What Happens if You Have Solar and the Power Goes Out?

Many residential solar power systems don’t work when the electricity goes out—unless they have a battery backup or they’re isolated from the broader electrical grid. That might seem unfair, especially if it’s a sunny day and you have perfectly good solar panels right there on the roof. Power outages should be a time for solar-powered homes to bask in the wisdom—and wattage—of their investment, right?

Yet, there are good reasons why some solar power systems don’t work during blackouts, including the need to protect utility workers as they repair the grid. And while a typical grid-connected system may be unavailable in a blackout, the situation is a little different with off-grid or battery-equipped systems, which could potentially keep supplying electricity even when the neighbors are all reading by candlelight.

Each type of system has pros and cons, and what works for one home, neighborhood, or region might not work for another. But in hopes of shedding more light on the issue, here is a closer look at how solar works if the power goes out.

How Do Solar Panels Work?

Solar power comes in many forms, from small panels on road signs to sprawling concentrated solar power plants, but most residential systems rely on more familiar-looking rooftop arrays of photovoltaic (PV) panels.

Each of these solar panels contains PV cells, which in turn contain a semiconductive material that sheds electrons when hit by sunlight, thus converting solar energy into electricity. The resulting flow of electrons forms an electric current, typically beginning as direct current (DC) power, then passing through an inverter to produce alternating current (AC) power for use in the home.

Aside from the panels themselves, the type of system you install is a big factor in determining whether you might be able to generate electricity in a power outage. Grid-connected solar power systems are commonly required by law to include safeguards against “islanding”—a term for a functioning system that continues sending extra electricity into the otherwise dark grid during a blackout, posing a potentially grave danger to utility workers as they try to resolve the outage. Many systems automatically shut down if the grid power goes out, but in some systems with energy storage and specialized anti-islanding gear, it is possible to enjoy the benefits of grid life along with some independence from blackouts.

Residential solar power systems can be lumped into a few general categories based on their relationship with the surrounding electrical grid:

Off-Grid Solar Power Systems

As the name suggests, an off-grid solar power system is not connected to its local electrical grid. Since it inherently lacks the potential baggage of a grid connection, it can continue generating electricity as long as the sun is shining and the panels are working, regardless of any outages on the local grid.

Without a way to store extra energy generated by day, however, a fully off-grid system would only provide electricity during literal daylight hours. That can be avoided with a battery energy storage system and/or a backup generator, both costly but important sources of resilience for many off-grid solar power systems.

Grid-Connected Systems With Energy Storage

There are advantages to embracing the grid, and it doesn’t necessarily mean losing the ability to generate electricity in a blackout. Retaining that ability in addition to a grid connection typically does involve more equipment and expense, though.

One major benefit of a grid-connected solar power system is net metering, a billing mechanism that gives credit to solar-powered homes for sending their extra solar energy into the grid. A grid connection offers security, too, with the grid acting like an energy storage system when too little sunlight is available to power your home.

There may still be value in an actual energy storage system, though, especially if you want to keep the lights on during power outages. In a solar-plus-storage system, lithium-ion batteries are typically used to store extra energy harnessed during the day, ideally preserving enough electricity to power the home overnight or during early morning and late evening, when sunlight levels are lower. The average U.S. household uses about 30 kilowatt-hours (kWh) of electricity per day, and a typical solar battery has a storage capacity of about 10 kWh. Solar batteries are expensive, often costing thousands of dollars in addition to the cost of installation.

Due to the dangers of islanding, however, batteries alone are unlikely to free you from the limitations that come with a grid connection. Energy storage may help maintain a consistent power supply in the grid’s absence, but in order to generate electricity in the first place during an outage, a solar power system must be capable of temporarily disconnecting itself from the grid.

In this kind of “islandable” solar power system, a specialized inverter may be necessary to detach from and reconnect with the outside grid, providing protection for utility workers and potentially enabling safe electricity generation from PV panels during a blackout. In its islandable mode, a system might be configured to power an entire house, or more commonly just certain critical loads like heating, cooling, and refrigeration. And, to continue defying a blackout at night, an islandable system will need some kind of energy storage, too, and possibly a backup generator.

Grid-Connected Systems Without Energy Storage

Energy storage is a costly addition to a solar power system, and along with the expense of islanding capabilities, it may not be worth the price just to avoid the relatively rare and typically mild inconvenience of power outages.

In places with reliable grid power, residential PV systems are commonly linked to the grid without a battery backup, a setup that saves money by accepting occasional power outages. It may lack the resilience of off-grid and islandable systems, but it’s a cheaper option that can make solar power accessible for more people.