One of the first homes to get the Tesla Powerwall is running. It's part of a one-of-a-kind partnership between Green Mountain Power and Tesla on an energy-storage project. We first told you about it back in May.

Here's a reminder of how the technology works. Large Tesla batteries are stationed outside and smaller ones are inside the homes of some Vermonters. During peak times of the day, when lots of people are using electricity, power is pulled from the batteries and sent across the state.

GMP representatives say that means they won't need to turn on costly generators, which saves customers money. The battery inside someone's home also acts as an energy-efficient generator when the power goes out. It's already helped one Vermonter keep the lights on as our Alexandra Montgomery found out.

"The Powerwalls are over here," Andy McMahan said. "This is it right here. There's two of them here, there's the back one and the front one."

It's a modern piece of technology running inside a Vermont log home.

McMahan is one of 102 Vermonters who have a Tesla Powerwall already up and running. I'm told 1,200 others are on a waiting list.

"I feel like a guinea pig, to a little point," McMahan said. "But someone's got to do it, right?"

McMahan says just days after her Powerwalls were installed, a wind storm knocked out power for thousands of Vermonters, including her.

"This went on, went off, went on, went off and we're like, 'oh boy,'" she said.

McMahan says after a call to Tesla's customer service and a few flipped switches...

"Boom! All the lights came on and we were golden after that," she said.

Despite the hiccup the first time around, she says the next time she lost power, she didn't even know.

"The seamlessness is just, you know, you don't have to go out and start a generator. It just-- it's quiet, doesn't use fuel, it's what it is-- it's powered by the sun," McMahan said.

McMahan has solar panels to recharge her Powerwall after GMP pulls power during peak times. But GMP reps say she isn't left uncharged if a sunny day isn't in the forecast.

"We're always making sure we're always looking at things like the weather, make sure that in those cases we would be ensuring that the storage devices are fully charged and ready for the customer to use," GMP CEO Mary Powell explained.

It's something Powell says is common sense and will be even easier to accommodate once more Powerwalls are installed. But the walls currently running are already making a difference.

"Having those 100 signed up is like virtually disconnecting, like taking 500 homes completely off the grid. That's the equivalent," Powell said. "So you can only imagine when we get up to 2,000 and when we go further."

Back in McMahan's home, she signed up for two Powerwalls and pays $15 a month for each through the program. Normally, it costs $7,000 to $8,000 to order one from Tesla's website.

"If these continue as good as they are, if there wasn't a lease agreement, I would buy one," McMahan said. "I seriously would."

People who use the Powerwalls have an app on their phone that shows them when their Powerwall is being used and how charged it is.