ABSTRACT
Abstract Understanding the solar radiation values in the surface is important for the development of solar energy projects, obtaining through radiometers installed in certain places or publications as in solar energy atlases. Typically, solar or weather stations do not have sensors to measure diffuse irradiation due to high investment and the need for constant maintenance. This paper presents methods for the determination of diffuse irradiation from surface measured data of global horizontal irradiation in the city of Curitiba, obtained through pyranometers installed at the Federal University of Technology - Paraná (UTFPR) headquarters and from Curitiba-A807 National Institute of Meteorology (INMET) station. Two models are presented for the estimation of the monthly mean daily diffuse irradiation, based on the studies of Liu and Jordan (1960) and Page (1961). Finally, these data were compared with those presented by the Solar Energy Atlas - Paraná, verifying the percentage differences presented. It was observed that the model elaborated by Page presented better results in the diffuse radiation estimates when compared to the values presented by the Paraná Atlas, with an average variation of -1.39% and -1.55%, for data from INMET and UTFPR respectively.