Green Mountain will be run as a standalone business within NRG.

NRG president and CEO David Crane said the acquisition of Green Mountain complements the company’s solar and wind portfolio.

"This combination enables us to match green wholesale and green retail in order to meet the American public’s growing demand for a fully sustainable alternative energy supplier," Crane added.

Green Mountain Energy Company CEO Paul Thomas said the acquisition will enable the company to pursue its mission to change the way power made more rapidly and also help it to expand the scope of its green products and services into various attractive markets.