The aquarium has signed a 25-year electricity supply agreement with Constellation Energy Group to buy a portion of its electricity from a new solar power plant in Cambridge.

Under the agreement, Constellation will fund and construct a 4.3-megawatt solar grid on about 22 acres in Cambridge. The system is being developed with the solar firm OneEnergy Renewables and is scheduled to be complete in March.

When it opens, the solar project will generate an estimated 5.8 million kilowatt hours in its first year. That's more than 40 percent of the aquarium's annual energy needs.

"This agreement with Constellation allows us to 'walk our talk' as a conservation organization," John Racanelli, CEO of the National Aquarium, said in a statement. "Now, a significant percent of our electricity will come from clean, renewable energy. We hope this will help set a precedent for supporting large-scale, off-site projects and inspire others to take action."

The aquarium will receive solar renewable energy credits and a fixed price for electrical supply as part of the partnership.

"Constellation is pleased to continue to support the National Aquarium's energy and environmental goals," Mark Huston, president of Constellation Retail, said in a statement. "Our power purchase agreement with the Aquarium demonstrates our commitment to developing products and services that give customers greater flexibility in managing their energy costs while supporting the use of clean, renewable energy."