scholarly journals Diffusion Characteristics of Solar Beams Radiation Transmitting through Greenhouse Covers in Arid Climates

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 472
Author(s):  
Ibrahim Al-Helal ◽  
Abdullah Alsadon ◽  
Mohamed Shady ◽  
Abdullah Ibrahim ◽  
Ahmed Abdel-Ghany
Keyword(s):  
Solar Radiation ◽  
Diffuse Radiation ◽  
Radiative Properties ◽  
Arid Climate ◽  
Beam Radiation ◽  
Transmitted Beam ◽  
Plastic Films ◽  
Diffusion Characteristics ◽  
Heating Load ◽  
And Diffusion

In hot and sunny regions, extensive solar radiation transmitted into greenhouses makes it essential to select a greenhouse cover with specific characteristics. Reflection and diffusion are the most important properties of covers for reducing solar heating load and scattering solar beams for better growth of plants. Three types of plastic films that are commonly used for covering greenhouses in arid climate were selected for this study. These were reflective-diffusive (RDF), diffusive (DF), and locally produced (CF) films. The films were used to cover three identical twin-span greenhouse models; the radiation components, air temperature (Ti), and relative humidity (RHi) were measured in each model. Transmission of solar radiation through each cover was characterized by determining: (i) The beam that is diffused during transmission, and (ii) the unscattered beam that is transmitted directly through the film. The results show that the diffuse radiation transmitted through the DF, RDF, and CF covers was enhanced, respectively by 77%, 85%, and 109% as a result of diffusing 34%, 33%, and 43% of the transmitted beam radiation by the DF, RDF, and CF covers, respectively during transmission. The diffusive nature of the tested covers increased the ratio of diffuse to direct beam radiation (D/B) from 0.3 outside the greenhouse to 0.77, 0.69, and 0.95 inside a greenhouse covered with DF, RDF, and CF, respectively. At around noon, the CF cover decreased Ti by about 5–10 °C and increased RHi by about 3%–5% compared to those under the DF and RDF covers. However, DF and RDF covers showed almost similar effects in Ti and RHi. The low-price CF cover showed higher diffusive-radiative properties than DF and RDF covers and can serve effectively in arid climate as an alternative covering material.

scholarly journals Modeling Approach for Determining Equivalent Optical Constants of Plastic Shading Nets under Solar Radiation Conditions

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
A. M. Abdel-Ghany ◽  
I. M. Al-Helal
Keyword(s):  
Solar Radiation ◽  
Optical Constants ◽  
Present Model ◽  
Incident Angle ◽  
Radiative Properties ◽  
Beam Radiation ◽  
Extinction Coefficients ◽  
Average Value ◽  
Texture Structure ◽  
Radiation Conditions

The radiative properties of several plastic shading nets were measured under natural solar radiation conditions. We found that the plastic nets behave as homogeneous translucent materials (e.g., plastic film, plastic sheets, and glass). Based on this behavior, we suggest that it is possible to treat plastic nets as translucent materials and to characterize them with equivalent optical constants (i.e., equivalent refractive indexes,neq, and equivalent extinction coefficients,σeq). Here a physical model to determineneqandσeqof plastic nets was described in analogy to homogeneous translucent materials. We examined three groups of nets based on their color (black, black-green, and beige). Each group consisted of nets with four or five different porosities. Nets of each group had almost the same texture structure. For each group, we derived an equation forneqas a function of the net porosity and determined an average value forσeq. Once values ofneqandσeqwere determined, the solar radiative properties of a net could then be calculated fromneqandσeqfor any incident angle of solar beam radiation without the need of measurements. The present model was validated by comparing the calculated with the measured radiative properties of three nets at different incident angle of solar beam radiation. The calculated radiative properties reasonably agreed with measured values.

Indoor Thermal Comfort Predicting Correlations in Subtropical Plateau Monsoon Climate

2012 ◽  
Vol 193-194 ◽  
pp. 231-234 ◽  
Author(s):  
Sheng Xian Wei ◽  
Qing Zhou ◽  
Shu Fen Tao ◽  
Guang Xue Chen
Keyword(s):  
Solar Radiation ◽  
Thermal Comfort ◽  
Air Temperature ◽  
Thermal Sensation ◽  
Environmental Parameters ◽  
Diffuse Radiation ◽  
Monsoon Climate ◽  
Beam Radiation ◽  
Newton’S Iterative Method ◽  
Indoor Thermal Comfort

Fanger’s PMV is the most famous thermal sensation index but it is too complex to be applied in practice. Besides, the PMV index does not include the effect of hourly solar radiation on the indoor thermal climate. In order to obtain simple and applicable correlations with considerations of outdoor hourly solar radiation, a one-year measurement was performed in a naturally ventilated residential room in Qujing Normal University of Yunnan province, China. PMV indices are calculated by using Newton’s iterative method based on the collected data. Correlations of the PMV and the environmental parameters (outdoor air temperature, indoor air temperature, mean radiant temperature, wind velocity, relative humidity, hourly beam radiation and hourly diffuse radiation) have been developed by the multivariable regression technique. It is convenient to use them to predict the indoor thermal comfort in the subtropical plateau monsoon climate.

Improved Accuracy Models For Hourly Diffuse Solar Radiation

2005 ◽  
Vol 128 (1) ◽  
pp. 104-117 ◽  
Author(s):  
T. Muneer ◽  
S. Munawwar
Keyword(s):  
Solar Radiation ◽  
Regression Models ◽  
Global Radiation ◽  
Diffuse Radiation ◽  
Evaluation Procedure ◽  
Accuracy Score ◽  
Error Statistics ◽  
Diffuse Solar Radiation ◽  
Energy Applications ◽  
Extensive Evaluation

Solar energy applications require readily available, site-oriented, and long-term solar data. However, the frequent unavailability of diffuse irradiation, in contrast to its need, has led to the evolution of various regression models to predict it from the more commonly available data. Estimating the diffuse component from global radiation is one such technique. The present work focuses on improvement in the accuracy of the models for predicting horizontal diffuse irradiation using hourly solar radiation database from nine sites across the globe. The influence of sunshine fraction, cloud cover, and air mass on estimation of diffuse radiation is investigated. Inclusion of these along with hourly clearness index, leads to the development of a series of models for each site. Estimated values of hourly diffuse radiation are compared with measured values in terms of error statistics and indicators like, R2, mean bias deviation, root mean square deviation, skewness, and kurtosis. A new method called “the accuracy score system” is devised to assess the effect on accuracy with subsequent addition of each parameter and increase in complexity of equation. After an extensive evaluation procedure, extricate but adequate models are recommended as optimum for each of the nine sites. These models were found to be site dependent but the model types were fairly consistent for neighboring stations or locations with similar climates. Also, this study reveals a significant improvement from the conventional k-kt regression models to the presently proposed models.

Organic Heterojunctions for Photovoltaic Applications: C60 Growth on Pentacene

2010 ◽  
Vol 1263 ◽  
Author(s):  
Rebecca Ann Cantrell ◽  
Paulette Clancy
Keyword(s):  
Atomic Scale ◽  
Short Axis ◽  
Energy Functions ◽  
Potential Energy Functions ◽  
The North ◽  
Diffusion Characteristics ◽  
Static Energy ◽  
Semi Empirical ◽  
Organic Heterojunctions ◽  
And Diffusion

AbstractUsing atomic-scale Molecular Dynamics (MD) and energy minimization techniques in conjunction with semi-empirical MM3 potential energy functions, we consider the adsorption of a C60 molecule on a series of hypothetical pentacene structures that vary only in the tilt of the angle that the short axis of the pentacene molecules makes with the underlying surface (the long axis lying essentially flat, as on a metal substrate). Important relationships were discovered between the angle adopted by the short axis of pentacene on the surface, φ1, and the adsorption and diffusion characteristics of C60. Static energy calculations show that there is a transition of the deepest energy minima from between the pentacene rows at low values of φ1 to within the rows at high values of φ1, where φ1 is the angle the pentacene short axis makes with the surface. MD confirms this trend by the predominant residence locations at the extreme φ1 values. Furthermore, MD results suggest that the C60 traverses the pentacene surface in the east-west direction for lower φ1 values (φ1 ≤ 40°) and in the north-south direction for higher φ1 values (φ1 ≥ 70°). Taking both static and dynamic results together, the most favorable tilt angles for mono-directional nanowire growth should occur between 70° and 80° off-normal.

The Negev Radiation Survey

2004 ◽  
Vol 126 (3) ◽  
pp. 906-914 ◽  
Author(s):  
David Faiman ◽  
Daniel Feuermann ◽  
Peter Ibbetson ◽  
Bryan Medwed ◽  
Amos Zemel ◽  
...  
Keyword(s):  
Power Plant ◽  
Solar Radiation ◽  
Site Selection ◽  
Thermal Power Plant ◽  
Meteorological Parameters ◽  
Thermal Power ◽  
Beam Radiation ◽  
Large Variability ◽  
Solar Thermal Power ◽  
Selection For

We present a summary of the principal findings in an ongoing, multiyear, survey of the solar radiation resource and associated meteorological parameters in Israel’s Negev Desert. The summary addresses calibration and monitoring issues, the format in which the annual results are published, availability of the data, and some of the more interesting results observed to date. In particular, we quantify the large variability observed in the direct beam radiation across neighboring sites. The year-to-year variation in this radiation component is also considerable. The variation in the global horizontal radiation is much smaller. Two practical examples are given of uses to which the Negev Radiation Survey has been put: Site selection for a proposed 500 MW solar-thermal power plant; and an estimation of the potential photovoltaic value of rooftops in the major cities.

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