Prediction of global solar radiation from bright sunshine hours and other meteorological data

Three existing empirical relations which predict global radiation from bright sunshine hours and meteorological parameters, were tried for 14 Indian stations where all relevant data was available. A large amount of error (±50%) was found. So a new empirical relation was established between global radiation and meteorological parameters. The new relation predicted the insolation within a ±10% error limit in most cases. Global radiation dependence on ambient temperature and relative humidity was introduced through atmosperic water content per unit volume. The relation is WAT = RH(4.7923+0.3647×T+0.0055×T²+0.0003×T³)G = G_ext(0.414+0.400×SS-0.0055×WAT)$\text{SS}\text{= S}\text{Z}\text{?}$     

Estimation of total solar radiation from bright sunshine hours in Turkey

Measurements of total solar radiation and bright sunshine hours in six different climatological locations in Turkey are used to develop an Angstrom type equation. The coefficients are found for a linear equation from regression analysis for these locations. A simple overall equation, which yields the solar radiation in any location in Turkey for bright sunshine hours, is developed. The results of this equation, together with the results obtained from five similar, internationally accepted correlations, are compared with measured data.     

Models of solar radiation with hours of bright sunshine: A review

In the design and study of solar energy, information on solar radiation and its components at a given location is very essential. Solar radiation data are required by solar engineers, architects, agriculturists and hydrologists for many applications such as solar heating, cooking, drying and interior illumination of buildings. For this purpose, in the past, several empirical correlations have been developed in order to estimate the solar radiation around the world. The main objective of this study is to review the global solar radiation models available in the literature. There are several formulate which relate global radiation to other climatic parameters such as sunshine hours, relative humidity and maximum temperature. The most commonly used parameter for estimating global solar radiation is sunshine duration. Sunshine duration can be easily and reliably measured and data are widely available.     

A method for estimating monthly global solar radiation

In this paper a method is followed for estimating monthly totals of global solar radiation from a combination of calculations of monthly cloudless global solar radiation, surface meteorological observations, and empirical formulae relating sunshine duration to global solar radiation. The percent deviation of calculated from observed values is not negligible, but is much less than errors obtained by using extraterrestrial solar radiation totals. In case of values of monthly global solar radiation which are estimated for other regions, the resulted possible errors should be determined again. Some techniques leading to adaptation of the regression equations for other areas are argued.     

Correlations for estimation of daily global solar radiation with hours of bright sunshine in Turkey

In this study, seven different empirical equations are employed to estimate the monthly average daily global solar radiation on a horizontal surface for provinces in the different regions of Turkey, using only the relative duration of sunshine. Daily global solar radiation and sunshine measurement data collected for the provinces of Turkey are obtained from the Turkish State Meteorological Service. The regression constants of the new models developed in this study are found for the provinces of Turkey, as well as that of some models given in the literature. In order to indicate the performance of the models, the statistical test methods of the mean bias error (MBE), mean absolute bias error (MABE), mean relative error (MRE), root mean square error (RMSE) and correlation coefficient (r) are used.     

A comparison of methods for estimating hourly diffuse solar radiation from global solar radiation

Four methods of estimating hourly diffuse irradiation from hourly global irradiation are compared, using global and diffuse irradiation data from the Australian Bureau of Meteorology for five widely separated Australian locations. A development of one of these methods with constants derived from the data for each place is found to perform best when judged on a criterion of absolute error, and this performance in maintained when constants averaged over the five locations are used. The derived constants are also given for all other Australian locations for which both global and diffuse data are available, and a method is suggested for deriving suitable values of the constants for places situated between 20° and 45° S for which only global radiation data are available. A previously reported dependence of the proportion of diffuse radiation on latitude is demonstrated.     

Application of extreme learning machine for estimating solar radiation from satellite data

In this paper, a simple and fast method based on extreme learning machine (ELM) for the estimation of solar radiation in Turkey was presented. To design the ELM model, satellite data of the National Oceanic and Atmospheric Administration advanced very high‐resolution radiometer from 20 locations spread over Turkey were used. The satellite‐based land surface temperature, altitude, latitude, longitude, month, and city were applied as input to the ELM, and the output variable is the solar radiation. To show the applicability of the ELM model, a performance comparison in terms of the estimation capability and the learning speed was made between the ELM model and conventional artificial neural network (ANN) model with backpropagation. The comparison results showed that the ELM model gave better estimation than the ANN model for the overall test locations. Moreover, the ELM model was about 23.5 times faster than the ANN model. The method could be used by researchers or scientists to design high‐efficiency solar devices such as solar power plant and photovoltaic cell. Copyright © 2013 John Wiley & Sons, Ltd.     

Technical note a multiple linear correlation for diffuse radiation from global solar radiation and sunshine data over Egypt

Measurements of global solar radiation, diffuse radiation and sunshine duration data during the period from 1982 to 1988 at different locations over Egypt were used to establish empirical relationships that would connect the daily monthly average diffuse irradiation with both relative sunshine duration and clearness index separately and in combination. The selected locations were chosen to represent the different weather conditions of North, Middle and South Egypt. Our correlation equations were tested using measured data for the year 1992 at the same locations. The correlation connecting diffuse radiation with both clearness index and percentage possible sunshine is found to be applicable over Egypt.     

An empirical method for estimating sunshine from total cloud amount

A new empirical method has been developed for computing sunshine S from total cloud amount. The equation used is of the form S = 1 − f₁ + f₂, where f₁ and f₂ are, respectively, functions of total cloud amount and latitude correction. The results obtained with this equation are compared with observed values and are found to be in good agreement. Tables 1 and 2 present these results.

Assuming extreme conditions, the maximum possible deviations of total solar radiation, net radiation and evaporation (or potential evapotranspiration), using the formulae of Reddy[1–4] are discussed for the case where calculated values of S deviate 0·10 from observed values of S. The formula can be usefully employed with considerable accuracy in water and energy budget studies.     

Equations for estimating global solar radiation in data sparse regions

The knowledge of the amount of solar radiation in an area/region is very essential in the field of Solar Energy Physics. In this work two equations are put forward for estimating global solar radiation from common climate variables in data sparse regions. The first is the Hargreaves equation, R_s=0.16R_aT_d^0.5 where R_a is the extraterrestrial solar radiation and T_d is the temperature difference (maximum minus minimum), while the second is the Angstrom equation, R_s=R_a(0.28+0.39n/N) where n and N are the measured sunshine hours and the maximum daylight duration respectively. The global solar radiation estimated by the two equations for three sites, Owerri (5°28′N, 7°2′E), Umudike (5°29′N, 7°33′E) and Ilorin (8°32′N, 4°46′E), located in different climate zones of in Nigeria, West Africa, are in agreement with those of earlier workers and that from Photovoltaic Geographic Information System (PVGIS) project. The implication of this in solar photovoltaic applications has been stressed.     

Analysis of monthly average solar radiation and bright sunshine for different thresholds at Cape Canaveral, Florida

Data for beam, global horizontal, and global normal radiation measured at Cape Canveral were analyzed for the period 1986–1991. Some empirical correlations between these parameters are proposed. A detailed analysis of the beam irradiance data also led to the derivation of sunshine fractions corresponding to different radiation thresholds. It is shown that the current WMO threshold of 120 W/m² corresponds to optimal radiation/sunshine correlations. Finally, improved monthly irradiation empirical fits using sunshine data are proposed.     

A method for estimating direct normal solar irradiation from satellite data for a tropical environment

In order to investigate a potential use of concentrating solar power technologies and select an optimum site for these technologies, it is necessary to obtain information on the geographical distribution of direct normal solar irradiation over an area of interest. In this work, we have developed a method for estimating direct normal irradiation from satellite data for a tropical environment. The method starts with the estimation of global irradiation on a horizontal surface from MTSAT-1R satellite data and other ground-based ancillary data. Then a satellite-based diffuse fraction model was developed and used to estimate the diffuse component of the satellite-derived global irradiation. Based on this estimated global and diffuse irradiation and the solar radiation incident angle, the direct normal irradiation was finally calculated. To evaluate its performance, the method was used to estimate the monthly average hourly direct normal irradiation at seven pyrheliometer stations in Thailand. It was found that values of monthly average hourly direct normal irradiation from the measurements and those estimated from the proposed method are in reasonable agreement, with a root mean square difference of 16% and a mean bias of −1.6%, with respect to mean measured values. After the validation, this method was used to estimate the monthly average hourly direct normal irradiation over Thailand by using MTSAT-1R satellite data for the period from June 2005 to December 2008. Results from the calculation were displayed as hourly and yearly irradiation maps. These maps reveal that the direct normal irradiation in Thailand was strongly affected by the tropical monsoons and local topography of the country.     

A hybrid model for estimating global solar radiation

In view of the site-dependence of Ångström correlation, this study developed a hybrid model to estimate global radiation H. Unlike Ångström correlation H=(α+βS/S₀)H₀, this model suggested that H=(a+b S/S₀)H_b+(c+d S/S₀)H_d, H_b and H_d are effective beam radiation and effective diffuse radiation, which imply latitude, elevation and seasonal effect on radiation. H_b and H_d are calculated by an arithmetic model derived from spectral model. The hybrid model was designed for estimating monthly mean daily global radiation with hourly-recorded bright sunshine time, and its applicability was verified at observatories in Japan.     

A new solar radiation database for estimating PV performance in Europe and Africa

The Photovoltaic Geographical Information System (PVGIS) is a web application for the estimation of the performance of photovoltaic (PV) systems in Europe and Africa, which has become widely used by the PV community in Europe. We here present the results of adapting the solar radiation data calculated from satellite data in the Climate Monitoring Satellite Application Facility (CM-SAF) to PVGIS. The CM-SAF solar radiation database is characterized by very low overall bias and shows good accuracy at validation sites. The application to PVGIS brings important improvements relative to the existing solar radiation databases within PVGIS.     

Calculation of monthly average global solar radiation on horizontal surfaces using daily hours of bright sunshine

Several statistical models calculating the monthly average global solar radiation on horizontal surfaces using the daily hours of bright sunshine have been extensively evaluated and compared for Canadian regions. Results show that Gariépy's model provides the best overall performance and Hay's model is rated next best, whereas Rietveld's model has been found to be the least accurate. Local performances of models have also been established throughout Canada that show that both Gariépy's and Hay's models perform quite well. Recommended models have been suggested for the studied regions.     

A method of estimating monthly average solar radiation on shaded receivers

The geometry of vertical solar radiation receivers shaded by overhangs is described. The instantaneous mean solar radiation on a shaded receiver is defined leading to a method of estimating , the monthly average daily radiation on a shaded receiver. Values of the monthly average beam irradiated fraction of the receiver area, , are presented in a series of figures. The effects of overhang extension and receiver azimuth on are considered. Example calculations are presented and the overall effect of an overhang as a shading device is discussed.     

Global solar radiation estimation from relative sunshine hours in Yemen

The existing measurements of global solar radiation and sunshine duration for Yemen are examined. The errors of estimating solar radiation from sunshine hour measurements using Angstrom's relation are evaluated. As a simple predictor for global radiation, an average Ansgtrom relations in the form

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for all stations is evaluated. Other Angstrom correlation relations are also proposed by classifying the stations under into four groups. The estimated results are compared and seem to be satisfactory in the latter case.