A generalized harmonic wavelets-based scheme is proposed for conducting joint time-frequency response analysis of a piezoelectric harvesting device subjected to non-stationary loading. Such devices are progressively employed in several applications, mostly for powering adjoining low power level devices. In this regard, utilizing the theory of the generalized harmonic wavelets, in conjunction with elements of the theory of the generalized matrix inverses, a solution treatment is proposed for quantifying the non-stationary and narrow band voltage response characteristics of such devices. The obtained results are compared with pertinent Monte Carlo simulation data.