Unlike Alstom's existing APS ground power supply system, which supplies power to the vehicle continuously while in operation, SRS charges banks of onboard supercapacitors or batteries during station stops. The system is capable of delivering 1.1MW of power, or 1500 amps at 750V dc in a 20-second charging cycle, well within typical station dwell time, with the system notifying the driver when the onboard power storage solution is completely charged. Equipment for the solution is located both onboard the vehicle and in cubicles located at stations.

The range of the vehicle's catenary-free operation is dependent on the capacity of the battery and Alstom says that in addition to its own vehicles the system is compliant with solutions from other manufacturers. Alstom has also worked closely with battery and supercapacitor manufacturers to develop SRS.

The manufacturer stresses that SRS does not spell the end of APS as a catenary-free electrification solution, which debuted in Bordeaux and is now in use on light rail networks around the world. "Networks in hot climates which require air conditioning are better suited to APS because these systems will drain the batteries very quickly," explains Mrs Cristina Anderiz, vice president for infrastructure at Alstom. "This is the case in Dubai and in Rio de Janeiro. It is also not that well suited for networks with steep gradients. However, it completes our portfolio so we can provide our customers with a range of solutions depending on their needs."

SRS diagram