Theoretically, making the chimney top larger than the chimney base can increase the driving potential of the Solar Chimney (SC) system. Based on this concept, the divergent chimney (DSC), the cylindrical chimney with a divergent outlet (DOSC) and the cylindrical chimney with a divergent inlet (DISC) are numerically examined in this study for revealing their aerodynamic features and the capability of power generation. The simulating outcomes indicate that the diffuser-type SCs generally have a better power generation performance than the cylindrical SC: the optimal output of the examined DSCs is similar to 13.5 times higher than that of cylindrical SC; the increase in the output from the DISCs ranges from 2 to 10 times while the optimal situation from the DOSCs is only similar to 5 times. The difference in the system performance is further found to be related to the chimney geometric parameters that have critical impacts on the expansion loss in the divergent flow channel. Based on the aerodynamic characteristics of the diffuser type SCs, a new controlling approach for the SC is proposed with a variable diffuser outlet and an example is illustrated by using the DOSC. The example reveals that the SC with the controlling treatment had a stable output for 7 h during the daytime and its power output is 60% higher than the SC without any control. (C) 2017 Elsevier Ltd. All rights reserved.