Robert Holt’s reaction after his neighborhood lost power in the recent storm was different than mine.
“This is, like, perfect! This is how it’s supposed to go!” he said, looking back at how his home performed.
Holt was happy because his home is one of the few in New Hampshire that uses batteries and solar panels rather than generators to provide its own electricity when the grid goes down. He says he hardly noticed a thing during the two days that power was out.
There’s no data about how many of these battery-backup homes exist in the state but queries from the Monitor, the Granite Geek newsletter and on the tech-happy site Reddit seeking examples drew just a couple of responses. Since such folks love to talk about their systems, I’m going to assume they are as rare as hen’s teeth – certainly rarer than in Vermont, where regulators and the utility support them.
Holt’s case is interesting because he lives in Sanbornton, just a few miles from a house that suffered a battery fire a week earlier. That house had a system made of three used electric-car batteries wired together by a licensed electrician. It had operated for three years but on Dec. 17 for unknown reasons one of the batteries experienced “thermal runaway” and burned down the garage, slightly injuring the homeowner.
Holt’s system is a Sonnen Eco 8.0/12 (it can produce 8 kilowatts and is expandable to 12 kilowatts) built new to provide whole-house power. He installed it in 2017 along with solar panels, 20 years after moving into the house, and says it performs flawlessly, including effortlessly keeping things running for two days during the storm.
Sonnen is one of a couple dozen companies that make home battery systems. Probably the only one you’ve heard of is Tesla and its Powerwall.
Swapnil Saket of Windham has two 13-kilowatt Powerwalls on his house, which he installed in September 2021 along with a Tesla Solar Roof that uses power-generating shingles. Saket says he had to replace the roof anyway and at the time, the Tesla system was about the same cost as getting a regular roof with solar panels installed on top as well as batteries.
Both Saket and Holt say a huge advantage of their systems is ease of use.
“Up until then we had a gas generator,” said Saket, who has been in his house four years. “We had lost power a couple of times and had to go out, turn on the generator, flip the switches, make sure everything is proper, wait for the power to come back up.”
With batteries, however, the system switched over automatically.
“I didn’t know power was out until I saw the app,” Saket said. Tesla had even anticipated the possibility of a black-out because of the weather forecast and automatically charged the batteries to 100% in preparation.
Saket also appreciates battery’s lack of year-round maintenance. “You don’t have to go out occasionally, run the generator, make sure you’ve got gas.”
Another advantage: Home batteries are almost always paired with solar panels, which can keep them operating almost indefinitely without the need to go get more fuel.
“It was about 45% (charged) at about 8 a.m. We’d been without power about 14 hours at that point,” said Holt. “The sun came out Christmas Eve and the battery started charging. We got power back about 1 or 1:30 (p.m.), and the battery was back up to about 90%,” even though it had been running most of the house all that time, including heavy items like the well pump, refrigerator and home heating system.
Saket’s experience was similar. The only difference is that his home is heated with a ground-sourced heat pump that takes a lot of electricity; he had to turn it down and use propane heating and the fireplace for a while.
“When power came back, the battery app estimated there was still 20-plus hours of backup available,” he said, and that’s before charging from his Solar Roof.
Incidentally, you can’t power your home from rooftop solar when the grid is down unless you have batteries. As when using a generator, you have to disconnect from the grid when powering yourself so you won’t harm repair crews, and that can’t be done with solar panels alone. My house was cold and unpowered for a while during the storm despite my rooftop solar since I don’t have batteries.
There are other advantages to battery systems. Even in New Hampshire, which lacks time-of-use rates that would better reflect their value to the grid, you can have a small financial advantage by using batteries to shift your electricity supply. Rather than selling your excess solar power to the utility at a cheap wholesale rate when it’s bright and sunny you can save it and use it at night to replace electricity that otherwise you’d have to buy at a higher retail rate.
And there’s the psychological pleasure of helping the grid become more future-proof, less reliant on big, expensive power plants.
So why doesn’t everybody with solar panels have battery backup? The same reason I don’t: Cost.
The Powerwalls cost Saket about $6,500 each, although the pairing with the Solar Roof complicates the calculation. Holt says his total battery system cost about $18,000.
That’s much, much more than getting a gas generator installed. Even though various grants and tax breaks are available for batteries, they will remain much more expensive than loud, inconvenient, carbon monoxide-spewing generators for a long time.
Home battery systems won’t become common without more government support, which is a shame because they have huge advantages for our increasingly-strained grid.
With the right planning, utilities can draw a little bit of electricity from a lot of home batteries when the need is great, such as hot summer afternoons or cold winter mornings, a much cheaper way of expanding electric supply than building power plants and distribution systems. Vermont’s Green Mountain Power says it has saved hundreds of thousands of dollars – probably millions by now – by doing just this with its home Powerwall program, which reduces the need to buy very expensive electricity during peak usage.
For now, however, home batteries are like solar panels were a decade ago. Fascinating, useful but expensive and rare. Let’s hope they follow the same trajectory.
“It’s kind of a luxury at this point, but on days like this, it feels like a good investment,” said Saket.