Bergen County officials say they will save millions in energy costs by building a small power plant for the county jail.

The natural-gas generator would provide electricity to the recently expanded 1,100-bed jail on River Street in Hackensack, and the heat it creates would be used to warm the jail - a process known as cogeneration.

"In essence, the engine will produce free heating," said Dominick Aiello, president of Metro Energy Solutions, the county's consultant on the project.

Freeholders approved a contract last week with Atlantic City-based DCO Energy LLC, which will build and maintain the plant. The freeholders next month will consider borrowing $2.9 million to fund the plant, which would save an estimated $5.8 million during the next 25 years, County Administrator Timothy J. Dacey said.

Cogeneration plants have become increasingly popular with government officials looking to offset rising gas and heating costs.

Essex County included a cogeneration plant at its new jail. Wayne is considering a $9.89 million plant to power its Township Hall, two schools, and the schools administration building.

And officials at the Bergen County Improvement Authority, which oversees Bergen Regional Medical Center in Paramus, are considering a similar plant at the county-owned hospital. Aiello is consulting the improvement authority on that project, and DCO Energy is in line to get that contract, said the authority's executive director, Edward H. Hynes.

The county wants to build a plant big enough to serve the hospital and a proposed juvenile detention center that would be built next to the hospital; cost and savings estimates were not yet available.

Democrats and Republicans on the freeholder board said they will support the jail plant project if it saves money.

But Republican Sheriff Joel Trella, who runs the jail, questioned the county administration's savings claims.

"The sheriff is extremely skeptical about the program," said spokesman Thom Ammirato. "It will probably increase overtime and manpower costs, because you're going to have to have people assigned to watch over the workmen."

Ammirato said backup generators at the jail already provide a safety net for the county.

If the freeholders approve the funding next month, the county will sign the contract with DCO Energy around the same time, an administration spokesman said. The plant could be running by May 2005.

The improvement authority hopes to be in a position to move ahead on its project within the next few months, Hynes said.