Estimation of hourly solar radiation for India

The ASHRAE constants predict high values of the hourly beam radiation and very low values of the hourly diffuse radiation when used to predict radiation at Indian locations. Hence a procedure has been developed for the estimation of direct, diffuse and global hourly solar radiation on a horizontal surface for any location in India. To calculate hourly solar radiation, an exponential curve, similar to the one used by ASHRAE, was fitted to the measured solar radiation data of six cities from different regions of India. The statistical analysis was carried out for the data computed using ASHRAE constants and the set of constants obtained for India using the measured data of four different Indian cities selected randomly. Three statistical indicators were used to compare the accuracy of the developed procedure. The results show that ASHRAE constants are not suitable to estimate hourly solar radiation in India. Hourly solar radiation estimated by constants obtained for India are fairly comparable with measured data. The mean percentage error with Indian constants for these four Indian cities was found as low as 2.27, −6.29 and −6.09% for hourly beam, diffuse and global radiation, respectively.

[1]  A. Rabl,et al.  The average distribution of solar radiation-correlations between diffuse and hemispherical and between daily and hourly insolation values , 1979 .

[2]  A. Whillier.  (National Mechanical Engineering Research Institute, South African Council for Scientific and Industrial Research, Pretoria) The Determination of Hourly Values of Total Solar Radiation from Daily Summations , 1956 .

[3]  J. Orgill,et al.  Correlation equation for hourly diffuse radiation on a horizontal surface , 1976 .

[4]  B. F. Raber,et al.  Refrigeration and air conditioning engineering , 1945 .

[5]  C.C.Y. Ma,et al.  Statistical comparison of solar radiation correlations Monthly average global and diffuse radiation on horizontal surfaces , 1983 .

[6]  H. Hottel,et al.  Evaluation of flat-plate solar collector performance , 1955 .

[7]  J. Bugler.  The determination of hourly insolation on an inclined plane using a diffuse irradiance model based on hourly measured global horizontal insolation , 1977 .

[8]  R. Bruno,et al.  A correction procedure for separating direct and diffuse insolation on a horizontal surface , 1978 .

[9]  Estimation of hourly global and diffuse solar radiation from hourly sunshine duration , 1992 .

[10]  Benjamin Y. H. Liu,et al.  The interrelationship and characteristic distribution of direct, diffuse and total solar radiation , 1960 .

[11]  S. S. Bhatti,et al.  Statistical comparison of global and diffuse solar radiation correlations , 1990 .

[12]  A. Zeroual,et al.  The diffuse-global correlation : its application to estimating solar radiation on tilted surfaces in Marrakesh, Morocco , 1996 .