Applying mobile energy storage system, asynchronous electric transport energy consumption might be significantly reduced as its braking energy can be stored for repeated use instead of being dissipated in brake resistors. Owing to comparatively rapid accelerations and decelerations, supercapacitors can be very appropriate for both energy storing and supplying due to their high power density. As a matter of fact, mobile energy storage devices not only ensure the possibility to store vehicles braking energy but also contribute in supplying trolleybus drive with power in acceleration mode, thus reducing overhead DC network energy transmission losses that are variable according to the distance between trolleybus and substation. This paper presents the chosen trolleybus model Škoda 27Tr simulations both without and with supercapacitor energy storage system. Due to additional storage device weighs, trolleybus mass increase impact on drive energy consumption and transmission loss energy is studied. Optimal supercapacitor module amount for different circumstances is analyzed.