Stationary or onboard energy storage systems for energy consumption reduction in a metro network

This article will compare the benefits and constraints of onboard and stationary energy storage systems (ESS) with the aim of reducing the overall energy consumption on a low DC voltage metro network. A dedicated simulation tool that models a metro line with conventional or hybrid trains and stationary supercapacitor (SC)-based ESSs has been developed for this purpose. The model can simulate the energy exchange among simultaneously running vehicles of a conventional metro line and evaluate the effect of a stationary ESS when installed along the line. Different traffic scenarios are considered for the study: high, moderate, and low traffic volume as this element has a strong influence on the energy exchange among the running vehicles and therefore on the energy available for storage in the ESS. This will eventually determine the energy consumption reduction. This simulation tool is used to study the most convenient ESS alternative for the case of a Brussels metro line. When compared with a conventional metro line, the total energy consumption reduction achieved with stationary ESS varies in function of the traffic conditions, ESS size, and ESS distribution along the line. With efficient metro trains, values of energy savings up to 18.7, 25.1, and 36.4 per cent can be obtained at high, moderate, and low traffic volumes, respectively. In contrast, using onboard ESS on every vehicle, the maximum energy savings achieved vary between 27.3 and 36.3 per cent at high and low traffic volumes, respectively. Results show that even though the energy savings achieved are higher with onboard ESS, the amount of SC cells needed is lower when using stationary ESS. However, benefits such as peak power shaving, voltage drop reductions, and reduced line losses are better attained by onboard ESS.