The results for seasonal performance are integrated over the entire longan drying period. The overall solar fractions are presented in Fig. 3 and Fig. 4. These results are for the average utilized capacity for each individual facility during the drying season (see Table 1). It is seen that the solar fraction reaches 15.3 and 19.6% for air channels height of 10 and 5 cm, respectively. These diagrams show the maximum collector area representing the total area of each facility's roof. The asymptotical behavior of the solar fraction with increasing collector areas is explained by the fact that as collector size increases, the efficiency drops (Fig. 5). With larger collectors, the additional sections render only a small temperature rise [17]. The condition then approaches an equilibrium state between heat gains and losses, decreasing the efficiency of the collector as a whole unit. This is true no matter if the increased dimension is the length or the width of the collector. For this study, the width was the variable collector dimension. The effect of wider collectors is a reduction in air speed in the channel and therefore a reduction in the convective heat transfer coefficient. Keeping other factors constant, decreasing the air channel height produces better efficiencies. This results from the improvement of the convective heat transfer coefficient from absorber to the air. Similar trends have been reported by others [17], [18] and [19]. The final result is better collector efficiency and larger solar fraction for all facilities without more collector area and material cost as a consequence.