What batteries does a SAPS use and how long do they last?
Vantara uses LiFePOâ‚„ (lithium iron phosphate) modules at 48 V nominal, 5 kWh nominal and 4.75 kWh usable per module, eleven modules as standard for 55 kWh installed. Rated at 8,000 cycles to 80% depth of discharge, with a maximum depth of discharge of 95%. Battery standards: IEC 62619, CE and UN 38.3.
Two numbers there deserve translation, because they are the ones that decide whole-of-life cost.
8,000 cycles at 80% depth of discharge means a system cycling once daily has a cycle-life horizon well beyond twenty years, which is longer than the asset planning horizon for most of these installations. In practice, calendar ageing and site conditions govern replacement, not cycles.
95% maximum depth of discharge is the figure that separates a lithium SAPS from a lead-acid one, and it is routinely under-appreciated. A lead-acid design typically limits daily discharge to 30–50% to preserve life, which means a nominal 100 kWh lead-acid bank delivers 30–50 kWh of usable energy. A 55 kWh lithium bank at 95% depth of discharge delivers about 52 kWh. Compare usable energy, not nameplate.
Battery warranty is five years, within a 24-month full-system warranty and a three-year inverter warranty.