Battery Storage
A home battery system (typically lithium iron phosphate) that stores excess solar energy for use at night or during grid outages.
Home battery storage allows solar owners to use their own generated electricity after sunset, during grid outages, or when time-of-use rates make grid power expensive. The dominant chemistry is lithium iron phosphate (LFP) — safer and longer-lived than older lithium-ion chemistries, though slightly less energy-dense.
Key battery specifications: usable capacity (kWh — the energy available after accounting for the depth-of-discharge limit), continuous power output (kW — how many appliances can run simultaneously), round-trip efficiency (typically 90–95%), and cycle life (the number of full charge-discharge cycles before capacity degrades to 80% — typically 3,000–6,000 cycles). The Tesla Powerwall 3 stores 13.5 kWh usable with 11.5 kW peak output. The Enphase IQ Battery 5P stores 4.96 kWh per module, scalable.
Battery economics depend heavily on local net metering policy and rate structure. Where utilities pay full retail for exported solar, batteries rarely make financial sense — you earn the same whether you use or export. Where export rates are low (NEM 3.0 in California) or time-of-use rates are high during evenings, batteries dramatically improve economics. Battery payback is typically 10–15 years, separate from panel payback.
Real-World Example
During Hurricane Ian, the family's two Powerwall units (27 kWh combined) kept their refrigerator, medical equipment, and basic lighting running for 38 hours without grid power while their neighbors were without electricity for four days.