Evaluation and development of temperature-based empirical models for estimating daily global solar radiation in humid regions

In the present study, 14 existing temperature-based empirical models for daily horizontal global solar radiation estimation were comprehensively reviewed, and six new temperature-based models (P1P6) were developed for solar radiation estimation in humid regions. The accuracy and suitability of these models were further evaluated for the humid subtropical and tropical regions of China as a case study using meteorological data during 1966-2015 from 20 radiation stations. The results indicated that despite most studied models were capable of estimating daily global solar radiation with reasonable accuracy, the accuracy of the single temperature-based models was much improved when daily precipitation and relative humidity were included in the models. The newly proposed polynomial model P2 was the top-ranked single temperature-based model for most radiation stations and thus recommended at sites where only air temperatures were available. In terms of complex temperature-based models, the proposed models P3 and P5 by incorporating a proposed logarithmic form of precipitation and the actual value of relative humidity were superior to the existing complex models. Generally, the proposed temperature-based models can be applied for daily global solar radiation estimation with higher accuracy in humid subtropical and tropical regions of China and maybe elsewhere with similar climates.