Calculation Of Solar Radiation Research Articles

Large-Scale Forcing and Cloud–Radiation Interaction in the Tropical Deep Convective Regime

Abstract The simulations of tropical convection and thermodynamic states in response to different imposed large-scale forcing are carried out by using a cloud-resolving model and are evaluated with the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment observation. The model is forced either with imposed large-scale vertical velocity and horizontal temperature and moisture advections (model 1) or with imposed total temperature and moisture advections (model 2). The comparison of simulations with observations shows that bias in temperature and moisture simulations by model 1 is smaller than that by model 2. This indicates that the adjustment of the mean thermodynamic stability distribution by vertical advection in model 1 is responsible for better simulations. Model 1 is used to examine effects of different parameterized solar radiative and cloud microphysical processes. A revised parameterization scheme for cloud single scattering properties in solar radiation calculations is fo...

Heat-Stress Regions in Israel

The data of 20 climatic stations have been examined to determine heat-stress regions in Israel. The data was interpolated and a model was developed for the calculation of direct and diffuse solar radiation. Thermal perception was calculated according to the energy-balance model of man which considers all relevant energy fluxes affecting the human thermo-regulatory system. It is based on the ‘Comfort Equation’ of Fanger (1972) and the ‘Klima-Michel-Modell’ of Jendritzky et al. (1990). Earlier approaches for the assessment of thermal environmental conditions have been done by Sohar (1980), based on the discomfort index. The average daily duration of severe heat stress which a person is exposed to during various activities in summer months has been analyzed in order to classify the thermal environmental conditions in Israel. Statistical evaluations have led to six heat-stress clusters and regions, respectively. A model calculating the spatial development of climatic data between two measuring stations was set up and served to determine the location of the distinctions between the regions. The resulting heat-stress map shows the different heat-stress regions in Israel. The regions are characterized by graphs that show the average monthly duration of light, medium and severe heat-stress. The average duration of severe heat-stress varies in July from approximately 3 hours along the coastal strip and in the higher mountain regions to approximately 13 hours in the Arava.

On Satellite Umbra/Penumbra Entry and Exit Positions

The problem of computing Earth satellite entry and exit positions through the Earth’s umbra and penumbra, for satellites in elliptical orbits, is solved without the use of a quartic equation. A condition for existence of a solution in the case of a cylindrical shadow is given. This problem is of interest in case one would like to include perturbation force resulting from solar radiation pressure. Most satellites (including geosynchronous) experience periodic eclipses behind the Earth. Of course when the satellite is eclipsed, it’s not exposed to solar radiation pressure. When we need extreme accuracy, we must develop models that turn the solar radiation calculations “on” and “off,” as appropriate, to account for these periods of inactivity.

97/02959 European solar radiation atlas. Solar radiation on horizontal and inclined surfaces

This atlas is a revised and updated version of the European Solar Radiation Atlas published in 1984. The revised version contains tables and maps displaying monthly means of global, diffuse and beam solar radiation as well as sunhours for a large number of represenative sites in Europe. Tables show radiation on both horizontal and inclined surfaces. The revisions reflect the political developments in the European Union and within neighbouring countries. The presentation of the tables has been improved and additional information is included. An enlarged text section provides an introduction to the systematics of solar radiation measurement and calculation. The solar data presented in this book is a useful source of information for the estimation of the energy harvest potential for solar systems. The data base is provided on two 3 1/2 disks for more ease in computer assisted design work.

Calculation of solar radiation intercepted by nubian vault and dome shaped buildings

Calculation of solar radiation intercepted by nubian vault and dome shaped buildings

Calculation of solar radiation intercepted by nubian vault and dome shaped buildings

This paper is concerned with the geometrical analysis of a Nubian vault and a hemispherical dome shaped building. From a rigorous analysis, exact expressions have been established for the angle of incidence of solar radiation at these surfaces. These expressions are then used to calculate the total incident solar radiation at different times and at various latitudes. Finally a comparison is made between the solar radiation intercepted by a unit area of each of these building geometries and a flat geometry. For a reference block of 17·4 m2 carpet area, it is found that for latitudes up to 40°N, a Nubian vault form building envelope with East–West orientation receives minimum solar radiation. © 1997 by John Wiley & Sons, Ltd.

Size optimization of a PV system installed close to sun obstacles

The assessment of the optimal size of a PV-array/battery-storage system, when the incident solar radiation is considerably obstructed, is presented in this article. An optimal dimensioning method is proposed based on a new procedure for the calculation of the actual solar radiation on the array surface, for installations located near obstacles. The optimum tilt of the PV array is also computed and the resulting optimal PV-array/battery-storage system is evaluated by an appropriate routine. The results of the application of the complete algorithm for a real case study inside a gorge are illustrated.

Solar radiation on Mars - Tracking photovoltaic array

A photovoltaic power source for surface-based operation on Mars can offer many advantages. Detailed information on solar radiation characteristics on Mars and the insolation on various types of collector surfaces are necessary for effective design of future planned photovoltaic systems. In this article we have presented analytical expressions for solar radiation calculation and solar radiation data for single axis (of various types) and two axis tracking surfaces and compared the insulation to horizontal and inclined surfaces. For clear skies (low atmospheric dust load) tracking surfaces resulted in higher insolation than stationary surfaces, whereas for highly dusty atmospheres, the difference is small. The insolation on the different types of stationary and tracking surfaces depend on latitude, season and optical depth of the atmosphere, and the duration of system operation. These insolations have to be compared for each mission.

A device for measuring the angular distribution of incident radiation on tubular solar collectors

The calculation of the incident solar radiation falling upon tubular collectors presents difficulties which do not exist when this is carried out for flat plate collectors. Due to their cylindrical shape, the solar incident radiation on their surface is a function of angle and time. This paper presents experimental results which were obtained by means of a device specially designed in order to measure the distribution of such radiation. The device's sensor element (a photodiode) was characterised, calibrated and subsequently used to measure the angular distribution of radiation incident on the inside surface of the inner tube of an evacuated solar collector. It was found that the experimentally measured distribution agrees with that obtained by the ray-tracing method which appears in the literature.

Photovoltaic Catenary-Tent Array for the Martian Surface

To provide electrical power during an exploration mission to Mars, a deployable tent-shaped structure with a flexible photovoltaic (PV) blanket is proposed. The array is designed with a self-deploying mechanism utilizing pressurized gas expansion. The structural design for the array uses a combination of cables, beams, and columns to support and deploy the PV blanket. Under the force of gravity, a cable carrying a uniform load will take the shape of a catenary curve. A catenary-tent collector is self shading which must be taken into account in the solar radiation calculation. The shape and the area of the shadow on the array was calculated and used in the determination of the global irradiance on the array. The PV blanket shape and structure dimensions were optimized to achieve a configuration which maximizes the specific power (W/kg). The optimization was performed for three types of PV blankets (silicon, gallium arsenide over germanium, and amorphous silicon) and two types of structural materials (carbon composite and arimid fiber composite). The results show that the catenary shape of the PV blanket corresponding to zero end angle at the base with respect to the horizontal results in the highest specific power. The tent angle is determinedmore » by optimizing the specific mass and the output power for maximum specific power. The combination of carbon fiber structural material and amorphous silicon blanket produces the highest specific power.« less

Estimation of Cirrus Optical Thickness from Sun Photometer Measurements

A method is proposed to estimate the optical thickness of cirrus clouds from ground-based sun photometry. Transfer calculations of solar radiation in ice clouds were made by the Monte Carlo method. A scattering phase function presented by Takano and Liou was employed for ice clouds. Simulations of sun photometry, which include strong forward scattering into the instrument's field of view, give a simple relationship between the true and apparent optical thicknesses. The correction method was applied to Sun photometer measurements for cirrostratus clouds observed at Tsukuba, Japan. The relationship between the visible optical thickness and the broadband solar flux transmittance obtained from observations agreed well with that theoretically expected for cloud optical thickness up to about 10.

Incorporation of a digital elevation model derived from stereoscopic satellite imagery in automated terrain analysis

A digital elevation model (DEM) was created from multispectral, stereoscopic SPOT (Systeme Probatoire d'Observation de la Terre) High Resolution Visible (HRV) satellite imagery using an automatic DEM generation program. The accuracy and use of this model was tested in automated terrain analysis of a moderate to high relief environment in southwest Yukon, Canada. An annual sum solar radiation calculation which incorporated a modification for horizon constraints was used in a classification of several subarctic terrain surfaces including four geomorphic process domains. Results of linear discriminant analysis indicated the potential to obtain classification accuracies for such surfaces that are comparable to those achieved using spectral data combined with DEMs created by digitizing 1:50,000 scale topographic maps or through stereoprocessing of medium-scale black and white metric aerial photographs. For example, mulitspectral SPOT HRV data alone provided an overall classification accuracy of 67.6%, which improved to 78.1% with the stereocorrelation variables of elevation, slope, and either solar radiation or incidence value. Additional improvements in accuracy may be possible through more complex image corrections, advanced image analysis techniques, or both.

Satellite based estimates of solar irradiance at the earth's surface—I. Modelling approaches

Various approaches to the calculation of solar radiation at the earth's surface using satellite data are reviewed. The methods range from qualitative and subjective use of hard copy satellite images at low spatial and temporal resolution to the use of high resolution digital data and spectral radiative transfer models. Operational techniques are also described. These can be either statistically or theoretically based with varying degrees of numerical complexity. The nature of the input data requirements also varies. Some methods use widely available hard copy satellite images while others are based on digital data. There is also a wide variation in the requirements for additional environmental data. Some models meet all such requirements by analysis of the satellite data. Other models need such information as precipitable water derived from upper air soundings or empirical calculations. The accuracy of various models is assessed. Accuracy increases dramatically with averaging period (hourly to monthly). Many models, even some of the more easily implemented ones, are able to match the accuracy of the models which use surface based observations of cloud or bright sunshine.

Fundamentals and characteristics of solar radiation

The calculation of solar radiation received at a particular place and at a particular time, involves many factors like rotation and revolution of the earth, atmospheric attenuations, atmospheric conditions, time of day and year, geographic location of place, and site location of collector, tilt of collector, type of its variation due to seasonal and atmospheric conditions and show how calculation for horizontal and tilted surfaces may be done based on geometrical and seasonal consideration. Certain angles have been defined for specification of the sun's position in the sky like solar altitude and azimuth angles and the sun's apparent path across the sky found on the celestial sphere. The method of defining position of a point on the earth's surface with respect to the sun's rays by means of latitude, hour angle and declination is also shown. Depletion of extraterrestrial radiation by absorption, scattering etc. is also discussed in detail in this paper.

External reflectors for large solar collector arrays, simulation model and experimental results

A model for the calculation of incident solar radiation from flat- and CPC-shaped external reflectors onto flat plate solar collector arrays has been developed. Assuming an infinite length of the collector/reflector rows, the basic calculations of incident radiation in the collector plane from the reflector become very simple. The direct radiation from the sun is projected into a vertical plane perpendicular to the collector and reflector plane. The incident radiation onto the collector, including corrections for shadowing and lost radiation above the collector, can then be calculated using 2-D geometry. For very short collector/reflector rows a 3-D model is given for correction for the loss of specular radiation in the east west direction. The diffuse radiation is assumed to be isotropic. The diffuse radiation in the collector plane is calculated using view factors. CPC-shaped reflectors can be treated with the same models by introducing an equivalent flat reflector. The incidence angle for the solar radiation from the reflector onto the collector is in most cases higher than the incidence angle for the radiation directly from the sun. Therefore the incidence angle characteristics of the collector glazing and absorber become more important in this application. Equations are given for the incidence angles for diffuse and beam radiation. An annual performance increase of over 30%, 100–120 kW h/m 2, has been measured for aged (four operating seasons) flat reflectors in the Swedish climate. With a CPC-shaped reflector and new reflector materials, a performance increase of up to 170 kW h/m 2 is not unrealistic. This means that the collector and ground area requirement can be reduced by more than 30% for a given load.

Delta‐Eddington approximation for solar radiation in the NCAR community climate model

Motivated by the desire for a more flexible and general solar radiation calculation in the NCAR community climate model (CCM), the δ‐Eddington approximation has been employed in the CCM version 2 (CCM2). Eighteen spectral intervals span the solar spectrum from 0.2 to 5.0 μm. Absorption parameterizations for H2O, O3, CO2, and O2 were developed by making use of the latest theoretical calculations. Water droplet scattering and absorption are parameterized as shown by Slingo (1989). An accurate and efficient convolution of the H2O vapor spectrum with water droplet clouds is presented that yields good agreement with available line‐by‐line (LBL) calculations for single‐layer clouds. A simple and efficient method to simulate partial cloud cover and cloud overlap is included. The simulated albedo‐solar zenith angle dependence agrees very well with adding/doubling scattering calculations. The CCM2 δ‐Eddington method will make possible many interesting applications of CCM2 in the years to come.

Calculation of direct solar radiation on tilted surfaces

This paper proposes formulae to convert on an arbitrary oriented tilted surface the unconcentrated or concentrated solar radiation data measured on a tilted surface. In the case of unconcentrated radiation, a widely used formula is shown to be a good approximation unless extreme situations are considered. The accuracy of the same formula decreases by increasing the concentration factor.

A procedure for calculating cooling load due to solar radiation: the shading effects from adjacent or nearby buildings

The current methods for calculating cooling loads consider the solar heat gain through the transparent component. The solar heat gain through the opaque components is also significant especially for buildings of different functions which may have bigger opaque surfaces. In this paper a simulation model is provided for the determination of the shading effect of the surrounding buildings on a building in a settlement. In the first phase of the calculation procedure, data for solar radiation calculations were obtained through a method by Öztürk and Kiliç, and used for determining correlation coefficients, relying on data for Turkey. In the second phase, the simulation of shaded areas on vertical surfaces of buildings, created by neighbouring buildings, used the shadow components of a vertical pole on a three-dimensional coordinate system. After determination of shaded areas on building façades, incidence of the total solar radiation can be calculated and sol-air temperature obtained by using climatic data and the calculated total solar radiation. Finally, a computer programme was developed to implement the calculation procedure and can be used to evaluate the thermal performance and cooling load of a building by taking into account the shading effect of the surrounding buildings. In the absence of computer facilities or where the settlement texture cannot be predicted, tables of the shading factors for the building envelope can be prepared as an output of the process.

Real-time thermal model for an oil-immersed, forced-air cooled transformer

A thermal model for predicting the real-time temperatures of an oil-immersed, forced-air cooled transformer is presented. The model consists of a set of three differential equations that are formulated into a computer program. Equations that can be solved for the average real-time temperatures of the core and coil assembly, oil, and tank are developed. Expressions for the convection heat transfer coefficients at all internal oil-solid interfaces, equations for calculation of the incident solar radiation, and correlations for the convective cooling rate from the external tank and cooling tubes are discussed in detail. The thermal model can predict the real-time transformer temperatures for any variation in electrical loading and for any type of ambient thermal environment. Since this model is more detailed than the ANSI/NEMA equations, the results can be expected to predict the transformer temperatures more accurately. The model yielded conservative estimates of the component temperatures when compared with temperatures measured on a distribution transformer. While this test does not verify the accuracy of the model for all types of transformers under all types of loading conditions, it does give initial credibility to the accuracy of the equations and their applicability to transformer heating. >

On the calculation of solar radiation in dust-free atmospheres in Ibadan

In an earlier work [Ideriah (1985), Solar Energy 34 , 271], a previous theoretical model [Ideriah (1981), Solar Energy 26 , 447] for calculating the direct and diffuse solar radiation was examined in detail for the harmattan haze season (November-January) of 1975–1980 at Ibadan, when the atmosphere is often heavily overcast with dust. This led to an improved method of calculating the transmission coefficients of insolation. This study extends the previous work to compute the daily global insolation received at Ibadan during the dust-free seasons (February-October) of the years 1975–1980. The calculated values of the daily global insolation generally fall within 10%, while the calculated 6-year monthly average values are largely within 6% of the experimental data provided by the International Institute of Tropical Agriculture (I.I.T.A.), Ibadan.