This communication presents the thermal analysis of passive and active solar distillation system by using the concept of solar fraction inside the solar still with the help of AUTOCAD 2000 for given solar azimuth and altitude angle and latitude, longitude of the place. Experiments have been conducted for 24 h (9 am to 8 am) for New Delhi climatic conditions (latitude 28 degrees 35'N, longitude 77 degrees 12'E) during the months of November and December for different water depths in the basin (0.05, 0.1 and 0.15 m) for passive as well as active solar distillation system. Analytical expressions for water and glass cover temperatures and yield have been derived in terms of design and climatic parameters. It is observed that (i) the solar fraction plays a very important role at lower values of solar altitude angle; (ii) the internal convective heat transfer coefficient decreases with the increase of water depth in the basin due to decrease in water temperature; (iii) there is a fair agreement between the experimental observation and theoretical prediction during daytime as compared to that during the night. (c) 2005 Elsevier Ltd. All rights reserved.