GenOn Energy Holdings, formerly Mirant Corporation, was a subsidiary of GenOn Energy, and is now a part of NRG Energy.
The company was spun off from its former parent, Southern Company, on April 2, 2001. The company was merged into GenOn Energy on 3 December 2010. The company then became part of NRG Energy in December 2012.
Mirant operated 13 plants in the states of California, Georgia, Maine, Maryland, Massachusetts, Michigan, New York, and Virginia and has the capacity to generate approximately 10,300 MW of electricity.
Mirant began its corporate existence in 1981 as Southern Electric International (SEI), a small consulting division of Southern Company that provided engineering and technical services to industrial companies, domestic and international utilities. With the Energy Policy Act of 1992 deregulation arrived in the US electric power sector, and SEI ventured into global markets with the acquisition of a 50% stake in Freeport Power, a Bahamian utility. In the years to come, other acquisitions followed, notably the acquisition of a British distribution utility - South Western Electricity Board later renamed SWEB (now known as Western Power Distribution); a controlling interest in Hong Kong based Consolidated Electric Power of Asia (CEPA), a stake in a German utility BEWAG, controlling interest in Empresa Electrica del Norte Grande, S. A. (EDELNOR) in Chile, and a hydroelectric generating facility in Argentina known as Hydroelectrica Alicura; giving it worldwide business interests in the Caribbean, Asian, South American and European energy markets. On the domestic front the company forged a joint venture in 1999 with Houston-based Vastar Energy to create Southern Company Energy Marketing, an electricity and gas trading company. That same year the company also acquired power generation facilities in New England (Canal station, Martha's Vineyard Diesels, Kendall Station), New York (Lovett and Bowline stations), California (Pittsburg, Potrero and Contra Costa stations). That same year SEI was renamed Southern Energy, in keeping with the broader theme of the products and markets that it pursued. Soon afterwards, its biggest domestic acquisition till date came in December 2000 with the purchase of the Morgantown, Chalk Point, Dickerson and Potomac River power generating assets from Potomac Electric Power Company (PEPCO). After an initial public offering of Southern Energy common stock in the fall of 2000, parent Southern Company completely spun off its interests in Southern Energy in April 2001 and a new publicly listed entity named Mirant Corporation began trading on the New York Stock exchange with the ticker symbol MIR. Between 2000 and 2003, the company continued its expansion in the U.S. markets with the acquisition or greenfield development of various gas-fired power plants in markets like Nevada, Texas, Wisconsin, Indiana, Arkansas, Louisiana, Georgia and Florida.