To accomplish the best operation of available solar energy, it is important to estimate the incident solar radiation over the specific region. The present study focuses on the estimation of solar radiation by using mathematical modelling. For that purpose, monthly average daily global solar radiations are estimated based on different parameters like minimum and maximum temperature, sunshine hour, and relative humidity. The location selected for this study is Kadapa ((14.47ºN, 78.87º E, and 138m asl) Southern part of India. The study period is from April 2016 to October 2018. The study focuses particularly on models based on the relative sunshine (S/S0) and clearness index (kt). The clearness index and relative sunshine were high in December (1.058±0.002 and 0.968±0.005) and low in July (0.952±0.05 and 0.734±0.072). The estimated clearness index based on sunshine models is best correlated with the calculated clearness index values. In temperature and relative humidity-based models the hybrid parameter-based models are better correlated with the single parameter based-models.