In the solar air flat plate collector, the insufficiency of the thermal exchange between the fluid and the absorber obliges the user to enhance their optimization. This low thermal exchange does not allow these systems to obtain their best performance or the best thermal efficiency. In our experimental study, which consists of a solar energy simulation, we have sought to improve the efficiency-temperature rise couple of the flat plate solar collector by considering several types of obstacles disposed in rows in the dynamic air vein of the flat collector. Thus, we have proceeded to the application of the best two systems (WDL1) and (TL) for drying an agricultural product grape. By comparing with the collector without obstacles (WO), the thermal transfers and, consequently, the output temperature (T-OC) and the collector efficiency (eta) are clearly improved. The drying times obtained with the proposed systems are very interesting. The heat quantities obtained in the case of WDL1 are very important compared with the collector WO. However, the entry to the drying cupboard of this high temperature (T-OC) in the vicinity of the solar midday must be limited to the maximal value demanded by the considered product. (C) 2003 Elsevier Ltd. All rights reserved.