Optimum collector slope and model evaluation: Case study for Gebze, Turkey

In this paper, various models for predicting radiation on an inclined surface are compared and an isotropic model, which provides the most accurate estimation of the total solar energy, has been used to determine the optimum collector slope based on the maximum solar energy availability. We derive theoretical equations which can be used to estimate the optimum slopes of the tilted, south-facing surfaces during a year for Gebze. The optimum slopes depend mainly on latitude, declination, clearness index, and diffuse-to-global radiation ratio. The general correlations developed are valid in Gebze and are both accurate and convenient to use in practice. These correlations are based on measured data between 1988 and 1994 from the TUBITAK-M.R.C. station in Gebze, Turkey. The correlations have been tested by using statistical error tests. (C) 1997 Elsevier Science Ltd.