The effect of variation of mass flow rate (m f ) and number of collectors (N) on the yearly efficiency of a single slope solar still by incorporating series connected N similar photovoltaic thermal flat plate collectors (NPVTFPCSS) has been investigated, keeping a constant water depth in basin as 0.14 m. The various parameters have been calculated, taking into account all four types of weather conditions for New Delhi using computing code developed in MATLAB-2015a. All equations and required data have been fed to the computing code for evaluating different relevant parameters. It has been concluded that the value of all types of annual efficiencies, except annual electrical efficiency, diminishes with increase in the value of m f at a selected value of N until m f = 0.10 kg/s and then becomes almost constant. Optimal values of N from annual overall exergy efficiency and annual overall thermal efficiency viewpoints have been found as four and ten respectively. © 2022 IWA Publishing. All rights reserved.