Lifetime is the main issue of wireless sensors net-works. Since the nodes are often placed in inaccessible places, thereplacement of their battery is not an easy task. Moreover, thenode maintenance is a costly and time consuming operation whenthe nodes are high in numbers. Energy harvesting technologieshave recently been developed to replenish part or all of therequired energy that allows a node to function. In this paper, weuse dedicated chargers carried by drones that can fly over thenetwork and transmit energy to the nodes using radio-frequency(RF) signals. We formulate and optimally solve the OptimalDrone Placement and Planning Problem (OD3P) by using a givennumber of flying drones, in order to efficiently recharge wirelesssensor nodes. Unlike other works in the literature, we assumethat the drones can trade altitude with coverage and rechargepower, while each drone can move across different positions inthe network to extend coverage. We present a linear program aswell as a fast heuristic algorithm to meet the minimum energydemands of the nodes in the shortest possible amount of time.Our simulation results show the effectiveness of our approachesfor network scenarios with up to 50 sensors and a50×50mterrain size.