High-availability applications such as data centers employ supercapacitors (SCs) as sources of transient and backup power. The miniaturization of SC stacks facilitates their integration into such systems, especially when size constraints are to be met. In this paper, a size-optimal discharge ratio (SODR) is derived to reduce the size of SC stacks while meeting the power and energy requirements of an application. The proposed SODR is compatible not only with the SC stack design algorithm outlined in this paper but also with existing design methods. Using the SODR, backup durations suitable for SCs are quantified in comparison to other storage technologies. Refinements of the analysis are outlined to accommodate parameter variation. The optimality of the SC stack size achieved by the proposed SODR-based design method for given load requirements and power and energy constraints is validated in circuit simulation and experiment.
