For some homes an outage is an inconvenience; for others — medical equipment, home offices, well pumps — it is a real cost. Grid-tied solar alone shuts down during outages for line-worker safety. If uptime matters, a battery is the only way solar keeps working when the grid fails.

Under time-of-use billing, evening electricity can cost double the midday rate. A battery charges on your solar surplus at noon and discharges into the expensive evening window, capturing the spread every single day — savings that exist even in years with zero outages.

Whole-home backup sounds appealing but often doubles the battery budget. Most families do well protecting a critical-loads panel — refrigeration, lighting, internet, and one or two circuits that matter. Ten to fourteen kilowatt-hours covers a typical home's essentials through an evening and overnight.

If your utility offers full net metering, outages are rare, and rates are flat, the grid genuinely is a decent battery — and the money may work harder buying more panels. Batteries can always be added later; good installers design the wiring so the upgrade is a clean bolt-on.