Improved Accuracy Models For Hourly Diffuse Solar Radiation

Renewable & Sustainable Energy Reviews, 2017

Renewable and Sustainable Energy Reviews, 2013

Solar radiation is a primary driver for many physical, chemical, and biological processes on the earth's surface. Solar energy engineers, architects, agriculturists, hydrologists, etc. often require a reasonably accurate knowledge of the availability of the solar resource for their relevant applications at their local. In solar applications, one of the most important parameters needed is the long-term average daily global irradiation. For regions where no actual measured values are available, a common practice is to estimate average daily global solar radiation using appropriate empirical correlations based on the measured relevant data at those locations. These correlations estimate the values of global solar radiation for a region of interest from more readily available meteorological, climatological, and geographical parameters. The main objective of this study is to chronologically collect and review the extensive global solar radiation models available in the literature and to classify them into four categories, i.e., sunshine-based, cloud-based, temperature-based, and other meteorological parameterbased models, based on the employed meteorological parameters as model input. Furthermore, in order to evaluate the accuracy and applicability of the models reported in this paper for computing the monthly average daily global solar radiation on a horizontal surface, the geographical and meteorological data of Yazd city, Iran was used. The developed models were then evaluated and compared on the basis of statistical error indices and the most accurate model was chosen in each category. Results revealed that all the proposed correlations have a good estimation of the monthly average daily global solar radiation on a horizontal surface in Yazd city, however, the El-Metwally sunshine-based model predicts the monthly averaged global solar radiation with a higher accuracy.

Renewable Energy, 2006

Proper design and performance predictions of solar energy systems require accurate information on the availability of solar radiation. The diffuse-to-global solar radiation correlation, originally developed by Liu and Jordan, has been extensively used as the technique providing accurate results, although it is latitude dependent. Thus, in the present study, empirical correlations of this type were developed to establish a relationship between the hourly diffuse fraction (k d ) and the hourly clearness index (k t ) using hourly global and diffuse irradiation measurements on a horizontal surface performed at Athalassa, Cyprus. The proposed correlations were compared against 10 models available in the literature in terms of the widely used statistical indicators, rmse, mbe and t test. From this analysis, it can be concluded that the proposed yearly correlation predicts diffuse values accurately, whereas all candidate models examined appear to be location-independent for diffuse irradiation predictions. r

This study aims to evaluate performance of 30 models (15 selected from literature and 15 newly developed) to estimate diffuse horizontal irradiance (H d) using high-quality measurements for nine stations having different climatic conditions. The models (divided into three categories) are based on extraterrestrial global horizontal irradiance (H o) and measured global horizontal irradiance (H g) using sunshine duration ratio, clearness-index, temperature, relative humidity, and periodicity factor as input parameters. The performance of models was evaluated using statistical parameters; the performance of H g based models (Category-II and Category-III) is better than H o based models (Category-I). The performance of newly developed models in three categories is better than best models selected from the literature, due to higher number of input parameters and higher powers used. The best models in Category-I, Category-II and Category-III have rMBE (rRMSE) ranges from − 0.3 to 0.6% (14 to 20%), − 0.6 to 0.1% (10 to 17%) and − 0.3 to 0.0% (10 to 17%) respectively. The performance of models varies in different zones, and different stations within same zone, due to variations of climatic conditions. The best models have rMBE within ±1% and rRMSE < 20%, and can be used for initial resource assessment of commercial solar PV projects for potential locations.

Building Services Engineering Research and Technology, 2010

Hourly solar radiation data are required in many building services applications. These are also reported in the Chartered Institution of Building Services Engineers Guides A & J. Data from 16 locations in the UK were used to evaluate the so called Liu and Jordan model 1 for monthly averaged hourly solar irradiation. Individual data sets spanned periods from 12 to 26 years between 1968 and 1994, and overall, provided data from practically the full range of latitude of the UK (50.228N-58.138N). For hourly estimation, the model only slightly underestimated both global and diffuse radiation before noon and overestimated, again only slightly, after noon. In addition, a discrepancy was observed between the measured data and the model's predictions at low sunset angles. Following earlier research work, an attempt was made to further improve the Liu and Jordan model. However, it was found that at least for the UK data set, any such attempts were futile. This behaviour was attributed to the highly random nature of UK's solar climate. Practical applications: Most meteorological stations report solar radiation data on a daily averaged basis. However, most building energy simulation software requires hourly radiation. Research studies have confirmed that the well-known Liu and Jordan model, which enables the above conversion, performs well for locations in the US. This paper evaluates the above model for locations in the UK and compares it with previously studied Indian locations. According to the evaluation, the average accuracy of the model to estimate hourly radiation from its daily counterpart is 85%. Nomenclature G monthly averaged daily global irradiation (kWh/m 2) E monthly averaged extraterrestrial radiation (kWh/m 2) g monthly averaged hourly global irradiation (Wh/m 2) G clear average clear day global irradiation (kWh/m 2) D monthly averaged daily diffuse irradiation (kWh/m 2) d monthly averaged hourly diffuse irradiation (Wh/m 2) K T monthly averaged clearness index a, b site-specific coefficients c 0 , c 0 , c 01 , c 02 , c 1 , c 11 , c 12 equation coefficients d 0 , d 0 , d 01 , d 02 , d 1 , d 11 , d 12 equation coefficients DEC solar declination (degree)

International Journal of …, 2011

A new model for collectable solar energy estimation via air temperature data is proposed. The model (to be called SEAT) runs in the standard way: first global solar irradiance is computed, and then a cloud cover correction is applied, to end with the summing up of the results for daily global solar irradiation. To address the issue that air temperature-based models are sensitive to their origin location, an adaptive algorithm is reported. Comparison of SEAT forecast with measured data from 15 European stations, located between 40 and 501 northern latitudes and altitudes lower than 500 m, shows an acceptable level of accuracy of the new model. The relative root mean square of monthly mean of daily global solar irradiation has been found between 0.055 and 0.112 for continental sites and between 0.064 and 0.156 for seacoast sites. The way of embedding cloudiness into the solar irradiance procedure calculation and the method of relating daily mean cloudiness with daily air temperature extremes are the main novelty features of SEAT. The approach for SEAT is described en detail to guide potential users either to further develop more complex similar models or to simplify them by particularization.

Applied Energy, 2012

The study introduces a new regression model developed to estimate the hourly values of diffuse solar radiation at the surface. The model is based on the clearness index and diffuse fraction relationship, and includes the effects of cloud (cloudiness and cloud type), traditional meteorological variables (air temperature, relative humidity and atmospheric pressure observed at the surface) and air pollution (concentration of particulate matter observed at the surface). The new model is capable of predicting hourly values of diffuse solar radiation better than the previously developed ones (R2 = 0.93 and RMSE = 0.085). A simple version with a large applicability is proposed that takes into consideration cloud effects only (cloudiness and cloud height) and shows a R2 = 0.92.

2016

An accurate knowledge of solar radiation considers the first step in solar energy availability assessment, also it is the primary input for various solar energy applications. In this regard, due to the lack of the solar radiation measurements, several models around the world have been proposed for estimating solar radiation. Generally, sunshine duration is the most common parameter used for estimating global solar radiation. Although, sunshine based models can't be apply at several locations, due to the unavailability of sunshine. Accordingly, this study aims to investigate the performance of 31 non-sunshine based models in estimating the monthly average of daily global solar radiation on a horizontal surface. For achieving this, over than 20 years of measured global solar radiation data in the location of the study (Latitude 30˚51 ̀ N and longitude 29˚34 ̀ E) are utilized for establishing and validating the models. The models are divided into six categories; (1) Only function of temperature; (2) Only function of cloud cover; (3) Only function of relative humidity; (4) Function of extraterrestrial solar radiation and solar declination angle; (5) Function of temperature and cloud cover; (6) Function of temperature and relative humidity. The mostly common statistical indicators are used to differentiate between the performances of these models and to identify the best model. The best model for every category is distinguished as well as the most accurate models among all models recognized. According to the results, some models are completely improper for applying in the region of the study, and other differ in the performance of prediction. Besides, InciTürk Toğrul model and Can Ertekin model (Eq. 19 and 18) which based on extraterrestrial radiation and solar declination showed the best performance, with excellent coefficient of determination values (R^2 ≥ 0.99). Therefore, InciTürkToğrul model and Can Ertekin model are the recommended models for estimating monthly average daily global solar radiation on a horizontal surface.

Agricultural and Forest Meteorology, 2006

Surface solar radiation is an important parameter in hydrological models and crop yield models. This study developed a model to estimate solar radiation from sunshine duration. The model is more accurate and more general than traditional Å ngström-Prescott models. It can explicitly account for radiative extinction processes in the atmosphere. Moreover, global data sets that describe the spatial and temporal distribution of ozone thickness and Å ngström turbidity were introduced in the model to enhance its universal reliability and applicability. The model was calibrated in lowland and humid sites and validated at a number of sites in various climate and elevation regions. The new model shows overall better performances than three Å ngström-Prescott models. Because this model follows the simple form of the Å ngström-Prescott model, and its inputs (sunshine duration, air temperature, and relative humidity) are accessible from routine surface meteorological observations, it can be easily applied to hydrological and agricultural studies. The source code and the auxiliary data of the model are available from the authors upon request. #