Question: What does your solar PV system do when your home loses grid power?

A: Your solar panels work like normal, delivering electricity to your home

B: Your solar panels automatically shut down and your home loses all electricity.

If you answered B, you are correct.

When your home loses grid power, your solar system automatically shuts off and your house goes dark (unless you also have a battery). When the grid comes back online, your solar system detects the restored grid power and automatically turns on again.

This fact is the most surprising piece of information that customers learn when we talk with them about solar. Why, people ask, would solar panels inconveniently stop working when the house still needs power?

There are two good answers why. The first is a safety issue. When grid power goes down, the utility is alerted immediately and starts the process of restoring grid power. Utility workers arrive on site to repair whatever damage or failure occurred on the power lines. The power lines must be completely dead (i.e. not transmitting any electricity) to ensure the safely of the workers. Due to net metering (review net metering here), solar arrays are designed to push excess electricity onto the grid when the system is producing more energy than the home is consuming. Unless the solar system is forced to shut off during a grid outage, the system could continue to leak excess electricity to the downed grid lines, compromising the safety of the utility crews. Therefore, utility regulations require all solar PV systems to automatically shut off during grid outages.

The second answer is a technical reason. The amount of energy your solar panels are producing at any one moment, and the amount of energy that your home is consuming at any one moment, are essentially never the same. They are usually not even close. Given that your solar array is always producing either too much or too little energy for your home, you can start to see the problems this creates. All your appliances and gadgets need exactly the right amount of power just at the moment they need it. When your solar system is producing like a fire hose, you need a way to give your appliances only the sips and gulps they need, and send the excess electricity somewhere else. When your solar system is only dripping electricity, you need an energy supplement to feed your appliances their required doses of power. Net metering provides this essential service during normal grid operations. When the grid is down, you’re out of luck. The mismatch of solar energy production and home consumption will end up wrecking your appliances, computers, and TV in short order.

If you have a battery installed with your solar system, the battery solves these problems and allows your solar panels to keep producing electricity. Read more about how battery systems work in our next blog post…