Our Powerwall Saved the Day During a Power Outage. Here's What I Learned - CNET

Commentary: A year ago, our family endured two major power outages. This year, a home battery kept the lights on when the winter storms arrived.

A pair of Tesla Powerwalls on a garage wall

At 4:39 p.m. Sunday, a windy winter rainstorm in the San Francisco Bay Area knocked out power for me and hundreds of neighbors. We joined thousands of others in the region with no electricity.

My family and I didn't even notice.

That's because, as of three weeks ago, our garage wall houses a pair of Tesla Powerwall batteries. When the power went out, the batteries kicked in. We'd charged them earlier with solar power, but you can also use power off the grid.

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Our first indication something was wrong with the grid's power supply was a text from friends two houses down the street, followed shortly by a power outage alert from the Tesla app. For more than 16 hours, the batteries powered our lights, refrigerator, internet network equipment, laptops, TV and microwave oven until the power was restored Monday morning.

My experience shows one of the big benefits of home batteries, and indeed having power during a power outage is the major reason we spent well over $10,000 on our Powerwalls. But on top of that benefit, home batteries also can help you cut your electrical bill and help out the power grid.

We didn't buy the Powerwalls on a whim. It was largely because of difficulties in 2023 when two winter storm outages left us without power for days. Both times, I scrambled to buy refrigerator ice, put phones into power-saving modes and crack out a portable power station to run laptops and our internet network equipment.

Powerwalls are big 250-pound batteries that mount on walls inside or outside a home. They charge up either off the grid or from solar panels, which is our setup. They can power your home if the power goes out, taking over seamlessly when a separate controller module detects an interruption in your supply.

You can also set Powerwalls to supply your house's power when it's expensive, if your electric utility company charges higher rates when demand is higher, as ours does. That can lower your bills and help relieve the grid during the evening hours of the day when it's most taxed. And that, in turn, can mean your house is helping in a small way to lessen the need for power companies to fire up greenhouse gas emitting natural gas peaker plants.

The Powerwall 2 models we got are each about 6 inches thick, 30 inches wide and 45 inches tall. Each has 13.5kWh of energy, which is the same capacity as 135 16-inch MacBook Pros.

It took a long time to get the two big white slabs installed onto our garage walls, with months of complications involving house wiring, a new roof and battery installer scheduling. But the Powerwalls arrived in the nick of time. Here's what I learned about living with home batteries in the three weeks we've had ours.

Our off-grid excursion wasn't all smooth sailing. When I heard the power went out from our neighbor, I expected to feel a warm glow of satisfaction that we were protected.

Instead, when I launched the Tesla app, the notice that the grid was down was accompanied by a warning message: "Reduce Power Immediately. Powerwall has critically low energy. Less than 1 backup hour remaining."

This despite the battery being charged at 95% when the power outage began.

On top of that, the app showed our house was drawing an absurdly high level of power and generating an absurdly large amount of solar power for late afternoon in February during a massive rainstorm. Instead of being reassured, I started freaking out that some wiring problem had revealed itself during the outage.

Left to right: The Tesla Powerwall app bungled the beginning of the power outage, incorrectly reporting our batteries to be almost out of power. It sorted out its problems eventually and showed us having more than 24 hours of power. The next morning, solar power took a load off our Powerwall. The last two screenshots show yellow where the batteries were charging from solar power and blue where the Powerwalls were powering our house.

But no. After about a half hour, the app updated to show more reasonable power usage and a much more comforting 24 hours.

The next discouraging moment had to do with Tesla's Storm Watch feature that's designed to monitor weather warnings and charging the battery from the grid if necessary and husbanding the charge in anticipation of trouble. But Tesla's software fell asleep on the job. Several Powerwall-owning neighbors complained of the same problem on Nextdoor and said this wasn't the first time. I was paying attention, though, so I manually intervened to make sure our Powerwalls and electric vehicles were charged ahead of the storm.

Six hours into the outage, the Tesla app sent a laughably late Storm Watch notification. "A storm is forecasted for your area and Powerwall is now charging to provide backup power," the notification said in a complete mischaracterization of the situation.

Tesla didn't respond to a request for comment.

Once we got past the spurious warning that our Powerwalls were about to fizzle out, we rode out our power outage just fine.

At night, I could see the power outage boundary up the hillside across the way, with a big patch of mostly dark houses to the north. A handful of generators blared at houses in the area. Our house wasn't dark, but it was silent.

Each Tesla Powerwall is about as big as a card table but weighs 250 pounds.

We have solar panels that recharge the Powerwalls during the day, though not very fast, especially when it's overcast or when the sun is low in the winter. Because I wasn't sure how long the Powerwalls would last, I still unplugged some inessential devices in the house to extend our off-grid abilities. We didn't do any laundry, run the dishwasher or charge our EVs, and I was more persnickety than usual about turning off lights in unused rooms.

When we ran a lot of electrical appliances at dinner, the Tesla app warned us we only had 15 hours of backup power, but we didn't sustain that rate of consumption, so pretty soon it extended our forecast to more than 24 hours again.

Other than that and obsessively checking the Tesla app, things were just fine. We watched a movie. We turned on the lights. Life went on.

At 8:04 a.m. Monday, we had enough sunlight to generate 200 watts of solar power, a small amount but enough to ease the burden on the Powerwalls. By 8:24 a.m. the solar panels were producing 400 watts, with 300 watts of that powering the house and 100 watts charging the Powerwalls again. At 9:12 a.m. Pacific Gas & Electric restored power.

In nearly 17 hours running on our Powerwall, our batteries' collective charge dropped 21 percentage points, from 95% to 74%. We could have lasted a day or two longer, even without a partial solar recharge.

That's just our story, of course. Things will be different if you need electricity to heat your home or water, and even gas furnaces rely on electric fans to blow air through ducts. In the Bay Area, it was hardly warm, but we've already had our heat mostly off since mid-January and are used to wearing a layer of fleece.

As a new Powerwall customer, I didn't know exactly what to expect during an honest-to-goodness power outage.

I'd tested its ability to take our house off the grid a few times, which was a bit of a rush at first but eventually felt as exciting as running my laptop on its battery. A real outage, without any real notion of when the power would come back, was a very different sensation.

Overall, I felt a lot more control and a lot less helpless than during the 2023 power outages. But not so much control that I was breezily confident about having sufficient power.

Other things I learned or observed:

There still are plenty of uncertainties about power usage and weather. But overall, the combination of solar panels and a home battery was great.

Article updated on February 7, 2024 at 5:00 AM PST

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