Monthly Average Daily Diffuse Radiation Research Articles

Forecasting the Diffuse Solar Radiation by using a New Modeling over Saudi Arabia

Within the arranging and execution assessment of solar energy projects, particularly within the planning and estimation of solar photovoltaic sources as elective energy sources within the future, exact evaluation of Diffuse Solar Radiation (DSR) is one of the essential and basic issues. The target of this article is to use the new model to predict DSR in four different locations in Saudi Arabia. The author explored the available meteorological and radiation data. The data covers the 25 years from 1990 to 2014 and were measured at Al-Baha, Abha, Jeddah and Taif locations in Saudi Arabia. Through detailed statistical evaluation and analysis, 19 empirical models were tested to construct the best empirical model to estimate the monthly average daily DSR of Saudi Arabia. Using widely used statistical errors, namely MBE, MPE, RMSE, U95, R, t-test and GPI the proposed correlation model was compared with 19 models provided in the literature. Through this analysis, the cubic empirical equation model is selected as the good model. Compared with these existing models, this model reveals accurate results with minimal statistical errors. Based on these results, Model 22 gives the highest GPI value. The conclusion is the cubic equation model of the diffusion fraction (i.e., D/G = 0.215+2.123 (S/So) -3.547(S/So)2+5.142 (S/So)3 is the best agreement model that has been mentioned in the previous discussion. This model is a generalized equation in Saudi Arabia, which can forecast the monthly average daily diffuse radiation on the horizontal plane at any site under similar climatic conditions without the measured climatic conditions. Experts or architects can use this model to perform site selection and technical and financial evaluation of solar energy applications and photovoltaic technology.

Developing of the new models in solar radiation estimation with curve fitting based on moving least-squares approximation

Recently, serious progress has been made in solar energy applications in developed and developing countries. Solar radiation on a horizontal surface is the basic parameter required for the design of solar energy systems and for evaluating the system performance. Therefore, solar radiation the exact determination of the amount of land in different latitudes on the earth's surface is of great importance in many solar energy applications. In this study, Angstorm coefficients were determined by Moving Least Squares Approximation (MLSA). Three different models were obtained by using the moving least squares method. In this study, new empirical models were developed for determining the monthly average daily global solar radiation on a horizontal surface for Antalya. The developed models were compared with the models in the literature by using different error analysis methods. The statistical compatibility of the investigated models was tested and the model closest to the measurements was determined. Although, this study concluded that the suggested methods are applicable to estimate the monthly average daily diffuse radiation on a horizontal surface for selected region, it has been observed that the performance of these models varies according to years and the error analysis test used. If the results are generally evaluated the developed linear model showed the best performance to estimate the global solar radiation on a horizontal surface for Antalya. Also, among the models used in the literature, the Togrul model showed the best performance for selected region.

A new empirical model for forecasting the diffuse solar radiation over Sahara in the Algerian Big South

Abstract Accurate estimation of diffuse solar radiation (DSR) is among the critical concerns in successful solar energy projects. This paper presents a systematic approach for DSR estimation over the Algerian Sahara. The authors explore the available meteorological and radiometric data. These data include the sunshine hour fraction (ratio of sunshine duration to maximum possible sunshine hours), and the relative clearness index. The data cover a period of six years from 2010 to 2015 measured in the Adrar region. Through an elaborated statistical performance analysis, thirty-five models were tested for constructing the most accurate empirical model for estimating the monthly average daily DSR over the Saharian medium. The proposed correlation models were compared with 8 models available in the literature using the widely used statistical indicators i.e. MPE, RMSE, U95, R, TS and GPI. From this analysis, the quadratic equation model is selected as the most accurate model. The study concluded that the suggested correlation is applicable to estimate the monthly average daily diffuse radiation on a horizontal surface for any location over the Algerian Sahara region, which can serve as a resource for the design of photovoltaic systems.

Statistical comparison of models for estimating the monthly average daily diffuse radiation at a subtropical African site

Nine correlations have been developed in this paper to estimate the monthly average diffuse radiation for Dakar, Senegal. A 16-year period data on the global ( H) and diffuse ( H d) radiation, together with data on the bright sunshine hours ( N), the fraction of the sky’s cloud cover ( Ne/8), the water vapour pressure in the air ( e) and the ambient temperature ( T) have been used for that purpose. A model inter-comparison based on the MBE, RMSE and t statistical tests has shown that estimates in any of the obtained correlations are not significantly different from their measured counterparts, thus all the nine models are recommended for the aforesaid location. Three of them should be particularly selected for their simplicity, universal applicability and high accuracy. Those are simple linear correlations between K ̄ d and N ̄ / N ̄ d , N ̄ e/8 or K ̄ t . Even presenting adequate performance, the remaining correlations are either simple but less accurate, or multiple or nonlinear regressions needing one or two input variables.

Estimating the diffuse component from daily and monthly measurements of global radiation

In this study ≈83 000 measurements of daily global ( R s) and diffuse ( R d) solar irradiance from 25 sites in Australia and Antarctica (12°S–67°S, 1971–1995) are used to develop correlations between the diffuse fraction ( R d/ R s) and the clearness index ( R s/ R o) where R o is the extra-terrestrial solar irradiance. A single set of parameters which are slightly dependent on latitude are derived for use with daily irradiance data (typical R 2 ≈ 0.90). Comparisons with previously published regressions from the northern hemisphere indicate that the model and parameters are also suitable for use in that hemisphere. A theoretical approach is used to scale the daily model to a monthly basis and subsequent testing established the validity of the theoretical approach. However, for practical applications, empirical relationships are necessary to estimate the variances and covariances which are part of the theory but which are not normally available in databases. A final empirical scaling model was developed to estimate the monthly average daily diffuse radiation (RMS = 0.91 MJ m −2 day −1, R 2 = 0.86, N = 2780). The methods are intended for use in broad scale carbon balance models but should be equally applicable to a broad range of solar engineering tasks.

Correlations to estimate the monthly average daily diffuse radiation on horizontal surfaces in Yunnan Province, China

Yunnan Province, China, has its unique “cubic climates” which means that the climates in the region vary greatly. There are seven meteorological stations in the province which have measured data of global solar radiation on horizontal surfaces, and only four of them (Kunming, Tengchong, Hekou and Jinhong) have measured data of diffuse radiation on horizontal surfaces. With these data and the relevant data of the geographic and meteorological parameters of these four stations, we develop, in this study, two kinds of correlations to estimate the monthly average daily diffuse radiation on horizontal surfaces in Yunnan Province. It is believed that these correlations are applicable at any site in Yunnan Province.

Dependence on latitude of the relation between the diffuse fraction of solar radiation and the ratio of global-to-extraterrestrial radiation for monthly average daily values

An approach for the prediction of the monthly average daily diffuse radiation, H d , was proposed by Page in 1961. The Page method is based on the use of the linear correlation H d H = c + d H H o , where H and H o are, respectively, the monthly average daily values of global and extraterrestrial radiation, both on a horizontal surface. The values of c and d are a function of atmospheric conditions. cloud cover conditions/types, as well as latitude. In the present work we study the dependence on latitude of c and d for European locations with 36°N < (γ) < 61°N (longitudes between 29°E and 11°W). The dependence is first studied using 28 values of c and d obtained using experimental values of H and H d . Next the dependence on γ is studied using experimental values of H for 64 European locations, obtained for the period 1966–1975, and corresponding values of H d estimated using the European Community Solar Radiation Model (E.C.S.R.M.). In both cases a minimum for c vs. γ and a maximum for d vs. γ are obtained for similar values of γ. Using the E.C.S.R.M. it is shown that both, the minimum and the maximum can be explained by the way H d H and H H o vary with γ.

The dependence on cloudiness and turbidity of the monthly average daily diffuse-global correlation

Correlations between HdH and HHo, HdH and HHo have been established using data obtained in the period 1951–1980 at Uccle (Belgium), Hd being the monthly average daily diffuse radiation, HD the monthly average daily direct radiation, H the monthly average daily global radiation, and Ho the monthly average daily extraterrestrial radiation, all of them on a horizontal surface. The correlations have been obtained for different sky conditions A, B, C. (A) Clear skies (fraction of possible sunshine = 1) and minimum turbidity, corresponding to the maximum values of radiation measured during the period considered; (B) clear skies and average turbidity, corresponding to all the values of radiation measured when the fraction of possible sunshine is 1 during the period considered; (C) any sky conditions, corresponding to all the solar radiation data collected during the period considered. Linear correlations obtained for data corresponding to condition B and 0.676 >HHo > 0.573 and for condition C and 0.437 >HHo > 0.254 are very similar to those obtained when both sets of data are used together. The following linear correlations obtained using both sets of data: HdH = 0.960–0.983HHo and HdH = 0.015+0.950HHo can be used with high accuracy for conditions B or C. When data obtained for condition A are used no linear correlations are obtained.

Diffuse solar radiation in Cairo, Egypt

In the present paper, the correlations of Page, Liu and Jordan, and Iqbal were employed to predict the monthly mean daily diffuse solar radiation in Cairo. However, it was found that the coefficients used in these correlations were not applicable in the case of Cairo. New coefficients were obtained and used in the above correlations in order to predict values of the monthly average daily diffuse radiation. The present coefficients were found to be very different from those obtained for conditions in other locations. The estimated diffuse radiations were compared with the measured values. It is concluded that all correlations (i.e. equations which use either the cloudiness index or the relative sunshine) with the present coefficients, may be used to predict the monthly mean daily diffuse radiation in Cairo.