ON THE RELATIONSHIP OF BEAM TRANSMITTANCE ON CLEARNESS INDEX FOR ATHENS, GREECE

Abstract

Proper design and performance prediction of solar energy systems requires accurate information on the availability of solar radiation. However, the complexity and cost of a reliable radiation measuring network dictates the need for developing alternatives that can replace and/or complement observations. Dependable solar radiation models are an alternative. In this paper, two years of solar radiation data from the National Observatory of Athens, Greece (37.5°N, 23.5°E, 107 m above MSL) are used to develop a continuous piecewise linear regression model that predicts hourly direct irradiation values when only global irradiation data are available. The applicability of the Randall-Whitson [7] and Jeter-Balaras [9] models in the area of Athens is also evaluated. For the urban atmospheric conditions of Athens the developed two year correlation provides a better fit to the empirical data.