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How solar can help you survive a power outage

Avatar for Ben Zientara
Published on 07/25/2017 in
Updated 03/20/2020
NYC hurricane Sandy blackout

What will you do when the power goes out? Even if you have solar panels on your roof, your answer will probably be “light a candle and wait it out.” Unless you know how to make it work.

It’s true: most solar panel systems aren’t designed to work during a power outage. Below, we’ll detail some options for people who want to use those solar kilowatt-hours even when grid goes down. But first, here’s a little background:

They say “the grid is your battery”

Most people with solar on their house have what’s called a “grid-tied” solar system, which means the panels are connected to an inverter and the inverter runs both to the main AC panel in the house and to a special smart electric meter that records both energy you use from the utility company and energy sent to the grid by your solar panels.

That’s why home solar people generally say “the grid is your battery.” When your solar panels are producing extra energy, you’re sending it out to your neighbors and getting credit for it, but when the sun goes down, you still need electricity from the utility company. If you play this balancing act just right, you can have a power bill near $0.

…until the power goes out

In the event of a blackout, a typical grid-tied system has a special automatic shut-off, to prevent that extra energy from being sent over power lines that may be damaged. It’s a safety feature intended to protect the line workers who go out to fix things when they break.

But that means your house doesn’t get the solar power either. In a blackout situation, the power from your solar panels goes… nowhere.

The best ways to back-up a grid-tied solar system

Maybe you’re thinking about installing solar, but you want to make sure you’ll have power if the grid goes down. Maybe you already installed solar and you’re looking for a simple way to upgrade your system to a hybrid with battery backup.

If you want to keep your house running when the power goes out, there are a few ways to do it:

  1. Use a backup generator
  2. Replace your inverter with a Sunny Boy
  3. Go full hybrid with backup batteries

1. Using a backup generator

We solar lovers out there don’t love this, but… the cheapest way to make sure you’ve got backup power in the event of a blackout is to buy a generator.

A Duro Max 9,500-watt gas generator.

For a little more than a thousand bucks—plus the costs of fuel and installing an external electrical plug—you can get a 9,000-plus-watt gas generator that can run your whole house while the utility workers bring the grid back online (Note: we’re not in the business of giving electrical systems advice. Consult a professional to setup this kind of system. As an Amazon affiliate, Solar Power Rocks may earn a commission on products you buy through links on our site).

With your generator and some fuel, you can usually outlast any prolonged outage of the grid, and even help a neighbor out if you need to. Your solar panels will remain off until the grid comes back up, but at least you’ll have power.

But the name of this website isn’t “Fossil Fuel Rocks,” right? These generators are for emergency use. They’re loud, smelly, and create all kinds of pollution from their use. Can you imagine the sound and smell if you and your ten closest neighbors all run your generators at the same time?

Finally, there’s the risk of a fire from stored fuel igniting or burning up when you refill near the hot metal parts of a long-running generator. That certainly doesn’t help matters if your power gets shut off because of increased fire risk. So let’s look at some purely solar options!

2. Replacing your inverter with a Sunny Boy

There’s one inverter on the market that is designed to allow you to use your solar power if the grid goes down, but the sun is still up. It’s called the Sunny Boy and it comes from a German company called SMA. It doesn’t give you full power, but if you need to keep some lights on and some devices charging, it’s the best way to do it.

While most solar inverters have that automatic shut-off we discussed above, the Sunny Boy has a special circuit that allows homeowners to switch over to pure solar power after a power outage.

A look at the Sunny Boy solution

How a sunny boy inverter provides opportunity power from solar panels

Here’s how it works:

  1. The home loses grid power
  2. The homeowner (that’s you!) goes down to the Sunny Boy and flips a special switch on a junction box wired to the inverter.
  3. The Sunny Boy performs some safety checks and makes sure there’s enough voltage coming from the panels
  4. The inverter directs power from the panels to an outlet in the junction box
  5. You plug in necessary appliances to the outlet and live like a king while others suffer!

To be certain, this isn’t the solution if you want to run all your home appliances on just your solar panels. The Sunny Boy can only produce up to 2,000 watts of power at a time, and it’s designed to shut down if the power draw is too great. And again, it only works if the sun is up.

2,000 watts might sound like a lot (20 100-watt light bulbs!), but it probably isn’t enough to start an air conditioner. Realistically, you can probably plug in your fridge and a lamp, along with a radio and your smartphone to keep you company.

The total cost for the Sunny Boy and the outlet might be $2,500 more than another brand of inverter without the backup feature. But factored over a 10-year span (the life of the inverter), you might find this an attractive option.

If you want to keep your full house running even when the grid is down, the only way is with a hybrid grid-tied battery back-up system:

3. Using solar plus battery backup to keep your house running during a blackout

The true way to have your solar cake and eat it too is to go hybrid. With a grid-tied solar system backed up by a robust solar battery bank, you’ll have the certainty that the grid provides; no matter how much energy you need or when you need it, it’ll be there. But you’ll also have the peace of mind that comes with battery backup; if the grid goes down, you can run your appliances for as many days as you can afford batteries for.

And unless you’re fairly wealthy, what you can afford will definitely be the limiting factor here. A typical grid-tied solar system with 5 kilowatts of solar panels costs $15,000 (professionally installed, before the federal tax credit and other incentives), and adding a hybrid inverter and batteries to power a home for 2 days can easily add $15,000 – $20,000 to the price.

The good news here is you have some choice in the matter of what batteries you install. The big companies like Tesla and Sunrun offer home solar batteries, and other companies like Sonnen, Panasonic, LG, and more also now offer backup power to homeowners through nearly all solar installers.

If you’d like to get competing quotes for solar and batteries online, fill out our quote request form and our solar expert partners will provide you with quotes tailored to your home.

How does a hybrid home solar system work?

A hybrid solar system is remarkably similar to an off-grid solar system. You’re still planning to be off the grid for up to a few days at a time and you’re still planning to mainly use solar power to make it happen. You’ll need some special equipment to keep the batteries charged at all times, and some additional wiring to make the system work during a blackout.

Here’s a great diagram of the system and how power travels from the panels to your home:

How a grid-tied solar system works with battery backup

Source: homepower.com

In the diagram above, solar energy follows the path pointed out by the arrows. The major components are the panels themselves, the charge controller that keeps the batteries charged and ready, the inverter that turns the DC solar power into AC power for your home, and the backup panel, which is always connected to your essential appliances.

That backup panel is important. If the power goes out, you probably won’t be needing the the pool pump or the home theater, but you probably do want your fridge, lights, and some other essential appliances. In the event of a power outage, all you have to do is turn off the AC disconnect (12 in the image above), and your batteries will provide as much power as you need to exactly the things you need most.

The bottom line for a solar system with battery backup

When the grid’s down, a hybrid system springs into action, essentially becoming an off-grid system. There’s a TON of information to learn about designing a system that can power your home with no grid power. Thankfully, we’ve developed an extensive off-grid solar page to help you learn!

If you’re interested in a hybrid grid-tied system, definitely check out what goes into choosing the panels, batteries, and other equipment for an off-grid solar system.

Last modified: March 20, 2020

18 thoughts on “How solar can help you survive a power outage

  1. Avatar for Ed Ed says:

    If I have solar panels and disconnect the main line coming in from the electric grid and I am running a back up generator why can’t i use my solar panels in addition to my generator? We just had a hurricane come through Louisiana and I have a generator connected to my house. The Main line coming in from the electric grid is turned off to prevent electricity from going out to the grid. Why did my inverter still say power failure even though it was getting power from the generator?

    1. Avatar for Ben Zientara Ben Zientara says:

      Hi Ed-

      I’m sorry you’re having to suffer through the power outages and I hope your loved ones and property made it through the hurricane okay.

      Because it’s designed to send power from solar panels to the grid, your inverter needs a reference frequency and voltage to be certain it is matching its output to what the grid needs. Without that reference, the inverter assumes the power has failed. There are off-grid inverter-chargers that can accept the input of a generator and don’t require a reference frequency/voltage, because any excess energy they process is sent to a charge controller that charges a battery bank, rather than a grid that needs a matched frequency and voltage.

      There are also new types of inverters that offer some modicum of power from solar in the event of an outage. One of them is the Sunny Boy TL-US series, which can send a small amount of power from solar panels (while the sun is shining) without batteries. As long as there is enough voltage from the solar panels, a dedicated outlet attached to the SMA TL-US inverter provides up to 1,500 watts of power to plug in things like a fan, phone charger, laptop, etc.

      Check out a video about these inverters here: https://www.youtube.com/watch?v=fF461YYNbtw

  2. Avatar for Ben Ben says:

    How many batteries would I need to run up to 91amps for a week

  3. Avatar for Dane Ericksen Dane Ericksen says:

    had a 15-panel, 3.5 kW solar voltaic system installed in 2009. SMA Sunny Boy 4000US inverter. It’s still performing great over ten years later (this is written in June 2020). When Pacific Greedy & Explosion (PG&E) started its Perfectly Stupid Power Shuttoffs (PSPS) in 2019, In bough a 8 kW gasoline/propane dual fuel standby generator. I then had a licensed electrician add a generator connection socket to back feed my breaker panel, along with an OEM and UL approved interlock to ensure that the generator could not back feed to the electric grid. Also had a building permit pulled to document the install. I thought “Aha, once my generator is fired up, my Sunny Boy inverter will again see 120 V/240 V 60 Hz (more or less) AC, and re-activate.” But in researching automatic standby generator systems I found warnings that a grid tie solar inverter must be completely isolated from generator power. I learned that grid tie inverters are really large DC amplifiers: They sample the incoming AC at perhaps 10,000 times a second, and that is how a grid tie inverter manages to match the commercial grid power in both frequency and phase. The inverter generates a slightly higher voltage than the incoming AC, so that power always flows from the inverter to either my house or back to the PG&E grid. Solar panels have a weird power transfer curve, they will either generate zero power (if disconnected) with a high DC potential, or, when connected to a load, will generate whatever power illumination by the Sun is providing at the moment. That power has to go somewhere: For a grid tie system, if my house is only drawing, say, 2 kW of AC power and my solar panels are generating 3 kW, then 1 kW of power goes to the grid, and everybody’s happy. But if you connect a standby generator, and your house is again only consuming 2 kW, the excess 1 kW of solar power still has to go somewhere, and in this scenario “somewhere” is the generator. But consumer grade standby generators are not designed to source power, only to generate power. It is quite likely that the generator’s electrical circuits would be overloaded and fail, perhaps spectacularly so. So, sorry, it’s still generator power only during a PSPS, unless you have the newer SMA SunnyBoy with its clever 2 kW Secure Power Supply (SPS) option. When it comes time to replace my SunnyBoy inverter, it will definitely be a SunnyBoy with the SPS.

  4. Avatar for Jesse Hicks Jesse Hicks says:

    I have a basic grid/electric question: I understand that solar panels don’t work during an outage because of an automatic shut-off that stops power from feeding into the grid. This protects workers trying to fix down lines from getting shocked. Got it.

    But my folks have a propane generator connected to their house’s electric system. When the power goes out, it automatically turns on and powers the home. The house is still connected to the grid, right? So isn’t there still the same risk of the generator’s electricity shocking a utility line worker? If not, why not? And if not – if there’s something preventing that generator power from going back out to the grid – why not employ that same thing so that solar panels can work during an outage, but workers don’t get shocked? It seems like ther has to be technology that just disconnects panels from the grid and only feeds your home during and outage, so you can use them. Like, I don’t know, an on off switch? (On=feed the grid, Off=disconnected from the grid). But that would make solar panels more useful, and why would the utility companies want that?

    1. Avatar for Ben Zientara Ben Zientara says:

      Hey Jesse-

      Great questions, and very timely! We just published an article about one kind of solution to this problem.

      But first, the answer to your question of why solar panels can’t power your home when the grid goes down is: they can, but you need to add more than just a switch. Because solar generation isn’t a steady power source like a generator, you need electricity from the panels to pass through an inverter/charger, to a battery bank, and then back through the inverter to your home. The reason is you have to maintain a steady voltage and the ability to increase amperage necessary to start up and run home appliances. Solar panels by their nature fluctuate in the amount of power they produce at any given time, and can’t be called upon to give more than they’re making at any one time, either.

      Things like lights are easy to run without much power, but starting up a microwave, vacuum, clothes dryer, or even the condenser of a refrigerator can require a lot of power on demand. If you don’t have something that can help you do that, like a battery bank or propane generator can (up to a point), you run the risk of damaging the electrical components of your appliances.

      For years, people have built these kinds of systems for off-grid use, but more and more, big companies are getting into home battery backup systems. We have an article about home batteries here, and that recent article I mentioned about the Enpahase Ensemble system, too.

      1. Avatar for Pete Cerutti Pete Cerutti says:

        So why can’t there be an automatic switch that does not allow the electric from leaving the home grid to the power lines. I was thinking of using a propane generator to power up the inverter during a blackout. Surely there is a way to self-contain the power to your home???

  5. Avatar for Josie O Josie O says:

    Well Thanks a lot! You just busted my bubble, but for the best. I was thinking of investing in Solar in MS. We get a lot of sun and I figured that if the power goes out, or survivalist, Solar would save me. OMG! So, I would have paid so much for nothing. A generator is the best option. The low cost, old school method it seems. What $20k + saved by reading this FREE article. My husband’s gonna love and thank you! Thank you again for this very simple to follow guide.

  6. Avatar for susan hoague susan hoague says:

    Are Sunny Boy Inverters legal to use in all states? In Massachusetts?

  7. Avatar for Ryan Ryan says:

    That’s not diesel

  8. Avatar for Chris Chris says:

    He asked for a diesel Generator. One linked is a gas generator. Big difference.

  9. Avatar for Joe Mac Joe Mac says:

    I bought a used Cumming 15kw 120/240 volt diesel generator with 529 hours on it. I added an ATS for another $500. And since I am electrically oriented no problem in installation.

  10. Avatar for Arturo Arturo says:

    It would be very sad to have a $20,000 solar system installed and to be in the dark during a blackout. Would it be possible to connect an automatic disconnect or a DPDT contactor that would disconnect the grid in the event of a blackout, then with a small inverter powered by the sun we can excite the big inverter this way we can have solar power off the grid in case of a black out.

  11. Avatar for Anonymous Anonymous says:

    If you have a plug-in hybrid, such as a Chevy Volt or Toyota Prius Prime, you can buy an inverter f

  12. Avatar for Craig Lechowicz Craig Lechowicz says:

    I think his point is the one you linked to is a GAS generator. I get you are solar guys, but there is a huge price difference between Gas generators and diesel generators, due to both basic engineering costs of the engine, and to economies of scale, since gas generators are sold in huge volumes, and diesel ones are pretty specialized.

  13. Avatar for Michael Doherty Michael Doherty says:

    Where do you buy a backup diesel 7kw generator for $1,000? I’ll take one now!

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