Battery Backup for Solar Panels: What to Know
Updated: Jul 15
Find out if a solar panel and battery combo is right for you. Plus, we correct one of the biggest solar misconceptions out there. (Hint: It’s about power outages!)
Photo courtesy of Tesla
35% of solar shoppers consider adding a solar power battery backup, according to a recent industry survey. And with plenty of good reasons: The average person in New Hampshire experienced 8 1/2 hours of power interruption in 2018, according to the U.S. Energy Information Administration.
Solar energy storage offers peace of mind, helps ensure that your system will always run, and has never been more accessible to homeowners. Granite State Solar is a certified Tesla Powerwall installer. Our experts explain the ins and outs of these resilient energy systems.
Protect Your Home from Power Outages
Never worry about another blackout. “Homeowners like having security knowing that they have, effectively, a future-proof system,” says Rob Dunn, Project Manager and experienced battery installer at Granite State Solar. “It will keep your lights going, keeps your essential loads going (like your fridge, a well pump, etc.)—it can keep your entire house going if you have enough of them.”
Best of all, this happens without you having to do anything. “It does not have to be turned on manually,” says Eric. “There’s going to be an automatic transfer switch that is installed with the battery system that will automatically start having the home work off of the battery completely seamlessly. So, the homeowner will probably not even know that the grid has gone down.”
“And you can see it from your phone,” Rob adds. “So, if you’re not home, you can check the app.” It uses 3G/4G cell signal, Wi-Fi, and ethernet, so even your internet goes down with the powerlines, you’ll still be able to see when your house is in backup power mode or not. “You could be on vacation and see that you had a storm and the power went out and your house is running on the Powerwall.”
But Wait. I Have Solar—Will Solar Panels Work in a Power Outage?
This is one of the biggest misconceptions in the solar industry: When you have a grid-tied system, solar panels will not work during a power outage.
“Without a battery, typical grid-tied solar systems, when the grid goes down, your solar panels will not be able to produce,” says Eric. “It’s a safety mechanism: The utility doesn’t want you exporting power to the grid during the day if power at the street is out. You could potentially hurt a lineman restoring power on the lines if you’re exporting power to the grid.”
Fortunately, the battery lets you work around this. “With a battery, you’re able to keep producing power with your panels and feed your house with that power,” says Eric. “And you can use this battery kind of like a generator during power outages.”
And you can continue to keep the battery charged as long as you get some sunny days. “You’ll likely get through night-time by drawing off the battery, and then the next day, the sun comes up, the sun comes up and will re-charge the batteries and that cycle will repeat itself all over again,” he adds.
What Can I Run with a Battery?
That depends largely on your preference. “One Tesla Powerwall gives homeowners 13.5-kilowatt hours of storage, at a full charge, with 5 kilowatts of continuous output,” says Eric. “If the homeowner is looking to just back up the essential loads—like your well pump, your refrigerator, your heating system—if it’s off of propane or oil, your lights, your modem or router—one Tesla Powerwall would be sufficient.”
But, this isn’t the limit. “You can daisy chain these batteries to give you more capacity if you’re looking to do a whole-home backup,” Eric adds. Our solar advisors help a customer determine their best options during a free site evaluation.
Should I Buy a Generator for My House?
While a small generator is cheaper, there’s more than just cash that factors into this decision.
For starters, there’s the maintenance. “The traditional portable generator needs to be continually refilled with gas every so often, which during the winter months can be a huge inconvenience,” says Eric. Generators also require regular maintenance—oil changes, annual service, checking filters, and spark plugs.
Modern solar panel energy storage, on the other hand, have basically no upkeep. This is a big improvement over past battery technology. Old batteries were much more finicky (needed to maintain a certain charge, be equalized now and then, and even have water added). Current battery technology is basically set it and forget it.
“Plus, they do not automatically turn on in the event of a power outage,” he adds. A battery, on the other hand, turns on instantly and you don’t have to do a thing. You may not even notice that there was a power outage. Not to mention the noise difference between a quiet battery and a noisy generator.
And, of course, generators run on fossil fuels—not great if you’re going solar to shrink your carbon footprint.
Another Upside: Energy Independence
“Another key benefit of batteries is you can use it in self-consumption mode,” says Eric. He explains that when your panels aren’t producing at night, rather than pulling power from the grid, you start to discharge the electricity from your battery. This means that you get to use the power you make right at home.
“And there’s an advantage to this,” he explains. “When you net meter and you sell your power back to the grid, you maybe sell your power at 12-cents, and then you have to buy it from the grid at 18 cents. So, instead of selling it to the grid, you can put your excess electricity into the battery and you’re going to be seeing a higher value for your solar power that’s generated because you’re storing it on site.”
Customers also appreciate the freedom from the utility that this affords them—no matter what, your panels will produce energy.
How Long do Solar Batteries Last?
Current battery technology is built to last much longer than old-school systems. The grid-tied solar energy storage batteries Granite State Solar offers all come with a 10-year warranty, though our experts suspect they’ll last you beyond that. “At that 10-year warranty, it’s assumed you’ll still have 70-90% your original capacity, depending on how you use them,” says Rob. “So, the likelihood of a homeowner to want to replace their system after 10 years is very slim.”
Tesla Powerwalls have an unlimited cycle life for the 10-year warranty. “That means that you can cycle it as much as you want in backup mode or self-consumption mode and it’s still covered under the warranty for 70% of the original capacity for that whole 10 years,” he says. “For these modes, it would be physically impossible to hit a cycle count that is greater than 2,800, so therefore Tesla just says a blanket statement that you do not need to consider cycles. It’s just a flat 10 years.”
Enphase batteries also come with a 10-year warranty. “The Enphase batteries do have a cycle limit, but if you did a true apples to apples comparison between the systems, it works out to be identical to Tesla’s 2,800 cycles,” Rob explains. “Which, when it’s in battery backup mode or self-consumption mode, is effectively impossible to hit before the 10-year warranty is up.”
What Do I Need to Know about Solar Energy Storage in New Hampshire?
One thing to consider when getting solar energy storage in New Hampshire is where you’ll install it—and how cold it gets there. “You wouldn’t want to mount it outdoors in the North East where we live,” says Eric. “The temperatures are too darn cold in the wintertime. These batteries like to be operating when the ambient temperature that they’re surrounded in is upwards of 50-degrees. Obviously, our winters are much colder than that, so the preferable spot for these is in someone’s basement.”
Fortunately, current battery technology is much smaller than old batteries, so it’s easy to fit into these spaces. “When comparing a lead acid bank to Powerwall, the Powerwall is roughly 1/8th of the total volume,” says Rob. “It used to be that an old-school system was a battery cabinet that was 2 feet tall, four feet wide and up to 8 feet long—and that’s a very similar energy capacity as one to two Powerwalls.” One Powerwall, for comparison, is only 45 inches tall, 30 inches wide, and 6 inches deep (approximately).
By Julia Westbrook