Why a piezo-solar hybrid energy harvester (meso-scale devices)?
- Multifunctional compliant structure integrates piezo and photovoltaic transductions.
- Ideal power source where there is intermittent presence of ambient wind and/or solar radiation.
- Reliable power source for powering low powered electronic devices year-round.
- Ideal solar usage scenario includes shaded regions (~ 100
and low wind velocities 3-15 m/s.
Design & fabrication
Proto 1 design was a clamped-clamped off-the shelf (Powerfilm) flexible solar module with piezo patches (Mide QP 16-N) laminated in a bimorph-configuration eat each clamped ends.
The design suffered from misalignment issues where the clamped ends would not align with each other and the mode shapes would deviate from the standard clamped-clamped mode shapes. Additionally, the clamped boundary condition made the structure very stiff to the wind-induced Limit Cycle Oscillations (LCOs).
Experimental setup
Proto 2 design looks like an inverted U shape. The vertical legs allow for a frequency doubling effect and the ribbon ends are now attached to a compliant vertical beam tip allowing for more deflection and hence more power output. Note that the tension is adjustable through the linear/rotary stage and is measured by the load cell (OMEGA LCFD 1Kgf).
When the ribbon (blue color) moved through one cycle, the vertical beams move through two cycles. This the cause of frequency doubling.
The schematic shows the wind-solar combined experimental setup for Proto 2 devices. The solar simulator is situated at the top of the wind-tunnel such that it projects the solar light on the vibrating ribbon.
- Polytec laser vibrometer
- Open channel, low turbulence intensity (0.23%) wind tunnel
- Photron Fastcam HS monochrome camera
- NI DAQ hardware
- Labview software interface
Experimental investigation
- Structural frequency range of interest < 200 Hz
- Sampling rate: 2000 Hz
- Data collection time at each wind speed: 30s
- Preload tension, T(N): [1, 2, 3]
- Preset,
: [0, 5, 10] - Windspeed,
: [0.5 0.5:12]
Classical flutter (
)
- At lower wind-speeds the structure showed classical heave-pitch flutter motion
Multi-frequency chaotic oscillations (
)
Wind-power output
Solar-power output
- Typical efficiencies of such flexible Powerfilm ribbons varies from 4 – 8 %
- It is counterintuitive to observe that solar output η remains invariant with h ̇
- It is hypothesized that solar cell efficiency increases with convective cooling