The paper presents a preliminarily study on an efficient, inexpensive and energy saving solar batch dryer for drying sludge. A concept of a mixed mode solar dryer was developed and designed. Air heated by the solar flat heater was forced through drying chamber by electric fans. A 3-D physical model was used to observe and predict the operation of the solar batch dryer at different time under designed conditions. The thermal performance and air movement of drying chamber in the designed dryer unit were evaluated through ANSYS-FLUENT software. By determining the external conditions, localization and the material properties, the model can predict temperature and humidity distributions in the designed drying chamber and sludge material layers, air-flow field according to the radiation and convection, as well as water quantity evaporated from the sludge. A special attention was paid to implementation of physical boundary conditions on the sludge surface, which is between air and dried sludge. The developed solar barn dryer can heat air at average temperature between 47°C and 57°C, which is optimum for dehydration of the sludge. The designed drying chamber can generate an adequate fow of hot air to increase the drying rate by above 30%.