In the article, entropy generation is calculated locally by the computational fluid dynamic simulation for the design improvement of a single slope solar still. A numerical approach based on SIMPLE algorithm is utilized to simulate the double diffusive natural convection in the solar still and solve the mass, momentum, energy, and concentration equations. The study investigates the effects of aspect ratio and temperatures of glass cover and water on different types of entropy generation containing frictional, diffusive, and thermal entropy generations. Obtained results indicate that an increase in different types of entropy generation is occurred with an increase in the glass and water temperatures. Moreover, the still with higher aspect ratio creates higher values of entropy generation than that of still with smaller aspect ratio. For example, there is 30% increment in diffusive entropy generation when the aspect ratio value is changed from A = 2.58 to A = 5.3 for Tg=30°C and Tw=40°C. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1112–1120, 2018