A standard grid-tied solar system shuts off during a power outage, even on a sunny day, so solar alone won't keep your lights on. Add a battery and the right equipment, and your home can island itself from the grid, run essential circuits from stored energy and recharge from the sun each day. Here's how solar-plus-battery backup works in Canada, what it can realistically power, and where its limits are, especially in winter.
Key takeaways
- Grid-tied solar turns off during outages by design, to protect line workers; a battery and a transfer mechanism let it keep running.
- Solar plus battery can extend backup from hours to days, but Canadian winter solar output is often too low to recharge a battery fully.
- Plan around essential loads (fridge, furnace blower, sump pump, internet, lights), not the whole house.
- Electric resistance heating, central air and EV charging will drain a typical home battery fast.
- Get the system configured for backup at installation; adding backup later can mean new equipment.
Why solar shuts off when the grid goes down
Grid-tied inverters are required to stop exporting power when they detect the grid is down. This "anti-islanding" protection exists because a home sending electricity back into dead lines could injure utility crews working to restore service.
A battery system solves this with an automatic transfer switch or gateway. When the grid fails, it opens a connection between your home and the utility, creating a safe "island." Your inverter can then keep running, powering your backed-up circuits and charging the battery from your panels.
How a solar-plus-battery backup system works
- Normal operation: Solar powers your home, charges the battery and exports any surplus according to your utility's rules.
- Outage begins: The gateway disconnects from the grid, typically within a fraction of a second to a few seconds. Many systems switch fast enough that clocks and computers don't notice.
- Island mode: The battery supplies your backed-up loads. During daylight, solar charges the battery and covers some of the load directly.
- Grid returns: The system reconnects automatically once the grid is stable.
Whole-home vs. critical-loads backup
- Critical-loads panel: An electrician moves essential circuits to a dedicated subpanel that the battery backs up. Less expensive and stretches battery capacity further.
- Whole-home backup: The battery backs up your entire main panel, with load management or smart breakers to keep big appliances from overwhelming it. More convenient, but it's easy to drain the battery without noticing.
What can it run, and for how long?
Here's a rough picture for a single battery of about 13 kWh usable, assuming no solar input:
| Load | Approximate daily use | Notes |
|---|---|---|
| Refrigerator | 1–2 kWh | Runs intermittently |
| Gas furnace blower | 3–6 kWh in cold weather | Depends on run time |
| Sump pump | 0.5–2 kWh | Varies hugely with rain/snowmelt |
| Internet, phones, laptop | 0.5–1 kWh | |
| LED lighting | 0.5–1 kWh | |
| Chest freezer | 0.5–1.5 kWh | |
| Well pump | 1–3 kWh | High startup surge |
A household running these essentials might use roughly 6 to 12 kWh a day, so one battery could last about one to two days without sun. With good solar production, the system can recharge and run indefinitely in spring, summer and early fall.
Loads that typically don't fit: electric baseboard heat, electric furnaces, electric water heaters, central air conditioning and Level 2 EV charging. A cold-climate heat pump can sometimes be backed up with a larger, multi-battery system, but it needs careful sizing.
The Canadian winter problem
Winter is when outages are most dangerous and when solar produces the least. Short days, a low sun angle and snow-covered panels can reduce December output to a small fraction of summer production. In much of Canada, a typical home system might generate only a few kWh on a clear December day and close to nothing when panels are buried in snow.
That means:
- In summer, solar plus battery can often ride through multi-day outages.
- In winter, think of the battery as your main backup and solar as a modest top-up.
- For long winter outages in rural areas, some households keep a small generator as a last-resort recharge source. Our generator vs. battery comparison covers the trade-offs.
Steeper panel tilt helps shed snow and catch the low winter sun, which is worth discussing with your installer if winter resilience matters to you.
Planning tips before you buy
- List your must-run circuits and estimate their daily energy use. Our battery sizing guide walks through the method.
- Check surge capacity if you have a well pump, sump pump or other motors.
- Ask how the system behaves when the battery is low: does it shed loads, and will it restart automatically when the sun comes up?
- Confirm cold-weather ratings for garage or outdoor installations.
- Look into local programs: some provinces and utilities offer support for solar-plus-storage. Requirements change, so search by address with our rebate finder.
- Make sure it's permitted and inspected, and tell your home insurer.
Frequently asked questions
Will my existing solar system work during an outage if I add a battery?
Usually yes, with the right equipment. An AC-coupled battery with a backup gateway can often be added to an existing system, though older inverters may need settings changes or replacement to work in island mode.
How fast does a battery take over when the power goes out?
Many modern systems switch over in well under a second to a few seconds. Some homes notice a brief flicker; sensitive electronics may benefit from a small UPS.
Can I run my whole house on solar and batteries during an outage?
You can run a lot of it, but rarely everything, especially in winter. Electric heating, central air and EV charging usually exceed what one or two home batteries can sustain, so most owners prioritize essentials.
The bottom line
Solar plus battery is one of the cleanest, quietest ways to keep essential power running when the grid goes down, and it shines during long summer outages. In a Canadian winter, plan around the battery's stored energy rather than daily solar recharge, size for your true essentials, and get the backup configuration right from day one. To see how solar performs in your region, check our provincial guides.
Sundamentals is an independent, non-profit education platform. Program details and prices change often — check current programs for your address in our rebate finder.