Blockchain technologies and smart contracts are getting more attention for potential smart grids applications as they are able to decentralize the data management in a secure and transparent way. In this work, a smart contract deployed in a simulated Ethereum blockchain is used to coordinate the decentralized solution of the Economic Dispatch (ED) problem of Distributed Generation (DG) units. The distributed optimization problem is first formulated and solved using the Alternating Directional Method of Multipliers (ADMM) and then a smart contract plays the role of the decentralized coordinator and data aggregator. Results from the combined simulation of the method are provided through a variety of scenarios, that investigate the efficacy and practical applicability of the method.