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Solar panels aren’t just for rooftops — power companies are using them to build massive solar panel farms in the deserts of the U.S., too. On Tuesday, NRG Energy and MidAmerican Solar announced that they’ve completed building the world’s largest operational solar panel farm across 2,400 acres (two Central Parks) near Phoenix, Arizona. The site has been live since late last year, and they’re announcing the progress today.

The farm — called the Agua Caliente Solar Photovoltaic Facility — can produce 290 MW of solar electricity, which is enough to power 230,000 homes at peak capacity. California utility PG&E is buying the power under a 25-year contract, and First Solar (s FSLR) both supplied the panels, as well as designed, built and will maintain the project.

The farm was built with a $967 million loan guarantee from the Department of Energy, as well as equity from owners NRG Energy and MidAmerican Solar, which is the energy-focused fund owned by Warren Buffett’s Berkshire Hathaway. MidAmerican bought 49 percent of the $1.8 billion farm in early 2012. The group say 400 jobs were created during construction.



Agua Caliente is important for its sheer size, and shows that solar panels can contribute a substantial amount of electricity if built in the right areas of the U.S. Average natural gas plants can be a similar size to the 290 MW solar farm, though average coal plants usually produce more power.

Solar panels are now at one of their cheapest times in history — weighted average solar panel system prices fell 15 percent in 2013, to reach a new low of $2.59/W in the fourth quarter of 2013, according to a SEIA and GTM report. More solar has been installed in the U.S. in the last 18 months than in the last 30 years, and almost a third of new electricity came from solar last year.