The moment the grid drops, a properly configured home battery takes over fast enough that your lights flicker at most and your router never reboots. No noise, no fuel, no waiting for a generator to start.
What most homeowners do not know until it happens: if you have solar panels but no battery, your house goes dark along with everyone else’s — even at noon on a cloudless day.
Why solar alone shuts down in a blackout
This is a safety requirement, not a product flaw. When utility power fails, crews go out to repair lines they need to treat as de-energized. A grid-tied solar system feeding power back into those lines would put them in danger.
So every grid-tied inverter is required to detect the outage and disconnect — a behavior called anti-islanding. Your panels stop producing anything you can use within milliseconds of the grid going down, and they stay off until it returns.
A battery system solves this by creating an intentional island: it disconnects your home from the grid at a transfer point, then runs your circuits from stored energy. Because your house is now electrically isolated, your panels can safely resume producing — into your battery and your loads, not into the utility lines.
What happens in the first second
The sequence is fast enough that most people only notice because the neighbors’ houses went dark.
The system detects the loss of grid voltage, opens the transfer switch to isolate your home, and the battery inverter begins supplying your backed-up circuits — typically within milliseconds. Sensitive electronics, medical equipment and network gear generally ride through without restarting.
Compare that with a standby generator, which senses the outage, cranks, stabilizes and transfers over roughly 10 to 30 seconds. Everything in the house reboots, and it runs loudly for as long as the outage lasts.
How long it will actually last
This depends entirely on what you back up, and it is where the industry tends to be least honest.
- Essentials only. Refrigerator, internet, lights, phone charging and a gas furnace blower typically run 12 to 24 hours on a single 10-13 kWh battery.
- Add a sump pump or well pump. Both draw heavily on startup. Feasible, but they shorten runtime noticeably and need to be sized for deliberately.
- Central air conditioning. The fastest way to drain a battery. Possible with sufficient storage, but expect hours rather than a full day.
- Electric resistance heat. Generally impractical on battery alone. If this is your heat source, plan differently.
- With solar recharging. This is the real difference. A clear day refills the battery, turning a one-night runtime into an indefinite one.
Whole-home versus critical loads
You are usually choosing between two configurations, and the cheaper one is often the smarter one.
A critical-loads subpanel backs up a defined set of circuits you choose in advance. It is less expensive, it makes the battery last far longer because it physically cannot power the loads that would drain it, and it forces a useful conversation about what actually matters to you.
Whole-home backup keeps every circuit live and typically requires more storage and more equipment. It is genuinely better if you have the budget and the outages to justify it, but many homeowners buy it and then discover they were only ever worried about the fridge and the sump pump.
Deciding whether it is worth it
Be honest about your outage history. If you lose power for an hour twice a year, a battery is a comfort purchase and you should treat it as one.
If you lose power several times a year, or you have well water, a sump pump in a basement that floods, someone at home who depends on refrigerated medication or a medical device, or you work from home and cannot afford to be offline, the value proposition changes entirely.
There is also a daily-use case independent of outages: on a time-of-use rate, a battery stores cheap off-peak power for expensive hours, and several utilities in our markets pay customers to let stored energy support the grid on peak days. That does not usually justify the purchase alone, but it improves the math for someone already leaning toward it.
Frequently asked questions
Will my solar panels charge the battery during an outage?
Yes, once the battery system has isolated your home from the grid. That is the mechanism that allows panels to operate safely during an outage, and it is what turns a single night of runtime into multi-day resilience.
How many batteries do I need?
Most homes backing up essentials do fine with one. A second is warranted when you want longer runtime, need to run well pumps or air conditioning, or want whole-home rather than critical-loads backup.
Is a battery quieter than a generator?
Completely silent. There is no engine, no exhaust and no fuel. It can be installed in a garage or basement with no ventilation or fuel-line requirements.
What happens when the battery runs out during a long outage?
Without solar, the house goes dark until the grid returns. With solar, the array recharges the battery during daylight and the cycle repeats — which is why the two together are far more useful than either alone.
Related pages
- Whole-home battery backup
- Residential solar with $0 down
- Storm damage roof repair
- How to lower your electric bill
- EV charger installation
- Book a free assessment
Size a battery around the outages you actually get
Tell us how often you lose power and what you cannot afford to have go down. We will look at your panel and your usage and tell you what size makes sense — including when the honest answer is that a battery is not worth it for you.