Optical nano-antennas have been proposed as an alternative option for solar energy harvesting. In this work the power conversion efficiency of optical antennas have been proposed as an alternative option for solar energy harvesting. In this paper, an investigation is presented into bowtie, polygonal and circle antennas for THz energy detection, with the aim of optimizing their geometrical parameters. HFSS Multiphysics based on the Finite Element Method FEM is used to simulate the golden nano-antennas, which are placed on a silica glass substrate with εr 2.09 . The dielectric properties of gold is obtained by fitting the experimental data into the Drude model. A performance comparison among these designs is presented in order to find the optimum solution for this application. The main goal of this study is to design and optimize nano-antennas for maximum solar radiation energy conversion. It is shown that increasing the edges of the patch consequently tapering of the patch, decreases the value of the converted electric field.