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# Accepted Manuscripts

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research-article
J. Sol. Energy Eng   doi: 10.1115/1.4039024
This paper discusses a Fiber-Optic Hybrid Day-Lighting system that can cut energy consumed by buildings and shelters for lighting significantly. The focus of the study is on mobile application. The system is comprised of two primary components: the solar collector and the Solar Hybrid Lighting Fixture. The solar collector, consists of a housing, structural stand, a dual axis tracking system, Fresnel Lenses, secondary optics, and fiber-optic cables. The collector is integrated into a dual-axis tracker, which is then mounted on a tripod. The collector with an aluminum housing holds eight 10-inch diameter Fresnel Lenses that focus sunlight onto eight secondary optics based on total internal reflection which filter UV/IR and deliver uniform light to the fiber-optic cables. The solar collector tracks the sun's movement through the day with a dual-axis tracker, ensuring the light is concentrated into the fiber-optic cables. The optics has been designed to have a high half-acceptance of 1.75o and can accommodate a tracking accuracy of 1.50o or better. The Hybrid Light Fixture (SHLF) consists of two components: a solar fiber-optic system and an LED system. The fiber-optic cable is coupled to an acrylic light diffusing rod that delivers the light into the room. During sunny periods, solar fiber-optic lighting could provide full illumination level. In order to keep the same level of lighting during cloudy periods, the LED portion of the light fixture will supplement the output of the SHLF.
TOPICS: Daylighting, Design, Fibers, Cables, Solar collectors, Solar energy, Optics, Ultraviolet radiation, Aluminum, Structures, Filters, Sunlight, Reflection
research-article
J. Sol. Energy Eng   doi: 10.1115/1.4039018
The evaluation of the performance and characteristics of a solar flat-plate collector (FPC) are reported for domestic and industrial requirements in the existing literature. A computer code was developed using MATLAB to model and evaluate the energetic and exergetic performance of a nanofluid-based FPC for steady state and laminar conditions. The analysis was performed using practical geometry data, especially the collector emittance, for a standard collector. Linear pressure losses in manifolds were taken into account, and a more accurate exergy factor corresponding to a correct value of 5770 K for the sun temperature was employed. The results demonstrate that copper-water nanofluid has the potential to augment the internal convection heat transfer coefficient by 76.5%, and to enhance the energetic efficiency of the collector from 70.3% to 72.1% at 4% volume concentration, when compared to the values with water. Additionally, it was revealed that copper nanofluid is capable of increasing the collector fluid's outlet temperature and decreasing the absorber plate's mean temperature by 3 K. The addition of nanoparticles to the water demonstrated a reduction in the total entropy generation by the solar FPC. Furthermore, increasing the nanoparticle size reflected a reduction in the overall performance of the solar collector.
TOPICS: Solar energy, Flat plates, Nanofluids, Water, Temperature, Copper, Nanoparticles, Exergy, Convection, Solar collectors, Entropy, Computers, Pressure, Steady state, Geometry, Manifolds, Matlab
research-article
J. Sol. Energy Eng   doi: 10.1115/1.4038961
Variation in direct solar radiation is one of the main disturbances that any solar system must handle to maintain efficiency at acceptable levels. As known, solar radiation profiles change due to earth's movements. Even though this change is not manipulable, its behavior is predictable. However, at ground level, direct solar radiation mainly varies due to the effect of clouds, which is a complex phenomenon not easily predictable. In this paper, dynamic solar radiation time series in a $2D$ spatial domain are obtained using a biomimetic cloud-shading model. The model is tuned and compared against available measurement time series. The procedure uses an objective function based on statistical indexes that allow extracting the most important characteristics of an actual set of curves. Then, a multi-objective optimization algorithm finds the tuning parameters of the model that better fit data. The results showed that it is possible to obtain responses similar to real direct solar radiation transients using the biomimetic model, which is useful for other studies such as testing control strategies in solar thermal plants.
TOPICS: Solar radiation, Shades and shadows, Biomimetics, Dynamic modeling, Time series, Solar energy, Testing, Pareto optimization, Algorithms, Transients (Dynamics)
research-article
J. Sol. Energy Eng   doi: 10.1115/1.4038983
A direct methodology for intra-day forecasts (1-6 hours ahead) of power output (PO) from photovoltaic (PV) solar plants is proposed. The forecasting methodology uses publicly available images from geosynchronous satellites to predict PO directly without resorting to intermediate irradiance (resource) forecasting. Forecasts are evaluated using four years (January 2012-December 2015) of hourly PO data from 2 non-tracking, 1 MWp PV plants in California. For both sites, the proposed methodology achieves forecasting skills ranging from 24--69% relative to reference persistence model results, with root mean square error (RMSE) values ranging from 90-136 kW across the studied horizons. Additionally, we consider the performance of the proposed methodology when applied to imagery from the next generation of geosynchronous satellites, e.g., Himawari-8 and GOES-R.
TOPICS: Solar energy, Errors, Image processing, Satellites
Technical Brief
J. Sol. Energy Eng   doi: 10.1115/1.4038962
This technical brief develops a theoretical model of all the pressure losses in the solar chimney power plant (SCPP, also called solar updraft power plant) and analyzes the pressure losses for different chimney internal stiffening appurtenance (SA) structures, different roof heights and different collector support parameters. Results show that the exit kinetic energy loss (EKEL) accounts for the majority of the total pressure loss (TPL), while other losses constitute only small proportions of the TPL, and the collector inlet loss is negligible. Pressure losses are strongly related to the mass flow rate, while reasonable mass flow rates excluding too low flow rates have little influence on the pressure loss ratios (PLRs, defined as the ratios of the pressure losses to the TPL) and the total effective pressure loss coefficient (TEPLC). Designing of the SA structure in view of reducing the drag, for example, using the ring stiffeners without wire spoked instead of the spoked bracing wheels (SBWs), reducing the width of the chimney internal rims of SAs, or reducing the number of SAs results in large reduction of the SA PLR and the TPL. Lower roof leading to higher velocity inside the collector, larger supports, or shorter inter-support distance leads to the increase in the support PLR. This technical brief lays a solid foundation for optimization of SCPPs in future.
TOPICS: Pressure, Power stations, Solar energy, Flow (Dynamics), Roofs, Wheels, Kinetic energy, Drag (Fluid dynamics), Wire, Bracing (Construction), Design, Optimization
research-article
J. Sol. Energy Eng   doi: 10.1115/1.4038849
The present research demonstrates scale-up studies with the development of concentrating and non-concentrating solar reactors employing suspended and supported TiO2 for the degradation of herbicide isoproturon (IPU) with total working volume of 6L. Novel cement beads were used as support material for fixing the catalyst particles. In case of non-concentrating slurry reactor, 85% degradation of IPU was achieved after 3 h of treatment with four number of catalyst recycling. Whereas, non-concentrating fixed-bed reactor using TiO2 immobilized cement beads took relatively more time (10 h) for the degradation of IPU (65%) due to mass transfer limitations but it overcame the implication of catalyst filtration post-treatment. The immobilized catalyst was successfully recycled for 10 times boosting its commercial applications. High photon flux with concentrating parabolic trough collector (PTC) using fixed catalysis approach with same immobilized catalyst substantially reduced the treatment time to 4 h for achieving 91% degradation of IPU. Working and execution of pilot-scale reactors is very fruitful to extend these results for a technology development with the present leads.
TOPICS: Slurries, Solar energy, Catalysts, Cements (Adhesives), Technology development, Parabolic troughs, Mass transfer, Photons, Recycling, Filtration, Particulate matter
research-article
J. Sol. Energy Eng   doi: 10.1115/1.4038811
A method for inverse design of horizontal axis wind turbines (HAWTs) is presented in this paper. The direct solver for aerodynamic analysis solves the Reynolds Averaged Navier Stokes (RANS) equations with an actuator disk representation of the rotor. The inverse problem is posed as follows: for a given selection of airfoils, the objective is to find the blade geometry (described as blade twist and chord distributions) which realizes the desired turbine aerodynamic performance at the design point; the desired performance is prescribed as angle of attack (\alpha$) and axial induction factor ($a$) distributions along the blade. An iterative approach is used. An initial estimate of blade geometry is used with the direct solver (RANS/ADM) to obtain$\alpha$and$a$. The differences between the calculated and desired values of$\alpha$and$a\$ are computed and a new estimate for the blade geometry (chord and twist) is obtained via nonlinear least squares regression using the Trust-Region-Reflective (TRF) method. This procedure is continued until the difference between the calculated and the desired values is within acceptable tolerance. The method is demonstrated for conventional, single-rotor HAWTs and then extended to multi-rotor, specifically dual-rotor wind turbines. The TRF method is also compared with the multi-dimensional Newton iteration method and found to provide better convergence when constraints are imposed in blade design, although faster convergence is obtained with the Newton method for unconstrained optimization.
TOPICS: Computational fluid dynamics, Design, Blades, Rotors, Horizontal axis wind turbines, Geometry, Chords (Trusses), Reynolds-averaged Navier–Stokes equations, Wind turbines, Turbines, Disks, Airfoils, Electromagnetic induction, Actuators, Optimization, Inverse problems, Newton's method
research-article
J. Sol. Energy Eng   doi: 10.1115/1.4038786
The potential applicability of a developed recycled textile material, based on acrylic spinning waste, as thermal insulation is conducted. The prepared acrylic spinning waste, termed here as AS, is thermo physically characterized in terms of density, air permeability and thermal conductivity. Results show that the density and air permeability are 10.583 kg/m3 and 1100 L/m2/s, respectively. In addition, the thermal conductivity is found to be 38.27 mW/ (m K). The developed thermal insulator is then tested in a thermally controlled reduced scale cavity. Two walls of the cavity are outfitted with AS at two different locations and compared to the walls without AS. The comparison is made based on the wall surface temperature and heat flux. A reduction on surface temperature is observed in the walls outfitted with AS, compared to wall without AS. Indeed, compared to a control wall, the peak heat fluxes are reduced by 27.23% and 18.67%, respectively related to the walls with AS at location 1 and location 2. The obtained results show that the acrylic spinning waste is a competitive thermal insulation material and can increase the thermal performance of the building walls.
TOPICS: Heat transfer, Textiles, Performance evaluation, Thermal insulation, Spinning (Textile), Spin (Aerodynamics), Thermal conductivity, Cavities, Permeability, Density, Temperature, Heat flux, Heat, Flux (Metallurgy)
research-article
J. Sol. Energy Eng   doi: 10.1115/1.4038787
The increase of operating temperature on a photovoltaic cell degrades its electrical efficiency. This paper is organized to describe our latest design of an aluminum substrate - based photovoltaic / thermal (PV/T) system. The electrical efficiency of the proposed PV/T can be increased by ~20% in comparison with a conventional glass substrate - based PV. The work will benefit hybrid utilization of solar energy in development of building integrated photovoltaic systems.
TOPICS: Cooling, Aluminum, Water, Electrical efficiency, Operating temperature, Glass, Design, Solar energy, Photovoltaic cells, Photovoltaic power systems
Technical Brief
J. Sol. Energy Eng   doi: 10.1115/1.4038788
This study addresses the method of adding heat to a salt gradient solar pond (SGSP) from external sources and investigates the thermal performance of the pond. In this case the external heat source is solar heat collected by evacuated tube solar collectors (ETSC) and collected heat is transferred to the lower-convective zone (LCZ) of the SGSP by circulating fluid from the LCZ. Results show that heat addition from the external source enhances the thermal performance of the SGSP in terms of heat recovery and thermal efficiency but with certain constraints. The heat addition efficiency reduces with increase in aperture area of the ETSC. Also with increasing heat addition the heat removal from the SGSP has to be increased otherwise the SGSP efficiency reduces rapidly. Heat removal from SGSP has to be performed keeping in mind the heat demand and the quality of heat. The latter reduces with increase of heat extraction beyond a certain limit. Hence optimizing the range of parameters in case of adding heat from external sources is very important for the best performance of a SGSP.
TOPICS: Heat, Solar energy, Solar heating, Thermal efficiency, Fluids, Heat recovery, Solar collectors
research-article
J. Sol. Energy Eng   doi: 10.1115/1.4038620
This work describes a new simple and effective method to extract the loss parameters of a solar panels (solar cells) and able to accurately represent their electrical behavior. This approach allows the extraction of the parameters of the single diode model using only the information provided by the manufacturer's data sheet. The proposed method presents a computational procedure of low complexity, which makes it possible to estimate the five parameters of any photovoltaic or generator cell. Using the complete equation of the single diode model, the number of parameters to be calculated is reduced only to two parameters by an equation exclusively connecting the series resistance and the diode current. Suitable validations on important case studies are presented, an experimental data from multi-crystalline MSX120 and thin film NA-F135 solar panels were used to test the single diode model. The experimental data are first collected at the same temperature at two different irradiances levels and at low irradiance level at a fixed temperature for MSX120. In the second stage, variations in temperature are considered at different irradiance level for NA-F135. The extraction results show that the I-V curves accurately fit the entire range of the experimental data. The results of the proposed procedure are compared to the most recent proposed techniques in literature. Furthermore, the results obtained show a highly accurate; in particular, at maximum power point the error is always less than 0.005%, which is quite far of the authorized error of 1%.
TOPICS: Solar energy, Temperature, Errors, Generators, Solar cells, Thin films