The rising demand for electrical energy and decreasing capital cost of photovoltaic (PV) panels led to rapid growth in large-scale solar PV system penetration in many countries, including Turkey. This article focused on a cost-effective and efficient decentralized voltage and reactive power (Volt/Var) control approach in distribution networks at the presence of high penetrated solar PV farms utilized as static synchronous compensator (PV-STATCOM) which has been recently proposed. A proper coordinated control of large number of PV-STATCOMs suggested to achieve optimal reactive power scheduling for the next day ahead. This article introduced implementation of a modified Levy flight-based firefly algorithm (MLFA) to multi-objective Volt/Var optimization problem, which was employed for minimizing active power loss and cost of energy. The validity and applicability of the proposed method were confirmed by implementing it on a real megavolt (MV) Turkish distribution network for various loading conditions. Simulation results show that the results of MLFA to this problem outperform those of other methods. Furthermore, application of the proposed method offers opportunity to distribution system operators for a large amount of cost savings and loss reduction without compromising voltage regulatory limits.