This paper reports the annual as well as seasonal performance analysis of single-slope passive solar stills having three different inclinations of condensing cover, namely 15, 30 and 45 degrees. The analysis is based on the experiments conducted throughout the year from June 2004 to May 2005 on one clear day every month. Each experiment has been carried over for 24 h for the New Delhi (Latitude: 28 degrees 37' North and Longitude: 77 degrees 13' East) climatic conditions. It was observed that the 15 degrees inclination of condensing cover gives maximum annual yield and distillation efficiency. The concept of solar fraction has been used for the validation of thermal modelling. The fair agreement has been noted between the values observed experimentally and calculated theoretically for temperatures and yield in all seasons. Copyright (c) 2007 John Wiley & Sons, Ltd.