Three identical solar tunnel greenhouse dryers under forced convection mode were installed for drying peppermint plants. Thermal analysis of the solar tunnel greenhouse peppermint dryer was investigated based on thermal balance equations in order to predict its performance. Performance of solar greenhouse dryer was studied as a function of change in plant conditions, air flow rates and peppermint loads under two fan operating systems and evaluated in terms of system temperatures, drying rate, drying efficiency, product quality and drying cost. The obtained data revealed that drying peppermint as leaves reduce the drying time and achieve the highest percent of volatile oil compared with drying whole plants. Drying peppermint at flow rate of 2.10 m(3)/min, load the greenhouse by about 4 kg/m(2) and operate the greenhouse by continuously fan operating system tends to increase the drying rate by 22.78% and 24.8% for whole plants and leaves comparing with periodical system. (C) 2016 Elsevier Ltd. All rights reserved.