The electrical grid is changing from a centralized system with predictable and controllable power generation to a system integrating large numbers of distributed energy resources including weather-dependent renewables. As a consequence, the future retail energy market for electrical energy will have many more participants and see more volatile prices than today, creating the need for new communication and trading infrastructures facilitating. In this paper, we briefly review PowerMatcher as a possible approach for such an infrastructure, and analytically evaluate its communication characteristics. PowerMatcher is a multiagent based smart grid communication framework developed by TNO which enables market integration of distributed energy resources and automatic demand supply matching. While the trading side of the framework is well understood, there is no study that considers the communication side. Our results show that PowerMatcher enables scalable retail energy transactions with millions of participants requiring only moderate resources on the communication's side.