The U.S. solar market grew 67 percent from a $3.6 billion market in 2009 to $6 billion in 2010, according to "U.S. Solar Market Insight: 2010 Year in Review," a report released this month by the Solar Energy Industries Association (SEIA) and GTM Research.

California installed the most photovoltaics last year, with 258.9 megawatts of direct current (MWdc), followed by New Jersey in second place with 137.1, and Nevada with 61.4. Others on the Top 10 list in order of greatest installations included Arizona, Colorado, Pennsylvania, New Mexico, Florida, North Carolina, and Texas.

The SEIA estimates that the U.S. now has a cumulative solar capacity of 2.6 gigawatts. Of that 2.6 gigawatts, there are 152,516 PV systems totaling 2.1 gigawatts (direct current) connected to the power grid. The U.S. also now has 17 concentrated solar plants totaling about 507 megawatts (alternating current), according to the SEIA.

The biggest reason for this growth could be attributed to the large amount of utility installations. There were a total of 113 megawatts as of 2009, and that increased to 242 megawatts by the end of 2010. The SEIA attributes a lot of those projects to the Department of Energy Loan program and says future growth outlook will depend in part on that program's fate.

Still, despite growth, the U.S. actually fell behind other countries in 2010 in terms of global photovoltaic installation. The U.S. was home to only 5 percent of the world's installed photovoltaics in 2010, compared with 6.5 percent in 2009. The SEIA attributed this to the European solar boom caused by government incentives that pushed countries like Spain, Italy, and Germany to install more solar plants.