A home battery backup system watches the grid, and when the power fails it disconnects your home (or a protected-loads panel) from the utility and switches essential circuits onto stored energy — typically in a fraction of a second, fast enough that the Wi-Fi doesn’t reboot. If you have solar, the panels recharge the battery each morning, so a well-sized system can ride through multi-day outages. Without a battery, a standard grid-tied solar array shuts itself off during a blackout.
Why does my solar shut off in a blackout without a battery?
Grid-tied inverters are required by the IEEE 1547 anti-islanding rule to stop exporting the moment the grid goes down, so line workers aren’t electrocuted by thousands of rooftop systems back-feeding the wires. The consequence surprises many owners: on a plain grid-tied system, a sunny-day outage still means a dark house. A battery with an automatic transfer switch (or a microgrid-forming inverter) is what creates the legal, safe “island” that lets your panels keep working while the grid is out.
What happens in the seconds after the grid fails?
The sequence is: the gateway senses voltage loss → it opens the grid disconnect → the battery inverter forms a local grid → protected circuits keep running. Modern systems like Tesla Powerwall and Enphase IQ Battery complete this in well under a second. Whole-home backup protects every circuit; partial-home backup moves your essentials — refrigerator, lights, internet, garage door, medical equipment — to a dedicated protected-loads panel. Heavy 240V loads (AC compressors, ovens, dryers) are usually excluded or load-managed, because they can drain a single battery in a couple of hours.
How long will a battery actually last in an outage?
A typical residential battery stores roughly 10–13.5 kWh usable. Running essentials only (a few hundred watts average), that’s 12–24 hours per battery — and effectively indefinite when solar recharges it daily. San Diego’s outage profile makes this math favorable: our grid events are usually short, but PSPS wildfire-safety shutoffs in East County (Ramona, Poway backcountry) can run multiple days, which is exactly the scenario solar-plus-storage handles and a portable generator handles poorly. One sentence to remember: batteries are sized for essentials over days, not for running the whole house like nothing happened.
Does a battery change my SDG&E bill too?
Yes — for many owners the daily economics matter more than the outages. Under California’s NEM 3.0 “net billing,” exported solar earns far less than it used to, while SDG&E’s evening peak rates are among the steepest in the country. A battery stores your cheap midday solar and discharges it into the expensive 4–9 p.m. window every single day. That’s why most new solar in San Diego County is quoted with storage attached — see our guide to current battery incentives like SGIP and the real cost of solar in San Diego County. Hans Energy Systems (CA LIC #967367) has designed battery backup for solar systems across the county since the NEM 2.0 era, including Tesla Powerwall installations.
Frequently asked questions
Will my AC run on battery backup?
Central AC is a heavy 240V load and usually excluded from single-battery backup. Multi-battery systems or soft-start-equipped heat pumps can support it. Most owners prioritize refrigeration, lights, internet, and medical devices.
How is a battery different from a generator?
A battery is silent, instant, fuel-free, and recharges from solar; a generator needs fuel, maintenance, and manual starting but has unlimited runtime if fuel keeps coming. In wildfire-season PSPS events, batteries avoid the fuel-scarcity problem entirely.
Can I add a battery to my existing solar system?
Almost always yes — either AC-coupled (works with any existing inverter) or DC-coupled (more efficient, sometimes needs an inverter swap). We retrofit batteries onto systems we didn’t originally install.
Do batteries qualify for rebates in San Diego?
California’s SGIP program offers battery rebates, with the largest amounts reserved for medical-baseline customers and homes in high fire-threat districts. Program budgets change — our incentives guide covers what’s current and how to claim it.
How long do home batteries last?
Manufacturer warranties typically run 10 years or a throughput limit. Lithium chemistry degrades gradually — expect roughly 70–80% of original capacity at the end of warranty, not a sudden death.
Now that you know how backup works, compare the hardware. Read Tesla Powerwall vs. Enphase IQ Battery for San Diego homes — or get sizing for your actual loads: request a battery consultation or call (619) 654-0055.
