In this paper, we develop an asynchronous distributed algorithm based on the Alternating Direction Method of Multipliers (ADMM), that is applied to local areas to achieve the global network objective. Compared to centralized and synchronous optimization schemes, the asynchronous distributed algorithm helps in reducing computational complexity, ressources usage and communication overhead. We prove that the distributed ADMM algorithm is applicable whether the network is divided into overlapping or non-overlapping areas. It appears to have good convergence properties and low complexity which makes it practical for smart power grids. As an application, we consider the Optimal Power Flow (OPF) problem in power grid networks. We solve this problem distributively and in an asynchronous manner, leading to smarter management of the grid. Simulation results are carried out on the IEEE 30 bus and 118 bus standard systems which illustrate the convergence, scalability and effectiveness of the proposed algorithms.