This paper focuses on the integrated management and design of a distributed energy systems (DES) with solar generation and energy storage. The DES remains voluntary simple as the objective is to focus on the design methodologies rather than the system complexity. The article aims at bridging the gap between conventional DES design strategies, made in a single stage fashion over a representative period, and expansion planning problems that perform dynamic sizing over decades with oversimplifications of the system operations. Especially, the paper investigates to what extent the value of the model is increased when aging is controlled over the system lifetime compared to standard methods based on a single equivalent year. To address these questions, a multi-time scale model is first implemented by coupling both the DES operation and the sizing. The optimal asset capacities are computed in the form of a dynamic investment plan over the system lifetime that can accommodate potential changes in energy prices or cost of technology. Then, the results are compared with single stage design strategies on a common simulation framework. The implemented multi-time scale planning displays good performances with up to 20% cost reduction compared to typical single stage designs. Finally, the impact of the energy rates and system self-sufficiency are investigated. The obtained results show that significant investments in energy storage arise for electricity prices multiplied by three compared to the baseline or with strong self-sufficiency constraint over 60%.