PITTSFIELD — Greener, cheaper energy is in store for city electric customers — unless they opt out.

But officials stress that the program will safeguard residents and business owners in the city against upcoming electricity rate hikes through Eversource, the electricity company that currently serves city customers.

During a news conference at City Hall on Tuesday to explain the program, Mayor Linda Tyer said it's a win-win for the city, as the deal furthers its commitment to the environment while offering a lower rate than Eversource's basic service rate come January.

"Not only are we greener, but we're less expensive," Tyer said. "This is just another example of Pittsfield furthering its investments in renewable energy."

Everyone in the city with an electricity meter will soon see a letter in the mail explaining that Pittsfield has entered a municipal aggregation agreement with NextEra Energy Services, which will become the city's energy supplier in January. And while officials said the envelope might look like junk mail, it's not.

The enclosed letter notes that customers will continue to receive a single bill from Eversource, which "will continue to respond to emergencies, read meters and maintain the distribution and transmission lines."

And it emphasizes, in capital letters, that users "will not notice any change" in electricity service. "This program only affects the supply portion of your monthly bill."

Also included is a card that consumers must fill out if they choose to opt out of the plan; otherwise, enrollment is automatic.

Officials said anyone in the city can opt out without penalty at any point, even after they have been automatically enrolled. After the three-year contract period, the service defers back to the market rate, at which time the city can unenroll or renegotiate a contract.

Officials will be on hand to answer questions during two upcoming public information sessions: one at 1:30 p.m. Thursday at the Ralph J. Froio Senior Center, and another at 6 p.m. Dec. 6 at the Berkshire Athenaeum.

There are already 12 other communities in Berkshire County that participate in a municipal aggregation program, an option made available in 1997 through an act of the state Legislature.

"This is the first time Pittsfield has pursued it," Tyer said.

Under the program, 5 percent of the city's energy supply employs renewable energy credits. That's about 25 percent more solar energy than the state minimum, officials said.

"Currently, your program is as green as anyone's in the state," said Mark Cappadona, president of Colonial Power Group, which serves as the consulting agent in the agreement. "That's a big deal in Massachusetts."

Eversource's basic service rate for residential properties currently is $0.0856 per kilowatt-hour, and $0.0931 per kilowatt-hour for small businesses. Last winter's rates were $0.0913 and $0.0933, respectively. In January 2018, those rates are expected to rise to $0.1064 for residential properties and $0.1156 for small businesses.

Pittsfield's new program locks all city consumers into a rate of $0.0998 per kilowatt-hour for the next three years.

Cappadona said he expects Eversource's rates will continue to hover higher than previous years' rates, which, he said, comes in response to the coal and nuclear energy markets.

"The higher cost for electricity is due to the increased price of natural gas for electric generators during the winter months," said Priscilla Ress, a spokeswoman for Eversource. "This is a direct reflection of the energy price volatility we continue to see in New England and more proof of the need for new energy infrastructure like gas pipeline capacity in the region."

Cappadona said that about half of the eligible municipalities in the state — any city or town that doesn't have a municipally owned utility — receive aggregated power. Though the city signed the agreement with NextEra in August, he said he advised waiting until now to inform the public. He said it's more effective to launch the public information campaign as residents are receiving the opt-out notices, so that it's fresh in their minds.

Jim McGrath, the city's natural resource program manager, said he has been working on the deal, inspired by the city's Green Commission, for about two years.

"We're trying to insulate the consumers in the community," he said.

Reach Amanda Drane at adrane@berkshireeagle.com, @amandadrane on Twitter or at 413-496-6296.