The knowledge of moisture diffusion, D-eff and convective mass transfer, h(m) coefficients during drying of food product is necessary in modeling and optimization of solar dryers. In the present paper, a methodology is proposed for the determination of these coefficients using variable drying parameters (lag factor, k(0) and drying coefficient, k). Mixed-mode solar dryer with potato cylinders and slices was used to obtain variable (temperature dependent) k(0) and k from drying kinetics. Results of investigation indicate the increasing trend of D-eff and h, with temperature and their values are found to be higher for cylinders compared to slices. Temperature rise from 33 to 48 degrees C for cylinder during drying results in the increase of 85.6% and 159% of D-eff and h(m), respectively, whereas these figures are 72% and 89% for slices. The statistical error analysis reveals that for each of the sample geometry, the proposed prediction models can better simulate experiments when variable parameters instead of constant ones are considered. (c) 2008 Published by Elsevier Ltd.