Saft, a manufacturer of high-tech industrial batteries, has supplied Ni-MH (nickel-metal hydride) integrated traction battery systems to Siemens Mobility for use in the development of a new generation of trams equipped with the Sitras HES hybrid energy storage system.

The Saft Ni-MH integrated battery system enables the tram to operate without an overhead contact line (OCL) for distances up to 2,500 metres, the company said.

The first tram with Sitras HES with Saft battery system has completed more than one year of successful passenger service trials in Portugal with the Siemens Mobility customer MTS (Metro Transportes do Sul), as it has been operating services between Lisbon cities Almada and Seixal since the end of 2008.

Each battery system, which incorporates an active cooling device and battery management control (BMC), is supplied to Siemens Mobility as a ‘plug and play’ package in a custom built tray complete with power and communications connections.

The 826 kg heavy battery systems provides a nominal 528V and capable of storing 18 kWh of energy and sustaining a peak power of 105kW, according to Saft.

The Sitras HES concept comprises two energy-storing components, including the Sitras MES mobile energy storage unit based on a double-layer capacitor (DLC) and the traction battery system, both of which work together to provide a very efficient energy storage system.

The company said that its Ni-MH traction batteries for the Sitras HES system were primarily chosen by Siemens Mobility because they were commercially available and could be integrated in the test programme quickly, without a long development period.

Saft claimed that the high energy Ni-MH battery also improves the reliability of the tram service as it allows continued operation when the OCL is temporarily unavailable, such as in the case of failure or planned maintenance.

Designed for roof-mounting on the tram, the Sitras HES system is electrically connected to the vehicle feed-in point by means of a DC/DC-chopper, which enables the energy storage system to be integrated into new trams or retro-fitted into existing vehicles.

The Sitras HES is expected to reduce the future energy demand of a vehicle by up to 30%, producing up to 80 tonnes less CO2 emissions per year, under optimum operating conditions, claimed Shaft.