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At present, frequency up-converted piezoelectric energy harvesters are disadvantaged by their narrow range of operating frequencies and low efficiency at ultralow-frequency excitation. To address these shortcomings, we propose herein an impact-driven frequency up-converted piezoelectric energy harvester composed of two driving beams and a generating beam. We find experimentally that the proposed device offers efficient energy output over an ultrawide-frequency-range and performs very well in the ultralow-frequency excitation. A maximum peak power of 29.3 mW is achieved under 0.5g acceleration at the excitation frequency of 12.7 Hz. The performance of the energy harvester can be adjusted and optimized by adjusting the spacing between the driving and generating beams. The results show that the proposed harvester has the potential to power miniaturized portable devices and wireless sensor nodes.

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This paper presents a novel scheme of analyzing the statistical properties and sizing the storage for wind-PV-storage hybrid systems, based on the data organization and treatment for system optimization. First, the partial Fourier transform (PFT) is derived for spectrum analysis with utilizing the periodic sparse properties of the solar data. Second, the storage for stabilizing the power variance caused by fluctuating renewable energies and varying grid loads is sized with spectrum analysis of the power data output from the System Advisor Model (SAM). Third, the weighting factor for storage sizing is achieved by constructing a hybrid probability distribution of renewable energies considering the coastal climates in South Eastern Australia, together with simplified parameter calculation methods. The real data sets including the hourly wind speed, solar irradiation, and grid load are used to design and validate the proposed scheme.