Roosevelt Island — The New York City Department of Parks and Recreation is responsible for 28,000 acres of green space. When a new power plant on Randall’s Island begins operating in 2009, the department will start managing another kind of green: renewable energy.

Using U.S. Department of Energy funds, the Parks Department is in final contract negotiations with a Highland, NY-based alternative energy firm to build a hybrid wind, solar and tidal-energy power plant on Randall’s Island in the East River. The department hopes to start generating power on the island by 2008, said spokesman Ashe Reardon, but the contractor gave a more conservative estimate of 2009.

The Parks Department has been very quiet about the project, which Reardon calls a “demonstration” – or experiment of sorts – so quiet that City Councilmember Melissa Mark-Viverito, whose district includes Randall’s Island, said Friday she had only just learned it was happening. “It’s news to us,” Mark-Viverito said, though she’s happy to see the green energy plant in her district.

“This is all very early, this is one small project,” Reardon said. “We’ve got to get this thing started, see how it goes from there, and see how it works.”

Reardon says the million-dollar facility, to be built by Natural Currents Energy Services, will be the first hybrid plant in the five boroughs. While Parks is building it as much to test green power technology as to keep the lights on over the ball fields on Randall’s Island, private companies in the city have been experimenting with alternative energy on a small scale for years – and some in the industry say that with the city’s overall sustainability plan due in March, the five boroughs are on the verge of a renewable energy boom.

More than 45 buildings around the city already use solar power for some of their energy needs, said Steve Hammer, an adjunct professor at Columbia University and president of Bronx-based energy and environmental policy research firm Mesacosa LLC. Some buildings are also adopting a technology called “Combined Heat and Power” that uses waste heat from a fossil fuel-burning power plant to warm the building, thus saving energy, Hammer said.

As the city’s new Office of Environmental Coordination works on the sustainability plan Mayor Bloomberg started talking about a year ago and promised in December, several green energy projects are in the works throughout the city. According to Hammer, the Staten Island borough president’s office is working with a Poughkeepsie-based energy firm to study wind patterns over Fresh Kills for a possible wind power plant. Fresh Kills is already a power source for the city, as gas emanating from the old landfill there has been collected for reuse since 1998.

The tidal turbines Natural Currents is building at the channel called Hell Gate to harness energy from the East River will have company, too. After two years of testing, Manhattan-based Verdant Power has been lighting the Gristedes supermarket on Roosevelt Island with a tidal turbine since mid-December and plans to build five more.

Verdant’s president, Trey Taylor, says tidal turbines – which, according to Natural Currents president Roger Bason, cost about half as much to install as solar panels – are promising because so far it appears they can generate reliable power without disturbing shipping, port security, or marine life.

“Because they’re modular in nature, it’s not like building a big central power plant. This is decentralized,” Taylor said. “Sprinkling it around,” he added, “it could have a minimal impact on the environment.”

Riverkeeper, an environmental organization, is keeping an eye on underwater turbines. Some mechanisms suck in and harm fish, damaging the local ecosystem and biodiversity, says Riverkeeper General Counsel Robert Goldstein. His group is waiting to see results of a study by Verdant. “If it doesn’t harm the fish, we not only approve,” but hope to see more such non-carbon-generating power sources, Goldstein said.

- Nick Judd