First of all, a state of the art regarding the methods to solve optimal power flow (OPF) and its application in electrical microgrids are presented in this article. Afterward, a mathematical algorithm based on the gradient method is proposed to implement OPF to a low-power electrical microgrid, with the objective of improving the voltage's characteristics and reducing the active power losses. Finally, the proposed algorithm is applied to low-power electrical microgrid with photovoltaic generation to demonstrate the effectiveness of the method.