Accepted Manuscripts

Prabhukhot Prachi and Prabhukhot Aditya
J. Sol. Energy Eng   doi: 10.1115/1.4037484
The power generated in wind turbine depends on wind speed and parameters of blade geometry like aerofoil shape, blade radius, chord length, pitch angle, solidity etc. Aerofoil selection is the crucial factor in establishing the efficient wind turbine. More than one aerofoils in a blade can increase the efficiency further. Previous studies of different aerofoils have shown that efficiency of small scale wind turbine increases when NREL S822 aerofoil is used for wind speed on and above 10 m/s. This paper introduces a study on effect of low wind speed (V = 5m/s) on performance of blade profile. Aerofoils NREL S822/S823 are used for micro wind turbine with S823 near root and S822 near tip. Blade of 3m radius with spherical tubercles over entire span is analysed considering 50 angle of attack. The CFD simulation was carried out using ANSYS FLUENT to study the behavior of blade profile at various contours. The study shows that blade experinces maximum turbulance and minimum pressure near trailing edge of the tip of blade. The region also experinces maximum velocity of the flow. These factors results in pushing the aerofoil in upword direction for starting the wind turbine to rotate at the speed as low as 5m/s.
TOPICS: Machinery, Wind velocity, Computers, Turbine blades, Wind, Airfoils, Blades, Wind turbines, Chords (Trusses), Computational fluid dynamics, Geometry, Shapes, Simulation, Pressure, Flow (Dynamics)
Technical Brief  
Ana Dyreson, S.A. Klein and Franklin Miller
J. Sol. Energy Eng   doi: 10.1115/1.4037379
Passive cooling by combined radiation-convection from black panels at night is a potential source of significant energy-efficient cooling for both homes and industry. Assessing the technology requires system models that connect cooling load, passive cooling technology performance, and changing weather conditions in annual simulations. In this paper the performance an existing analytical model for a passive cooling panel is validated using a full two dimensional finite differences model. The analytical model is based on a solar hot water collector model but uses the concept of adiabatic surface temperature to create an intuitive, physically meaningful sink temperature for combined convection and radiation cooling. Simulation results are reported for cooling panels of different sizes and operating in both low temperature (comfort cooling) and high temperature (power plant) applications. The analytical model using adiabatic minimum temperature agrees with the high-fidelity finite differences model but is more practical to implement. This model and the validations are useful for the continued study of passive cooling technology, in particular as it is integrated into system-level models of higher complexity.
TOPICS: Cooling, Modeling, Temperature, Convection, Radiation (Physics), Simulation, Stress, Hot water, Power stations, Solar energy, Simulation results, High temperature, Engineering simulation, Low temperature
Technical Brief  
Marzieh Piri, Mehdi Niroomand and Rahmat-Allah Hooshmand Hooshmand
J. Sol. Energy Eng   doi: 10.1115/1.4037377
This paper proposes a new method based on Markov model to calculate the reliability of grid-connected PV systems. This system is a grid-connected PV system consisting of PV modules, a multiphase DC-DC converter, an inverter, an inverter controller, and an MPPT controller at University of Isfahan. This system is considered repairable. Also, different levels of operation are considered for the system equipment. Reliability of the PV modules, the multiphase DC-DC converter and the inverter have been calculated by the Markov model. Finally, the reliability of the entire PV system is calculated by the Markov model. The Proposed algorithm is applied to the PV system positioned at University of Isfahan. Simulation results show the applicability of this method for calculating the reliability of grid-connected PV systems.
TOPICS: Reliability, Modeling, Photovoltaic power systems, Control equipment, Simulation results, Algorithms
Wei-Lin Yang, Po-Hung Chen, Kun-Rui Wu and Likarn Wang
J. Sol. Energy Eng   doi: 10.1115/1.4037378
Ion implantation is an advanced technology to inject dopants for shallow junction formation. Due to the ion-induced sputtering effect at low implant energy where dopants tend to accumulate at the silicon surface, the excess ion doses can be easily removed via a surface chemical wet etching process. By taking advantage of the dose limitation characteristic, we proposed a novel method to form shallow emitters with various dopant densities. Two integration flows have been investigated: 1) Wet etch after implantation before junction anneal; 2) Wet etch after implantation and junction anneal. The two integration flows observed a difference in the density of doping impurities during the thermal process, which is related to the substrate recombination rates. Selective emitter (SE) structures with the two types of integration flows were characterized. Comparing the blanket emitter and SE structures with two types of etching methods, the device with wet etch before annealing process achieved the best effective carrier lifetime of 53.05 µs, which leads to a higher short circuit current density. Hence, this selective emitter cell demonstrated a better blue response and shows an improvement in the conversion efficiency.
TOPICS: Ion implantation, Chemical etching, Solar cells, Etching, Junctions, Flow (Dynamics), Annealing, Sputtering (Irradiation), Silicon, Circuits, Current density, Density
Yan Wang, Ruifeng Hu and Xiaojing Zheng
J. Sol. Energy Eng   doi: 10.1115/1.4037380
Leading edge erosion is a considerable threat to wind turbine performance and blade maintenance, and it is very imperative to accurately predict the influence of various levels of erosion on wind turbine performance. In present study, an attempt to investigate leading edge erosion effects is undertaken by calculating the performance of wind turbine airfoil by Computational Fluid Dynamics (CFD). Two-dimensional incompressible RANS equation and k-? SST turbulence model are adopted to compute the aerodynamics of a S809 airfoil at various erosion depths, pits densities, erosion area and locations based on a pitting erosion model proposed in this work. The results indicate that pitting erosion has remarkably undesirable influences on the aerodynamic performance of the airfoil. The critical erosion depth, pits density and erosion area has been obtained from the numerical simulation. Moreover, a path-coefficient analysis was also carried out and demonstrated that the concerning factors are independent of each other, and Reynolds number and pits density are the most dominant parameters.
TOPICS: Airfoils, Erosion, Wind turbines, Computational fluid dynamics, Density, Aerodynamics, Maintenance, Turbulence, Computer simulation, Reynolds number, Blades, Reynolds-averaged Navier–Stokes equations
Luis Coco Enríquez, Javier Muñoz-Antón and José María Martínez-Val
J. Sol. Energy Eng   doi: 10.1115/1.4037381
An opportunity for increasing the parabolic solar power plant efficiency is substituting the actual subcritical Rankine power cycles with the innovative s-CO2 Brayton cycles. In this paper three configurations are assessed: the recompression cycle, the partial cooling with recompression cycle, and the recompression with main compression intercooling cycle, with one reheating stage. The thermodynamic parameters are optimized with three algorithms: SUBPLEX, UOBYQA and NEWOUA, and the results validated with Thermoflow Software. The parabolic troughs and linear Fresnel solar collectors are studied with different heat transfer fluids: Solar Salt, HITEC XL, Dowtherm A, Therminol-VP1, Syltherm 800 and Therminol 75. The Dual-Loop solar field, combining thermal oil and molten salt in the same solar plant, is also analysed. The plant power output and plant energy efficiency is translated into solar field aperture area and cost at Design-Point. From the point of view of the plant efficiency, the parabolic troughs with Solar Salt coupled to a s-CO2 Brayton RCMCI cycle is selected as the optimum design solution, providing a gross efficiency 51.43%. But from the point of view of minimizing the plant cost, the solar field with Dowtherm A coupled to the RCMCI is the most cost competitive design solution.
TOPICS: Solar energy, Optimization, Supercritical carbon dioxide, Thermodynamic power cycles, Cycles, Design, Parabolic troughs, Solar power stations, Solar collectors, Brayton cycle, Rankine cycle, Compression, Computer software, Heat transfer, Cooling, Fluids, Energy efficiency, Algorithms
Sara Benyakhlef, Ahmed Al Mers, Ossama Merroun, Abdelfattah Bouatem, Hamid Ajdad, Noureddine Boutammachte and Soukaina El Alj
J. Sol. Energy Eng   doi: 10.1115/1.4037382
Reducing levelized electricity costs of concentrated solar power (CSP) plants can be of great potential in accelerating the market penetration of these sustainable technologies. Linear Fresnel reflectors (LFRs) are one of these CSP technologies that may potentially contribute to such cost reduction. However, due to very little previous research, LFRs are considered as a low efficiency technology. In this type of solar collectors there is a variety of design approaches when it comes to optimizing such systems. The present paper aims to tackle a new research axis based on variability study of heliostat curvature as an approach for optimizing small and large scale LFRs. Numerical investigations based on a ray tracing model have demonstrated that LFR constructors should adopt a uniform curvature for small scale LFRs and a variable curvature per row for large scale LFRs. Better optical performances were obtained for LFRs regarding these adopted curvature types.An optimization approach based on the use of uniform heliostat curvature for small scale LFRs has led to a system cost reduction by means of reducing its receiver surface and height.
TOPICS: Optimization, Solar energy, Concentrating solar power, Ray tracing, Solar collectors, Green technology, Optical mirrors, Design
Ali El maihy and Ahmed Elweteedy
J. Sol. Energy Eng   doi: 10.1115/1.4037383
Extensive solar field performance testing is often required as part of the plant commissioning process in order to ensure that actual solar field performance satisfies both technical specifications and performance guaranties between the involved parties. In this study, short duration (15 minutes) steady state performance acceptance test for Kurymat Integrated Solar Combined Cycle (ISCC) solar field was carried out in agreement with the general guidelines of the earlier National Renewable Energy Laboratory (NREL) report on parabolic trough collector fields [1-2], which is in full agreement with the plant documentations provided by FLAGSOL [3]. This work includes measurement of the thermal power output of Parabolic Trough (PT) system under clear sky conditions over a short period during which thermal steady state conditions exists. The methodology of the solar field testing is presented while a special consideration is provided for the model formulation, and uncertainty associated with the measured data. The measured results together with the associated uncertainties were compared with model predictions. All tests for both northern and a southern collector subfields that satisfy the test conditions are accepted based on acceptance test evaluation criteria.
TOPICS: Solar energy, Parabolic troughs, Uncertainty, Steady state, Testing performance, Testing, Renewable energy, Combined cycles, Thermal energy
Tingting Zhu, Yanhua Diao, Yaohua Zhao, C. Ma, T. Y. Wang and J. Liu
J. Sol. Energy Eng   doi: 10.1115/1.4037385
In this study, a comparison investigation of two types of micro heat pipe array (MHPA) flat plate solar air collectors (FPSAC) based on exergy analysis has been conducted. The thermal performance of MHPA-type solar air collectors (SACs) with two different shape fins is experimentally evaluated. A detailed parametric study is also conducted to examine the effects of various fins, operation parameters, and inlet air temperature at different mass flow rates on thermal and exergy efficiencies. Results indicated that using V-shaped slotted fins at the specified range of mass flow rates can enhance exergy efficiency. Exergy efficiency can be considered as the main criterion to evaluate the performance of MHPA FPSACs. Attaching V-shaped slotted fins on the condenser section of MHPA is more effective than attaching rectangular fins at high mass flow rates. By contrast, the latter is more effective than the former at low mass flow rates.
TOPICS: Solar energy, Exergy analysis, Flat plates, Fins, Flow (Dynamics), Exergy, Heat pipes, Temperature, Condensers (steam plant), Shapes
Pei Wang, J.B. Li, Kambiz Vafai, L. Zhao and Ling Zhou
J. Sol. Energy Eng   doi: 10.1115/1.4037350
Optimization based on reconstruction of the velocity, temperature, and radiation fields in a porous absorber with continuous linear porosity or pore diameter distribution is carried out in this work. This study analyzes three typical linear pore structure distributions: increasing ('I'); decreasing ('D'); and constant ('C') types, respectively. In general, the 'D' type porosity (?) layout combined with the 'I' type pore diameter (dp) distribution would be an excellent pore structure layout for a porous absorber. With a large inlet porosity (?i > 0.8), the larger porosity 'D' type gradient (Gp) has a better thermal performance; however, the 'I' type dp layout with a smaller inlet pore diameter (di< 1.5mm) and a larger pore diameter gradient (Gd) is recommended when considering the lower pressure drop. The poor performance range, which should be avoided in the absorber design, is established. Different pore structure layouts ('D' type or 'I' type) have a significant effect on the pressure drop, even with the same average ?a and da. The maximum deviation can be up to 65.7%. The comprehensive performance evaluation criteria (PEC) value shows that the 'D' type ? layout with a larger ?a has an excellent thermal-pressure drop performance, and most PEC values for the 'I' type dp layout are greater than unity. The vale thermal efficiency (? ) area is found to be within a wide range of porosity layouts (?i = ~ 0.7, ?o = 0.5 ~ 0.8) and pore diameter layouts (di = 1.5mm ~ 3.5mm do = 1~3mm), respectively.
TOPICS: Optimization, Solar energy, Pressure drop, Porosity, Thermal efficiency, Performance evaluation, Pressure, Temperature, Radiation (Physics), Design

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