In estimating the amount of solar energy that can be used in applications, the selection of a suitable algorithm takes into account the availability of meteorological data as input. The air temperature is an all-important parameter recorded by all meteorological stations around the world, but it is not a common parameter for the computation of solar radiation. However, temperature maxima, minima, mean or amplitude have been included in solar energy modeling as a task in crop simulation models, developed recently for agriculture. Because temperature measurements are simple and robust, there is a reason for such models to be adapted for estimating daily solar energy with reasonable accuracy in various applications, such as photovoltaics.
The chapter is organized as follows. In the first section models which use air temperature together with cloudiness as parameters are described while in the second section self-contained air temperature daily irradiation models are presented. The third part is dedicated to estimation of solar radiation inside fuzzy logic. Two verified recipes for drawing up temperature based solar radiation models, one in the frame of classical statistics and the other one inside fuzzy logic, are outlined. A C program included on the CD-ROM, which enable fuzzy calculation for daily global solar irradiation is presented. Finally the accuracy of all the enumerated models is assessed under Romanian climate (Eastern Europe) in comparison with models which use sunshine duration or cloudiness at input.
The arguments that follow are leading to the conclusion that air temperature can be used with success in the estimation of the available solar energy.
West University of Timisoara, Romania, e-mail: marius@physics. uvt. ro