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-theshelf 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.

This paper presents results from experiments and simplified numerical simulations on the flow-induced dynamics and power generation of inverted flags that combine flexible piezoelectric strips with photovoltaic cells to simultaneously harvest kinetic wind energy and solar radiant energy. Experiments were conducted in a wind tunnel under controlled wind excitation and light exposure, focusing in particular on the dynamics and power generation of the inverted flag harvester. Numerical simulations were carried out using a lattice-Boltzmann fluid solver coupled with a finite element structural solver via the immersed-boundary method, focusing in particular on minimizing the simulation run time. The power generated during the tests shows that the proposed inverted flag harvester is a promising concept, capable of producing enough power (on the order of 1 mW) to supply low-power electronic devices in a range of applications where distributed power generation is needed. Notwithstanding key simplifications implemented in the numerical model to achieve a fast execution, simulations and measurements are in good agreement, confirming that the lattice-Boltzmann method is a viable and time-effective alternative to classic Navier–Stokes-based solvers when dealing with strongly coupled fluid–structure interaction problems characterized by large structural displacements.

Experiments were carried out to study the dynamics of hanging cantilever flexible filaments in air cross-flow. Thirteen flexible filaments of 0.61 mm diameter and lengths from 20 mm to 60 mm were tested with wind speeds in the range of 1 m/s to 15 m/s, corresponding to Reynolds numbers of 25