This letter investigates the energy harvesting capabilities of a novel hybrid wind and solar transduction device. The proposed device is an inverted-U shaped structure with a pair of piezoelectric benders connected by a flexible, tensioned photovoltaic ribbon. The tensioned photovoltaic ribbon member undergoes aeroelastic flutter limit cycle oscillations (LCOs) at low wind speeds, leading to time-varying tension forces applied to the piezoelectric benders, producing cyclic deflections and output voltage. Experimental characterization of the proof of concept energy harvester indicates that it is possible to obtain several milliwatts (mW) of power using the centimeter scale device, with an output power of ∼12.1 mW at a combination of 12 m s −1 wind speed and 100 W m −2 of solar irradiance, for indirect solar applications. It is shown here that an optimal combination of applied tensile preload and preset angle of attack exists which produces the highest wind power output of the system. An explanation of this behavior is also provided through the analysis of data collected on the photovoltaic ribbon velocity, piezoelectric voltage signals, and high-speed imagery, providing further insight to the motion kinematics of the highly nonlinear system response. Interestingly, the solar power output has been observed to remain invariant with increasing vibration velocity. This suggests that the gain in solar power efficiency from vibration-induced convective cooling negates any losses from the deflected incidence angle of the photovoltaic ribbon. These results illustrate that there is a negligible performance penalty in adding wind energy harvesting capability to the solar cells with this device concept.

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This paper proposes a multifunctional compliant structure that can harvest electrical power from both incident sunlight and ambient mechanical energy including wind flow or vibration. The energy harvesting device consists of a slender, ribbon-like, flexible thin film solar cell that is laminated with piezoelectric patches. The harvester is mounted in longitudinal tension and subjected to a transverse wind flow to excite flow-induced aeroelastic vibrations. This paper formulates an analytic model of the bending dynamics of the device. We present a Transfer Matrix formulation that also accounts for the changes in natural frequencies and mode shapes of the system when subjected to axial loads in a beam. It also observed that mode shape obtained using TMM formulation shows numerical stability even for very high tensile loads providing results consistent with the geometric boundary conditions applied at the ends of a beam. This article also discusses about structurally modeling a piezo -solar energy harvester using TMM methodology, where a thin clampedclamped solar film is bonded with piezo patches having a much higher bending stiffness. Additionally, the effect of axial tension on the mode shape of the thin host structure of the piezo-solar ribbon is presented and it is shown how this tension can be used advantageously to affect the strain distribution of the entire structure and introduce higher strains at the piezo patches.

This article presents a nonlinear structural modeling framework to analyze a tensioned doubly clamped energy harvesting device. The device is investigated for energy harvesting under base excitation loading, where the structure undergoes bending motion and aerodynamic loading, where the structure undergoes combined bending–torsion motion. Transfer-matrix method for analyzing torsional motion is modified to include the effects of applied axial preload tension. The tension-modulated mode shapes and natural frequencies of the structure, obtained using transfer-matrix method, are found to be in good agreement with the results obtained using a commercially available Finite Element software. Under base excitation loading, it is shown that the effects of tension on electromechanical coupling and stiffness create competing influences on the power efficiency of the system. For aerodynamic loading, increasing preload tension increases the cut-in wind speed of the device. However, beyond the cut-in wind speed, with proper selection of the preload tension, the tensioned structure can produce an order of magnitude more power than the untensioned case at the same flow speed.

CHATTERJEE, PUNNAG. Structural Modeling of a Compliant Flexure Flow Energy Harvester. (Under the supervision of Dr. Matthew Bryant). This thesis presents the concept of a flow-induced vibration energy harvester based on a one-piece compliant flexure structure. This energy harvester utilizes the aeroelastic flutter phenomenon to convert flow energy to structural vibrational energy and to electrical power output through piezoelectric transducers. This flexure creates a discontinuity in the structural stiffness and geometry that can be used to tailor the mode shapes and natural frequencies of the device to the desired operating flow regime while eliminating the need for discrete hinges that are subject to fouling and friction. An approximate representation of the flexure rigidity is developed from the flexure link geometry, and a model of the complete discontinuous structure and integrated flexure is formulated based on transfer matrix method. The natural frequencies and mode shapes predicted by the model are validated using finite element simulations and are shown to be in close agreement. A proof-of-concept energy harvester incorporating the proposed flexure design has been fabricated and investigated in wind tunnel testing. The aeroelastic modal convergence, critical flutter wind speed, power output and limit cycle behavior of this device is experimentally determined and discussed.