Quoted from:Bahel V ,  Bakhsh H ,  Srinivasan R . A correlation for estimation of global solar radiation[J]. Energy, 1987, 12(2):131-135.https://www.sci-hub.ren/10.1016/0360-5442(87)90117-4

We present a simple ngstrom-type correlation for estimating the monthly average daily horizontal global radiation. We have developed this correlation using the bright sunshine and global radiation data of 48 locations around the world, with varied meteorological conditions and a wide distribution of geographical locations. Our study shows that this correlation provides good estimates of solar radiation. We have also statistically compared the performance of our correlation with Rietveld's equation, which is believed to be applicable anywhere in the world and has been found by Ma and Iqbal (1984) to give better estimates than other published correlations. Our correlation yields better estimates than Rietveld's equation for a majority of the stations considered.

INTRODUCTION

Bright sunshine hours are measured at many locations around the world, while global radiation is measured at selected locations only. To overcome this deficiency, scientists have developed many empirical formulae which relate radiation to various climatological parameters.Among the various correlations used, the modified version of Angstrom equation has been the most convenient and widely used correlation relating the monthly average, daily horizontal radiation to the mean daily bright sunshine. The development of this type of correlation requires only a few parameters. Our work uses the Angstrom-type regression model.

The objective of this study is to develop a single correlation between global radiation and bright sunshine hours, which can be used to estimate solar radiation with the input of only bright sunshine records. This procedure will be implemented by using the measured records for both of these parameters for 48 stations which are widely distributed and represent a variety of meteorological conditions. We also compare statistically the performance of our correlation with the formulae of Rietveld and Hay,which are believed to be universal in character and have been found to give good estimates of global radiation for a variety of locations.Computations are based on the new solar constant of 1367 W/m ² adopted by the World Meteorological Organization.

Bahel et al. also developed the following thirdorder correlation based on the measured data of global and bright sunshine hours for 48 stations around the world:

\( 𝐻/𝐻_0 =0.16+0.87 S/S_0 −0.61(S/S_0)^2 +0.34(S/S0)^3. \)