National Grid and a Newton solar company are developing a 1-megawatt solar array on a former brownfield site.
Construction on the project has begun and is expected to finish in 2010, said John Tourtelotte, managing director of solar developer Rivermoor Energy.
The project is being built on a 5-acre former industrial site on Hilldale Ave., owned by National Grid.
The array will be owned by National Grid and will generate electricity for the utility.
The project more than doubles the power output of the Brockton Brightfields, which at 425 kilowatts has been touted as one of the largest brownfield-to-solar projects in New England.
National Grid received regulatory approval for the Haverhill project last October. The array will be comprised of 3,600 panels mounted on the ground, according to the utility. The general contractor for the project is Boston-based Fischbach & Moore.
National Grid recently completed a solar array in Waltham and is pursuing five other projects, including Haverhill. Under state law, renewable sources must contribute one-fourth of utilities' power by 2020.
Rivermoor has also developed a project to erect a 240-kilowatt solar array on the roof of the Boston Water and Sewer Commission building. That project is under construction and expected to be complete in the fall.