The St. Peters, Missouri-based company and its publicly traded subsidiary, TerraForm Power, said Monday that they are buying First Wind for $1.9 billion now and $510 million in payments if First Wind completes certain projects.
First Wind, based in Boston, develops, owns and operates wind projects across the U.S.
SunEdison, which develops and operates solar power plants, said the deal will make it the world's largest renewable energy development company.
Based on the anticipated impact of the deal, SunEdison raised its 2015 installation guidance from a range of 1.6 to 1.8 gigawatts to a range of 2.1 to 2.3 gigawatts.
One gigawatt can provide energy for up to 750,000 homes.
TerraForm raised its 2015 dividend guidance to $1.30 per share, up 44 percent from its current rate of 90 cents.
The deal is expected to close in the first quarter.
SunEdison Inc. shares rose 6.6 percent to $17.70 in extended trading. TerraForm Power Inc.'s shares gained 1.2 percent to $26.15.