May 4--PEPPERELL -- The snarling Nashua River gathers pace toward the Main Street Bridge that butts against the top of the dam.

The white water crashes down, splashing against the riverbed 28 feet below. The impact creates more than wild waves for geese to ride. The rumbling water bursts through the gates of a hydropower plant 600 feet downstream and spins the iron blades of the turbines connected to generators that make electrons jump up and down, all the way to your house through the utility wires.

Welcome to Pepperell Hydro, a neighborhood source of renewable energy. Built in 1918, the plant featuring a 13-foot-diameter wood stave penstock that channels the water from the dam, used to crank out power for the paper mill across the river. The red brick structure with multipane windows became a ghostly reminiscence of Pepperell's industrial past when the mill closed in 2002.

After a painstaking restoration by Swift River Hydro Operations Company Inc. of Wilbraham, however, the plant now stands as an icon of the green energy movement, putting out 7.2 GWh of electricity annually -- enough to power about 720 homes year-round.

The resurrection of the Pepperell plant comes amid the growing interest in hydropower nationwide. Just take a look at the U.S. Energy Regulation Commission's statistics, says Tom Tarpey, president of the Bay State Hydropower Association. The federal agency issues permits for people to study potential hydropower generation sites, and there

has been an "explosion" in the number of permit applications in the past year, Tarpey says. Many applicants hope to convert dams that have existed for irrigation or navigational purposes into power-producing plants.

Massachusetts doesn't have such a hydro boom. That's because dams and plants were created at almost all possible locations nearly a century ago, according to state Department of Energy Resources Commissioner Philip Giudice. Many plants are attached to former paper and textile

mills and tend to smaller in scale, Tarpey says. Still, some plants are incorporating high-tech equipment to maximize electrical output. For example, the new crest gate that Lowell's Boott Hydropower recently installed in place of the old-fashioned wooden flashboards atop the dam does just that, according to Tarpey. The state is also trying to determine if it could create some new hydropower facilities on state-owned land.

"Hydropower is one of our oldest and most reliable zero-carbon energy sources we have in the country," Giudice said.

Swift River bought the Pepperell plant from Perry Videx, LLC, in 2003 for $400,000.