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) for 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 based ESSs has been developed for this purpose. The model can simulate the energy
exchange among the 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 since 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 %
can be obtained at high, moderate and low traffic volume respectively. On the other hand using
onboard ESS on every vehicle, the maximum energy savings achieved vary between 27.3 % and 36.3 %
at high and low traffic volume respectively.
Results show that even though the energy savings achieved are higher with on-board ESS, the amount
of supercapacitor cells needed is lower when using stationary ESS. However, benefits such as peak
power shaving, voltage drops reductions and reduced line losses are better attained by onboard ESS.