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Recent developments on the use of the piezoelectric effect in ZnO nanorod-based p-n junctions for energy harvesting applications are presented. We describe a hybrid p-n nanostructured ZnO energy device combined with the semiconducting polymer poly(3,4-ethylene-dioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) to produce a kinetic energy harvesting. The load resistance-dependent power output from this p-n junction device is compared with the more common ZnO-PMMA device, which we make from ZnO nanorods manufactured using an identical process. It is shown that the PMMA device generates an open-circuit voltage of 150mV with a maximum power of 0.24μW/cm2 giving 0.03nJ of available energy when on a load resistance of 324 kΩ. The PEDOT:PSS device generates significantly more power, 28.9μW/cm2, when it is matched to a 1.6 kΩ load resistance. The energy output of the PEDOT:PSS device is 2.22nJ. Our results demonstrate the importance of measuring energy delivery to an electrical load to fully understand the output capability of these devices. By analysis of the time-dependent output of the devices the energy can be calculated giving a reasonable estimation as to the available energy and power in any given system.