Xcel Energy Inc. is a utility holding company based in Minneapolis, Minnesota, serving more than 3.3 million electric customers and 1.8 million natural gas customers in Minnesota, Michigan, Wisconsin, North Dakota, South Dakota, Colorado, Texas and New Mexico. It consists of four operating subsidiaries: Northern States Power-Minnesota, Northern States Power-Wisconsin, Public Service Company of Colorado, and Southwestern Public Service Co.

Xcel Energy was built on three companies: Minneapolis-based Northern States Power Company (NSP), Denver-based Public Service Company of Colorado (PSCo), and Amarillo-based Southwestern Public Service (SPS). Southwestern Public Service Co. (SPS) dates its origins to 1904 and the Pecos Valley in New Mexico when Maynard Gunsell received an electricity franchise for the city of Roswell, New Mexico and its 2,000 residents. The financial strain of creating this new enterprise soon overwhelmed him and he sold the franchise to W.H. Gillenwater, who named his utility the Roswell Electric Light Co. He later sold the company to an investment firm in Cleveland, Ohio, which already owned the Roswell Gas Co.

Northern States Power Company's timeline begins with the organization of the Washington County Light & Power Co. in 1909. When H. M. Byllesby began building his utility holding company across the Northwestern region of the US, he renamed it the Consumers Power Co. in 1910 and which was renamed the Northern States Power Co. in 1916. While the bulk of NSP's territory grew across central and southern Minnesota (starting from the Twin Cities), it acquired territory in North Dakota (centering on Fargo, Grand Forks, and Minot) and extended southwest into South Dakota (centering on Sioux Falls). NSP's system also extended east into Wisconsin, but because of utility ownership laws in that state, it was operated as an entity separate from the rest of the company.

Public Service Company of Colorado (PSCo) was formed in 1923 to provide an electric generating station for the Denver area. By 1924, it had acquired most of the electric companies in northern and central Colorado. Originally a subsidiary of Cities Service Company, it became an independent autonomous operation in November 1943. By this time, it served 80 percent of Colorado’s gas and electricity needs. As demand for energy continued to grow, so did PSCo. Eventually, the company merged with SPS to form New Century Energies (NCE) in 1995.

Northern States Power and Wisconsin Energy Corporation had planned to merge into a new outfit that was to be called Primergy - but the merger fell through because of the time it was taking to gain the required approvals from state and federal agencies. After the failed Primergy merger, NSP (both the Minnesota and Wisconsin companies) merged with New Century Energies to form Xcel Energy. In 2005, Xcel sold Cheyenne Light, Fuel and Power to Black Hills Corporation. Cheyenne Light, Fuel and Power had been a subsidiary of PSCo since the 1920s, and had become an operating company of NCE after the merger with SPS.

The Cabin Creek Fire occurred on October 2, 2007 at Xcel Energy’s Hydropower Generation plant in Georgetown, Colorado. On June 1, 2011, Federal prosecutors opened their charges that Xcel Energy was criminally liable for the deaths of the five RPI workers. On June 28, the jury found Xcel Energy not guilty. On December 19, 2011, RPI Coating pleaded guilty to workplace safety violations and paid $1.55 million in a cash settlement. The company took responsibility for the deaths of five workers and the injuries to three.

Xcel Energy currently has 13 coal plants with a capacity of 7,697 MW. Seven of those plants are operated in Colorado. Xcel Energy owns and operates three wind farms. In October 2011, Xcel Energy set a world record for electricity from wind power.

Xcel Energy generates over 500 megawatts of hydroelectric power from 27 plants in Wisconsin, Minnesota, and Colorado. This accounts for only four percent of their electricity generation. They also purchase large amounts of hydro-generated electricity from Manitoba Hydro.

Biomass electricity comes from organic fuel sources. Xcel Energy has contracts for about 110 megawatts of electricity from biomass generators. Two in northern Minnesota are fueled by forest harvest residue, such as treetops and limbs. A third facility, brought on line in 2007 in western Minnesota, generates power using turkey litter.

Xcel Energy's Bay Front plant in Ashland, Wisconsin, is a three-unit generating station that has become a model for the creative use of fuels: coal, waste wood, railroad ties, discarded tires, natural gas, and petroleum coke. Two of the three Bay Front operating units already use biomass as their primary fuel. Xcel Energy recently proposed a plan to install biomass gasification technology at Bay Front. The waste-to-energy facilities use waste that would otherwise end up in landfills. The Wisconsin waste-to-energy plant burns wood waste in combination with refuse-derived fuel (RDF).

Xcel Energy owns and operates two nuclear power plants, Monticello Nuclear Generating Plant near Monticello, Minnesota, and Prairie Island Nuclear Generating Plant near Red Wing, Minnesota and stores the spent fuel from these nuclear plants on site in independent spent fuel storage installations. (ISFSIs).

Xcel Energy operates the fourth largest transmission system in the United States, spanning 10 states, or 20 percent of the country. In 2011, Xcel Energy’s transmission system was worth $3.3 billion.

The transmission system is operated on a non-discriminatory basis under the open access requirements of the federal government. This means that all wholesale buyers and sellers of electricity can use the transmission system under the same terms and conditions used to serve Xcel Energy’s own retail customers. The transmission lines are utilized to carry 115,000 volts, 230,000 volts, and 345,000 volts. There is also a 500,000 volt transmission line that runs from the Dorsey Substation outside of Winnipeg, Manitoba in Canada to the Chisago Substation located in Chisago County just north of St. Paul, Minnesota.

Since 1998, Xcel Energy's Windsource program has allowed customers to designate that part or all of their electricity comes from a renewable energy source. In 2015, about 96,000 people were enrolled in Windsource. In 2011, more than 2.3 million electric and 261,800 natural gas customers took part in Xcel Energy’s energy efficiency programs for homes and businesses.

Xcel Energy also offers customers incentives to install solar panels. At the end of 2011, more than 10,600 photovoltaic systems had been installed, with a capacity of about 121 megawatts (DC). In early 2011, Xcel Energy suspended the solar rebate program before reaching a settlement a month later with representatives of solar power companies to restore the solar incentive program until it is fully reviewed by the Public Utilities Commission.

On August 1, 2002, Xcel Energy Inc. was sued because of engaging in "round-trip" energy trades that provided no economic benefit for the company, and because the company lacked the necessary internal controls to adequately monitor the trading of its power. Xcel paid $80,000,000 in a settlement.

In early October 2007, a flash fire within a penstock at Xcel Energy's hydroelectric plant at Cabin Creek occurred which resulted in the death of 5 contract workers. The U.S. Chemical Safety and Hazard Investigation Board conducted an investigation of the incident. Its report can be found on the CSB website. It is considered one of the worst unmitigated incidents to occur in a permit required confined space.