Instantaneous Solar Radiation Research Articles

Estimasi Intensitas Radiasi Matahari Sesaat dengan Metode Konversi Energi

The intensity of solar radiation provides information of amount energi that is transferred by the sun in a unit time. The information is used in many sectors for designing and assembling systems with solar energi sources. The measurement of the intensity of solar radiation directly requires a complex set of tools and procedures. This study aims to provide an estimate of instantaneous solar radiation by using energi conversion methods. The working principle of the method used is to capture the flux of solar radiation with a piece of black copper plates and then extract the energi into the water medium through direct contact of the water-copper plates. The increase of fluid temperatur is measured as a function of the time duration of radiation exposure. The radiation intensity value is obtained from derivation of the gradient value of the increasing temperatur. The results show that the energi conversion method gives the radiation intensity value matching the radiation intensity value based on the calculation of astronomical formulation. In the location of the experiment, at noon, the energi conversion method gives an instantaneous solar radiation intensity of 1149, 63 W/m 2 with a difference of 0.59% with the calculation result of the astronomical formula.

Estimasi Intensitas Radiasi Matahari Sesaat dengan Metode Konversi Energi

The intensity of solar radiation provides information of amount energi that is transferred by the sun in a unit time. The information is used in many sectors for designing and assembling systems with solar energi sources. The measurement of the intensity of solar radiation directly requires a complex set of tools and procedures. This study aims to provide an estimate of instantaneous solar radiation by using energi conversion methods. The working principle of the method used is to capture the flux of solar radiation with a piece of black copper plates and then extract the energi into the water medium through direct contact of the water-copper plates. The increase of fluid temperatur is measured as a function of the time duration of radiation exposure. The radiation intensity value is obtained from derivation of the gradient value of the increasing temperatur. The results show that the energi conversion method gives the radiation intensity value matching the radiation intensity value based on the calculation of astronomical formulation. In the location of the experiment, at noon, the energi conversion method gives an instantaneous solar radiation intensity of 1149, 63 W/m 2 with a difference of 0.59% with the calculation result of the astronomical formula.

Thermal modelling of asymmetric overlap roof greenhouse with experimental validation

ABSTRACTGlobal solar radiation availability model and thermal model for newly designed asymmetric overlap roof shape (AORS) greenhouse are presented and experimentally validated. Instantaneous solar radiation flux is utilised in a dynamic thermal model to ascertain the hourly plant and inside air temperature. The AORS is also compared with the previously developed two best greenhouse shapes. An experimental validation of both the models is carried out for the measured instantaneous solar radiation, plant and inside air temperature for a typical day in summer at Ludhiana (31°N and 77°E), Punjab, India. During the experimentation, a tomato crop was grown inside the greenhouse. From the results, it can be inferred that an east–west orientation AORS greenhouse should be preferred due to a lesser solar radiation capture in summer months. The predicted plant and air temperatures are in good agreement with the measured data having a root mean square error of 4.69 and 3.7, respectively.

Dynamic Simulation of Solar Heating System in Summer and Winter

This paper presents a dynamic model of the solar heating system composed by an inclined solar flat collector coupled to heat storage tank. A Matlab/Simulink based model has been developed to predict the instantaneous solar radiation intensity, the outlet temperature of collector working fluid, the tank temperature and the solar energy utilization of the system. As a case study, this paper analyzed the simulation of Beijing area in winter and summer, the results show that 50~60 degree of inclination of collector can receive more energy and that the performance of the heat collector is stable which efficiency is basically stable at 0.65. The results demonstrate that the maximum outlet temperature of the collector was 35.4°C in winter and 71.1°C in summer. Through the daytime heat storage, the temperature of the heat storage tank can reach 55°C in summer, which is 24°C higher than that in winter. The simulation results can predict the operation of the solar system and provide the research foundation for the dynamic simulation of the solar energy as an auxiliary energy system.

Daily Variation Law of Solar Radiation Flux Density Incident on the Horizontal Surface

The instantaneous solar radiation flux density incident on the horizontal surface near the ground, consisted of three sections, direct radiation, scattered radiation, and thermal radiation flowing down through the atmosphere, directly or indirectly comes from the sun. The dynamics of the solar radiation flux density incident on the horizontal surface near the ground influence all life processes and environment. In this study, the daily variation law of solar radiation flux density incident on the horizontal surface developed. The results showed that generally, sky conditions is stable, and the daily dynamic in the solar radiation flux density incident on the horizontal surface near the ground is the function of time, and can be described by a normal distribution model in a day. The main parameters of the model change with date and the meteorological conditions in a day.

Estimation of daily average downward shortwave radiation from MODIS data using principal components regression method: Fars province case study

Abstract Downward shortwave radiation is a key quantity in the land-atmosphere interaction. Since the moderate resolution imaging spectroradiometer data has a coarse temporal resolution, which is not suitable for estimating daily average radiation, many efforts have been undertaken to estimate instantaneous solar radiation using moderate resolution imaging spectroradiometer data. In this study, the principal components analysis technique was applied to capture the information of moderate resolution imaging spectroradiometer bands, extraterrestrial radiation, aerosol optical depth, and atmospheric water vapour. A regression model based on the principal components was used to estimate daily average shortwave radiation for ten synoptic stations in the Fars province, Iran, for the period 2009-2012. The Durbin-Watson statistic and autocorrelation function of the residuals of the fitted principal components regression model indicated that the residuals were serially independent. The results indicated that the fitted principal components regression models accounted for about 86-96% of total variance of the observed shortwave radiation values and the root mean square error was about 0.9-2.04 MJ m−2 d−1. Also, the results indicated that the model accuracy decreased as the aerosol optical depth increased and extraterrestrial radiation was the most important predictor variable among all.

Normalizing land surface temperature data for elevation and illumination effects in mountainous areas: A case study using ASTER data over a steep-sided valley in Morocco

The remotely sensed land surface temperature (LST) is a key parameter to monitor surface energy and water fluxes but the strong impact of topography on LST has limited its use to mostly flat areas. To fill the gap, this study proposes a physically-based method to normalize LST data for topographic - namely illumination and elevation - effects over mountainous areas. Both topographic effects are first quantified by inverting a dual-source soil/vegetation energy balance (EB) model forced by 1) the instantaneous solar radiation simulated by a 3D radiative transfer model named DART (Discrete Anisotropic Radiative Transfer) that uses a digital elevation model (DEM), 2) a satellite-derived vegetation index, and 3) local meteorological (air temperature, air relative humidity and wind speed) data available at a given location. The satellite LST is then normalized for topography by simulating the LST using both pixel- and image-scale DART solar radiation and elevation data. The approach is tested on three ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) overpass dates over a steep-sided 6km by 6km area in the Atlas Mountain in Morocco. The mean correlation coefficient and root mean square difference (RMSD) between EB-simulated and ASTER LST is 0.80 and 3°C, respectively. Moreover, the EB-based method is found to be more accurate than a more classical approach based on a multi-linear regression with DART solar radiation and elevation data. The EB-simulated LST is also evaluated against an extensive ground dataset of 135 autonomous 1-cm depth temperature sensors deployed over the study area. While the mean RMSD between 90m resolution ASTER LST and localized ibutton measurements is 6.1°C, the RMSD between EB-simulated LST and ibutton soil temperature is 5.4 and 5.3°C for a DEM at 90m and 8m resolution, respectively. The proposed topographic normalization is self-calibrated from (LST, DEM, vegetation index and in situ meteorological data) data available over large extents. As a significant perspective this approach opens the path to using normalized LST as input to evapotranspiration retrieval methods based on LST.

A simple and efficient procedure for increasing the temporal resolution of global horizontal solar irradiance series

The intermittent nature of instantaneous solar radiation has a considerable impact on the nonlinear behavior of solar energy conversion systems. The time resolution of the Numerical Weather Prediction Models (NWPM) or satellite derived solar irradiance data are typically limited to 1-h (at best 15-min). Unfortunately, this resolution is not sufficient in the design and performance of many solar systems. In this study, a new methodology has been developed to increase the temporal resolution of GHI series from 1-h to 1-min. This methodology uses the clearness index kt (the ratio of GHI to top-of-atmosphere irradiance on the same plane) to characterize the GHI high-frequency dynamics from a 1-year measurement campaign at a given site. The evaluation of the method with 2 years of measured data in different climatic zones has resulted in KSI(%) (Kolmogorov–Smirnov test Integral parameter) and normalized root mean square deviation values below 8.0% and 1.7% respectively for each month, with negligible bias. Indicators of overall performance show an excellent agreement between measured and modeled 1-min GHI data for each month: average values for Nash-Sutcliffe efficiency, Willmott index of agreement and Legates coefficient of efficiency are found to be 0.94, 0.99 and 1.00, respectively.

Hourly Solar Radiation Forecast Based on k-NN Nonparametric Regression Model

It is hard to accurately predict solar radiation due to its very prominent nonlinear feature, so four major models based on the k-NN model, which have time, sunshine hours, temperature, wind speed and humidity as input data, are presented in the paper for hourly solar radiation forecasting. The models forecasting instantaneous solar radiation values in the Xining region have been created through experiments carried out in Qinghai University. The accuracy of the optimum model is up to 88.7% on average and 97.01% at most on the premise and the allowed absolute percentage error is lower than 20%.

Temperature and wind speed impact on the efficiency of PV installations. Experience obtained from outdoor measurements in Greece

Although efficiency of photovoltaic (PV) modules is usually specified under standard test conditions (STC), their operation under real field conditions is of great importance for obtaining accurate prediction of their efficiency and power output. The PV conversion process, on top of the instantaneous solar radiation, depends also on the modules' temperature. Module temperature is in turn influenced by climate conditions as well as by the technical characteristics of the PV panels. Taking into consideration the extended theoretical background in the field so far, the current study is focused on the investigation of the temperature variation effect on the operation of commercial PV applications based on in-situ measurements at varying weather conditions. Particularly, one year outdoor data for two existing commercial (m-Si) PV systems operated in South Greece, i.e. an unventilated building-integrated (81 kWp) one and an open rack mounted (150 kWp) one, were collected and evaluated. The examined PV systems were equipped with back surface temperature sensors in order to determine module and ambient temperatures, while real wind speed measurements were also obtained for assessing the dominant effect of local wind speed on the PVs' thermal loss mechanisms. According to the results obtained, the efficiency (or power) temperature coefficient has been found negative, taking absolute values between 0.30%/°C and 0.45%/°C, with the lower values corresponding to the ventilated free-standing frames.

Assessing the solar potential of roofs in Valparaíso (Chile)

A computer routine was created with the aim of estimating the solar energy potential in an urban area of Valparaiso (Chile) constituting 366 houses, characterized by a high heterogeneity of roofing in terms of geometry and spatial orientation. The program routine is able to provide useful data for large scale assessment of domestic solar which includes the total hourly instantaneous solar radiation received on every roof for each hour of the year, as well as the yearly total solar radiation considering the roof geometry, tilt angle and orientation. To this end, aerial photographs were taken and topographic groundwork was carried out to produce a spatial-geometry database of the houses, which, together with local meteorological data, was used as numerical input to produce solar radiation mapping of the analysis zone. The results reflect the effect of the high heterogeneity of the input data for tilt angle, orientation and surface area of roof planes in the final values for yearly total incident solar radiation. The software routine could be used by local authorities, urban planners, energy advisers and private individuals to promote the uptake of solar energy in Valparaíso and in other cities around the world.

A three-state model for the probability distribution of instantaneous solar radiation, with applications

Based on a new set of data covering a 13-month period and a wide range of the average clearness indices, the probability distribution for instantaneous solar radiation is modeled. The data’s probability density function is shown to be capably represented by a linear superposition of three (truncated) normal distributions. The variable of the distribution is the “normalized clearness index”, κ, which is the clearness index kt divided by its value under clear sky conditions—a quantity now available for most locations on the globe. It is shown that usingκ as the variable makes the distribution independent of the air mass. The only other parameter in the distribution is the mean value, κ¯, of κ. The latter quantity fixes the parameters and the respective weights of the normal distributions, through empirically-derived fits. A physical interpretation of these findings is presented, whereby each normal distribution is associated with one of the three possible states of the atmosphere: namely (a) clear sky conditions, (b) overcast conditions, and (c) all other conditions. This interpretation predicts that the mean of the clear-sky state normal curve will be unity, and this has been confirmed for the data in hand. Also lending support to the three-state interpretation, is its ability (demonstrated in this paper) to predict the fraction of time of bright sunshine. Based on this new three-state model, a preliminary first-principle model for the mean diffuse fraction is given, as well as expressions for mean radiation on inclined surfaces and the instantaneous utilizability. The instantaneous utilizability is found to be greater than that for hourly or daily time periods and to depend in a significant way on the clear sky value of kt.

Relationship between sunshine duration and solar radiation

This paper examines the relationship between sunshine duration and solar radiation received on the earth’s surface. Sixty-nine thousand pairs of sunshine–radiation readings from 670 sites were analyzed. A generalization of the Ångström–Prescott equation of the form K¯=K¯clear[β+(1-β)Sγ] was found to most efficiently fit the data and suggests the relationship between the average daily atmospheric transmittance K¯ and the sunshine fraction S is non-linear. The suggested reason for this non-linearity is that a reduced sunshine fraction not only decreases the clear sky radiation duration, but also the radiation transmitted through clouds, i.e. clouds get optically thicker with decreasing S. This finding is supported on theoretical grounds and by analyzing instantaneous solar radiation measurements from Australia and Germany.Representing the sunshine fraction in terms of the proportion of beam radiation reaching the earth’s surface S=H¯b/H¯b,clear leads to a fundamental connection between the monthly average diffuse fraction and the sunshine–radiation relationship. Moreover, it confirms the non-linearity of the latter relationship, which was previously questioned because of limited data and/or poor quality sunshine measurements.

便携式全自动太阳光度计的研制及其应用

A set of portable autocontrol muti-wavalength sun-photometer base on Visual Basic,which is real-time and obvious,is developed.It can measure and display instantaneous solar radiation and atmospheric aerosol optical thickness and precipitable water as well.It is also provided with the on-line detection function of electric engine operation,sun tracing,heating temperature et al.This instrument is improved based on the prototype developed by ourselves.The sun-photometer is more portable and can more accommodate to the abominable environment,more miniaturize and improve the ratio of his performance and price.The measured results of this device are satisfactory via the analysis and compare of measured data.Also the instrument calibration and its application are described.

Experimental investigation of single-phase and two- phase closed thermosyphon solar water heater systems

This study represents an experimental performance comparison between single-phase and two-phase closed thermosyphon solar water heater systems (SWHS). For this aim, two identical small-scale SWHSs were constructed side-by-side. The tests were performed under same environmental and load conditions. In the first one of these systems, water was used as working fluid in the solar collector in the conventional SWHS called single-phase. In the second one of these systems, R-134a was used as working fluid in two-phase SWHS. The performance of these systems under clear-sky conditions were investigated in July under the field conditions of Konya in Turkey. In both of these systems, the temperatures of collector inlets and outlets and water storage tanks were measured. Instantaneous solar radiation data were also taken from Konya Directorship of Meteorology Citation. Cumulative efficiencies of two-phase and single-phase systems by daily were determined. When the two-phase system is compared with the conventional single-phase system, it is derived that the two-phase system is 42.8% more efficient than the other. Key words: Two-phase solar collector, closed thermosyphon, heat-pipe, refrigerant charged, solar water heater.

Estimation of daily actual evapotranspiration from remotely sensed data under complex terrain over the upper Chao river basin in North China

Daily actual evapotranspiration over the upper Chao river basin in North China on 23 June 2005 was estimated based on the Surface Energy Balance Algorithm for Land (SEBAL), in which the parameterization schemes for calculating the instantaneous solar radiation and daily integrated radiation were improved by accounting for the variations in slope and azimuth of land surface and terrain shadow in mountainous areas. The evapotranspiration (ET) estimated from satellite data in this study for the whole watershed ranges from 0 mm to 7.3 mm day−1 with a mean of 3.4 mm day−1, which was validated by Penman–Monteith approaches for water body and paddy land. The comparison of ET estimates for a wide range of land cover types reflected distinct mechanisms of energy partition and water removal of various land cover types, showing differences in the spatial distribution pattern of ET, which could be not only the reflection but also the driving force of advection and local circulation that may violate the surface energy balance equation in the vertical direction. The spatial variation in daily solar radiation and ET estimates under the complex terrain of forest land were elaborated and evaluated by exploring the relationship between ET estimates and elevations for wood land and grass land. In addition, the utility and limitations of SEBAL's applicability to watersheds with various land cover types and complex terrain were analysed.

Performance evaluation method of solar-assisted heat pump water heater

The present study derives a simple linear correlation for the performance evaluation of different solar-assisted heat pump water heater (ISAHP). The correlation was derived from the principle of energy conservation with some simplifications. The correlation is then verified using the long-term outdoor field test data of four different ISAHP. The problems of seasonal repeatability and method of data scattering were examined. From that, a standard performance test method is proposed. The test method suggests that only the measurement of instantaneous solar incident radiation on horizontal surface, ambient temperature, hot water temperature in the storage tank, total mass of water in the storage tank and total power input to the ISAHP are required. It is suggested to select the value of COP at T f − T a,ave = 15 °C as the characteristic COP for performance comparison of ISAHP. It is found from the test results that the same performance correlation holds for ISAHP operating with single or dual energy source.

Accurate spin axes and solar system dynamics: Climatic variations for the Earth and Mars

Celestial mechanical simulations from a purely classical point of view of the whole solar system, including our Moon and the Mars moons { Phobos and Deimos { are carried out for 2 millions of years before present. Within the classical approximation, the results are derived at a very high level of accuracy. Eects from general relativity for a number of variables are investigated and found to be small. For climatic studies of about 1 Myr, general relativity can safely be ignored. Three dierent and independent integrations schemes are used in order to exclude numerical anomalies. The converged results from all methods are found to be in complete agreement. For verication, a number of properties such as spin axis precession, nutation, and orbit inclination for Earth and Mars have been calculated. Times and positions of equinoxes and solstices are continously monitored. As also observed earlier, the obliquity of the Earth is stabilized by the Moon. On the other hand, the obliquity of Mars shows dramatic variations. Climatic influences due to celestial variables for the Earth and Mars are studied. Instead of using mean insolation as in the usual applications of Milankovitch theory, the present approach focuses on the instantaneous solar radiation power (insolation) at each summer solstice. Solar radiation power is compared to the derivative of the icevolume and these quantities are found to be in excellent agreement. Orbital precessions for the inner planets are studied as well. In the case of Mercury, it is investigated in detail.

On the relationship between duration of sunshine and solar radiation on the earth’s surface: Ångström’s equation revisited

The paper presents a relationship between the relative sunshine duration and solar irradiation on the earth’s surface. Following a review of the literature on Ångström’s equation and the properties of instantaneous solar radiation, the sunshine–radiation relationship is derived from monthly average values of daily beam radiation which are used as a measure for the fraction of clear sky, f clear = H ̄ b / H ̄ b,clear . The resulting (non-linear) relationship, f clear =( K ̄ / K ̄ clear ) 2 , unlike the Ångström–Prescott relation, does not contain empirical constants and only requires the monthly average clear sky atmospheric transmittance to account for the climate of a particular location ( K ̄ clear is typically between 0.65 to 0.75). The relationship is verified for monthly intervals for Perth and Townsville, Australia and compared to existing Ångström–Prescott equations for a wide range of climates and locations. The excellent agreement of the proposed relationship with the average value of data in the latter comparison suggests that it may be universally valid and that the Ångström–Prescott equation is a local (linear) approximation of the derived relationship. For daily time intervals the sunshine–radiation relationship changes to f clear=( K/ K clear) 3. The paper closes with a discussion on applications of the new relationship including the performance prediction of solar energy systems.

A new model to predict direct normal instantaneous solar radiation, based on laws of spectroscopy, kinetic theory and thermodynamics

The attenuation of solar radiation by the atmosphere is caused by two simultaneous processes: (a) scattering by air molecules and by the atmospheric turbidity; and (b) absorption by O 3, H 2O and CO 2. Since the atmospheric turbidity is closely related to horizontal visibility, V (meteorological optical range), the terrestrial direct normal solar radiation can be expressed as: I bn =I on exp(−N s K s − K t V −N o K o −N c K c −N w K w )mƒ where I on is direct normal extraterrestrial solar radiation; N o, N s, N c, and N w are thickness of the ozone layer in precipitate cm, the total number of gas moles, the number of CO 2 moles and the number of H 2O moles in the vertical atmosphere column, respectively; V is visibility in km; K s, K t, are the Rayleigh and the modified turbidity scattering coefficients; K o, K c, K w are the absorption coefficients of ozone, carbon dioxide and water vapour, respectively; m is relative air mass; f is the empirical function for air mass correction. Based on experimental measurements of direct normal solar radiation at different locations: Murmansk (polar zone), St Petersburg, Moscow, Kharkov, Crimea (Russia and Ukraine), Kabul (Afghanistan), and Gaborone (Botswana), a new physical model to calculate all variables and coefficients involved in the above equation is proposed. The model is based on laws of spectroscopy, kinetic theory and thermodynamics. A special software to predict direct normal solar radiation is developed. Comparison of the model proposed with the experimental measurements of I bn showed that the accuracy of the direct normal solar radiation obtained with this program is within 5% of the experimental data. For countries where the meteorological conditions do not change very much the accuracy can be improved to 3%. The model can be used at any location from the Northern to the Southern Pole, with only meteorological input data (pressure, temperature, relative humidity and visibility).