Data physicalizations are growing popular in many societal domains which indicates a strong potential for fostering public engagement thanks to public exhibition (e.g. in train stations, in airports, on roundabouts, and in enterprises). We focus on dynamic physical charts for visualizing renewable energy forecasts in public spaces. To get charts readable from any point of view around, we propose a physical ring chart inspired by stone cairns. To build this physical chart, we designed an expandable and stackable illuminated ring. In this paper, we describe the design process and the limitations of the first prototype of such a ring.