This paper presents a novel wind/solar energy-harvesting device based on the inverted flag concept that combines flexible piezoelectric strips with flexible photovoltaic cells to simultaneously harvest both wind and solar energy. Three inverted flags built using off-the-shelf components were experimentally investigated under controlled wind and illumination conditions to analyse their dynamics and electrical power generation capability. Our results provide an improved understanding of the dynamics of inverted flags that incorporate flexible piezoelectric strips and flexible solar panels, and indicate that the piezoelectric strips mainly increase the damping of the flags, while the solar panels act as an added mass. The power measurements show that the wind/solar energy-harvesting device proposed here is a viable concept that is capable of generating up to 3-4 mW of total power, enough to meet the demand of remote sensors and small-scale portable electronics, for wind speeds varying from 0 m/s (calm) to about 26 m/s (storm/whole gale) and 1.8 kLux constant light exposure, suggesting a rather diversified range of potential practical applications.