When people think of solar power, they tend to think of panels on rooftops. That kind of small-scale, distributed solar power is the most visible, gets the most press, and, from the consumer perspective, has the most sex appeal.
But the humble workhorse of solar power is the utility-scale solar power plant, usually defined as a solar array larger than 5 megawatts.
Solar power plants can consist in either PV panels or mirrors that focus sunlight on a fluid that boils and turns a turbine ("concentrating solar power," or CSP). In practice, most new solar plants these days use PV, which has gotten so cheap so fast that it's outcompeted CSP and every other solar segment, at least for now.
In 2007, there were zero utility-scale solar power plants in the US. Today there are hundreds, ranging from the 579 MW Solar Star project (the world's largest solar farm) in California down to dozens upon dozens of 10, 20, and 50 MW projects in communities across the country. (SEIA counts 2,100 solar PV projects over 1 MW.)
Big solar power plants still provide a measly 0.6 percent of overall US electricity. But they are headed up a steep growth curve.
Residential rooftop solar is the fastest growing solar segment, but utility-scale solar is bigger. There's more installed, so even with its slower growth rate it adds more capacity each year — in 2015, it accounted for 57 percent of all new installed solar capacity.