A solar chimney power plant (SCPP) converts solar thermal energy into electricity by generating a buoyant flow in a chimney. To assist the air flow in shifting its direction from horizontal to vertical, a guide wall (GW) is usually set in the collector-to-chimney transition region. The primary objective of this study is to examine the impact of the GW geometry on the power output of a SCPP. A reduction in mass flow rate after adding a GW in the system was observed in a small-scale experimental prototype. Numerical simulations on a large-scale SCPP further found that the mass flow rate was linearly and inversely proportional to the increase of GW height. The driving force, however, nonlinearly increased with increasing the GW height. Subsequently, the potential maximum power output, which was mainly governed by the driving force, increased with increasing the GW height. Furthermore, a divergent chimney system which can improve the performance of SCPPs had different reactions with the geometry of GWs compared with a cylindrical-chimney system. Under the optimal GW configuration, the power output of the SCPP increased by similar to 40% in a cylindrical-chimney system and by similar to 9.0% in a divergent chimney system with respect to the system without a guide wall. (C) 2016 Elsevier Ltd. All rights reserved.