Smart grids, the next generation of electric grids, require the deployment of sophisticated monitoring and control systems to enhance their operational efficiency. Wireless Sensor Networks (WSNs) have been considered as a promising communication technology for the monitoring and control of smart grid operation. They bring significant advantages such as, rapid deployment, low cost and scalability. However, the deployment of WSNs in smart grids brought new challenges mainly due to the electric grid features. Consequently, traditional WSN communication protocols have been shown inadequate and several recent research efforts were dedicated for their optimization. This paper provides a comprehensive survey on related literature, discusses the still-open research issues, and identifies the most common validation platforms for experimenting WSN communications in smart grid. We believe this survey will pave the way for the research community to (i.) understand important concepts related to WSN-based smart grid communications, (ii.) identify gaps and make valuable contributions in this timely and exiting field and (iii.) choose the convenient experimental platform for the validation of proposed solutions.