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New England's Largest Battery Is Hidden Inside A Mass. Mountain08:44

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Inside the Northfield Mountain pumped storage hydroelectric station (Jesse Costa/WBUR)closemore
Inside the Northfield Mountain pumped storage hydroelectric station (Jesse Costa/WBUR)

It was Boston-born Ben Franklin who first used the term "battery" to describe an electric storage device. Now, nearly three centuries later, Massachusetts is hoping to jump-start the development of new kinds of batteries to power the future.

The state has launched a $10 million Energy Storage Initiative. The 10-year goal: Save electric ratepayers hundreds of million dollars, make the electrical grid more reliable and resilient, and reduce greenhouse gas emissions.

Today's batteries come in all shapes and sizes. The largest in New England -- and once the world -- was built 45 years ago and is still working.

But it's hidden, on top and deep inside a mountain in north-central Massachusetts.

'Well, There's A Power Plant Underground'

The upper reservoir is the battery that powers the Northfield Mountain pumped hydroelectric station. (Jesse Costa/WBUR)
The upper reservoir is the battery that powers the Northfield Mountain pumped hydroelectric station. (Jesse Costa/WBUR)

Northfield Mountain is a naturalist's wonderland. But if you look around, you'll see an unnatural site: a 5-billion-gallon battery.

"So what you're looking at right here is the upper reservoir, and I consider this to be the battery for the station," says Gus Bakas, director of Massachusetts hydro operations for FirstLight Power Resources.

The company owns and operates the Northfield Mountain pumped storage hydroelectric station. The generators are powered by this manmade mountaintop lake.

"So this is our supply, our stored energy, similar to a battery," Bakas continues. "So when we need that battery to turn on, we would take this water and we would run it into the facility to produce power."

The hydroelectric generating facility is located hundreds of feet below the reservoir, hidden deep inside the hollowed-out Northfield Mountain. But you'd never know it, except for an occasional hint.

"There are people that have been coming here for 30 years," Bakas says, "and somebody will ask, 'What are those wires?' And somebody will explain, 'Well, there's a power plant underground.' "

Typically public tours aren't allowed, in part due to security concerns. Typically...

The Batcave

The entrance to the plant (Jesse Costa/WBUR)
The entrance to the plant (Jesse Costa/WBUR)

We go past a security fence, under the watchful eyes of surveillance cameras. We come to a hole in the mountain, chiseled out of gray granite. It's wider than Boston's Sumner Tunnel.

"Right now we're going to drive through a portal door that gives us access to the underground project," Bakas says.

It's enormous, and looks like the Batcave.

"That's funny, that's what we call it sometimes," Bakas says. "It's like James Bond, or 'Get Smart' — remember 'Get Smart' from the '60s?"

The Northfield pumped hydro plant was built in the late 1960s. The tunnel leads to the giant generating station inside.

"When this facility was built, it was actually the largest pumped storage facility in the world," Bakas says. "This facility here is capable of just under 1,200 megawatts, so we're good for well over a million homes."

Water from the reservoir, now high overhead, flows through four 18-foot-diameter conduits drilled into the rock. Gravity and powerful pumps force the water down to the hydro plant carved into Northfield Mountain. The water spins the electric-generating turbines.

To recharge the battery and get water back up to the mountaintop reservoir, the pumps work in reverse.

When Northfield was constructed, the electricity for the pumps came from the then-just-built Yankee nuclear power plant located a few miles up the Connecticut River.

"Vermont Yankee being a nuclear power plant generates power 24/7, or what they call base load," Bakas says. "So as a result of that at night they had all this excess power on the grid. So somebody needed to take it. So this plant was conceived and built to take that off-peak power and utilize it through pumping water during off-peak periods."

Actually, the Sisyphean labor of pumping water up and down the mountain is a net energy loss -- more electricity is used then generated. But because off-peak electricity costs less than the price Northfield gets for what it generates when demand is high, the system is a moneymaker.

Buy low, sell high.

'The Sound Of Money'

The road into the entry portal of the "Batcave" (Jesse Costa/WBUR)
The road into the entry portal of the "Batcave" (Jesse Costa/WBUR)

We arrive at the underground workaday world of operations manager Doug Bennett.

"So right now you're about 750 feet inside the mountain, about a half a mile in, and you're in the control room," Bennett says. "And this is where the guys here are going to start the machines, and they're going to monitor that operation."

The Northfield Mountain pumped storage hydroelectric station is still in the process of converting from old analog controls to digital systems.

An ancient red rotary telephone stands at the ready. It's a direct link to ISO New England, which operates the electrical grid and decides which plants go online.

"When they call there it's either to confirm something going on or there's an urgent need," Bennett says. "We like the sound of that phone; that is the sound of money."

We go next onto an observation deck overlooking the four generators.

"The facility here is about 100 yards long and 10 stories high," Bakas says. "You know, you can read about it, you can look at videos online, but to be underground and actually see it and experience it, I think really drives the point that this is a pretty unique facility."

The Northfield Mountain pumped storage station provides nearly instantaneous power on demand. When the red phone rings and the call comes from ISO New England, energy, in the form of the water battery, flows into the turbines at 27,000 gallons a second.

And the generators roar. Each produces nearly 400,000 horsepower, together producing as much electricity as the Seabrook Station Nuclear Power Plant in New Hampshire.

"We could theoretically provide from zero megawatts to 1,168 megawatts in about 10 minutes," Bakas says, "so if there was a contingent loss on the grid, we could make it up pretty quick."

And the generators can produce electricity for about eight hours, flat out.

'Where Does Pumped Storage Play Going Forward?'

Gus Bakas, director of Massachusetts hydro operations for FirstLight Power Resources (Jesse Costa/WBUR)
Gus Bakas, director of Massachusetts hydro operations for FirstLight Power Resources (Jesse Costa/WBUR)

The U.S. Department of Energy has big plans for battery systems like this. Pumped hydro is the most cost-effective way to store electricity. Ninety-nine percent of the bulk electric storage in the world is pumped hydro, and by 2050 the department wants to nearly double the amount now produced: enough to serve nearly 25 million homes.

"I guess the question is," Bakas says, "where does pumped storage play going forward?"

He says Northfield Mountain is now undergoing re-licensing to run for another 50 years and believes the half-century-old facility can serve a new role in the future.

Since the Vermont Yankee nuclear plant shut down two years ago, Northfield has been buying its off-peak operating power straight off the grid. But as more solar and wind comes online, Bakas believes the pumped storage generating station could one day run as a totally climate-friendly supplier of electricity.

"I think the goal of our facility would be to look at the opportunities to purchase purely green, renewable power and be able to supply green power to the grid," he says.

At the foot of Northfield Mountain, the company operates an 18,000-panel solar farm. It covers 10 acres and generates two megawatts.

It's just a drop in the bucket of that produced by the pumped hydro station, but it's a start.

Correction: An earlier version of this post misstated the size of the company's solar farm. We regret the error. 

This story aired on December 2, 2016.

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Bruce Gellerman Reporter
Bruce Gellerman is an award-winning journalist and senior correspondent, frequently covering science, business, technology and the environment.

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