In this paper we present a solar energy harvesting circuit for low-power applications describing circuit architecture and guidelines design. We evaluate the performance of two implemented prototypes intended to power a wireless embedded system under intensities and different switching frequencies. Measurements show that higher switching frequencies allow reaching the (~90%) at higher light intensities, whereas lower operating frequencies perform better under lower irradiance. Experimental circuit optimization depends on light conditions and the proposed solar energy harvester can autonomously supply the nodes sensor network WSN.