VRLA batteries in photovoltaic energy storage systems for telecom applications

The Swiss PTT has installed an active repeater station powered by a photovoltaic energy storage system (PVES) on the peak Pit Muttler situated in the vicinity of the border corner Switzerland-Austria-Italy at an altitude of 3294 m. The PVES system consists of 72 60 W (4.32 kW-36m/sup 2/) solar panels with associated maximum power trackers and charging controllers. The photovoltaic energy is stored in 24 V batteries using 2 V VRLA Compact Power cells with a nominal capacity of 1000 Ah (C/sub 10/) per cell. In order to evaluate the worst case conditions of extremely low temperatures within the battery room, the low temperature (-30/spl deg/C) and the low voltage (0.00 V/cell) behaviour of such cells is reported. Batteries survive freeze/thaw cycles unscathed and can be recharged with the electrolyte "frozen". >