A comparison of lead-acid and lithium-based battery behavior and capacity fade in off-grid renewable charging applications

The effects of variable charging rates and incomplete charging in off-grid renewable energy applications are studied by comparing battery degradation rates and mechanisms in lead-acid, LCO (lithium cobalt oxide), LCO-NMC (LCO-lithium nickel manganese cobalt oxide composite), and LFP (lithium iron phosphate) cells charged with wind-based charging protocols. Poor pulse charge acceptance, particularly for long pulses, contributes to incomplete charging and rapid degradation of lead-acid cells due to apparent high rates of sulphation and resistance growth. Partial charging and pulse charging, common lead-acid stressors in off-grid applications, are found to have little if any effect on degradation in the lithium-based cells when compared to constant current charging. These cells all last much longer than the lead-acid cells; the LFP batteries show the greatest longevity, with minimal capacity fade observed after over 1000 cycles. Pulse charge acceptance is found to depend on pulse length in lead-acid and LFP cells, but not in LCO and LCO-NMC cells. Excellent power performance and consistent voltage and power behavior during cycling suggest that LFP batteries are well-suited to withstand the stresses associated with off-grid renewable energy storage and have the potential to reduce system lifetime costs.