Calculation Of Solar Radiation Research Articles

Analysis of the atmospheric turbidity levels at two Tunisian sites

Atmospheric turbidity coefficients have been estimated in many locations, either on the basis of spectral irradiance or on broadband direct irradiance data. The Ångström turbidity coefficient, β, linked to the absorption and diffusion of aerosols, is very important since many solar radiation models for clear days use this parameter. The Linke turbidity factor, T L, is of specific importance for the calculation of beam and diffuse solar radiation in a determined locality. Furthermore, an atmospheric turbidity index in a determined locality can be associated with the pollution level at that place. Direct solar radiation data, measured with a pyrheliometer in a coastal tourist location in Tunisia (Sidi Bou Saïd), are used to investigate the diurnal and monthly variations of the atmospheric turbidity using Linke's factor T L during 1999. Computed T L values vary between 2.5 and 8 with a frequency of about 53% greater than 5.0. Highest and lowest turbidity levels have been observed in August and December, respectively. Values of the turbidity coefficient β have been determined in Thala (a continental and nonindustrialized region in Tunisia), for 8 months in 2001, based on a direct fitting method of the Angström power low expression using sun-photometer data. Monthly averaged values of β coefficient vary between 0.15 and 0.33 with highest turbidity recorded in July and October and lowest in April. Measured meteorological parameters represent a valuable supplement to the data sets with the sun-photometer and the pyrheliometer measurements. The analysis of the results shows that there is a high correlation between atmospheric turbidity and local weather conditions, especially wind speed and wind direction.

Climate change and glacier retreat in northern Tien Shan (Kazakhstan/Kyrgyzstan) using remote sensing data

This paper presents an analysis of precipitation and temperature trends and a GIS-supported investigation of the related glacier change in the mountain ridges Zailiyskiy and Kungey Alatau, which represent an important part of the northern Tien Shan. The recent glacier coverage was delineated in a semi-automated way using a TM4/TM5 ratio image of a Landsat ETM Scene from the year 1999 and a merged ASTER/SRTM3-DEM. The extent of these glaciers is compared to that of the glaciers in the Soviet Glacier Inventory [UdSSR, Academica Nauk (1966 to 1983). Katalog Lednikov SSSR (in Russian), Gidrometeoizdat. Leningrad], which represents the situation in study area in approx. 1955. Regionalization of temperature and precipitation as well as solar radiation calculation was conducted in order to determine the climate situation at the glaciers. Trend and correlation analysis for the period from 1879 to 2000 at 16 climate stations showed a temperature increase, which have become pronounced since the 1950s. Another strong increase occurred at the beginning of the 1970s and since around 1980, the temperatures have generally stayed at this high level. The trend coefficient was about 0.8 K/100a for the period 1900 to 2000 and about 2.0 K/100a on average for the second half of the last century. The increase was about two times higher than the global average in northern Tien Shan from 1950 until 2000, where the increase was mainly due to temperature rise in autumn and winter. The increase is less pronounced in the mountainous areas, but still obvious. However, the higher temperature increase at the lower stations, located for the most part in cities or larger settlements, may be due in part to increased urbanization. For precipitation, there was a small increase on average, but no clear trend. On the average, the decrease in glacier extent was more than 32% between 1955 and 1999 in the investigated valleys of Zailiyskiy and Kungey Alatau. The glacier retreat was not homogeneous, but depended strongly on the size, location and climate regime at the glaciers. The area loss of the continental-type glaciers with very predominant summer accumulation, as for those situated in the deeply incised Chon-Kemin valley between Zailiyskiy and Kungey Alatau, was conspicuously less, in parts, than the loss at the more maritime glaciers on the northern slope of Zailiyskiy Alatau. This is consistent with the small increase in summer temperatures. However, under dryer conditions with high solar radiation input, such as with glaciers in the Chon-Aksu valley in Kungey Alatau, the area retreat of the continental-type glaciers can be even more pronounced than that of the more maritime glaciers.

A quasi-analytic solution of the radiative transfer equation for three-dimensional atmospheres

In this study, we present a new solution of the three-dimensional (3-D) radiation transfer equation (RTE). The solution employs a discretization technique to separate the independent variables involved in the 3-D RTE, and the doubling-adding method to solve the RTE explicitly and quasi-analytically. The remarkable feature of the present solution is the application of scaling-function expansion to those terms that are dependent on horizontal coordinates. Scaling-function expansion is suitable for representing irregular horizontal inhomogeneities with small-scale variations. By applying scaling-function expansion, the 3-D RTE can be formulated in the form of a vector–matrix differential equation; matrices involved in the equation are generally sparse and dominantly diagonal matrices, and this considerably reduces the labor involved in matrix calculations. We tested the performance of the present solution via radiative transfer calculations of solar radiation in horizontally inhomogeneous two-dimensional cloud models. The calculated results indicate that even if the resolution of the scaling-function expansion is too coarse in regions around small-scale variations, the influence does not spread problematically to other regions far from the variations; this illustrates the advantage of the scaling-function expansion. The present solution can be used to investigate quantitatively and to estimate the effects of cloud spatial inhomogeneity on the corresponding radiation field.

Distributed modeling of direct solar radiation on rugged terrain of the Yellow River Basin

Due to the influences of local topographical factors and terrain inter-shielding, calculation of direct solar radiation (DSR) quantity of rugged terrain is very complex. Based on digital elevation model (DEM) data and meteorological observations, a distributed model for calculating DSR over rugged terrain is developed. This model gives an all-sided consideration on factors influencing DSR. Using the developed model, normals of annual DSR quantity with a resolution of 1 km × 1 km for the Yellow River Basin was generated, with DEM data as the general characterization of terrain. Characteristics of DSR quantity influenced by geographic and topographic factors over rugged terrain were analyzed thoroughly. Results suggest that: influenced by local topographic factors, i.e. azimuth, slope and so on, and annual DSR quantity over mountainous area has a clear spatial difference; annual DSR quantity of sunny slope (or southern slope) of mountains is obviously larger than that of shady slope (or northern slope). The calculated DSR quantity of the Yellow River Basin is provided in the same way as other kinds of spatial information and can be employed as basic geographic data for relevant studies as well.

Solar radiation calculation methodology for building exterior surfaces

The present article shows a new methodology of calculation of the direct, diffuse and reflected incident solar radiation, in all type of surfaces, either in open urban environments or inside buildings. This methodology is applicable in problems related to solar access (space heating in buildings, shadowing of open spaces), solar gains (space cooling in buildings), and daylighting. Solar radiation is the most important contribution to the surface and volumetric energy balance during the daytime. Particularly, solar radiation is the main contributor to heat gains in buildings, especially in residential buildings, where internal gains are very low. Utilization of daylight in buildings may result in significant savings in electricity consumption for lighting while creating a higher quality indoor environment. Additional energy savings may also be realized during cooling season, when reduction of internal heat gains due to electric lighting results in a corresponding reduction of cooling energy consumption. The analysis of the existing calculation methods and proposed in the scientific bibliography for the calculation of the solar radiation in problems of solar access in winter, solar gains in summer, and daylighting, takes us to the necessity of outlining a new and complete methodology. This new methodology is applicable to all these problems with a great accuracy and calculation speed.

Meteosat and GOES-East Imager Visible Channel Calibration

Abstract As a preliminary step to solar irradiance calculations, the Centre de Météorologie Spatiale (CMS) has developed a pragmatic approach to calibrate the visible channels of Meteosat and GOES-East imagers. The responsivity of the Meteosat visible channel has been monitored with three desert targets from 1989 to 2002. The annual degradation rate has been estimated to 1.8% for Meteosat-4, 1.4% for Meteosat-5, and 1.9% for Meteosat-7. A reference calibration coefficient for Meteosat-7 has been derived from a comparison with Clouds and Earth's Radiant Energy System (CERES) data in summer 1998. Meteosat and GOES-East data corresponding to homogenous pixels along longitude 37.5°W and around 1200 LST have been compared on a monthly basis, leading to a calibration of GOES-East visible channel. GOES-8 data have been processed from June 1998 to December 2002 and the annual degradation rate obtained during this period is 4.0%. GOES-12 data have been processed from April to August 2003. During this short period, no degradation rate can be estimated but only a mean value of the calibration coefficient, which corresponds to a 7% increase of the prelaunch coefficient.

Comparative study of Ångström’s and artificial neural networks’ methodologies in estimating global solar radiation

The aim of the present research is the comparative development of a variety of models for the estimation of solar radiation on a horizontal surface. By using two different methodologies, models of various complexities have been developed and tested. The first methodology refers to the traditional and long-utilized Ångström’s linear approach which is based on measurements of sunshine duration. The second methodology refers to the relatively new approach based on artificial neural networks (ANN) and it can be based on sunshine duration measurements but also on other climatological parameters. Three Ångström-type models and seven ANN-type models are presented. All of these models are verified against independent data and compared. Lack of sunshine duration measurements renders Ångström’s approach inapplicable; hence the feasibility of applying the ANN models for the calculation of solar radiation in places where there is a lack of sunshine duration measurements is investigated.

Adjustment factors for the ASHRAE clear-sky model based on solar-radiation measurements in Riyadh

The solar-radiation variation over horizontal surfaces calculated by the ASHRAE clear-sky model is compared with measurements for Riyadh, Saudi Arabia. Both model results and measurements are averaged on an hourly basis for all days in each month of the year to get a monthly-averaged hourly variation of the solar flux. The measured data are further averaged over the years 1996–2000. The ASHRAE model implemented utilizes the standard values of the coefficients proposed in the original model. Calculations are also made with a different set of coefficients proposed in the literature. The results show that the ASHRAE model calculations generally over-predict the measured data particularly for the months of October → May. A daily total solar-flux is obtained by integrating the hourly distribution. Based on the daily total flux, a factor Φ (<1) is obtained for every month to adjust the calculated clear-sky flux in order to account for the effects of local weather-conditions. When the ASHRAE model calculations are multiplied by this factor, the results agree very well with the measured monthly-averaged hourly variation of the solar flux. It is recommended that these adjustment factors be employed when the ASHRAE clear-sky model is used for solar radiation calculations in Riyadh and localities of similar environmental conditions. Instantaneous, daily and yearly solar-radiation on various surfaces, such as building walls and flat-plate solar collectors, can then be conveniently calculated using the adjusted model for different orientations and inclination angles. The model also allows the beam, diffuse and ground-reflected solar-radiation components to be determined separately. Sample results characterizing the solar radiation in Riyadh are presented by using the “adjusted” ASHRAE model.

Incorporating Bias Error in Calculating Solar Irradiance

Solar irradiance is an important input parameter to many crop simulation models. It is not measured at the same spatial density as air temperature and precipitation, which has lead to the development of algorithms to calculate solar irradiance from air temperature and precipitation data. Fourteen algorithms were evaluated using 10 yr of measured air temperature, precipitation, and solar irradiance data from Mead, NE. All algorithms had similar root mean square errors (RMSE). When the bias error (the difference between measured and simulated values) was plotted against day of year, only one version of the algorithm showed a simple pattern not dependent on fitting a Fourier series to the data. This pattern of the bias error formed the basis for a correction factor that was applied to all calculations of solar irradiance. Using independent meteorological data from nine locations in eastern and western portions of Kansas, Nebraska, and South Dakota, the corrected algorithm developed from the Mead data calculated solar irradiance with RMSE ranging from 3.6 to 4.7 MJ m−2 d−1. Using the Erosion Productivity Impact Calculator, simulated yields of wheat (Triticum aestivum L.), maize (Zea mays L.), and soybean [Glycine max (L.) Merr.] were significantly different when using the measured and uncorrected solar irradiance; however, the yields were not significantly different when using the measured and modified solar irradiance. Using this modification, solar irradiance measured at one location can be used to calculate solar irradiance at locations up to 600 km away in the U.S. Great Plains.

Calculation of direct solar and diffuse radiation in Israel

AbstractThis study deals with the calculation of direct solar radiation and diffuse radiation for locations in Israel as hourly values. The model is based on the calculation of the Linke turbidity factors for the stations Bet‐Dagan, Jerusalem, Beer Sheva, Sedom and Eilat, which have been determined from radiation measurements. The turbidity factors for clear sky conditions showed a characteristic yearly pattern and the differences between the stations were related to their geographical locations. The model requires different algorithms for calculations in the Rift Valley system and the rest of Israel. The calculations proved to be very accurate for clear sky conditions with high radiation values (average deviation: 7.3% or 61.6 W/m2 for values above 600 W/m2). The presence of clouds and lower sun angles lead to less accurate results, which are nevertheless still acceptable within the range for further applications. Copyright © 2001 Royal Meteorological Society

Calculation of solar radiation using a methodology with worldwide potential

Surface meteorological observations from the DATSAV2 database provide the capability to use the METSTAT (meteorological/statistical) model to calculate hourly values of direct normal, diffuse horizontal, and global horizontal solar radiation for locations throughout the world. Opaque cloud cover, a key input parameter to the METSTAT model, is derived from the DATSAV2 layered cloud cover information. Resulting multiyear data sets include solar radiation and other meteorological data such as dry bulb temperature, dew point temperature, wind speed, and atmospheric pressure. Data filling procedures ensure that the multiyear data sets are serially complete. A minor revision to METSTAT improved solar radiation estimates for conditions of high cloud amounts and low ceiling heights. The methodology was applied to regions of Southern Africa and Saudi Arabia.

Using relict rockglaciers in GIS-based modelling to reconstruct Younger Dryas permafrost distribution patterns in the Err-Julier area, Swiss Alp

Differences in mean annual air temperature between the Younger Dryas period and today were estimated at the fronts of 32 relict rockglaciers in the Err-Julier area, eastern Swiss Alps. The analyses were based on a case-by-case calculation of direct incoming solar radiation and mean annual air temperature using a digital elevation model (DEM) and meteo data of recent years. Our results suggest that mean annual air temperature during the Younger Dryas was lowered by c. 3C to 4C, and that the lower limit of permafrost occurrence was depressed considerably more than glacier equilibrium lines. This indicates strongly reduced precipitation (30% to 40% reduction) and much larger abundance of mountain permafrost at that time. A model simulation of the corresponding spatial permafrost distribution during the Younger Dryas indicates that glaciers in the study area were mostly surrounded by permafrost at that time and probably had a polythermal structure of englacial temperatures.

Biophysical and potential vegetation growth surfaces for a small watershed in northern Cape Breton Island, Nova Scotia, Canada

Surfaces of potential vegetation growth in this paper represent the spatial distribution of growing conditions (habitat) for six deciduous tree species native to the Clyburn River valley watershed of northeastern Cape Breton Island, Nova Scotia. Development of potential growth surfaces is based on integrating point calculations of (i) net potential solar radiation, (ii) net long-wave radiation, (iii) growing season degree-day accumulation, and (iv) mean summer soil water content with species-specific evaluations of long-term species environmental response. Functions describing potential species response to available environmental resources are based on generalised mathematical functions that scale species response values between 0 and 1, where 0 represents unsuitable growing conditions and 1, optimal growing conditions. Limitation effects of resource deficits on potential growth are addressed as a multiplication of individual environmental responses. Derived species distributions of potential growth are compared with aerial photo-interpreted distributions of forest vegetation found within the Clyburn River valley watershed. Modelled and photo-interpreted valley distributions demonstrate nearly similar geographic ranges. Actual percent cover for shade-tolerant species displays a positive correlation with modelled potential growth (r2 = 0.5). This is not the case for shade-intolerant species considered, whereby r2 [Formula: see text] 0.

Analysis by simulation of a solar still integrated in a greenhouse roof

This paper presents a simulation model for fresh water production and derived performance parameters for a water desalination system integrated in a greenhouse roof. Several typical daily weather patterns taken from a 10-year period for three arid regions in Tunisia were analyzed. The simulation model is based on a set of heat balance equations including material layers and a brackish water layer. The equations are solved with the more general PC-program, Engineering Equation Solver. For calculation of solar irradiation, the simulation code TRNSYS (Transient System Simulation) was used in the model. The influence of solar irradiation, optical material properties and process parameters on the fresh water production and total light transmission was studied. The most important conclusion is that the roof-integrated still concept has a fresh water production capacity on a sufficient level for irrigation of plants in greenhouse environments. As about 40% of the solar irradiation has to be transmitted, the thermal efficiency is around one-third of the efficiency for tilted types of conventional stills. Further research and technical development are needed in order to optimize the thermal and optical performance of the concept. The solar energy yield could be improved through better design of the greenhouse shape and more selective absorbers.

Simulation Model for Calculating Pavement Temperatures Including Maximum Temperature

A simulation model has been developed to calculate the temperatures of asphalt concrete during summer. Input data to the simulation model are hourly values for solar radiation, air temperature, and wind velocity. Longwave radiation incident to and outgoing from the pavement surface is calculated from the air and pavement surface temperatures, respectively. The portion of the incident shortwave radiation absorbed by the pavement surface is calculated from the albedo of the surface. By means of a finite difference approximation of the heat transfer equation, the temperatures are calculated under the surface. Apart from radiation and heat transfer, convection losses from the pavement surface are also calculated depending on wind velocity, air temperature, and surface temperature. The formulas used for the calculation of radiation and the simulation model as a whole are validated by comparison with measurements, showing good agreement. A method for the calculation of direct solar radiation from a clear sky, at an arbitrary location and time, is used to create input data to the simulation model in order to calculate maximum pavement temperatures. The formulas used with Superpave to calculate maximum pavement temperatures are based on the assumption that there is an equilibrium when a maximum temperature is reached. Such an equilibrium assumption can be strongly questioned, and its consequences are discussed.

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