Why doesn’t solar work during a power outage?

(Last modified on January 26th, 2022.)

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Why do power outages shut down solar?

One of the biggest misconceptions we hear most often is that a home with a grid-tied solar system (without battery backup) will continue having power during a utility power outage. This stems from a misunderstanding of how grid-tied installations work.

Although both a grid-tied system and an array with battery backup utilize power generated by their respective solar panels, the latter, by definition, stores some of its energy. It then follows that a system without battery backup must therefore constantly back-feed its excess energy to the grid. If these systems back-fed during a power outage, they would make for hazardous conditions.

If we experience a power outage and the utility company needs to send linemen to inspect or repair power lines, they need to be able to do their work without being electrocuted. Because a solar array without a battery backup system is constantly back-feeding excess energy, the system shuts down for several reasons when it senses a grid outage.

First, it must by law automatically shut off for worker safety. Secondly, a solar array without batteries cannot function during an outage because the excess energy has nowhere to go. And thirdly, all solar systems are equipped with an inverter. Standard gird-tied inverters can only function by synchronizing to a power source other than the array itself, in this case the grid. For these reasons, an array without an energy storage system cannot provide power to a home during an outage.

Although a solar system with batteries can also back-feed to the grid, it can operate independently during an outage only because this system functions as a micro-grid: the batteries give power to appliances, and the array provides only enough power to refill the batteries to 100%. Then the system must shut off its connection to the grid, just like grid-tied systems, so as to not back-feed.

What needs to change for solar (without batteries) to work during an outage?

For solar to function during a power outage, not only does technology need to advance but regulations also need to change.

First, all of the appliances in the home would need to be smart appliances so as to communicate with the inverter.

Second, the inverter would need to be able to prioritize these appliances so that in case of an outage in combination with increment weather or a cloud passing overhead, it could dictate which to keep on and which to shut off. This would be essential because if your appliances were completely dependent on solar energy and a cloud passed overhead, the available supply of energy would diminish and the lull would damage the appliance’s motor/s. (If this weren’t automized, it would also complicate homeowner-solar manufacturer relations: who’s fault would a damaged motor be?)

Additionally, the system would need a dump load connected to it, like a heating element, to use up the excess power produced. This would prevent the system from back-feeding excess energy to the grid.

This scenario is further complicated by the fact that each state and country has different utility regulations. Today, rapid shut down switches require systems to shut down at the power source (the panels) when an outage is detected in the grid. So if the technology above evolved and was implemented, the hope is that the utility companies would revise these regulations to allow systems in this particular configuration to bypass the rapid shutdown law and continue powering homes during an outage.

BUT even with all of this in place, the solar system would still only be producing power during a daytime power outage. At night, you would still have no electricity since your excess daytime production has nowhere to be stored. The only way to bypass this is to install battery backup.

To determine whether battery storage is right for you or to know more about battery options available to you, follow these link.

2 thoughts on “Why doesn’t solar work during a power outage?

  1. Why , on Earth, can’t we use automatic transfer switch (ATS) to isolate the house with solar system from the grid during power outage? This is done routinely with commercial or industrial systems equipped with emergency diesel power generators.

    1. Hi Carl, In a solar only grid-tied installation, the solar requires a grid voltage reading to stay operational. In the example you state, the ATS switches over to the generator and the generator provides power to the site while the solar remains off until the grid comes back on. That’s why they’re emergency generators, because even in emergencies, the solar is not the source of energy feeding the site. The only solar grid-tied option that allows the solar to stay operational during an outage is a system with a battery backup because the solar NEEDS to be able to back feed excess production. If the grid is down, there is nowhere to back feed, unless you have a battery to store the excess solar energy. Please feel free to give us a call if you have any more questions.

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