Accepted Manuscripts

Osama Bany Mousa and Robert Taylor
J. Sol. Energy Eng   doi: 10.1115/1.4040840
Solar harvesting designs aim to optimize energy output per unit area. When it comes to choosing between rooftop technologies for generating heat and/or electricity from the sun, though, the literature has favored qualitative arguments over quantitative comparisons. In this paper, an agnostic perspective will be used to evaluate several solar collector designs - thermal, photovoltaic (PV), and hybrid (PV/T) systems - which can result in medium temperature heat for industry rooftops. Using annual TRNSYS simulations in several characteristic global locations, it was found that a maximum solar contribution (for all selected locations) of 79.1% can be achieved for a sterilization process with a solar thermal (ST) system as compared to 40.6% for a photovoltaic system (PV). A 43.2% solar contribution can be obtained with a thermally - coupled PV/T, while an uncoupled PV/T beam splitting collector can achieve 84.2%. Lastly, PV and ST were compared in a side-by-side configuration, indicating that this scenario is also feasible since it provides a solar contribution of 75.2%. It was found that the location's direct normal incident (DNI) and global horizontal irradiation (GHI) are the dominant factors in determining the best technology for industrial heating applications. Overall, this paper is significant in that it introduces a comparative simulation strategy to analyze a wide variety of solar technologies for global industrial heat applications.
TOPICS: Solar energy, Heating, Heat, Simulation, Solar collectors, Temperature, Irradiation (Radiation exposure), Photovoltaic power systems, Sterilization
Dimitrios Potamias, Ivo Alxneit, Erik Koepf and Alexander Wokaun
J. Sol. Energy Eng   doi: 10.1115/1.4040842
The accuracy of radiometric temperature measurement in radiatively heated environments is severely limited by the combined effects of intense reflected radiation and unknown, dynamically changing emissivity which induces two correlated and variable error terms. While the recently demonstrated Double Modulation Pyrometry (DMP) eliminates the contribution of reflected radiation, it still suffers from the shortcomings of single-waveband pyrometry: it requires knowledge of the emissivity to retrieve the true temperature from the thermal signal. Here, we demonstrate an improvement of DMP incorporating the in-situ measurement of reflectance. The method is implemented at Paul Scherrer Institute (PSI) in its 50 kW high-flux solar simulator and used to measure the temperature of ceramic foams (SiSiC, ZrO2 , and Al2O3) during fast-heat-up. The enhancement allows DMP to determine the true temperature despite of a dynamically changing emissivity and to identify well-documented signature changes in ZrO2 and Al2O3 . The method also allows us to study the two dominant error sources by separately tracking the evolution of two error components during heat-up. Furthermore, we obtain measurements from a solar receiver, where the cavity reflection error limits measurement accuracy. DMP can be used as an accurate radiometric thermometer in the adverse conditions of concentrated radiation, and as a diagnostic tool to characterize materials with dynamic optical properties. Its simple design and ability to correct for both errors makes it a useful tool not only in solar simulators but also in concentrated solar facilities.
TOPICS: Reflectance, Emissivity, Errors, Solar energy, Temperature, Radiation (Physics), Heat, Cavities, Signals, Thermometers, Ceramic foam, Reflection, Temperature measurement, Accuracy and precision, Design
Sridharan M., Jayaprakash G., Chandrasekar M., Vigneshwar P., Paramaguru S. and Amarnath K.
J. Sol. Energy Eng   doi: 10.1115/1.4040757
In recent years solar PV/T water collectors has been identified as one of the most promising hybrid devices. It is a combination of solar PV and solar FPC systems capable of generating electrical and thermal power simultaneously. This study presents a model which predicts solar PV/T collector power output using fuzzy logic techniques. A fuzzy logic model was established to predict power output of PV/T with respect to changes in input process and FPC output power. Membership functions were allocated in connection with each model input. Experimental tests conducted during the month of December 2016 are compared with the developed fuzzy model to verify predicted results. The results indicate an agreement between fuzzy model and experimental results with accuracy of 94.38% and error of 5.62%.
TOPICS: Fuzzy logic, Solar energy, Errors, Water, Thermal energy
Asif Soopee, Abdel Anwar Hossen Khoodaruth, Anshu Prakash Murdan and Vishwamitra Oree
J. Sol. Energy Eng   doi: 10.1115/1.4040758
The effects of thermal separators within the evacuated tubes of a water-in-glass solar water heater (SWH) were numerically investigated using the commercial Computational Fluid Dynamics (CFD) software ANSYS Fluent. To validate the 3D model, an experiment was performed for the passive operation of the SWH for a fortnight period, of which 3 hours of recorded data was selected. The Boussinesq's approximation was employed and the respective solar irradiance and ambient temperature profiles incorporated. A maximum deviation of only 2.06% was observed between the experimental and numerical results. The model was then adapted for the case where thermal separators are inserted within the evacuated tubes of the SWH and both cases were run for two tilt angles, 10o and 40o. The temperature and velocity profiles within the evacuated tubes were analyzed alongside the temperature contours, thermal stratification, and overall thermal efficiency of the SWH. At a 40o tilt, without thermal separators, the flow streams within the evacuated tubes are restrained and a chaotic thermal behavior was observed, thereby restricting thermal distribution to the water stored in the SWH tank. A lower tilt angle (10o) provided a more desirable thermal distribution. With thermal separators, however, the tilt angle preference was reversed. A faster and more uniform thermal distribution within the water tank, with a sizeable reduction in thermal stratification at 40o tilt. The overall thermal efficiency of the SWH was improved by 8.22% and 8.28% for tilt angles of 10o and 40o, respectively.
TOPICS: Glass, Solar energy, Water, Significant wave heights, Thermal stratification, Thermal efficiency, Computational fluid dynamics, Temperature, Solar radiation, Approximation, Computer software, Temperature profiles, Flow (Dynamics), Three-dimensional models, Preferences
Technical Brief  
Venugopalan S. G. Raghavan and Harish Gopalan
J. Sol. Energy Eng   doi: 10.1115/1.4040756
The accurate prediction of the direct and diffuse solar radiation is of foremost importance for deployment of photovoltaic systems. A number of solar radiation forecasting techniques have been developed for longer and shorter forecasting times. Numerical weather prediction (NWP) models provide the best results for the longer forecasting times (4-6 hours), required by utility companies. However, NWP methods are usually developed for clear-sky and open areas. These methods cannot be directly applied to urban areas with shading, trees, multi-surface reflection and other sources of solar radiation losses. To overcome these issues, improvement to existing prediction tools are required. In this study, we develop an automated radiation forecasting tool for urban areas. This tool combines a numerical weather prediction model (Weather Research and Forecasting model) and a solar calculator (developed in the numerical toolbox OpenFOAM) to compute shading, reflection and other losses in the urban canopy. An algorithm for extraction of building outlines, and heights (if they are publicly available) is also developed as a part of the tool. Finally, the coupled solar power estimator can be applied to past, present, or future solar power predictions. Initial results obtained using the developed tool are demonstrated for an urban neighborhood in Singapore.
TOPICS: Solar energy, Cities, Solar power, Solar radiation, Reflection, Shades and shadows, Weather forecasting, Photovoltaic power systems, Algorithms, Radiation (Physics), Public utilities
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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