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Accepted Manuscripts

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research-article  
Hamid Ajdad, Yousra Filali Baba, Ahmed Al Mers, Ossama Merroun, Abdelfattah Bouatem, Noureddine Boutammachte, Soukaina El Alj and Sara Benyakhlef
J. Sol. Energy Eng   doi: 10.1115/1.4040064
A solar heating compound parabolic collector (CPC) using air and palm oil as heat carrier fluid is proposed and analysed within this study via heat transfer and ray tracing simulations. This collector is placed above a linear Fresnel solar field prototype with an area of approximately 70m2 erected at the platform of the Green Energy Park (32° 14' N 7° 57' O), southern Morocco (Benguerir). The system is a linear focusing solar system intended to be used for applications across a broad range of industrial sectors for generating medium temperature heat up to 250°C. The Monte Carlo ray tracing method was used to predict the optical performances of the receiver. We have developed a simplified thermal model to investigate and analyze the thermal performances of the receiver under different conditions. It has been demonstrated that the investigated receiver satisfactorily matches the heat demand by producing low and medium temperature heat with an annual system efficiency of 45%.
research-article  
Xiankun Xu, Xiaoxin Wang, Peiwen Li, Yuanyuan Li, Qing Hao, Bo Xiao, Hassan Elsentriecy and Dominic Gervasio
J. Sol. Energy Eng   doi: 10.1115/1.4040065
The eutectic mixture of MgCl2-KCl molten salt is a high temperature heat transfer and thermal storage fluid able to be used at temperatures up to 800 oC in concentrating solar thermal power systems. The molten salt thermophysical properties are reported including vapor pressure, heat capacity, density, viscosity, thermal conductivity, and the corrosion behavior of nickel-based alloys in the molten salt corrosion at high temperatures. Correlations of the measured properties as functions of molten salt temperatures are presented for industrial applications. The test results of tensile strength of two nickel-based alloys exposed in the molten salt at a temperature of 800 oC from one-week length to sixteen-week length are reported. It was found that the corrosion and strength loss is rather low when the salt is first processed to remove water and oxygen.
research-article  
Jinsong Liu and Lance Manuel
J. Sol. Energy Eng   doi: 10.1115/1.4039984
As offshore wind turbines supported on floating platforms extend to deep waters, the various effects involved in the dynamics, especially those resulting from the influence of moorings, become significant when predicting the overall integrated system response. The combined influence of waves and wind affect motions of the structure and induce tensile forces in mooring lines. The investigation of the system response under misaligned wind-wave conditions and the selection of appropriate mooring systems to minimize the turbine, tower, and mooring system loads is the subject of this study. We estimate the 50-year return response of a semi-submersible platform supporting a 13.2 MW wind turbine as well as mooring line forces when the system is exposed to four different wave headings with various environmental conditions (wind speeds and wave heights). Three different mooring system patterns are presented that include 3 or 6 mooring lines with different inter-line angles. Performance comparisons of the integrated systems may be used to define an optimal system for the selected large wind turbine.
TOPICS: Semi-submersible offshore structures, Mooring, Offshore wind turbines, Waves, Integrated systems, Wind turbines, Wind waves, Water, Wind, Turbines, Dynamics (Mechanics), Wind velocity, Stress
research-article  
Cody M. Unrau and M.F. Lightstone
J. Sol. Energy Eng   doi: 10.1115/1.4039985
This study investigates the temperature profiles predicted by TRNSYS one-dimensional thermal storage tank models for typical charging conditions. Simulation parameters, such as grid spacing and time step size, were varied to observe the changes in the numerical error when compared with an exact analytical solution. A Taylor series expansion was also performed on the discretized, one-dimensional, convection-diffusion equation to obtain an expression for this numerical error. A numerical diffusion term was found which could be used to improve the prediction of the temperature profile in a storage tank simulation. Finally, the influence of this error on predictions of the annual solar fraction for a domestic hot water system was explored.
TOPICS: Errors, Storage tanks, Temperature profiles, Diffusion (Physics), Simulation, Hot water, Convection, Solar energy, Thermal energy storage
research-article  
Jian Chen, H.T. Xu, Zhiyun Wang and Shoupeng Han
J. Sol. Energy Eng   doi: 10.1115/1.4039986
The heat transfer characteristics of a rectangular water tank used in a solar water heating system with a Fresnel Len were investigated qualitatively and quantitatively through the theoretical and numerical methods. The water tank is 450 mm×400 mm×500 mm in size and consists of 15 layers of coil pipe placed at its center. The MIX number and exergy efficiency were studied to quantify the thermal stratification of this water tank. A flow field analysis was also carried out to understand the heat transfer mechanism inside the water tank. Results indicate that the Nusselt number of shell side is increased with the growth of Reynolds number. The mix number suggested that the thermal stratification is enhanced and then reduced with increasing flow rate. A correlation is proposed to predict the Nusselt numbers on the shell side. A detailed flow field analysis indicated that the thermal stratification is highly related to the runoff time, buoyancy force, mixing process, and geometry of the water tank.
TOPICS: Lenses (Optics), Solar energy, Water, Thermal stratification, Flow (Dynamics), Heat transfer, Shells, Solar water heating, Buoyancy, Geometry, Reynolds number, Exergy, Numerical analysis, Pipes
research-article  
Justin P Freedman, Hao Wang and Dr. Ravi Prasher
J. Sol. Energy Eng   doi: 10.1115/1.4039988
Solar-to-thermal energy conversion technologies are an increasingly promising segment of our renewable energy technology future. Today, concentrated solar power plants provide a method to efficiently store and distribute solar energy. Current industrial solar-to-thermal energy technologies employ selective solar absorber coatings to collect solar radiation, which suffer from low solar-to-thermal efficiencies at high temperatures due to increased thermal emission from selective absorbers. Solar absorbing nanofluids (a heat transfer fluid seeded with nanoparticles), which can be volumetrically heated, are one method to improve solar-to-thermal energy conversion at high temperatures. To date, radiative analyses of nanofluids via the radiative transfer equation have been conducted for low temperature applications and for flow conditions and geometries that are not representative of the technologies used in the field. In this work, we present the first comprehensive analysis of nanofluids for concentrated solar power plants in a parabolic trough configuration. This geometry was chosen because parabolic troughs are the most prevelant CSP technologies. We demonstrate that the solar-to-thermal energy conversion efficiency can be optimized by tuning the nanoparticle volume fraction, the temperature of the nanofluid, and the incident solar concentration. Moreover, we demonstrate that direct solar absorption receivers have a unique advantage over current surface-based solar coatings at large tube diameters. This is because of a nanofluid’s tunability, which allows for high solar-to-thermal efficiencies across all tube diameters enabling small pressure drops to pump the heat transfer fluid at large tube diameters.
TOPICS: Solar energy, Nanofluids, Parabolic troughs, Energy conversion, Nanoparticles, Concentrating solar power, Heat transfer, Fluids, Coatings, High temperature, Emissions, Absorption, Solar radiation, Radiative heat transfer, Flow (Dynamics), Temperature, Geometry, Pressure drop, Renewable energy, Low temperature, Pumps
research-article  
Francisco J. Arias and August Salvador De Las Heras
J. Sol. Energy Eng   doi: 10.1115/1.4039893
The basis of a novel method for passive solar water heating homologous to the thermosyphon but driven by induced salinity which circulates a fluid without the necessity of a mechanical pump and with inverse natural convection is outlined. The \emph{brinesyphon} operates -as its homologous thermosyphon, by harnessing the tendency of a less dense fluid to rise above a denser fluid to cause fluid motion through a collector as in a thermosyphon, but with two exceptions: buoyancy is controlled by induced salinity gradients an not by thermal gradients, and second, as result, natural convection is in the opposite direction than its homologous thermosiphon, i.e., hot fluid flows down and cold fluid rises up. A brinesyphon may be more suitable for solar domestic water-heating systems than the thermosyphon because the direction of flow allows to transport hot fluid from the roof where solar collector are placed to the bottom ( e.g., inside the house) without any kind of mechanical pumping system.
TOPICS: Pressure, Fluid dynamics, Flow (Dynamics), Buoyancy, Fluids, Hot water heating, Natural convection, Pumps, Solar collectors, Solar energy, Osmosis, Roofs, Temperature gradient, Solar water heating
research-article  
Prashant Singh Chauhan, Anil Kumar, Chayut Nuntadusit and Shyam Sunder Mishra
J. Sol. Energy Eng   doi: 10.1115/1.4039891
A greenhouse dryer under forced convection mode is designed and fabricated with integration of solar collector. The developed system is used for bitter gourd flakes drying in three different air mass flow rates (0.0275, 0.0551 and 0826 kg/s). Moisture content of bitter gourd flakes was decreased effectively from 96.8 % to 12.2 % in 17 h with optimum air mass flow rate 0.0551 kg/s, whereas, open sun drying was taken 26 h to reach 20.7 % moisture content. The average greenhouse dryer efficiency was found 19.7 % at 0.0551 kg/s air mass flow rate. Percentage of shrinkage of dried bitter gourd flakes was found higher at 0.0275 kg/s air mass flow rate due to higher inside greenhouse room air temperature. Hardness of dried bitter gourd flakes was found highest as 365 gm at 0.0275 kg/s air mass flow rate due to less air exchange rate and high inside room temperature. On the basis of statistical analysis, Prakash and Kumar and Logarithmic model were selected as best drying models for greenhouse and open sun drying respectively. The dehydration of higher moisture content crops inside developed greenhouse dryer was found more consistent. The developed dryer is recommended to produce better quality of dried product as compared to open sun drying for high moisture content crop.
TOPICS: Drying, Forced convection, Economic analysis, Flow (Dynamics), Temperature, Shrinkage (Materials), Statistical analysis, Solar collectors
research-article  
Kalameshwar Patil, Kaushik S.C. and Sat Narayan Garg
J. Sol. Energy Eng   doi: 10.1115/1.4039656
Light pipes are popularly used for transporting outdoor sunlight into deep spaces of the building and hence use of artificial lighting could be substantially reduced. Performance prediction of a light pipe is an essential step before its use in buildings, so that energy saving potential of the light pipe could be quantified. This paper deals with experimental validation of three existing semi empirical models for light pipes, with different aspect ratios, installed on a windowless test room, at IIT Delhi, New Delhi. Two new semi empirical models, based on the existing correlations are developed. The better performing new model is used for the prediction of internal illuminance, energy saving potential and CO2 mitigation potential of light pipe system for the test room. New model found to perform better with mean bias error and root mean squared error of 0.076 and 0.01 respectively. Monthly average energy saving potentials of the light pipe - fluorescent tube light system are found to be 50 % for continuous dimming control, 38% for three step on-off control. Results show that the light pipe-fluorescent tube light system, with different lighting controls, could reduce CO2 emissions to 15-50%.
TOPICS: Composite materials, Energy conservation, Pipes, Climate, Errors, Carbon dioxide, Space, Brightness (Photometry), Sunlight, Emissions, Structures
research-article  
Desh Bandhu Singh, Navneet Kumar, Sanjay Kumar, V K Dwivedi, J K Yadav and GN Tiwari
J. Sol. Energy Eng   doi: 10.1115/1.4039632
This paper deals with the enhancement in exergoeconomic and enviroeconomic parameters for single slope solar still by incorporating N identical partially covered photovoltaic (PVT) collectors. Three cases: (a) single slope solar still incorporating N identical partially covered PVT flat plate collectors (N-PVT-FPC-SS), (b) single slope solar still incorporating N identical partially covered PVT compound parabolic concentrator collectors (N-PVT-CPC-SS) and (c) conventional single slope solar still (CSSSS) have been taken to assess the improvement in various parameters. The various parameters have been computed at 0.14 m water depth, selected values of mass flow rate and number of collectors considering four climatic conditions of New Delhi for each month of year. It has been concluded that N-PVT-FPC-SS performs best followed by N-PVT-CPC-SS and CSSSS on the basis of exergoeconomic and enviroeconomic parameters; however, CSSSS performs better than N-PVT-FPC-SS and N-PVT-CPC-SS on the basis of productivity measured in terms of ratio of monetary value of output and input. The kWh per unit cost based on exergoeconomic parameter is higher by 45.11 % and 47.37 %; environmental cost is higher by 65.74 % and 90.02 %; however, the output per unit input based on productivity is higher by 12.09 % and lower by 26.83 % for N-PVT-FPC-SS than N-PVT-CPC-SS and CSSSS respectively.
TOPICS: Solar stills, Flat plates, Water, Flow (Dynamics)
research-article  
Zakaria El Jaouhari, Youssef Zaz, Salah Moughyt, Omar El Kadmiri and Zakaria El Kadmiri
J. Sol. Energy Eng   doi: 10.1115/1.4039098
A design of solar tracker with a new tracking method based on computer vision techniques is presented in this paper. The proposed method extracts the sun coordinates (orientation ?, elevation f) in real time from hemispherical sky images using an image processing algorithm and then drives a pair of motors to move solar panels (or heliostat) toward the sun. To ensure a wide field of view, a camera equipped with a fisheye lens is used to acquire the whole sky images. The advantages of such a system are the high sensitivity to brightness comparing to the traditional photo sensors based trackers that making the system more efficient and able to determine the sun position even in cloudy days. It also operates independently of time and position which makes it reliable in case of mobile solar station, contrary to systems based on astronomical equations.
TOPICS: Design, Solar energy, Computers, Image processing, Sensors, Lenses (Optics), Motors, Brightness (Photometry), Algorithms

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