It is necessary to develop thermal test procedure that can assist performance comparison between various solar dryer designs on common basis. In order to achieve this objective, the laboratory model of mixed-mode solar dryer is specially designed to perform indoor drying experiments with cylindrical potato samples. Sixteen drying kinetic curves are obtained over a wide range of various drying process variables. The variables investigated are absorbed thermal energy, air mass flow rate, food sample thickness and loading density. Based on experimental data of moisture content ratio-drying time, new concept to develop standard test method for performance evaluation of a given dryer is proposed. The proposed methodology facilitates to generate single generalized characteristic curve representing 16 drying kinetics and dimensionless parameter called dryer performance index (DPI) characterising the effectiveness of dryer system is identified. Different solar dryers with potato, banana and wheat are also tested in real climatic conditions to validate the proposed methodology. DPI with consistent values for all test conditions, indicating high degree of independence of operating conditions and food product characteristics, can therefore be used as a test parameter for performance comparison between different dryer designs on equitable basis. © 2012 Elsevier Ltd.