Planning of renewable resources is an essential study in active power distribution systems. In this paper, an optimal sizing of wind/solar mix is presented with the consideration of the security of the generation resources. The proposed methodology employs the negative correlation between solar and wind output power to ensure a certain level of supply security and load fulfillment. The effect of formulating the design optimization problem on the optimal wind/solar mix and power system operation is addressed. The IEEE 38-bus system with selected candidate locations for renewable resources demonstrates the proposed design methodology. The forward/backward sweep power flow technique is used to evaluate the obtained design results. Minimizing the squared difference between generated power and load demand, as the objective function led to a significant performance in meeting load demand without degrading the power system operational constraints.