This article presents a structure of a dryer using solar energy and heat of geothermal water from a natural field for heating the dryer air. It also presents a model of the temperature-humidity processes in the dryer chamber using solar energy for heating the air. The steady state model determining the distribution of air temperature and humidity in the dryer depends upon climatic (solar radiation, temperature and humidity of external air and wind velocity) and working conditions (mass flow rate of air and material for drying). It also presents an experimental performance of the dryer in "dry experiment" (without moisture) and real drying processes. Comparing between the results obtained from the model and experimental results shows that the model is adequate. (C) 2001 Elsevier Science Ltd. All rights reserved.