In this study, the experiments were conducted from December 2000 to November 2001 to evaluate solar fraction (F-n) for quonset type empty greenhouse. Solar radiation was measured at different points inside and outside the greenhouse weekly once. The iriodel based on Auto-CAD 2000 has been used for a given solar altitude and azimuth angles. Calculations have also been carried out for a typical day of each month of the year. It is observed that the solar fraction obtained by using Auto-CAD 2000 are very close to the value determined by using experimental observations and its value is more during winter months. Copyright (C) 2002 John Wiley Sons, Ltd.