This paper describes the performance of a high efficiency energy management system for a fixed wireless sensor load with a varying energy harvesting input. An in-depth loss analysis of the high efficiency switched supercapacitor circuit with a varying energy harvesting input is described in detail. Efficiencies of up to 94% are shown for the switched supercapacitor system which is significantly higher than that of the existing best performing solution for an indoor solar cell source and an equivalent wireless sensor load.