Distribution Generation (DG) is widely used in distribution systems to enhance the dynamic characteristics of the network such as improving the voltage profile, minimizing active and reactive power losses. A variable voltage load model is assumed in many distribution systems. Therefore, the results are more reliable and accurate. This paper proposes an analytical technique to size and site a photovoltaic based DG unit to minimize a multi objective function that depends on active and reactive power losses and voltage deviation taking into consideration the variable load model and mixed load between residential, commercial and industrial.