Maxwell Technologies’ ultracapacitors enabled Woojin Industrial Systems, a manufacturer of electric rail vehicles and rail system equipment, to complete installation of its energy storage system (ESS) ultracapacitor-based braking energy recuperation systems in seven Metro stations in Seoul, Daejon, Incheon and the Korea Train eXpress (KTX) high-speed rail depot in Seoul.

Beginning with installation of demonstration systems in 2009 under a contract with the Korean federal government's Korean Railroad Research Institute (KRRI), Woojin and rail system operators have achieved grid power consumption savings of more than 20% and realized additional benefits in the form of system voltage stabilization, which reduces power infrastructure requirements and helps to ensure uninterrupted operation.

The recuperation systems, ranging from 750 to 1,500 volts, employ Maxwell Technolgies ultracapacitors to absorb energy during rail vehicle braking and deliver the stored energy to the vehicles' electric motors for propulsion and to stabilize voltage throughout the system.

Each installation employs up to 200 of Maxwell's 48-volt multi-cell ultracapacitor modules. Based on their positive experience to date, Woojin and rail system operators are planning several additional installations in 2014 and 2015.

Unlike batteries, which produce and store energy by means of a chemical reaction, ultracapacitors store energy in an electric field. This electrostatic energy storage mechanism enables ultracapacitors to charge and discharge in as little as fractions of a second, perform normally over a broad temperature range (-40 to +65 degrees Celsius), operate reliably through one million or more charge/discharge cycles and resist shock and vibration.

Maxwell offers ultracapacitor cells ranging in capacitance from one to 3,000 farads and multi-cell modules ranging from 16 to 125 volts.