Many Ontario homeowners believe rooftop solar panels will keep their lights on during a blackout. That assumption is dangerous. A standard grid-tied solar system shuts off when the utility grid fails. This is not a defect. It is a required safety feature built into every certified grid-tied inverter.
The grid goes down more often than most people remember. The May 2022 derecho knocked out power to more than 1 million customers in Ontario and Quebec. Some homes waited over a week for service restoration. A solar array on the roof did nothing for most of them because it was not paired with battery storage or an approved backup inverter.
You can design a solar backup system for outages. The solution starts with a hybrid inverter, a battery bank, and a critical loads panel. This guide explains why standard solar panels stop working, what equipment actually keeps them running, and how to choose the right backup setup for an Ontario home.
| Option | Best For | Runtime | Installed Cost Range | Key Limitation |
|---|---|---|---|---|
| Solar battery with hybrid inverter | Homes with existing solar panels | 12 to 24 hours per charge, recharges from sun | $15,000 to $30,000 | High upfront cost, limited winter output |
| Standby generator | Whole-home backup for long outages | Days to weeks with fuel | $12,000 to $20,000 | Fuel supply and maintenance, noise, CO risk |
| Portable generator | Short outages, essential circuits | 8 to 12 hours per tank | $500 to $2,500 | Manual setup, extension cords, CO risk |
| Portable power station / solar generator | Small loads, apartments, travel | 2 to 24 hours depending on size | $800 to $5,000 | Limited surge capacity, slow solar recharge |
Why Do Most Grid-Tied Solar Panels Shut Off During an Outage?
A standard rooftop solar array produces direct current. The grid-tied inverter changes that DC power into alternating current and pushes it into your home or back to the grid. That inverter must synchronize with utility voltage and frequency. When the grid goes down, the inverter no longer sees a stable reference. It stops exporting power within seconds. The solar panels are still receiving sunlight, but the inverter output is zero. This shutdown is required by product certification and by Ontario electrical rules.
CSA Group publishes standards such as CSA C22.2 No. 107.1 for grid-connected inverters. These standards adopt IEEE 1547 and UL 1741 test procedures. Under IEEE 1547, an inverter must disconnect within 2 seconds of an abnormal voltage or frequency condition. That means a blackout trips the inverter almost immediately. It will not restart until grid voltage and frequency return to normal for a set period. Many inverters wait 5 minutes before reconnecting.
Homeowners sometimes wonder if they can bypass this feature. The answer is no for a standard grid-tied system. The inverter has no battery input and no ability to form a local AC bus. Without a grid signal, it simply stops. To keep solar energy flowing during an outage, you need a system designed for backup from the start or a retrofit with battery storage.
How Does Anti-Islanding Protection Keep Line Workers Safe?
Islanding occurs when a local generator keeps a section of the grid energized after the utility feed is removed. That section may look dead to utility workers. If a solar inverter continued to export, it could feed power back onto the line. A line worker who touches that line could be electrocuted. Firefighters and neighbours could also be at risk. This is the main reason grid-tied inverters are required to shut down.
In Ontario, the Electrical Safety Authority (ESA) enforces the Ontario Electrical Safety Code. The code incorporates Canadian Electrical Code Part I rules for renewable energy systems. Inverters must be certified to Canadian standards. They monitor grid voltage and frequency continuously. When voltage or frequency drifts outside a narrow band, the inverter stops exporting. This anti-islanding function is automatic. It does not depend on the homeowner to switch anything off.
Anti-islanding also prevents equipment damage. If the utility reconnects while your inverter is out of sync, the sudden phase difference could damage sensitive electronics. The inverter waits until the grid is stable, then reconnects gradually. This protects your solar equipment and your home wiring. It is a purposeful limitation, not a design flaw.
What Equipment Allows Solar Panels to Keep Producing Power Off Grid?
To use solar power when the grid is down, you need a place to store energy. A solar battery is the most common solution. A hybrid inverter manages the flow among solar panels, battery, home loads, and the utility grid. During normal conditions, it can charge the battery from solar or the grid. When the grid fails, the hybrid inverter disconnects from the utility and forms a local microgrid. It draws from the battery immediately and recharges from solar as the sun returns.
There are two main retrofit routes. An AC-coupled system adds a battery inverter to an existing solar array. The original grid-tied inverter stays in place. During a blackout, the battery inverter supplies a local AC reference. That allows the solar inverter to run and charge the battery. A DC-coupled system connects the solar panels directly to the battery through a charge controller. This can be more efficient because it avoids one conversion step. Both methods require a professional design and ESA approval.
A critical loads panel is also part of most installations. It is a small subpanel that holds only essential circuits. The refrigerator, furnace blower, internet router, and a few lights are typical. Whole-home backup is possible but costs more. You can compare whole house battery backup options to see what fits.
Some people use a solar generator, which is a portable power station with solar charging. It will not automatically power a house, but it can keep small loads running. See solar generators for emergency backup for more detail.
- Hybrid inverter rated for grid-tie and backup operation
- Battery bank sized for your essential loads
- Critical loads panel or automatic transfer switch
How Does Solar Backup Compare to Generators and Portable Power Stations?
Solar battery backup is quiet, emission-free, and automatic. A standby generator can run for days as long as fuel is available. A portable power station is light and simple. Each option has tradeoffs in cost, runtime, and installation. The right choice depends on how long your outages last and what you need to run.
For homeowners who already have solar panels, adding a battery is logical. It uses the solar energy your array already produces. But batteries cost more upfront than a portable generator. A 10 kWh battery may keep essential circuits running for 12 to 18 hours. That depends on the season and how many loads you back up.
Generators remain strong for long winter outages. They need fuel, regular testing, and careful carbon monoxide awareness. Read generator safety tips before you operate one. For smaller loads, a portable power station can run lights, internet, and a fridge for a limited time. Whole-home backup is different from a solar battery or a portable unit.
How Much Does Solar Battery Backup Cost in Ontario?
Costs vary widely by home and system size. A hybrid inverter upgrade for an existing solar array can cost $4,000 to $8,000 installed. A lithium iron phosphate battery bank typically runs $1,000 to $1,500 per kWh of usable capacity installed. A 10 kWh system often lands between $15,000 and $25,000 before incentives. Adding a critical loads panel can add $1,500 to $3,000.
Ontario’s net metering regulation allows renewable energy systems up to 500 kW to receive credits for exported electricity. Net metering does not provide backup power during an outage. Battery incentives have changed over time. Check Natural Resources Canada for current federal programs and energy efficiency support.
If a full battery system is too expensive, a portable generator is a lower-cost entry point. A portable power station is another option. But neither automatically keeps a rooftop solar array producing. The investment in a battery makes the most sense when you want silent, automatic backup and already generate solar power.
A 10 kWh battery often stores enough energy to run a refrigerator, a furnace blower, and a few lights for 12 to 18 hours. This makes it a usable but not unlimited source during a multi-day outage.
How Do You Size a Solar Battery System for a Winter Power Outage?
Winter outages demand more electricity than summer outages. A gas furnace blower draws 400 to 800 watts while running. A sump pump can draw 800 to 1,500 watts during startup. A refrigerator uses 150 to 300 watts once running, but it surges higher when the compressor starts. Add lights, internet equipment, and phone chargers and the essential load often averages 500 to 1,000 watts.
Battery usable capacity matters. Many batteries allow 90 to 100 percent depth of discharge. A 10 kWh battery may deliver 9 to 10 kWh. At a 700 watt average load, that is about 13 to 14 hours. If you add a 1,500 watt electric space heater, the same battery can drain in under 7 hours. Electric resistance heating is not a good match for small battery banks.
Cold weather affects lithium batteries. Lithium iron phosphate batteries are safer and last longer than older lithium-ion, but they should not be charged below 0°C unless the battery has a built-in heater. Many modern home batteries include self-heating. If the system is in an unheated garage, confirm the cold-weather specifications with your installer.
Use the same load calculation method as generator sizing. Our guide to sizing a generator for your home walks through the process. For a multi-day outage, pair the battery with a backup generator or a larger solar array. See how to survive a week-long power outage for a practical plan.
Frequently Asked Questions
Will my solar panels work during a power outage if I have no battery?
No. A standard grid-tied inverter must shut down when the grid fails. The solar panels still receive sunlight, but the inverter stops exporting AC power.
Can I add battery backup to my existing solar system?
Yes. An AC-coupled battery inverter can be added to many existing solar arrays. A licensed electrician must install it and the ESA must inspect the work.
How long will a solar battery run my refrigerator and furnace?
A 10 kWh battery can often run a refrigerator, gas furnace blower, and a few lights for 12 to 18 hours. Runtime drops significantly if you add electric heating.
Do I need a permit to install a solar battery backup system in Ontario?
Yes. Battery backup systems require an electrical permit and an ESA inspection. A licensed electrical contractor must perform the installation.
Are solar batteries safe in cold Canadian winters?
Most are safe, but lithium iron phosphate batteries should not be charged below 0°C unless they have a built-in heater. Check the manufacturer specifications before installing in an unheated space.
Can I use a portable generator instead of a solar battery?
Yes. A portable generator costs less upfront and can run essential loads during an outage. It needs fuel, ventilation, and careful carbon monoxide safety. It will not keep a grid-tied solar array producing.
What Should You Remember?
- Grid-tied solar stops during an outage unless you have a hybrid inverter and battery.
- Anti-islanding protection is required by Ontario electrical safety rules to prevent backfeed.
- A solar battery creates a local microgrid and lets existing panels recharge it.
- Critical load panels keep essential circuits running without oversizing the battery.
- Battery backup costs more than a generator but offers silent, automatic operation.
- Winter outages require careful sizing because heating loads drain batteries quickly.
- Always use licensed installers and get an ESA inspection for battery and transfer equipment.
This article is for general information only. Always follow manufacturer instructions, local electrical codes, and hire a licensed electrician for transfer switches and standby generator installation. Carbon monoxide is deadly , never run a generator indoors.
