**Quoted from:****Zhou J , Wu Y , Gang Y . General formula for estimation of monthly average daily global solar radiation in China[J]. Energy Conversion & Management, 2005, 46(2):257-268.**

**https://www.sci-hub.ren/10.1016/j.enconman.2004.02.020**

Solar radiation and sunshine duration data from 69 meteorological stations in China was used to develop the formula for estimating the monthly average daily global radiation on a horizontal surface. Several models and correlations that embrace such variables as the fraction of sunshine duration, the latitude and the altitude have been selected, tested and compared to decide which model is recommended on the basis of statistical error tests. In this study, using the relative duration of sunshine as a single independent variable, the most accurate equation that is expressed in a third order form was obtained for each station. The results show that the coefficients are site dependent. Subsequently, taking the radiation data and geographical parameters at all 69 stations as reference, a countrywide general equation was established. Compared with the equation using the relative duration of sunshine as a single independent variable, the general equation shows relatively lower accuracy, but estimating the global solar radiation by this equation has proved sufficiently reliable. This equation can be used to estimate the monthly average daily global radiation in areas where the radiation data is missing or not available, so that a geographical distribution of global solar radiation across the country may be obtained.

**INTRODUCTION**

Of the 194 meteorological stations in China, there are only 69 stations provided with global solar radiation recorders. The extent of records at most of these stations are about 40 years. In contrast to solar radiation, sunshine duration has been abundantly measured in the country. A few attempts to develop knowledge about the variation of global solar radiation in China have been found in the literature. Wenxian et al utilized observed data for only several stations in the Yunnan Province, China, to obtain correlations between monthly average global solar radiation and relative duration of sunshine, but these studies are valid only for the locality used in the analysis, i.e. they cannot be considered of universal application in China.

The objective of this paper is to validate and compare the models to predict monthly average daily global radiation on a horizontal surface based on solar radiation data from 69 meteoro logical stations in China, to select the one with the highest accuracy and then to determine the general formula for use in locations where radiation data is not available, so that a geographical distribution of global solar radiation across China may be obtained.

Jin et al. proposed the following relation:

\( 𝐻/𝐻_0 = 0.1332 + 0.6471 𝑆/𝑆_0 . \)

This equation showed the best estimation of global solar radiation on a horizontal surface for China by means of the MPE (1.206%), MAPE (8.054%), MBE (0.024 MJ/m ^{2}), MABE (1.027 MJ/m ^{2}) and RMSE (1.404 MJ/m ^{2}). This equation can be used to estimate the global solar radiation in areas where the radiation data is missing or not available.