In times of increasing material scarcity and still not widespread availability of renewable energy, it is inevitable to seize all opportunities to improve the resource efficiency of any product. In particular, this promotes lightweight design as a key technology to reduce both material and energy consumption across the entire product lifecycle. Therefore, systematically exploiting lightweighting potentials already on a functional level remains a major challenge requiring methods of product development to be applied in the early phase of each development cycle ensuring the implementation of the holistically best solution from a sustainability point of view. Thus, the proposed “functional lifecycle energy analysis” (FLCEA) provides a remedy to effectively implement lightweight design in products by identifying recommendations for action regarding future product generations, resulting in a holistic energy optimization. In this contribution, the methodology is presented in parallel to its implementation in the use case of conceptual designing a semi-mobile handling system. As a result of this study, it was not only possible to identify lightweighting potentials of the system-in-development, but also to analyze technical product functions requiring modifications in view of the circular economy to holistically improve the ecological sustainability of the entire system.