America's newest "largest solar photovoltaic plant," the Copper Mountain Solar Facility, opened a few weeks ago. It's in the Nevada desert (40 miles southeast of Las Vegas), covers 380 acres, and produces 48 megawatts at full capacity. That's enough to power something like 20,000 homes. The power has been sold to Pacific Gas & Electric, so it'll be keeping the lights on for people in the Southern half of California. We're getting there, folks.
The largest solar photovoltaic power plant in the world, by the way, is the Sarnia plant in Ontario, Canada.