LiFePO4 batteries for solar
Lithium iron phosphate.
LiFePO4 (lithium iron phosphate) is the dominant choice for new off-grid and backup systems. It allows deep discharge (around 80–100% usable), has high round-trip efficiency, long cycle life and stable chemistry, at a higher upfront cost than lead-acid. It must not be charged below freezing without a heater or BMS cutoff.
Sizing a LiFePO4 bank
Because LiFePO4 allows about 80% usable depth of discharge, a bank for the same daily load will differ in size from other chemistries. To deliver the same usable energy, a chemistry with a lower usable depth needs more nominal capacity — a lead-acid bank at 50% usable must be roughly 60% larger than a LiFePO4 bank at 80% to give the same delivered energy, before efficiency and temperature are even considered. Use the battery bank size calculator with LiFePO4 selected, or the full system calculator for a complete design.
How LiFePO4 behaves in real use
Round-trip efficiency of about 95–98% means some of the energy you put in is lost on the way back out, so your solar array has to be sized to cover both the load and that loss. Temperature sensitivity is rated low: this determines how much usable capacity changes with the seasons, which matters most for a bank kept in an unheated space, a garage or outdoors. With a rated cycle life of 3,000–6,000 cycles, LiFePO4 also sets how many full charge-discharge cycles you can expect before capacity falls off, which in turn drives the long-run cost per kWh delivered.
To see what a LiFePO4 battery really delivers after depth of discharge, temperature and round-trip losses, try the real vs nameplate capacity tool, and check that your loads stay within a safe discharge rate with the C-rate calculator.
How it compares
The right chemistry is a balance of upfront cost, usable depth, efficiency, cycle life and cold tolerance. Compare LiFePO4 against the alternatives on the battery chemistry comparison page to decide which fits your budget and climate.
Values are typical datasheet ranges; see the methodology & sources. Educational guidance, not an electrical design.