Iarnrod Eireann has awarded a €3m electricity supply contract for Dublin's DART to Energia.
The contract involves the annual supply of 3 Megawatts (MW), the equivalent usage of over 3,000 homes.
Energia will supply electricity from its gas fired power generating station at Huntstown in Dublin.
Energia's parent company, Viridian Group is investing €250m in a second new power plant in Dublin.
Dublin Area Rapid Transit (DART) carries up to 90,000 commuters daily and is currently undergoing a €176m expansion with 40 new carriages being phased into service.