In this paper, a new radiation model for a single-slope solar still has been developed which for the first time takes into account the effect of all walls of the still on the amount of incident solar radiation on the water surface and each wall. In this model, the walls are projected on the cover to calculate the amount of beam radiation received by any components inside the still. This is in contrary to the previous models in which stills' walls were projected on a horizontal surface and their shadows on the water surface and the walls were either neglected or not computed properly. The predictions of the proposed model are compared with the experimental data obtained in the present work and data from the literature. It was found that there is a good agreement between the theoretical results and the experimental data. Moreover, time variations of the incident beam radiation on different parts of a single-slope solar still are investigated. The results show that the effect of the back and side walls is not inconsiderable and they should be taken into consideration to improve the accuracy of the thermal radiation analysis of single-slope solar stills' performance. (C) 2010 Elsevier B.V. All rights reserved.