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Pepperell Hydro uses water, sun to power grid
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PEPPERELL — The folks at Pepperell Hydro have been generating power for several years. This summer, they added another environmentally-friendly power generator.

The hydroelectric plant dates from 1921 when it was built to power the paper mill. Now, Pepperell Hydro also sends solar-generated electricity back to the grid, thanks to a new array of solar panels.

“Green is green,” said Peter B. Clark, president of Swift River Company. Pepperell Hydro is part of a small group of hydroelectric plants in Massachusetts managed and operated by Swift River.

The new array will reduce the plant’s operating expenses through the energy credits it will receive, he said. Like the hydropower the plants makes, the solar power is from a renewable source.

“Everything goes up to the grid,” said Martha Brennan, director of regulatory affairs at Swift River. The hydropower is sold to the Reading Municipal Light Department. The solar goes on the grid through National Grid.

Even though the hydro plant generates huge amounts of electricity, the plant still needs to purchase electricity for day-to-day operations.

The transformers must stay warm and the lights need to be kept on even when the plant is not generating electricity, said Quincy Vale, director for business development at MassAmerican Energy.

MassAmerican specializes in commercial solar installations, usually 100 kilowatts and larger, Vale said.

“This is one of our smaller ones,” he said. The new solar panels on the roof of the red garage beside the bridge on Main Street will generate 13 kilowatts, two to three times the average size of a residential installation.

The amount was low enough that Pepperell Hydro was not affected by the net metering cap that put the brakes on a planned solar installation on the capped Pepperell landfill. As long as a commercial array that is connected via a three-phase power connection is under 25 kilowatts, it does not hit the limit, Vale said.

The installation in Pepperell presented its own challenges.

“We didn’t have an easy way to interconnect that hydro facility to the grid,” Vale said. The plant has a high-voltage connection to the grid, but the solar needed a normal connection from the street.

“We looked at a whole bunch of different things for Pepperell Hydro,” Vale said.

Rather than run a power line from the bridge along the new penstock to the plant, putting the solar panels on the roof of the garage made better economic sense, he said. The building already had three-phase power.

The red garage is used to store materials to maintain the dam, Clark said.

The dam regulates the water in Pepperell Pond, Brennan said. The hydro-plant uses a run-of-the-river model, keeping the water level in the pond at a consistent level.

In the earlier days, when the plant was generating power for the paper mill that owned it, the water levels would change, she said. Now, it is more environmentally-friendly.

Vale was very enthusiastic about the Pepperell installation. The American-made panels give the best return on investment, he said.

Thanks to innovative wiring, they can generate electricity even when only part of the panel is in the shade. Snow will slide off easily because of the steep angles of the panels.

Fire is no danger because the system cannot spark or arc, Vale said. A typical commercial installation operates at 600 to 1,000 volts, he said. Pepperell Hydro’s installation comes in at 57 volts, not high enough to support an arc.

The installation is a good investment for the owners, Vale said. It will cover 50 or more percent of their electricity costs.

And, he said, it’s good for the environment.

Follow Anne O’Connor on Twitter and Tout @a1oconnor.