NRG Energy, Inc., together with its subsidiaries, operates as an integrated wholesale power generation and retail electricity company. The company engages in the ownership, development, construction, expansion, modification, refurbishment, and operation of power generation facilities. It is also involved in the trading of energy, capacity, and related products; transacting in and trading of fuel and transportation services; and the supply of electricity, energy services, and cleaner energy products to retail electricity customers in deregulated markets. In addition, the company engages in the investment, deployment, and commercialization of alternative energy technologies focused on the areas of distributed solar, solar thermal, and solar photovoltaic; and low or no greenhouse gases emitting energy generating sources, such as the fueling infrastructure for electric vehicle ecosystems. The company operates natural gas-fired, coal-fired, oil-fired, nuclear, solar, and wind power plants. As of December 31, 2011, it had power generation portfolio of 189 operating fossil fuel and nuclear generation units with an aggregate generation capacity of approximately 23,585 megawatt (MW), as well as had ownership interests in renewable facilities with an aggregate generation capacity of 545 MW in the United States; and 1,005 MW of generation capacity internationally. Further, it engages in the district energy business with steam and chilled water capacity of approximately 1,170 megawatts thermal equivalent. NRG Energy, Inc. was founded in 1989 and is headquartered in Princeton, New Jersey.