Drone stations (DBSs) can provide wireless coverage on the ground. This letter investigates the optimal DBS deployment to achieve energy efficient wireless coverage. We formulate a problem to minimize the average transmit power of a DBS that serves a set of ground users. We firstly consider a case where the DBS transmits signals to each user with an equal power. In this case, we propose a decoupling-based placement algorithm to obtain the optimal DBS location. For the case without allocating the equal transmit power to each user, we further propose a DBS placement algorithm based on the successive convex approximation (SCA) technique. Simulation results show that increasing the drone altitude can obtain the line-of-sight (LoS) propagation advantage of the AtG link, which results in the power savings by our proposed algorithms. The case without assuming the equal transmit power to each user enjoys the lowest average transmit power.