Investment in energy inverter system in Gdynia's trolleybus network

PKT GDYNIA has continuously been striving to implement solutions aiming at energy usage optimization, frequently with substantial help from EU funds. In their undertakings within the EfficienCE project PKT attempts to limit existing energy losses in the trolleybus traction network by retrieving unused recuperated braking energy generated by trolleybuses, with the implementation of an energy inverter system which will divert this otherwise wasted energy to power the depot building.

In the first phase of the project PKT Gdynia has mainly focused on the preparation of technical specifications of the pilot installation necessary for the organization of the tendering procedure. A technical concept was developed, technical specifications were drawn up and tender documentation was completed in December 2019. On 19 December in accordance with the Sectoral Regulations obliging PKT a tendering procedure was launched by publishing a request for quotation regarding the „Implementation of the device for processing excess energy from braking trolleybuses for the depot’s own needs of 400V AC in PKT LLC in Gdynia”.

On 14 February the tender was won by the Polish company INTECO (from Gliwice, south of Poland). Subsequently a contract between PKT and INTECO was signed. The contract states that selected company is to deliver and start up the energy inverter system by 1 October, however, PKT has been recently informed by the contractor that due to the COVID lockdown there will occur a slight delay in the completion of the investment and it will most probably start its operation in December 2020. If necessary, a required annex to the contract concerning the change of dates will be signed by both parties.


Within the EfficienCE project PKT attempts to limit existing energy losses within the trolleybus traction network by making use of unused recuperated braking energy. If not used directly by the braking vehicle’s auxiliary units or other nearby vehicles on the network, recovered braking energy is otherwise dissipated in the form of heat in the braking resistors placed on the grid and thus irreversibly lost. What is also a crucial aspect here is that in the near future, within next five years, PKT Gdynia is planning to build a 0.5MW peak PV-power plant on the roof of the depot which will produce annually roughly 450MWh of clean energy (investment to be funded outside of EfficienCE project). The energy will be fed directly to the trolleybus grid and will cover as much as 5% of its total usage. Owing to the investment made within EfficienCE the recovered unused braking energy (as well as the surplus of unused solar energy in the future) will be used to power the building of the trolleybus depot. This will be realised by deploying an innovative energy inverter allowing to feed the otherwise wasted energy directly into the building’s energy system. For this it is necessary to have a specifically designed DC/AC inverter placed in the depot for connecting the DC traction grid and the building’s AC grid. The DC/AC inverter will thus enable to recover unused braking energy and feed it into the depot building. The device will also control the level of energy consumption in the traction network, detect unused energy appearance and thoroughly control the energy consumption of the depot building, advancing its energy monitoring system (EMS). It will control the voltage of the DC network and the load of the building’s system from the AC public grid. The DC/AC inverter will have the following technical parameters: DC input voltage 400 – 800 V (nominal 600 V), AC output voltage 3x400 V, power 50 kW, galvanic insulation between input and output. The inverter system will be also equipped with an innovative storage energy system, which will accumulate recovered unused recuperation energy in case there is no load on AC output. For this purpose, PKT will use one battery module of a traction battery from a trolleybus.

In addition, the energy inverter can also serve another aim connected with energy storage, namely it will be possible to use it as independent external, portable source of energy supplied from the trolleybus catenary, for e.g. supplying electric vehicles charging station.