This article analyzes a stochastic supercapacitor model and uses the model to estimate the losses for different balancing methods. In addition, it proposes guidelines for designing a supercapacitor bank that includes balancing networks. Supercapacitors (SCs) can be used as the main part of an energy storage system (ESS) that transfers high power to a DC or AC grid. This is needed in grids with a high penetration of renewable energies in order to balance generation and consumption. The design method is based on a supercapacitor model which uses stochastic variables: capacitance, series resistance and self-discharge current. As the balancing network affects the overall efficiency of the SC bank, dissipative and non-dissipative balancing networks are studied. Then different strategies are compared taking into account the complexity, cost and efficiency of the balancing network in the bank.