With the rise of sustainable energy generation, the need for integrated building energy storage solutions increases. Supercapacitors have not yet been considered a viable alternative to Li-ion batteries, often because of their space requirements. We present the function integration of supercapacitors into a facade, where space is abundant when using novel lightweight Carbon Reinforced Concrete (CRC) construction designs. We develop real prototypes. While materials and processes for the approach have been characterized for manufacturability in earlier studies, the resulting sustainability potential remains an open question. This study therefore assesses and supports the design process of that multifunctional facade with the help of Life Cycle Assessment (LCA). LCA results shall guide design choices on materials and constructional alternatives. We further elaborate on the potential of the multifunctional facade to compete with a Li-ion battery system as the current benchmark for residential energy storage. While the proposed design is still a prototype, the cradle-to-site LCA models a full-scale production to allow for that comparability. We calculate the greenhouse gas (GHG) minimization potential for the multifunctional facade with integrated supercapacitors. It is significantly lower by a factor of around 20 in comparison to Li-ion battery energy storage. We further use different functional units to interpret the LCA results, considering both the function of the facade and energy storage. Overall, results show that the choice of the functional unit affects the material and constructional recommendations.