The Portland City Council voted unanimously to allow the city manager to join a renewable energy consortium and commit to purchasing a certain amount of electricity from it.

The consortium was made possible after state law was changed to allow municipalities and other commercial energy users to receive cash credits for using solar energy, rather than only kilowatt hour credits. Officials say this is the first consortium of its kind in the state.

Troy Moon, the city’s sustainability coordinator, has said the city could save $500,000 a year in energy costs once the solar arrays are developed for the city and other consortium members, including L.L. Bean, the University of Maine System and Nestle Waters.

It also would allow the city to make progress toward its goals of using 100 percent renewable energy and eliminating carbon emissions by 2040 or sooner.

An attorney who represented the city in negotiating the agreement said current market conditions are favorable to saving money through net energy billing credits, but she warned the council that the 20-year contract is not without risks.

“Again, (there’s) a lot of risk,” Aga Dixon said. “Some of this is speculative.”

But city councilors said there is inherent risk in all energy markets and that joining the consortium is a risk worth taking, especially if the city wants to reach its goal of being carbon neutral by 2040.

“There is a risk – it’s unavoidable,” Councilor Justin Costa said. “But if we mean what we say in that we’re trying to green our city and make use of renewable and solar energy, this is what that actually means. There is no other way.”

The energy would be provided almost entirely by new solar projects.

The consortium was assembled by the Portland-based Competitive Energy Service, which received solar farm proposals from 19 developers, representing 119 separate projects, in response to its request for proposals for renewable energy providers, according to the city. State law limits the size of each solar farm to 5 megawatts, or 20-25 acres.

Once the solar farms are developed, Portland expects to purchase 20 million kilowatt hours of electricity a year, which would provide two-thirds of the power used by all city and school operations.

By contrast, the 4-acre solar farm the city recently built on the Ocean Avenue landfill provides 1.2 million kilowatt hours of electricity annually, roughly enough to power City Hall and Merrill Auditorium.

About a half dozen people, including several students, spoke on behalf of the proposal.

“These (sustainability) goals are meaningless without tangible action,” said Sarah Pierce, a Casco Bay High School student and member of the Solarize Portland, a student-led group looking to add solar panels to schools. 

The council voted 8-0 in support with Councilor Nicholas Mavodones absent.