Experiments are performed to investigate the effects of wake galloping on the range of flow speeds over which a galloping-based piezoaeroelastic energy harvester can be effectively used. Two different upstream cylinders and a wide range of spacing between the upstream and downstream cylinders are considered. Bifurcation diagrams and type of instability for different setups are determined. The results show a complex relation between the upstream circular cylinder size, the spacing between the two cylinders, the flow speed, and the load resistance on one hand, and the level of harvested power on the other hand. (C) 2013 AIP Publishing LLC.