Quoted from:Katiyar A K ,  Pandey C K . Simple correlation for estimating the global solar radiation on horizontal surfaces in India[J]. Energy, 2010, 35(12):5043-5048.

https://www.sci-hub.ren/10.1016/j.energy.2010.08.014

INTRODUCTION

A long range fifive years (2001-2005) measured data of the global solar radiation on horizontal surface along with the bright sunshine hours of four prominent cities viz. Jodhpur, Calcutta, Bombay, and Pune of India have been analyzed. The under considered cities have varying weather conditions of the country. The regression constants have been calculated for the fifirst, second and the third order Angstrom type correlations for each location using regression analysis method. Comparisons of monthly mean global solar radiation ðHÞ between the measured and the calculated values have been made. The statistical errors are also performed for testing the accuracy of regression constants. It is observed that in comparison to fifirst order, second and the third order Angstrom type correlations do not improve the accuracy of the estimated global radiation. Therefore, using the measured data of all four cities together, we developed the fifirst order Angstrom type correlations and presented new regression constants, applicable to all Indian locations. Furthermore, these regression constants of all India correlation are validated by comparison with the experimental and the other theoretical results available in literature.

The objective of the present study is to analyze the measured data of the global solar radiation and sunshine duration of different parts of the country and propose a new set of regression constants applicable to entire region of the country. For this, we considered four Indian cities viz. Jodhpur (Latitude 26.30°N, Longitude 73.03°E), Calcutta (Latitude 22.65°N, Longitude 88.35°E), Bombay (Latitude 19.12°N, Longitude 72.85°E) and Pune (Latitude 18.53°N, Longitude 73.91°E). The data of these cities are used to obtain new constants considering fifirst, second and third order Angstrom type correlations for the locations under consideration. The performance of the new constants for each station is checked by comparing it with the measured and other available theoretical values. Since statistical comparisons did not show improvement in the accuracy of second and third order Angstrom type correlations, only fifirst order linear correlations between the monthly average daily clearness index H/H0 and the relative possible sunshine duration s/s0Þhave been proposed. This correlation predicts the data of global solar radiation for all Indian locations; hence we call it all India horizontal correlation (AIHC).Furthermore, the accuracy of this AIHC has been tested not only for some important cities of India but also for well known Egyptian locations.

Katiyar and Pandey reported the following first-order Angstrom-type correlations for four locations (Jodhpur, Calcutta, Bombay, and Pune, India), respectively, for the estimation of global solar radiation using the long range measured data of five years (2001–2005):

\( 𝐻/𝐻_0 = 0.2276 + 0.5105 𝑆/𝑆_0 , \)

\( 𝐻/𝐻_0 = 0.2623 + 0.3952 𝑆/𝑆_0 , \)

\( 𝐻/𝐻_0 = 0.2229 + 0.5123 𝑆/𝑆_0 , \)

\( 𝐻/𝐻_0 = 0.2286 + 0.5309 𝑆/𝑆_0 . \)

further, in order to develop the first-order correlation applicable to all Indian locations, the authors combined the entire measured data of all the four locations together and analyze to obtain the following correlation:

\( 𝐻/𝐻_0 = 0.2281 + 0.5093 𝑆/𝑆_0 . \)

Over the years, the following authors study the constants of Angstrom equation.

It provides estimation of H for any location of India with absolute values of the MPE less than 5%. Therefore we recommend the AIHC for the estimation of monthly average daily global radiation on horizontal surface. All India correlation may also be extended for other locations which have the same values of the maximum clearness index.