Microgrids are considered as a cost-efficient and reliable energy sources to rural areas and regions with unreliable power supply. The key potential for a low-cost operation and uninterrupted power supply lies in the optimal operation of such microgrids. Optimizing the microgrid operation consists of the optimal management of the power dispatched from the microgrid components for covering the load demand with a minimum cost while satisfying all technical and operational constraints. This leads to a complex optimization problem which is not easy to be solved. This paper presents an active-reactive optimal power dispatch strategy based on the concept of an economic model predictive controller (EMPC). In this operation strategy, the battery lifetime cost, the active-reactive power generation cost and the grid blackout problem are considered. In addition, a cost model for the dispatched reactive power from the PV-system and battery storage system is developed. Furthermore, a new cost model for reactive power generation from the diesel generator is introduced. The computation result shows that the proposed EMPC framework is able to manage the power dispatch in the microgrid in a cost-effective and reliable manner for both grid-connected and islanded mode. Moreover, the proposed operation strategy leads to a significant reduction in the total costs of the dispatched active-reactive power and battery lifetime loss. Furthermore, it is approved that the PV-inverter is able to generate reactive power with very low cost compared to other energy sources in the microgrid.