The surprise many new solar owners discover
It seems logical that a home with solar panels should keep its lights on when the grid goes down, especially on a sunny day. In practice, most standard grid-tied solar systems switch off during a power outage. Understanding why, and what equipment changes that, will help you decide whether backup power belongs in your plans and how much to spend on it.
Why grid-tied systems shut down
A typical rooftop system is connected to the utility grid through an inverter, which converts the panels' direct current into the alternating current your home uses. When the grid goes down, the inverter is required to stop sending power out. This safety feature, often called anti-islanding, protects utility workers who may be repairing lines and expecting them to be de-energised. Because the standard setup has no way to separate your home from the grid, the whole system goes quiet until grid power returns.
So a grid-tied system without backup equipment provides no power during an outage, even in full sun.
Option 1: Add a home battery
A battery system paired with the right inverter and switching equipment can isolate your home from the grid during an outage and keep selected circuits running. While the grid is down, the panels can recharge the battery during the day, and the battery supplies power at night. Things to understand before buying:
- Whole-home vs. essential loads. Many systems back up only a sub-panel with chosen circuits, such as the refrigerator, lights, internet and some outlets. Backing up an entire home, including large loads like central air conditioning, usually needs more battery capacity and higher power output.
- Capacity and power are different. Capacity, measured in kilowatt-hours, is how much energy is stored. Power, measured in kilowatts, is how much can be delivered at once. A battery can have enough energy for a night of lights but not enough power to start a well pump.
- Weather matters. During several cloudy days in a row, the panels may not fully recharge the battery.
Batteries can also provide value outside outages in some areas, for example by storing solar energy to use in the evening when electricity may cost more. Our guide to home batteries covers that side in more detail.
Option 2: Inverters with limited daytime backup
Some inverters can supply a small amount of power to a dedicated outlet when the grid is down and the sun is shining, without a battery. This can be handy for charging phones or running a small appliance, but output depends entirely on current sunlight and stops at night. Ask installers whether the inverter they propose has this feature and what its limits are.
Option 3: A generator
Standby or portable generators are another way to cover outages, with or without solar. They can run for longer periods as long as fuel is available, but they require fuel storage or a gas connection, regular maintenance and proper installation with a transfer switch. Connecting a generator incorrectly can back-feed the grid and endanger line workers, so this should be done by a qualified electrician. Some homes combine solar, a battery and a generator for longer outages.
How to decide what you need
Start with your situation rather than the equipment:
- How often does your area lose power, and for how long?
- Does anyone in the home rely on powered medical equipment?
- Do you depend on a well pump, sump pump or electric heating?
- Which appliances do you truly need during an outage?
List the essential appliances and their approximate power needs, then ask installers to size a backup option around that list. Compare that cost against the alternatives, including a generator or simply riding out short, infrequent outages.
Questions to ask installers
- Will my proposed system provide any power during an outage? Under what conditions?
- Which circuits would be backed up, and can I choose them?
- How long would the battery last for my essential loads, based on what assumptions?
- Does adding backup require an electrical panel upgrade or extra permits?
- Can a battery be added later if I skip it now?
Bottom line
Standard grid-tied solar lowers electricity bills but does not keep the power on during a blackout. If backup power matters to you, plan for it from the start with a battery-ready design, even if you add the battery later. For a broader look at whether solar suits your home, visit our homeowner FAQ.