases with the increase of the inlet temperature of the HTF, are obtained, which indicates the LSSVM method is competent to optimize the solar collector systems. As a result, the new approach will provide meaningful data for developing the parabolic trough solar thermal power plant in China.     

Experimental Study on Performance Enhancement of Evacuated Tube by Constant Heat Flux Mode

The evacuated tube collector with U shape copper absorber tube is considered for the analysis. The experimental investigation is conducted on parabolic trough collector with U shape tube as absorber tube. The effect of the sudden fluctuations in the solar radiation on the performance of the collector is reduced by means of evacuated tube collector filled with thermic fluids. The analysis is performed with different thermic fluids such as dowtherm, therminol66, glycol water and ethylene glycol, are filled in the annular space between inner glass tube and U shape copper absorber tube. The experimentation is carried out at various mass flow rates from 20 to 100 LPH with the step-up flow rate of 20 LPH. A comparative study is carried out on various parameters such as effect of mass flow rate over instantaneous efficiency, useful heat gain and work input, etc. The characteristic curve of cylindrical parabolic trough collector (PTC) is also discussed. Experimental results show that, ethylene glycol gives better efficiency over mass flow rate and therminol66 gives best power heat ratio. Heat transfer mediums and its properties [specific heat capacity, thermal conductivity and dynamic viscosity] for all specified heat transfer fluids are also discussed. The results obtained with various specified heat transfer fluids filled in the annulus space of evacuated tube are compared with plain evacuated tube. It is observed that there is significant enhancement of overall instantaneous collection efficiency of the parabolic trough collector.     

Design, manufacture and testing of fiberglass reinforced parabola trough for parabolic trough solar collectors

The design and manufacture of a smooth 90° rim angle fiberglass reinforced parabolic trough for parabolic trough solar collector hot water generation system by hand lay up method is described in this paper. The total thickness of the parabolic trough is 7 mm. The concave surface where the reflector is fixed is manufactured to a high degree of surface finish. The fiberglass reinforced parabolic trough was tested under a load corresponding to the force applied by a blowing wind with 34 m/s. Distortion of the parabola due to wind loading was found to be within acceptable limits. The thermal performance of the newly developed fiberglass reinforced parabolic collector was determined according to ASHRAE Standard 93 [ASHRAE Standard 93, 1986. Method of testing to determine the thermal performance of solar collectors. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, GA]. The standard deviation of the distribution of the parabolic surface errors is estimated as 0.0066 rad from the collector performance test according to ASHRAE Standard 93 (1986), which indicates the high accuracy of the parabolic surface.     

EXPERIMENTAL INVESTIGATION ON CONCENTRATOR-ASSISTED SOLAR-STILLS

The performance of a simple basin solar-still and a similar still coupled to an external trough type concentrator is investigated. The stills are basin-mounted inverted-V roof type, 1.67 m² area each. The assisting concentrator is a single trough-type finned tube 840 cm² receiver area with an adjustable trough half angle. The receiver tube and the basin form a thermosyphone closed loop generating a weak motion of the saline inside the stilt basin. Experiments have been conducted at Jeddah, Kingdom of Saudi Arabia ( Latitude 21^°45') for an average daily solar flux 300–500 w/ m² with water levels of 5–7 cm. A single correlation to predict the stills yield is obtained on basis of data for stills of different compass orientation. The productivity of the assisted still is 22% higher than that of the simple still under the same climatic conditions. For the present results, with fixed concentrator inclination, variation of the trough half angle has no appreciable effect upon the distillation process.     

Solar photoreactors comparison based on oxalic acid photocatalytic degradation

Solar heterogeneous photocatalytic degradation of oxalic acid in water is carried out in four different solar photoreactors: a parabolic trough concentrator (PC), a tubular collector (TC), a compound parabolic collector (CPC), and a V-trough collector (VC). The reactors operate under equal conditions of solar irradiance, collection surface and fluid flow rate to ensure a better comparison between the systems. The effects of TiO₂ catalyst concentration and radiation incidence angle on the degradation are studied. Oxalic acid degrades without appreciable generation of intermediates, and a simple kinetic model is proposed to describe the process. There are differences in the degradation rates depending on the collector geometry. The CPC shows the best overall performance in terms of accumulated energy, followed closely by the VC. Incidence angle affects the total amount of energy collected but does not reduce very much the efficiency of the reactors to use this energy in the photocatalytic process.     

Performance assessment of parabolic dish and parabolic trough solar thermal power plant using nanofluids and molten salts

The present study has been conducted using nanofluids and molten salts for energy and exergy analyses of two types of solar collectors incorporated with the steam power plant. Parabolic dish (PD) and parabolic trough (PT) solar collectors are used to harness solar energy using four different solar absorption fluids. The absorption fluids used are aluminum oxide (Al₂O₃) and ferric oxide (Fe₂O₃)‐based nanofluids and LiCl‐RbCl and NaNO₃‐KNO₃ molten salts. Parametric study is carried out to observe the effects of solar irradiation and ambient temperature on the parameters such as outlet temperature of the solar collector, heat rate produced, net power produced, energy efficiency, and exergy efficiency of the solar thermal power plant. The results obtained show that the outlet temperature of PD solar collector is higher in comparison to PT solar collector under identical operating conditions. The outlet temperature of PD and PT solar collectors is noticed to increase from 480.9 to 689.7 K and 468.9 to 624.7 K, respectively, with an increase in solar irradiation from\ 400 to 1000 W/m². The overall exergy efficiency of PD‐driven and PT‐driven solar thermal power plant varies between 20.33 to 23.25% and 19.29 to 23.09%, respectively, with rise in ambient temperature from 275 to 320 K. It is observed that the nanofluids have higher energetic and exergetic efficiencies in comparison to molten salts for the both operating parameters. The overall performance of PD solar collector is observed to be higher upon using nanofluids as the solar absorbers. Copyright © 2015 John Wiley & Sons, Ltd.     

Solar assisted multi-generation system using nanofluids: A comparative analysis

In this comparative study, a parabolic trough solar collector and a parabolic dish solar collector integrated separately with a Rankine cycle and an electrolyzer are analyzed for power as well as hydrogen production. The absorption fluids used in the solar collectors are Al₂O₃ and Fe₂O₃ based nanofluids and molten salts of LiCl–RbCl and NaNO₃–KNO₃. The ambient temperature, inlet temperature, solar irradiance and percentage of nanoparticles are varied to investigate their effects on heat rate and net power produced, the outlet temperature of the solar receiver, overall energy and exergy efficiencies and the rate of hydrogen produced. The results obtained show that the net power produced by the parabolic dish assisted thermal power plant is higher (2.48 kW–8.17 kW) in comparison to parabolic trough (1 kW–6.23 kW). It is observed that both aluminum oxide (Al₂O₃) and ferric oxide (Fe₂O₃) based nanofluids have better overall performance and generate higher net power as compared to the molten salts. An increase in inlet temperature is observed to decrease the hydrogen production rate. The rate of hydrogen production is found to be higher using nanofluids as solar absorbers. The hydrogen production rate for parabolic dish thermal power plant and parabolic trough thermal power plant varies from 0.0098 g/s to 0.0322 g/s and from 0.00395 g/s to 0.02454 g/s, respectively.     

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.     

Thermal enhancement of solar parabolic trough collectors by using nanofluids and converging-diverging absorber tube

Parabolic trough collectors are the most mature technology for utilizing the solar energy in high temperature applications. The objective of this study is the thermal efficiency enhancement of the commercial parabolic collector IST-PTC by increasing the convective heat transfer coefficient between the working fluid and the absorber. There are two main factors which influence on this parameter, the working fluid type and the absorber geometry. For this reason three working fluids are investigated, thermal oil, thermal oil with nanoparticles and pressurized water. Moreover, a dimpled absorber tube with sine geometry is tested because this shape increases the heat transfer surface and increases the turbulence in the flow. The final results show that these two techniques improve the heat transfer coefficient and the thermal efficiency of the collector. More specifically, the use of nanofluids increases the collector efficiency by 4.25% while the geometry improvement increases the efficiency by 4.55%. Furthermore, collector parameters such as the heat loss coefficient, the exergetic efficiency, the pressure losses and the absorber temperature are presented for all the examined cases. The model is designed with Solidworks and is simulated by its flow simulation studio.     

Cost analysis of different solar still configurations

The enhancement of the productivity of the solar desalination system, in a certain location, could be attained by a proper modification in the system design. Therefore, different design configurations could be found in literatures. However, the increase in the system productivity with high system cost may increase also the average annual cost of the distillate. Cost analysis of different design configurations of solar desalination units is essential to evaluate the benefit of modification from the economical point of view. The main objective of this work is to estimate the water production cost for different types of solar stills. In this paper 17 design configurations are considered. Systems with higher and lower values of productivity are considered in this investigation. A simplified model for cost analysis is applied in this study. The results show that, the best average and maximum daily productivity are obtained from solar stills of single-slope and pyramid-shaped. The higher average annual productivity for a solar still is about 1533 l/m² using pyramid-shaped while the lower average annual productivity is about of 250 l/m² using modified solar stills with sun tracking. The lowest cost of distilled water obtained from the pyramid-shaped solar still is estimated as 0.0135 $/l while highest cost from the modified solar stills with sun tracking is estimated as 0.23 $/l.