The number of works addressing the role of energy efficiency in the software development has been increasing recently. But, designers and programmers still complain about the lack of tools that help them to make energy-efficiency decisions. Some works show that energy-aware design decisions tend to have a larger impact in the power consumed by applications, than code optimizations. In this paper we present the HADAS green assistant, which helps developers to identify the energy-consuming concerns of their applications (i.e., points in the application that consume more energy, like storing or transferring data), and also to model, analyse and reason about different architectural solutions for each of these concerns. This tool models the variability of more or less green architectural practices and the dependencies between different energy-consuming concerns using variabilty models. Finally, this tool will automatically generate the architectural configuration derived from the selections made by the developer from an energy consumption point of view.