calibration and validation of different methods for estimation of daily solar radiation (case study: rasht)

abstract solar radiation (rs) has many applications in most sciences such as agriculture and irrigation however, its measurement has been done in few weather stations of iran. therefore, estimation methods were used. in this study, weather data of rasht station, from 2004 to 2006 were employed for calibration of some equations, and weather data of years 2007 and 2008 were used for evaluating the obtained equations for estimating rs. for this purpose the cloudy and clear- sky days were separated. the results for non-cloudy days showed that the angstrom equation was more appropriate than the other equations. also, the results for cloudy days demonstrated that none of the equations were appropriate however, the equation proposed by allen et al., (1998) can be used with low accuracy.