Estimation of global solar irradiation on horizontal and inclined surfaces based on the horizontal measurements

Solar radiation data are essential in the design of solar energy conversion devices. In this regard, empirical models were selected to estimate the global solar radiation on horizontal and inclined surfaces. The hourly solar radiation data measured at the study area during the period of 2004–2007, were used to calculate solar radiations using selected models. The selected models were compared on the basis of statistical methods. Based on the results, a new model, H/Ho = 0.19490 + 0.4771(n/N) + 0.02994 exp(n/N) has been developed, based on Kadir Bakirci linear exponential model. This is highly recommended to estimate monthly mean daily global solar irradiation, on a horizontal surface. Further, a model to convert horizontal solar global radiation to that of radiation on a tilted surface is also presented. It is based upon a relatively simple model proposed by Olmo et al. which requires only measurements of horizontal solar radiation. The developed model appears to give excellent results and has the advantage of being relatively simple for applications. The present work will help to improve the state of knowledge of global solar radiation to the point where it has applications in the estimation of global solar radiation, both on horizontal and inclined surfaces.

Research highlights
► The monthly average daily global solar irradiation on horizontal surface can be estimated using linear exponential regression equation H/Ho = 0.1949 + 0.4771(n/N) + 0.02994 exp(n/N).
► The monthly average daily global solar irradiation on inclined surface can be estimated using Olmo et al. model for the state of Terengganu, Malaysia.
► These two models are relatively simple models to estimate monthly average daily global solar irradiation.